MESOZOIC conditions in retrospect

[Life]

THE ARCTIC PROXY

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CAPTION: Preliminary results from a Smithsonian Institution project led by Scott Wing and Brian Huber, showing Earth's average surface temperature over the past 500 million years. For most of the time, global temperatures appear to have been too warm (red portions of line) for persistent polar ice caps. The most recent 50 million years are an exception. Image adapted from Smithsonian National Museum of Natural History.

A Smithsonian Institution project has tried to reconstruct temperatures for the Phanerozoic Eon, or roughly the last half a billion years. Preliminary results released in 2019 showed warm temperatures dominating most of that time, with global temperatures repeatedly rising above 80°F and even 90°F—much too warm for ice sheets or perennial sea ice. About 250 million years ago, around the equator of the supercontinent Pangea, it was even too hot for peat swamps!

Geologists and paleontologists have found that, in the last 100 million years, global temperatures have peaked twice. One spike was the Cretaceous Hot Greenhouse roughly 92 million years ago, about 25 million years before Earth’s last dinosaurs went extinct. Widespread volcanic activity may have boosted atmospheric carbon dioxide. Temperatures were so high that champsosaurs (crocodile-like reptiles) lived as far north as the Canadian Arctic, and warm-temperature forests thrived near the South Pole.

Another hothouse period was the Paleocene-Eocene Thermal Maximum (PETM) about 55-56 million years ago. Though not quite as hot as the Cretaceous hothouse, the PETM brought rapidly rising temperatures. During much of the Paleocene and early Eocene, the poles were free of ice caps, and palm trees and crocodiles lived above the Arctic Circle. ----[1]

More information in following link: www.science.org/content/article/500-million-year-survey-earths-climate-reveals-dire-warning-humanity

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MASS EXTINCTION EVENTS

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For some 3.7 billion years, life and the planet continued to evolve together, entwined in a mutual ebb and flow of evolutionary creation and cataclysmic devastation. Temperature records—compiled from miles-long ice cores filled with preserved gas bubbles and the remains of unicellular ocean-dwellers—can be compared to the fossil record to help scientists fill in the timeline of Earth’s history. The Cambrian explosion, for example, some 541 million years ago, saw a proliferation of complex life in the world’s oceans, possibly brought about by an increase in oxygen. The Permian extinction 252 million years ago, sparked by a rapid increase in volcanic activity and CO2 in the atmosphere, wiped out some 90 percent of all marine species and 70 percent of terrestrial species. ----[1]

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Emergence of dinosaurs

Dinosaurs emerged AFTER the Permian extinction event in the Carnian age of the Mesozoic time scale:

The Carnian witnessed the beginning of the dinosaur radiation, although taxa attributed to this clade are still rare (Langer et al. 2010, Nesbitt et al. 2009). This radiation has been studied in the light of the climatic changes registered in the end of the Triassic (Tucker and Benton 1982, Golonka and Ford 2000). In the Late Triassic strata of Rio Grande do Sul, these events are represented by an aridity increase during the Carnian (Zerfass et al. 2003), leading to the establishment of a mesoxerophytic flora dominated by the gymnosperm Dicroidium and concomitant faunal changing (Azevedo et al. 1990). ----[3]

Theropoda outcompete Paracrocodylomorpha in the Triassic? - smoking gun in respiratory systems

This study provides genera-level data on non-avian Theropoda and paracrocodylomorphs postcranial skeleton pneumaticity (PSP) using the Pneumaticity Index (PI) to quantify the evolution of pneumatization. The presence of foramina and fossae with continuous internal chambers as evidence of an avian-like respiratory system. Ancestral state reconstruction showed the evolutionary trends of pneumaticity in Theropoda and Paracrocodylomorpha, and a likely character state for the common ancestor between the two. O₂ levels during the Triassic were low (11–14%) and correspond inversely with the high levels of atmospheric CO₂. These findings also have implications for the predatory guild transition between Theropoda and Paracrocodylomorpha, as well as the decrease in diversity and disparity of paracrocodylomorphs through the Triassic. Increased PI values in Theropoda throughout the Late Triassic imply the presence of foramina in Theropoda were advantageous in the wavering O₂ and CO₂ environments however, fossae present in paracrocodylomorphs may not have been as advantageous as foramina, causing a reduction in pneumatization. The outcome resulting in a reduction in size of Paracrocodylomorpha with being replaced with more efficient Theropoda and becoming the subsidiary predator niche group. Presence of foramina in theropod skeletons before the changes in O₂ and pCO₂ levels suggest the character is an exaptation evolved for an earlier use for weight reduction, then later co-opted for the lower oxygen and CO₂ environment. In summary, the rise of Theropoda may have been a multi-faceted event that persisted for millions of years, with the combination of the Carnian Pluvial Episode causing empty niches in Paracrocodylomorpha for Theropoda to occupy, the decreasing oxygen and wavering CO₂ in the Triassic, and the selective advantage of foramina for efficient gas exchange in low oxygen levels may have played a critical role in the subsequent evolutionary success in Theropoda over Paracrocodylomorpha. ----[4]

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Mesozoic time scale for reference

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Documented shifts in the Mesozoic

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The Mesozoic Era was the time of the fragmenting of supercontinent Pangaea, implicating in dramatic changes concerning:

- paleocontinental positioning and shoreline configuration;

- intensity of volcanism and LIP emplacement;

- pattern of oceanic circulation;

- paleoclimate zonation;

- evolution of life.

The Era began under extreme severe “hothouse” conditions during Early Triassic, had mainly greenhouse conditions until Mid-Jurassic, when the first of a series of noticeable temperature drops occurred, inaugurating a phase of variable climates, where greenhouse conditions were followed by “cold snaps” or mini ice ages, but also eventual and short-lived hothouse conditions.

The mechanisms and interaction of the several climate-controlling factors such as the change in paleocontinental positioning, the opening of sea-ways modifying the oceanic circulation, the LIP emplacements enhancing CO₂ and the impact events triggering “nuclear winters”, are still a controversy and debated matter. Some facts and events are closely related and might explain some paleoclimatic conditions, such as the global heating events and the atmospheric CO₂ content. Other events, such as the Triassic humid pulses, are harder to explain.

The fact is that the major extinction events in Earth history can be found in the Mesozoic. The Phanerozoic extinction record suggests that a 10% generic turnover per stage can be considered as overall background extinctions or “normal faunal turnovers” (Keller, 2008). Hence, rates greater than 10% are considered extinction events, and such events did occur several times during the Mesozoic. The Triassic period records an important extinction event during the Norian/Rhaetian (> 30% extinction rate). Three noticeable extinctions occurred in the Jurassic (Pliensbachian, Callovian and Tithonian, all with extinction rates close to 20%), and three in the Cretaceous – during the Aptian (extinction rate ~15%), the Cenomanian (extinction rate ~18%) and specially the Maastrichian extinction that finished the reign of the dinosaurs on land and the ammonites in the oceans (extinction rate close to 45%).

Concerning Brazilian Mesozoic basins and tetrapod evolution, many questions arise if one compares the fossil record with the paleoenvironmental characterization of the different Mesozoic periods. For instance, the rock succession of the Recôncavo Basin probably records an important paleoclimatic change, from the cool greenhouse conditions in the Berriasian/Valanginian to warmer greenhouse regime of the Hauterivian/Barremian. Warm greenhouse to hothouse conditions had prevailed during the deposition of the basal part of the Bauru basin succession, while the upper part was deposited under cool greenhouse conditions. To what extend are these climatic variations linked to or, at least, the key control to the tetrapod evolution as recorded in those Brazilian basins? Brusatte et al. (2010) stated that it is essential to understand not only the climatic and environmental backdrop of dinosaur history, but also the absolute and relative ages of dinosaur fossils and whole dinosaur assemblages. A sound understanding of dinosaur evolution relies on geological data, which are fundamental to large-scale macroevolutionary studies. Especially for the Triassic and Early Jurassic, correlations between sedimentary successions on both local and global scales are extremely difficult, but should become a primary goal in future studies in dinosaur evolution. Fine-tuned studies, linking and correlating high resolution paleoclimatic data with full biostratigraphic range of dinosaur taxa in Brazilian basins, are still in their infancy, but are hopefully one of the outgrows of the 2013 symposium. ----[6]

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An alien world

The rifting of Pangaea occurred during the Mesozoic, eventually fragmenting this supercontinent into several plates which will form the modern continents. This break-up had profound consequences not only for the paleocontinental configuration, but also for paleoclimates and for the evolution of life; because it significantly modified the paleoposition and shoreline configurations of the land masses, generated huge epicontinental seas and altered profoundly the oceanic circulation.

Due to its unique paleoclimatic conditions, with several times of very high temperatures (mean global temperature > 25^oC) alternating with less warmer intervals and even with short-lived ice-ages, the Mesozoic Earth was, in comparison to the present, an “alien world”, paraphrasing Sellwood & Valdes (2006). Fischer (1982) introduced the nowadays widely used terms ‘greenhouse’ and ‘icehouse’ to characterize the two major climatic states of the Earth during the Phanerozoic. Kidder & Worsley (2010, 2012) proposed that there are actually three basic states for Earth climate: Icehouse, Greenhouse (subdivided into Cool and Warm states), and Hothouse. The ‘Icehouse’ (IH) displays polar ice, strong latitudinal temperature gradient (50–60°C) and alternating glacial–interglacial episodes in response to orbital forcing. This climatic state apparently did not occur during the whole Mesozoic. The ‘Cool Greenhouse” (GH-c) shows some polar ice and alpine glaciers, but no ice streams calving icebergs into the ocean. Global average temperatures are thought to range between 21° and 24°C. Atmospheric CO₂ levels are thought to have been between 2 and 4 times those of today (600–1,200 ppmv). The high to low latitude temperature gradient is weaker that in the icehouse (ca. 40°C). The ‘Warm Greenhouse’ (GH-w) is devoid of any polar ice. Global average temperatures might have ranged from 24° to 30°C. Kidder and Worsley (2012) believe that atmospheric CO₂ levels ranged between 4 and 16 times the present ones (1,200–4,800 ppmv) during GH-w stages. Seasonal reversals of the atmospheric pressure systems around the poles should have occured. The lower latitudinal temperature gradients (< 34°C) thus mean reduced winds, and the warmer ocean would absorb even less oxygen. Isolated basins could become bottom oxygen-depleted. The “Hothouse” (HH) condition is relatively short-lived (< 1 to ca. 3 Ma) and results from anomalously large inputs of CO₂ into the atmosphere during the formation of Large Igneous Provinces (LIPs), when atmospheric CO₂ concentrations may rise above 16 times (4,800 ppmv).

The Mesozoic Earth had been experiencing the cool greenhouse, warm greenhouse and the hothouse climatic states. Hence, Mesozoic climate was very variable, what is corroborated by several global-scale studies. For instance, Veizer et al. (2000) demonstrated the variability of the Mesozoic global climate relying on a study on atmospheric CO₂ and global tropical sea surface temperatures anomalies (TSSTA), reporting positive anomalies for the Early to Middle Triassic and for the Late Cretaceous, and negative anomalies during Early Jurassic and specially for the Mid-Jurassic, when the mean surface temperatures were 4^oC higher than today.

Global sea levels throughout the Mesozoic were generally much higher than at present, with exceptions for the sea level lowstand in the Early Induan (i.e, the beginning of the Triassic, cf. Haq et al. 1988) and two noticeable lowstands in the early Jurassic (Hettangian/Sinemurian) and in the early Cretaceous (Valanginian) (Haq, 2014).

Mesozoic atmospheric oxygen content was also different when compared to current values. Theoretical calculations, based on both chemical and isotopic composition of sedimentary rocks and admitting a wide margin of error (about +10%), indicate that atmospheric O₂ had been varying between 15 and 25% (Campbell & Allen, 2008, Royer, 2014). The transition from Permian to Triassic is marked by a huge drop of the atmospheric oxygen content, falling from ~30% to less than 15% according to some authors (e.g. Dudley, 2000; Berner et al., 2003). During Induan/Olenekian (Early Triassic), the O₂ content was about 15%, then it increasing to 20% (i.e. close to the present-day level) until the Early Jurassic and finally to 25% toward the Late Cretaceous (Berner & Canfield, 1989; Berner et al., 2003; Holland, 2006).

Why did the Mesozoic have such a different and overall hotter climate when compared, for instance, to the present day world? The main factors are:

(1) the paleocontinental configuration: the assembling of a supercontinent, forming an almost pole-to-pole continuous land mass, is one of the climate-driving factors. The combination of a gigantic land mass (Pangaea covered an approximate surface of 130 million km²) and a lower global sea level (associated with reduced rates of tectonic movement) resulted in an arid climate during the Early Mesozoic, as stated by Frakes (1979). Parrish (1993) assigned to the Triassic the maximum development of megamonsoons, due to an almost symmetrical position of Pangaea over the equator. This megamonsoonal regime would have caused the displacement of the arid belt towards the poles, causing a decrease of the precipitation/evaporation rate in the mid-latitudes of Pangaea interiors, where huge semi-arid to arid belts characterized that period. The rifting of the supercontinent began during the Triassic, and the major break-up of Pangaea took place during the Jurassic (when Laurasia rifted from Gondwana and Africa separated from Antarctica/Australia); and continued during the Cretaceous (when Africa and South America rifted apart, and Greenland separated from North America). The break-up and the consequent continental drift modified the paleoposition and shoreline configurations of the land masses, generated huge epicontinental seas, separated land masses by interior sea ways, and altered profoundly the oceanic circulation. These factors helped controlling climate change during Middle and Late Mesozoic.

(2) the degassing process linked to plate tectonics: intense sea-floor spreading enhanced greenhouse conditions thanks to degassing of H₂S, CH₄ and CO₂ (Seton et al., 2009; Royer, 2014), and rifting events are frequently linked to flood basalts and to the emplacements of large igneous provinces (LIPs) both continental and oceanic. It is a climate-controlling factor: since during these events the short term cooling is followed by warming induced by CO₂ degassing and enhanced greenhouse effect on climate (e.g. Kidder & Worsley, 2010; Chui & Komp, 2014). During the entire Mesozoic the CO₂ levels were relatively high (1,000–2,000 ppmv), with transient excursions to even higher values (>2,000 ppmv; Retallack, 2001), and extremely elevated CO₂ concentrations at the Triassic/Jurassic boundary (Steinthorsdottir et al., 2011). Times of high atmospheric CO₂ and the consequent warm-wet paleoclimatic conditions led to the so-called “greenhouse crises” (Retallack, 2013), which are belived to have played a role in mass extinctions and long-term evolutionary trends during the entire Phanerozoic (Retallack, 2009). Greenhouse gases would have not only disrupted life on land with warmer and wetter climates, but with spreading tropical pathogens, long-distance plant and animal migrations, sea level rise, low-oxygenated ground water and water acidification. Atmospheric oxygen depleted by massive emissions of CH₄ and H₂S (Berner, 2006) would have challenged animals with pulmonary edema, high elevations might have become uninhabitable, later reducing habitat for many animals (Huey & Ward, 2005), and animals with small–medium body size and short muscular limbs (e.g. Lystrosaurus), would be the evolutionary outcome of such a greenhouse crisis (Retallack et al., 2003).

The evolution of terrestrial vertebrates seemingly was another climate-controlling factor. During Mesozoic, herbivorous vertebrates display an evolutionary trend towards gigantism; hence, methane emissions from that kind of reptilian biotas are also considered a climate-controlling factor: the vast herds of grazing reptiles might have released enhanced methane content in the atmosphere and therefore elevated the warm to hot greenhouse conditions of the Mesozoic world (Wilkinson et al., 2012).

(3) the impact events: the collision of huge asteroids produces a huge amount of ejecta which is smeared through atmospheric circulation over huge areas or even globally, causing the so-called “impact winter“ which is a period of prolonged cold weather resulting from blocked sunlight (e.g. Covey et al., 1994; Chapman & Morrison, 1994), hence, inducing severe ecological alterations that could lead to extinction (e.g. Raup, 1992). ----[6]

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Paleo-climatic conditions of the dinosaur-bearing Brazilian basins

NOTE: Contents of this section will be revisited/expanded from time-to-time.

Mesozoic periods	Basins	Description	Formations and dinosaurian footprints and/or impressions	Classification
Triassic	The Paraná Basin		Triassic dinosaurs in Brazil were exclusively collected from rocks of the Santa Maria and the overlying Caturrita formations, in central Rio Grande do Sul (Fig. 1, Table I, II, Langer et al. 2007a). These units belong to the Rosário do Sul Group (Andreis et al. 1980), which corresponds to the Gondwana Supersequence II of the Paraná Basin (Milani 2004). Recent studies explain the origin of this Supersequence as the infilling of tectonically restricted half-graben depocenters (Milani 2001, 2004, Zerfass et al. 2003). The Santa Maria Formation is composed predominantly of red mudstones (Andreis et al. 1980, Scherer et al. 2000, Silva et al. 2003) and encompasses two distinct faunal associations of Ladinian and Carnian age (Barberena 1977, Langer et al. 2007a), as also suggested by stratigraphic studies (Zerfass et al. 2003). The Ladinian sequence represents a more humid phase within a generally seasonal and semi-arid climate. Fossil tetrapods were preserved either in lacustrine environments or in flood plains of an anastomosed fluvial system (Scherer et al. 2000, Zerfass et al. 2003). The Carnian sequence was formed in a similar environment, but the presence of aeolian deposits suggests an increased aridity (Zerfass et al. 2003). The coarser-grained, red sandstones of the Caturrita Formation represent the establishment of a perennial braided fluvial system, hinting at the return of more humid conditions (Holz and Scherer 2000, Zerfass et al. 2003). The age of this unit has been generally accepted as Norian (Rubert and Schultz 2004, Bonaparte et al. 2007, Langer et al. 2007a) [3]. The only possible dinosaur recovered from the Ladinian sequence of the Santa Maria Formation is Spondylosoma absconditum Huene, 1942 (Table II) [3]. The Carnian witnessed the beginning of the dinosaur radiation, although taxa attributed to this clade are still rare (Langer et al. 2010, Nesbitt et al. 2009). This radiation has been studied in the light of the climatic changes registered in the end of the Triassic (Tucker and Benton 1982, Golonka and Ford 2000). In the Late Triassic strata of Rio Grande do Sul, these events are represented by an aridity increase during the Carnian (Zerfass et al. 2003), leading to the establishment of a mesoxerophytic flora dominated by the gymnosperm Dicroidium and concomitant faunal changing (Azevedo et al. 1990) [3].	Sauropodomorpha [3] Silesauridae [3] Theropoda [3] Herrerasauridae [3]
Jurassic
Cretaceous	The Recôncavo Basin	The Recôncavo Basin, located in northeastern Brazil, is a typical example of a continental rift basin. It is the southern part of the Recôncavo–Tucano–Jatobá rift system, which developed during the break-up of Gondwana, during the Late Jurassic and Early Cretaceous. The basin is characterized by asymmetric graben structures comprising three fault-delimited compartments (southern, central and northern), and is exposed over an area of 11,500km2. In the depocenter, a maximum basinal infilling of up to 6,500 meters is reached. The rift sequence is characterized by fluvial–deltaic, lacustrine and alluvial fan deposits (Holz et al., 2014), and according to the paleoclimatic zonation shown in Figure 7, the basin was located in an arid zone during the entire Cretaceous. However, correlation with the global temperature curve (Appendix 1) suggests that the Recôncavo Basin developed during the aforementioned noticeable global temperature increase mapped for the Valanginian-Hauterivian transition (Appendix 1), indicating that the main rift sediments were deposited under warm greenhouse conditions [6].	The dinosaur fossil record is poor up to date, only isolated vertebrae are recorded (Bitencourt & Langer, 2011), without any taphonomic information [6].
Cretaceous	The São Luis/Grajaú Basin	The São Luis/Grajaú Basin is located in the equatorial portion of Brazil and covers an area of 250,000km2. Its genesis is related to the processes of continental rupture and consequent formation of the South Atlantic rift initiated during the Late Jurassic and Early Cretaceous (Góes and Rossetti, 2001). The sedimentary record consists almost entirely of Cretaceous rocks that can be divided into three depositional sequences sensu Rossetti (2001). Sequence S1 accumulated during the Late Aptian and Early Albian, and includes sandstones, shales and limestones deposited in shallow marine, lacustrine and fluvio-deltaic environments that make up the Grajaú and Codó Formations. Sequence S2, of Early–Middle Albian age, consists of sandstone and mudstones of shallow marine and fluvio-deltaic environments that form the Itapecuru and Codó formations. Sequence S3 developed between the Middle Albian and Cenomanian. It comprises sandstones and mudstones referred to the Alcântara and Cujupe Formations. This is the most important dinosaur-bearing unit of that basin, with a taphocoenosis represented by thousands of logs, bone fragments and teeth. Thin section analysis of the rock matrix revealed fine-grained fragments and even “bone flour”, evidencing intense reworking of the bones prior to final burial. The dinosaur taphocoenosis of the Alcântara Formation are actually high-order sequence boundaries coinciding with erosive trangressive surfaces. They were produced by sea-level fall, when the dinosaur bones were transported basinwards in a highly selective manner, and were reworked during the subsequent transgressive events, resulting in highly chaotic and mixed-up fossil deposits. It is a rare example of dinosaur fossils marking transgressive surfaces within an incised valley infill (Holz, 2003). [6].	Most of the assemblage represents a continental paleocommunity similar to the coeval northern African fauna, including dinosaurs such as Carcarodontosaurus, Spinosaurus, titanosaurs and a rebbachisaurid form (Medeiros et al., 2007). The dinosaurian fauna lived in an arid to semi-arid environment, according to paleoenvirommental discussion by Medeiros et al. (ibidem) and Lindoso et al. (2013); that is concurrent with the global paleoclimatic characterization of the Early Cretaceous as shown in figure 7A [6].	Titanosuaria [3] Diplodocoidea [3] Carcharodontosauridae [3] Spinosauridae [3] Deinonychosauria [3]
Cretaceous	The Araripe Basin	The Araripe Basin, also located in the northeastern region of Brazil, is a small interior rift basin (area of ~9000km2) where Assine (2007) identified four unconformity-bounded units: a Palaeozoic Sequence (represented by the alluvial Mauriti Formation), an Early Jurassic Pre-Rift Supersequence (Brejo Santo and Missão Velha Formations), a Barremian to Hauterivian Rift Supersequence (formed by the Abaiara Formation); and a Albian/Aptian Post-Rift Supersequence, formed by the Barbalha, Santana, Araripina and Exu Formations [6].	Dinosaur-bearing strata are linked to the Albian/Aptian Santana Formation of the Post-Rift supersequence, under warm greenhouse conditions, with global temperature peaking during the Albian/Cenomanian (cf. Zhou et al., 2012). All dinosaurs from the Santana Formation are theropods and at least four different clades were identified (Bitencourt & Langer, 2011). Fragments of rostrum, skulls, ribs, isolated teeth and feathers are preserved in carbonate concretions from both fluvial and lacustrine strata [6].	Enantiornithes [3] Compsognathidae [3] Tyrannoraptora [3] Spinosauridae [3]
Cretaceous	The Parecis Basin	The Parecis Basin is a large intracratonic sag (~500,000km2), with an E-W elongation, located in central Brazil, with a sedimentary succession up to 6km thick. The oldest sedimentary rocks are Neoproterozoic to Ordovician and Siluro–Devonian, while the youngest ones are Mesozoic and Tertiary, but very little chronostratigraphic information is available for this basin (Goldberg et al., 2013). Actually, it is one of the least explored sedimentary basins of Brazil. According to its paleocontinental location, the area of the basin had displayed arid climate throughout the entire Cretaceous (Fig.7) [6].	Cretaceous deposits of the northwestern margin of the Paraná Basin crop out in the state of Mato Grosso (Fig. 1). Their strata have been referred to the Cambambe Formation (sensu Weska et al. 1996), which was deposited in a fluviolacustrine system associated to distal parts of alluvial fans under a semi-arid to extremely arid climate (Rosa et al. 1991, Weska 2006). This unit has been traditionally referred to the Bauru Group (FrancoRosas et al. 2004, Lacerda Filho et al. 2004), but recent work suggests that all Cretaceous rocks deposited south of the Paraguai fold belt (Almeida 1984) in Mato Grosso should be included in the Parecis Group (Weska 2006). These deposits accumulated on a crust depression formed by tectonic distension events related to the magmatic plume of Trindade (Weska 2006). The basalts of the Paredão Grande Formation, at the base of the Parecis Group, were dated 83.9 ± 0.4 Ma (Gibson et al. 1997), i.e. Late Santonian (Gradstein and Ogg 2004). This geophysical and other paleontological evidence (FrancoRosas et al. 2004) suggest a Campanian-Maastrichtian age for the dinosaur fauna of the Parecis Group [3]. Pieces of dinosaur post-cranium and isolated teeth, vertebrae and tibia are recorded for the Late Cretaceous Parecis Group (Bittencourt & Langer, 2011), but no piece of taphonomic information is available so far [6].	Titanosauria [3] Abelisauridae [3] Deinonychosauria [3]
Cretaceous	The Bauru Basin	The Bauru Basin is an intracratonic basin with a Late Cretaceous (Cenomanian to Maastrichtian) infilling [6]. During that period, a broad zone with excessive evaporation extends from the equator to beyond 30°S, embracing central Africa and the central parts of South America, where the Bauru Basin is located. The predominantly arid climate of that zone is corroborated by several faciological and taphonomical evidence (e.g. Carvalho et al., 2010, Araujo & Marinho, 2013) and fits with the global Late Cretaceous climate characterization (Fig.7) [6].	The Cretaceous of the Bauru Group (sensu Soares et al. 1980) has so far provided the most significant record of Brazilian dinosaurs (Kellner and Campos 2000). Its strata are also referred to as Bauru Supersequence (Fig. 1, sensu Milani 2001) and were formed in an extensive subsidence area created by the lithostatic load of the Early Cretaceous basalts of the Serra Geral Formation, upon which the Bauru beds are discordantly deposited (Fulfaro and Perinotto 1996, Fernandes and Coimbra 2000, Milani 2004) [3]. The Bauru dinosaurs (Table I, II) are commonly found in localities of western São Paulo and Minas Gerais, where the Adamantina and Marília formations are widely known for their rich fossiliferous content (Bertini et al. 2003, Candeiro et al. 2006a, 2008) [3]. Dinosaur remains, mostly from Adamantina and Marília Formations (Bauru Group), are allocthonous, preserved in deposits of alluvial fans and braided river systems, where periodical flash-flood events reworked previously exposed soil sediments (caliche) [6].	Titanosuaria [3] Carcharodontosauridae [3] Abelisauridae [3] Deinonychosauria [3] Enantiornithes [3]

Table II of [3] for reference:

[3]

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Figure 7 in [6] for reference:

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Figure 7 – (A) Early Cretaceous climatic zones as depicted in Scotese & McKerrow (1990); (B) Late Cretaceous climatic zones as modeled by Sellwood & Valdes (2006), drawn using GCM. In both maps, note the location of important dinosaur-bearing Brazilian basins: 1 – Bauru Basin, 2 = Parecis Basin, 3 – Recôncavo Basin, 4 – Araripe Basin, 5 = São Luis Basin, 6 – Amazonas Basin. Note that the paleoclimatic zone of the São Luis and Amazonas basins varied from arid to humid during the Cretaceous.

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Paleo-climatic conditions of the Morrison Formation

NOTE: Contents of this section will be revisited/expanded from time-to-time.

Mesozoic periods	Description	Dinosaurian footprint and/or impressions	Classification
Jurassic	The Morrison Formation contains six plant taphofacies: Wood, whole-leaf, leaf-mat, root, common carbonaceous debris, and rare carbonaceous debris. None of these taphofacies is common in the Morrison; particularly striking is the paucity of wood, even in more reducing environments. The flora of the Morrison Formation is distinct in the Kimmeridgian and Tithonian parts of the section. The plant taphofacies are consistent with a predominantly herbaceous vegetation. Evidence from the plant taphofacies, floras, and sedimentology of the Morrison is consistent with a warm, seasonal, semi-arid climate throughout, changing from dry semi-arid to humid semi-arid from the Kimmeridgian to the Tithonian parts of the formation [7]. The flora of the Morrison Formation was predominantly herbaceous and, in the Kimmeridgian part of the formation, resembled that of modern savannahs in which trees are not abundant and are most common in the riparian environments. Although the vegetation in the Tithonian part of the Morrison was still predominantly herbaceous, it included elements that are consistent with a slightly more humid climate. We propose that the climate was slightly wetter in the Tithonian because either precipitation was higher or cooling led to lower evaporation rates, or both [7]. The taxonomic composition of the floras in the Kimmeridgian and Tithonian parts of the Morrison Formation is strikingly different, and it is therefore misleading to consider the flora of the entire formation as a single vegetational unit [7].	Efficient Sauropods vs. others and niche partitions In light of diverse geological evidence that indicates a seasonal, semiarid climate for the time of deposition of the Morrison Formation, one can assume these general environmental conditions for the purpose of reconstructing the ancient ecosystem. Wet environments that preserved plant fossils and some invertebrates and small vertebrates in the Morrison can be interpreted as representing local conditions limited in space and/or time. These elements of the biota and the smaller dinosaurs were probably restricted to such wetland areas at times of environmental stress [8]. A diverse fauna of large, herbivorous, sauropod dinosaurs ranged throughout the environment. Although this seems to be inconsistent with an environment with sparse resources, large size confers physiologic advantages that are adaptive for just such conditions. The scaling effect of large size makes large herbivores very efficient relative to their size in needing proportionately less food and food of poorer quality than smaller herbivores. They can also survive starvation longer and travel more efficiently to reach widely separated resource patches. Although few in number at any time, the sauropod dinosaurs are locally abundant and seemingly ubiquitous in the fossil record of the Morrison Formation because of overrepresentation of their highly preservable remains in an attritional fossil assemblage [8]. Sauropod dinosaur species partitioned the food resources by varied feeding strategies, possibly including vertical stratification of browsing levels. High-browsing brachiosaurs were probably relatively rare, while camarasaurs browsing on course vegetation at intermediate height were more common. Diplodocids browsed on the low-growing herbaceous plants. Predatory dinosaurs of varying size occupied the same range as their prey species [8]. The very large predatory dinosaurs may have specialized as scavengers on the large carcasses of sauropods. This habitat might expand during a wet season or be reduced to small, widely separated refugia during periods of severe drought. Relatively small populations of adult sauropods utilized very large geographic ranges, traveling long distances between resource areas, especially during times of drought. Other, smaller, herbivorous dinosaurs, including juvenile sauropods, may have been more specialized feeders and ranged less widely than the adult sauropods [8]. In his study of the paleoecology of the Morrison, Foster (1998) analyzed the various ecological guilds represented in the Morrison with respect to taxonomic diversity and adult body mass. He found that for herbivores, the greatest diversity occurs at very large and very small body size, with much lower diversity in intermediate sizes. He offered two possible explanations for this pattern: that the intermediate body size classes may have been filled by the juveniles of the very large species (sauropods), or that the intermediate size herbivores may have been more vulnerable to predation by moderate to large predators [8]. This size distribution of species might also be explained as a result of two successful strategies for survival in an environment such as that postulated for the Morrison. At times of limited availability of water, the large sauropods could survive by traveling from one resource patch to another. Smaller species were confined to those small areas with persistent water resources, but smaller body size enabled them to maintain larger populations and greater diversity, and rapidly expand their populations when resources were more abundant. Times of severe drought would be especially harsh on herbivores of intermediate body size. Sauropods would have to grow through such an intermediate size, and would be especially vulnerable to severe drought at that point in their development [8].  --- The Morrison mammals are not instructive The mammals of the Morrison Formation (Engelmann and Callison, 1998) are far removed from any living mammals in their history of adaptive modification. They are therefore of little value as environmental indicators. The specific adaptations of the Morrison mammals are not apparent from what is known of their anatomy. It seems likely that at least some, such as the triconodonts and dryolestoids, depended on a diet of small invertebrates and possibly small vertebrates. Whether some of the Morrison mammals, such as the multituberculates, may have been partly or completely herbivorous, cannot be determined with confidence. Thus, some, and possibly all of the Morrison mammals, as secondary consumers, were not immediately dependent on the vegetation for food. One characteristic common to the Morrison mammals is their small size. The largest were only the size of a modern ground squirrel, and many were much smaller. Because of their small size, the mammals probably would have been restricted to areas where water was continuously available. However, resource requirements for very small individual organisms are small, and a population of mammals could survive on very limited resources. Small animals also may be able to take advantage of microhabitats that offer more favorable conditions. For example, they may have been primarily nocturnal, sheltering in burrows to avoid the heat of the day. On the other hand, small size also implies short generation times, allowing surviving populations to expand rapidly when resources are relatively abundant [8]. --- Unique ecosystem The extinct ecosystem of the Morrison does appear to be unique, with no completely satisfactory modern analogue. One of its most peculiar features is the diverse fauna of sauropod dinosaurs. They undoubtedly had a central role in the ecosystem, and their presence and activities probably affected it in ways we have not considered or even imagined. However, we believe the scenario we have suggested resolves the information we have about the Morrison from diverse sources [8]. --- The Morrison invertebrates are instructive The invertebrate faunas in the Upper Jurassic Morrison Formation have received little attention in comparison to their better-known dinosaurian counterparts. Unlike the more prolifically preserved dinosaurian assemblages, invertebrates are rare as body fossils with some groups, like insects, being virtually absent from the fossil record (Gorman et al., 2008; Hasiotis, 2004; Lara et al., 2020; Zherikhin, 2003). Incorporating traces fossils, such as burrows, tracks, borings and feeding marks, has revealed a more complete picture of invertebrate diversity within Late Jurassic ecosystems in North America, and the ichnological record of invertebrate traces made on geological substrates has been documented from sites across the Morrison Formation (Hasiotis, 1999, 2004; Turner & Peterson, 2004). Among previous works examining invertebrate traces, those specifically left on vertebrate bone have received less targeted research [9]. Here, we present a robust dataset of invertebrate traces on vertebrate fossil material from the Upper Jurassic Mygatt-Moore Quarry (MMQ) in western Colorado [9]. The MMQ was discovered in 1981 by J.D. and Vanetta Moore and Pete and Marilyn Mygatt while hiking Rabbit Valley in the McInnis Canyons National Conservation Area, near the Utah-Colorado border (Fig. 1). The site preserves a dinosaur-dominated fossil assemblage within the Brushy Basin Member of the Upper Jurassic Morrison Formation [9]. Invertebrate faunas can also provide insights into paleoclimatic conditions in the fossil record (Elias, 2010; Guiot et al., 1993; Hasiotis, 2004; Holden et al., 2017). Data from experimental studies using dermestid and clerid beetles have demonstrated that these organisms prefer desiccated, though not wholly dry, vertebrate carcasses (Timm, 1982; Zanetti, Visciarelli & Centeno, 2014, 2015) and typically inhabit areas with temperatures above 20 degrees Celcius (Wilches et al., 2016). As dermestids, or behaviorally convergent taxa, are putative actors for the majority of this dataset, we can infer widespread desiccation among the modified remains and a warm, arid paleoclimate, consistent with previous interpretations of ecologically-stressed, resource-poor, drought-induced death assemblages in the Morrison Formation (Foster et al., 2018; Turner & Peterson, 2004) (Fig. 8). However, the presence of gastropods in the assemblage, as both body fossils and potential actors for Trace Type 3, reveals the fluctuation of the local climate at the MMQ and support the presence of periodic wet episodes. Additionally, sedimentological evidence of small (<1 cm2) interference ripple marks in the top 50 cm of the horizon and isolated pockets of bioturbation in the lowest meter of the horizon, presumably from dinosaurian faunas churning the smectitic muds like a boggy mire (Foster, 2003, 2014; Foster et al., 2018; McHugh, 2018; McHugh et al., 2018; Mygatt, 1991; Trujillo et al., 2014), support interpretations of the wet/dry seasonality at the MMQ. The disproportionate abundance of Trace Type 1 (dermestid or clerid beetles) compared to Trace Type 3 (gastropods or beetles) in the dataset indicates the dominance of dry conditions during the accumulation of vertebrate carcass remains at the site [9]. --- Two-thirds of biota represent just 1 Ma interval of existence? Two new chemical abrasion thermal ionization mass spectrometry U/Pb dates establish the age of the top of the Brushy Basin Member, Morrison Formation, at Flat Top (also known as Terrace Hill), north of the Fruita Paleontological Research Natural Area (FP), and of the lower part of the Brushy Basin Member, in the region of the Trail through Time (TT) and Mygatt-Moore Dinosaur Quarry in westernmost Colorado. Strata at both locations preserve a fossil record of large dinosaurs, including bones, dinosaur nests, and trace fossils, as well as fossils of unionid bivalves, fish, turtles, crocodilians, microvertebrates, logs, and other plant material. We report here a new weighted mean 206Pb/238U date of 149.43 +/- 0.059 Ma for three zircon grains sampled from a stratigraphic level 99 m above the base of a 101-m-thick Brushy Basin Member FP section and a new weighted mean 206Pb/238U date of 150.208 +/- 0.094 Ma for three zircon grains sampled from a stratigraphic level 39 m above the base of a 79-m-thick Brushy Basin Member TT section. These dates place the Brushy Basin strata in the Tithonian Stage of the Upper Jurassic Series. The 149.43 Ma date from Fruita is the youngest reliable date from near the top of the formation. The new dates also indicate a relatively short interval of deposition—less than 1 My—for the upper Brushy Basin Member. Thus, two-thirds of the dinosaur and other vertebrate fossils known from the Morrison Formation represent a biota that existed for only 1My. However, it is possible that some taxa persisted during some of the time represented by the K-1 unconformity [10].	Saurophaganax maximus noticed in the Morrison Formation of Oklahoma [11]. Torvosaurus tanneri from the Morrison Formation in Colorado, Utah, and Wyoming [11]. Genus Allosaurus [11] Genus Ceratosaurus [11]

Figures (1 - 2) in [8] for reference:

[8]

Figure 8 in [9] for reference:

[9]

Figure 8: Artist Reconstruction.
Dry season at the Mygatt-Moore Quarry showing Allosaurus feeding on a rotting, bug-infested carcass. Illustration by Brian Engh, dontmesswithdinosaurs.com (modified with permission from Drumheller et al., 2020).

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REFERENCES

[1] LINK: www.climate.gov/news-features/climate-qa/whats-hottest-earths-ever-been

[2] LINK: organismalbio.biosci.gatech.edu/biodiversity/mass-extinctions-and-climate-variability-2/

[3] Bittencourt, J. S., & Langer, M. C. (2011). Mesozoic dinosaurs from Brazil and their biogeographic implications. Anais da Academia Brasileira de Ciências, 83(1), 23-60.

[4] Hudgins, M. N., Uhen, M. D., & Hinnov, L. A. (2020). The evolution of respiratory systems in Theropoda and Paracrocodylomorpha, the end-Triassic extinction, and the role of Late Triassic atmospheric O2 and CO2. Palaeogeography, Palaeoclimatology, Palaeoecology, 545, 109638.

[5] Adopted from the following link: www.geosociety.org/GSA/Education_Careers/Geologic_Time_Scale/GSA/timescale/home.aspx

[6] Holz, M. (2015). Mesozoic paleogeography and paleoclimates–a discussion of the diverse greenhouse and hothouse conditions of an alien world. Journal of South American Earth Sciences, 61, 91-107.

[7] Parrish, J. T., Peterson, F., & Turner, C. E. (2004). Jurassic “savannah”—plant taphonomy and climate of the Morrison Formation (Upper Jurassic, Western USA). Sedimentary Geology, 167(3-4), 137-162.

[8] Engelmann, G. F., Chure, D. J., & Fiorillo, A. R. (2004). The implications of a dry climate for the paleoecology of the fauna of the Upper Jurassic Morrison Formation. Sedimentary Geology, 167(3-4), 297-308.

[9] McHugh, J. B., Drumheller, S. K., Riedel, A., & Kane, M. (2020). Decomposition of dinosaurian remains inferred by invertebrate traces on vertebrate bone reveal new insights into Late Jurassic ecology, decay, and climate in western Colorado. PeerJ, 8, e9510.

[10] Galli, K. G., Buchwaldt, R., Lucas, S. G., & Tanner, L. (2018). New chemical abrasion thermal ionization mass spectrometry dates from the Brushy Basin Member, Morrison Formation, western Colorado: implications for dinosaur evolution. The Journal of Geology, 126(5), 473-486.

[11] Drumheller, S. K., McHugh, J. B., Kane, M., Riedel, A., & D’Amore, D. C. (2020). High frequencies of theropod bite marks provide evidence for feeding, scavenging, and possible cannibalism in a stressed Late Jurassic ecosystem. Plos one, 15(5), e0233115.

[Life]

Temperate rainforests near the South Pole during peak Cretaceous warmth

Abstract

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years^1,2,3,4,5, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume⁶. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian–Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

Citation: Klages, J. P., Salzmann, U., Bickert, T., Hillenbrand, C. D., Gohl, K., Kuhn, G., ... & Dziadek, R. (2020). Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature, 580(7801), 81-86.

LINK: www.nature.com/articles/s41586-020-2148-5

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Palaeoclimate


Multi-proxy evidence from our mid-Cretaceous sedimentary record reveals an environment at a palaeolatitude of ~82° S on the Antarctic continental margin that was characterized by a regional temperate climate warm enough to maintain a diverse temperate rainforest (Fig. 3) only ~900 km from the palaeo-South Pole. Our palynomorphbased climate reconstruction following the approach outlined in ref. ⁴⁶ returns a mean annual temperature of 13 °C with precipitation of around 1,120 mm yr⁻¹. The average temperature of the warmest summer month was 18.5 °C. Previous quantitative climate analyses from Antarctic records ~2,500 km further north resulted in Coniacian–Santonian (~89–84 Ma) mean annual air temperatures of 15–21 °C (refs. ^47,48), suggesting a shallow temperature gradient towards our site. Estimates of the Late Cretaceous climate based on NLRs generally agree well with other temperature proxies⁴⁷. However, the approach assumes similarity of climate requirements for fossil taxa and their NLRs. With increasing age, the phylogenetic relationships of a fossil taxon become more disparate and the assumption thus becomes less robust. We therefore applied an independent geochemical palaeothermometer (HTI₃₀) based on the distribution of the heterocyst glycolipids (ref. ⁴⁹), which corroborated our bioclimatic reconstructions by indicating austral summer lake or river-surface water temperatures of ~20 °C for the swampy rainforest (Extended Data Fig. 4; see Methods). Our record contains, to our knowledge, the hitherto southernmost evidence of Cretaceous terrestrial environmental conditions and reveals a mid-Cretaceous ‘greenhouse climate’ that was capable of maintaining temperate conditions much farther south than previously documented¹⁴.


Palaeoclimate modelling


In light of extremely limited mid-Cretaceous CO₂ proxy data⁶ and widely scattered existing data estimates⁵, and to identify some of the pivotal driving mechanism of high-latitude mid-Cretaceous environmental conditions reconstructed for our new record, we ran the global climate model COSMOS⁵ in a coupled atmosphere–ocean configuration with fixed vegetation. We did so under present-day (Fig. 4a–c) and mid-Cretaceous configurations at 90 Ma (Fig. 4d–g) for 1^×, 2^×, 4^× and 6^× pre-industrial (PI) CO₂ levels of 280 ppmv (280, 560, 1,120 and 1,680 ppmv, respectively; see Methods). Although the model predicts a mid-Cretaceous climate in West Antarctica that is already warmer under PI CO₂ levels (Fig. 4d), summer surface air and water temperatures of ~20 °C at ~82° S can only be reproduced by forcing the climate with very high atmospheric CO₂ levels between 1,120 and 1,680 ppmv (Fig. 4f, g). Our reconstructed mean annual air temperature of 13 °C, however, still remains strongly underestimated by the model (Fig. 4g).

We conclude that a temperate climate at such a high latitude with more than four months of complete polar night darkness requires a combination of both strongly elevated atmospheric CO₂ concentrations and dense surface vegetation that generates a low planetary albedo with an associated high radiant energy absorption and pronounced seasonality. This largely precludes the existence¹⁰ of any substantial ice-sheet and sea-ice cover in and around Antarctica during the Turonian to Santonian stages of the Late Cretaceous epoch, an interpretation supported by palaeogeographic reconstructions of that period⁵⁰. Conversely, the present Antarctic Ice Sheet and its associated climate feedbacks, such as ice albedo, would provide a stabilizing cooling effect in a future high-CO₂ world (Fig. 4a–c).


To further elaborate on the importance of additional forcing mechanisms, to discover the interdependency of surface vegetation and temperature sensitivity in more detail and to explore the drivers of the paradox in the late Cretaceous latitudinal temperature gradient visible in Fig. 4, future work should aim to run the model with various types of vegetation cover coupled with other drivers such as palaeogeography⁵⁰ or changes in cloudiness⁵¹.


Our findings highlight the importance of including land–ice changes in long-term climate simulations to accurately estimate climate sensitivity on these extended timescales⁵². We provide key data for constraining the response of polar terrestrial ecosystems to very high atmospheric CO₂ concentrations and for assessing the impact of Antarctic ice sheet presence under high-CO₂ scenarios— both of which are essential for modelling past and future climate change⁵³.

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Comments: These findings are IN SYNC with Figure 7 in [6] of the review.

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[Life]

Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate

Abstract

Seasonal variability in sea surface temperatures plays a fundamental role in climate dynamics and species distribution. Seasonal bias can also severely compromise the accuracy of mean annual temperature reconstructions. It is therefore essential to better understand seasonal variability in climates of the past. Many reconstructions of climate in deep time neglect this issue and rely on controversial assumptions, such as estimates of sea water oxygen isotope composition. Here we present absolute seasonal temperature reconstructions based on clumped isotope measurements in bivalve shells which, critically, do not rely on these assumptions. We reconstruct highly precise monthly sea surface temperatures at around 50 °N latitude from individual oyster and rudist shells of the Campanian greenhouse period about 78 million years ago, when the seasonal range at 50 °N comprised 15 to 27 °C. In agreement with fully coupled climate model simulations, we find that greenhouse climates outside the tropics were warmer and more seasonal than previously thought. We conclude that seasonal bias and assumptions about seawater composition can distort temperature reconstructions and our understanding of past greenhouse climates.

Citation: De Winter, N. J., Müller, I. A., Kocken, I. J., Thibault, N., Ullmann, C. V., Farnsworth, A., ... & Ziegler, M. (2021). Absolute seasonal temperature estimates from clumped isotopes in bivalve shells suggest warm and variable greenhouse climate. Communications Earth & Environment, 2(1), 1-8.

LINK: www.nature.com/articles/s43247-021-00193-9

[Life]

Climatic constraints on the biogeographic history of Mesozoic dinosaurs

Highlights

• Sauropod dinosaurs never invaded polar palaeolatitudes
  
• Sauropods were constrained to lower latitudes more than the other dinosaurs
• Sauropods were more abundant in the Southern rather than in the Northern Hemisphere
• Sauropod ranges were more sensitive to temperature than those of other dinosaurs

Graphical abstract

Summary

Dinosaurs dominated Mesozoic terrestrial ecosystems globally. However, whereas a pole-to-pole geographic distribution characterized ornithischians and theropods, sauropods were restricted to lower latitudes. Here, we evaluate the role of climate in shaping these biogeographic patterns through the Jurassic–Cretaceous (201–66 mya), combining dinosaur fossil occurrences, past climate data from Earth System models, and habitat suitability modeling. Results show that, uniquely among dinosaurs, sauropods occupied climatic niches characterized by high temperatures and strongly bounded by minimum cold temperatures. This constrained the distribution and dispersal pathways of sauropods to tropical areas, excluding them from latitudinal extremes, especially in the Northern Hemisphere. The greater availability of suitable habitat in the southern continents, particularly in the Late Cretaceous, might be key to explaining the high diversity of sauropods there, relative to northern landmasses. Given that ornithischians and theropods show a flattened or bimodal latitudinal biodiversity gradient, with peaks at higher latitudes, the closer correspondence of sauropods to a subtropical concentration could hint at fundamental thermophysiological differences to the other two clades.

Citation: Chiarenza, A. A., Mannion, P. D., Farnsworth, A., Carrano, M. T., & Varela, S. (2022). Climatic constraints on the biogeographic history of Mesozoic dinosaurs. Current Biology, 32(3), 570-585.

LINK: www.sciencedirect.com/science/article/pii/S096098222101647X

The temperature-dependent distribution of sauropods has potential relevance to hypotheses of their biology and physiology, although precise implications cannot be constrained without additional data, such as histological or geochemical correlates of their thermophysiology. Nevertheless, the pattern of higher sauropod diversity at lower palaeolatitudes (Figure 3),⁴² and their absence from high-latitude dinosaur assemblages, particularly during cooler intervals (e.g., Poropat et al.,⁴³ Averianov et al.,⁴⁴ Benson et al.,⁵⁴ and Vavrek and Larsson⁹⁴) and in the Northern Hemisphere, raises the question of whether sauropod physiology was most efficient in warmer environments. The palaeolatitudinal distribution of sauropod diversity is broadly similar to that of crocodylomorphs,⁴² with temperature being a primary driver in shaping the latter group’s latitudinal extent throughout their evolutionary history.^{95, 96, 97, 98, 99} Given that extant crocodylomorphs (i.e., crocodylians) are ectothermic¹⁰⁰ and that the thermophysiology of at least some extinct members appears to be comparable,¹⁰¹ this could indicate that sauropods had a similar thermoregulatory strategy. Furthermore, given that crocodylomorph body size appears to have a positive correlation with temperature¹⁰² (though see Godoy et al.¹⁰³ for a contrasting result), this might explain the occurrence of the largest known sauropods (>50 tonnes) in the latest Albian–Cenomanian hothouse,^8,104 as well as some of the smallest known sauropod species (<10 tonnes) in the late Campanian–Maastrichtian,¹⁰⁵ coinciding with one of the coolest intervals of their evolutionary history.¹⁰⁶ Additionally, other observations, summarized below, raise the possibility of genuinely distinct and biologically induced distributional ranges between different dinosaur clades.

A mix of traits might have conferred on sauropods a higher adaptation for heat dissipation (compared to modern mammalian analogs), including an avian-like respiratory system,¹⁰⁷ long necks and tails shaping their overall morphology into a higher proportional body surface area,^108,109 and unusual adaptations in their neurovasculatory networks.¹¹⁰ By comparison, many non-avian and all avian theropods were characterized by the presence of insulating integument, which has been suggested as an anatomical correlate of endothermy.¹¹¹ Similarly proposed homologous structures have also been found in early diverging ornithischians.^112,113 No similar integumentary structure has yet been found in sauropods (or the more inclusive clade Sauropodomorpha), with evidence of scaly integument with osteoderm-like structures even in embryonic specimens,^114,115 making inferences of feather-like integument in sauropods even less likely.¹¹⁶

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Related information in following link: www.sciencedirect.com/science/article/pii/S0960982221017395

Sauropod reproductive strategies also differed from their theropod and ornithischian cousins, and this may also contribute to differences in palaeolatitudinal ranges between the dinosaur groups. Theropods probably relied on direct body heat for incubating their nests, whereas ornithischians seem to have used heat-generating microbial decay for incubation¹². These strategies of two homeothermic groups (where animals maintain a stable internal temperature regardless of external influence) contrasted with sauropods, where palaeontologists have found evidence of mound and in-filled hole nesting, which are dependent on solar or geothermic heat sources. This peculiar biology not only excluded sauropods from polar zones, but also constrained their ability to disperse to high latitudes; instead of roaming widely, they relied on ‘climate corridors’, such as their route from South America to Australasia via Antarctica during the warmest interval of the Cretaceous¹³.

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[Life]

Cretaceous climates: Mapping paleo-Köppen climatic zones using a Bayesian statistical analysis of lithologic, paleontologic, and geochemical proxies

Highlights

• Quantitative, proxy-based paleo-Köppen climate maps for nine Cretaceous time slices.
  
• New Cretaceous temperature and precipitation databases (n > 10,000 data points).
• New Bayesian statistical approach for combining quantitative & censored proxies.
• Cretaceous paleo-Köppen maps give new insight into greenhouse climate systems.
• Maps provide new database for Cretaceous proxy/model comparison studies.

Abstract

The Cretaceous Period (145 to 66 Ma) was a prolonged warmhouse to hothouse period characterized by high atmospheric CO2 conditions, elevated surface temperatures, and an enhanced global hydrologic cycle. It provides a case study for understanding how a hothouse climate system operates, and is an analog for future anthropogenic climate change scenarios. This study presents new quantitative temperature and precipitation proxy datasets for nine key Cretaceous time slices (Berriasian/Valanginian, Hauterivian/Barremian, Aptian, Albian, Cenomanian, Turonian, Coniacian/Santonian, Campanian, Maastrichtian), and a new geostatistical analysis technique that utilizes Markov Chain Monte Carlo algorithm and Bayesian hierarchical models to generate high resolution, quantitative global paleoclimate reconstructions from these proxy datasets, with associated uncertainties. Using these paleoclimate reconstructions, paleo-Köppen (-Geiger) climate zone maps are produced that provide new insights into the changing spatial and temporal climate patterns during the Cretaceous. These new paleoclimate reconstructions and paleo-Köppen climate maps provide new insight into the timing of the initiation of the Early Cretaceous equatorial humid belt over Gondwana and reveal temporal shifts in the width of the subtropical arid belts from the Early to mid- to Late Cretaceous. A comparison of these proxy-based reconstructions and model simulations of Cretaceous climate reveal continued proxy/model differences. In addition, the methodology developed for this study can be applied to other time periods, providing a framework for better understanding ancient climate, environments, and ecosystems.

Citation: Burgener, L., Hyland, E., Reich, B. J., & Scotese, C. (2023). Cretaceous climates: Mapping paleo-Köppen climatic zones using a Bayesian statistical analysis of lithologic, paleontologic, and geochemical proxies. Palaeogeography, Palaeoclimatology, Palaeoecology, 111373.

Link: www.sciencedirect.com/science/article/pii/S0031018222005442

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This paper presents a new synthesis of global climate for nine subdivisions of the Cretaceous Period (145 Ma – 66 Ma) in the form of quantitative temperature and precipitation reconstructions and paleo-Köppen(-Geiger) climate zone maps. The Cretaceous was a warmhouse to hothouse world that was generally characterized by hot to temperate continental climates that stretched from pole to equator (Scotese et al., 2021). During the cooler, early Cretaceous, there is some evidence for snow and ice at high latitudes, but no geological evidence of permanent ice caps. If permanent icecaps were present they would have been small (20% the size of the modern Antarctic icesheet) and ephemeral (Bornemann et al., 2008; Ladant and Donnadieu, 2016). In many respects, the Cretaceous was the antithesis of the ice house worlds of the last 40 million years during which time the South Pole and more recently the North Pole (∼last five million years), were covered in snow and ice. Though the climates of the Cretaceous were very different from the modern climate system, they represent a natural laboratory for studying how earth's climate may evolve under future climate change scenarios.

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Perhaps the most distinctive feature of our Cretaceous climate reconstructions is the dominance of the Temperate, Humid Subtropical (Ca) and Tropical Savannah (As/Aw) climate zones. In the modern, these two zones are also relatively large (second and third largest, respectively; Table 7) and together represent 24% of land area; however, in the Cretaceous these two zones represent a combined 63% (Coniacian-Santonian) to 84% (Albian) of land area (Fig. 5). Based on these observations, we suggest that during the Cretaceous higher Earth surface temperatures and reduced latitudinal temperature gradients resulted in less climate and environmental diversity than in the modern world. This hypothesis is supported by three lines of evidence. First, using the Zhang et al. (2016) paleo-Köppen classification system, the modern climate can be classified into 13 unique climate zones, but our Cretaceous analysis windows only have 6 to 12 unique zones. Second, the mean size of the modern paleo-Köppen climate zones is 7.7% of modern land area, while the mean size of Cretaceous paleo-Köppen climate zones ranges from 8.3 (Maastrichtian) to 16.2% (Coniacian-Santonian and Cenomanian), suggesting that Cretaceous climate zones covered more land area than their modern equivalents. Third, the variance in size between the modern paleo-Köppen climate zones is just 24.5%, but it ranges from 273% (Maastrichtian) to 450% (Cenomanian) for the Cretaceous analysis windows. This is consistent with the observation that the thirteen modern climate zones are similar in size to one another, while the Cretaceous climate zones tend to be dominated by one or two climate zones that cover significantly more area than the remaining climate zones. We note that these results hold true even when considering the paleo-Köppenelev Cretaceous reconstructions that take into account the elevation-dependent temperature lapse rate. Importantly, this hypothesis is consistent with paleo-Köppen climate zone calculations based on prior Community Earth System Model (CESM) version 1.2 simulations of latest Paleocene, Paleocene-Eocene Thermal Maximum (PETM), and Early Eocene Climatic Optimum (EECO) climates (Lunt et al., 2017, Lunt et al., 2021), and Global Fluid Dynamics Laboratory Climate Model 2.1 (GFDL CM2.1) simulations of the Eocene-Oligocene Transition (EOT) climate (Hutchinson et al., 2018, Hutchinson et al., 2019, Hutchinson et al., 2021). The CESM and GFDL CM2.1 models predict mean terrestrial MATs of 10.4 °C, 25.1 °C, 17.0 °C, and 10.3–15.9 °C, and 11, 7, 8, and 11–12 unique climate zones for the latest Paleocene, PETM, EECO, and EOT, respectively.

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In summary, both the proxy-based reconstructions and model simulations (this study; Scotese et al., 2021; Valdes et al., 2021; Li et al., 2022) produce temperatures much warmer than the modern world (Fig. 16). Tropical temperatures were, on average, 6 °C warmer than the modern world and polar temperatures were much warmer (+24 °C) than the modern world. The proxy-based reconstructions and the model simulations produce very similar average global temperatures (∼22 °C, Table 7). It is important to note that despite the similarity in global average temperatures produced by the proxy-based reconstructions and model simulations, the latitudinal temperature gradients produced by each technique are systematically different. As can be seen in Fig. 16 and Table 7, the model simulations of temperature (blue lines) are warmer near the equator than the proxy-based temperature estimates (red lines). Conversely, at high latitudes the model simulations of temperature are cooler than the proxy-based temperature estimates.

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Comments: Absolutely.

The much-hyped Prehistoric Planet documentary uses MODERN WEATHER EXTREMES as a PROXY to predict and depict CRETACEOUS WEATHER EXTREMES in Maastrichtian, but this modeling technique is problematic on many counts. Modern continental PLAN is very different from the Cretaceous continental PLAN and modern oceanic circulation system is very different from the Cretaceous oceanic circulation system.

1. Modern environmental conditions facilitate glaciation in polar latitudes as well as El Niño and La Niña CYCLES, which are known to affect when and where "extreme weather events" take place.

www.climate.gov/enso

www.climate.gov/news-features/blogs/enso/what-el-ni%C3%B1o%E2%80%93southern-oscillation-enso-nutshell

www.nationalacademies.org/based-on-science/climate-change-global-warming-is-contributing-to-extreme-weather-events

2. Anthropogenic GLOBAL WARMING is contributing to MODERN WEATHER EXTREMES as well:

Our analysis of observations and model simulations consistently shows a strong spatial dependence of climate extremes. This has led to frequently concurrent climate extremes in different parts of the world. We find that the global pattern of spatial dependence of climate extremes, which is also evident in the historical simulations with natural forcing only, primarily arises from the internal climate variability. This is because regional climates around the globe are interconnected through teleconnections, and the global drivers of atmospheric variability, such as the El Niño–Southern Oscillation, can bring about climate extremes simultaneously in far distant regions (37). The strong spatial co-occurrence of temperature extremes over tropical regions is probably driven by the warm phases of the Pacific Decadal Oscillation (38), while concurrent climate extremes in the mid- and high-latitude regions are likely related to Rossby wave patterns (13, 39). We also demonstrate that anthropogenic climate forcing has greatly enhanced the spatial co-occurrence strength of temperature extremes over 56% of global region pairs and will continue to increase the frequency, intensity, and extent of co-occurring climate extremes over global land regions, particularly in the tropics and northern high latitudes. Future amplification of global concurrent climate risks is especially strong in high-end forcing SSP585, while the ambitious emissions mitigation pathway of SSP126 substantially moderates future exacerbation of concurrent climate extremes, especially for the high-risk regions.

www.science.org/doi/10.1126/sciadv.abo1638

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Berriasian-Valanginian paleo-Köppen climate zones (Burgener et al., 2023):

Hauterivian-Barremian paleo-Köppen climate zones (Burgener et al., 2023):

Aptian paleo-Köppen climate zones (Burgener et al., 2023):

Albian paleo-Köppen climate zones (Burgener et al., 2023):

Cenomanian paleo-Köppen climate zones (Burgener et al., 2023):

Turonian paleo-Köppen climate zones (Burgener et al., 2023):

Coniacian-Santonian paleo-Köppen climate zones (Burgener et al., 2023):

Campanian paleo-Köppen climate zones (Burgener et al., 2023):

Maastrichtian paleo-Köppen climate zones (Burgener et al., 2023):

vs.

Modern climatic zones (Burgener et al., 2023):

The most obvious contrast between the modern and Cretaceous terrestrial climate systems is the dominance of the Polar (E) climate zone, which accounts for 15% of land area in the modern world, but is completely absent in all of the Cretaceous analysis windows. In contrast, all of the Cretaceous analysis windows are dominated by the Temperate, Humid Subtropical (Ca) and Tropical Savannah (As/Aw) climate zones. The Temperate, Humid Subtropical zone accounts for just 12.9% of land area in the modern world, but ranges from a maximum of 63 ± 0.4% in the Albian to a minimum of 32 ± 0.3% in the Turonian. The Tropical Savannah zone ranges from a maximum of 39 ± 0.4% in the Turonian to 19 ± 0.3% in the Berriasian-Valanginian.

Maastrichtian [does] show significantly expanded Db (continental, warm summer) and Dc/Dd (continental, subarctic) climate zones in comparison to earlier Campanian Db (continental, warm summer) and Dc/Dd (continental, subarctic) climate zones, but Maastrichtian Db (continental, warm summer) climate zone remained much bigger in scale.

Arctic cold waves stem from glaciation in polar latitudes and reach mid-latitudes from time-to-time in modern times:

scied.ucar.edu/learning-zone/climate-change-impacts/why-polar-air-keeps-breaking-out-arctic

But Polar climate zone DID NOT EXIST in Maastrichtian. WE cannot be certain of MODERN WEATHER EXTREMES occurring even in Maastrichtian Dc/Dd (continental, subarctic) climate zones, therefore.

REPEAT: Modern environmental conditions facilitate glaciation in polar latitudes as well as El Niño and La Niña CYCLES, which are known to affect when and where "extreme weather events" take place. These conditions DID NOT EXIST at any point in time during Cretaceous. And anthropogenic GLOBAL WARMING was NOT occurring in Maastrichtian either.

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Feathered dinosaurs are often cited as PROOF of adaptation to [supposedly] freezing temperatures near the Poles throughout the Cretaceous timeline. Alternatively, feathers were an evolutionary step towards development of GLIDE or FLIGHT capability:

Results show that, irrespective of its wing configuration, Microraptor was aerodynamically unstable at low SCR (Fig. 2c) and would have been unable to glide with maximum aerodynamic efficiency (that is, high L/D). Thus, Microraptor would have been better off adopting a high SCR, lower L/D wing configuration to quickly generate the high lift at low speeds needed to minimize initial height loss in short glides from moderate heights. This high-lift, high-drag flight strategy (Fig. 3) would have been very efficient for leaping from moderate heights (ca. 20–30 m), consistent with tree sizes in the Jehol podocarp forest.

+

In sum, Microraptor likely indulged in some climbing behaviour, some terrestrial foraging behaviour and glided on occasion; it may thus have foraged across a vertical gradient, using a body plan different from that of extant species. The likely presence of microraptorines in the Late Cretaceous¹⁹ combined with new evidence that a phylogenetically diverse range of Mesozoic birds³², including Archaeopteryx⁸, possessed feathered legs as well as wings suggests that this generalized, perhaps primitive, form of aerial adaptation was persistent across paravian history and was not a short-lived evolutionary event.

www.nature.com/articles/ncomms3489

Model-based approaches are needed to explore the varieties of aerial and nonaerial locomotor strategies that extinct dinosaurs may have employed. These must take into account not only the diverse locomotor strategies in living birds but also potential differences in feather properties, shape, and plumage organization.

www.science.org/doi/abs/10.1126/science.1235463

Modern flying birds molt to replace old and worn feathers that inhibit flight performance, but its origins are unclear. We address this by presenting and evaluating a ~150 million year old record of molting in a feathered dinosaur from the early bird Archaeopteryx. Laser-Stimulated Fluorescence revealed feather sheaths that are otherwise invisible under white light. These are separated by one feather and are not in numerical sequential order and are mirrored in both wings. This indicates that a sequential center-out molting strategy was already present at the origins of flight, which is used in living falcons to preserve maximum flight performance. This strategy would have been a welcome advantage for early theropod flyers that had poor flight capabilities. This discovery provides important insights into how birds refined their early flight capabilities before the appearance of the keeled sternum, pygostyle and triosseal canal.

www.nature.com/articles/s42003-020-01467-2


And numerous dinosaurs were NOT feathered to begin with: 

Among averostrans, squamous skin is confirmed in Ceratosauria (Carnotaurus), Allosauroidea (Allosaurus, Concavenator, Lourinhanosaurus), Compsognathidae (Juravenator), and Tyrannosauroidea (Santanaraptor, Albertosaurus, Daspletosaurus, Gorgosaurus, Tarbosaurus, Tyrannosaurus), whereas dermal ossifications consisting of sagittate and mosaic osteoderms are restricted to Ceratosaurus. 

theworldofanimals.proboards.com/thread/3936/dinosaur-skin-morphology-focus

Sauropods were particularly well-equipped to cope with HARSH CLIMATIC CONDITIONS and existed in tropical to subtropical latitudes during Cretaceous [see (Chiarenza et al., 2022) above].

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There [is] evidence of snowfall and glaciation circa 132 Ma but this condition did NOT last.

The Cretaceous, particularly the mid-Cretaceous, was a period of large amount of volcanism, which contributed to elevated atmospheric CO₂ levels and heat:

www.climate-policy-watcher.org/global-climate-2/cretaceous-era.html

Volcanism continued till the K-Pg boundary:

www.science.org/doi/abs/10.1126/science.aay5055

Following statement makes sense:

The hypothesis that Cretaceous climates were characterized by fewer, more extensive climate zones makes intuitive sense, because significantly higher land surface temperatures should result in the expansion of the warmest zones (e.g., Tropical and Hot Dry zones), and the elimination of the coldest zones (e.g., Polar).

www.sciencedirect.com/science/article/pii/S0031018222005442

There is some difference in Human respiratory system and Dinosaur respiratory system:

www.science.org/content/article/superlungs-gave-dinosaurs-energy-run-and-fight

Dinosaurs could do well in hot climatic conditions and oxygen-poor conditions of the Mesozoic in fact.

But some Paleonerds involved in much-hyped projects such as Prehistoric Planet and Prehistoric Kingdom want YOU to believe that global environmental conditions of the Cretaceous resemble that of modern times and there were locations where humans would freeze to death in hypothetical terms. This is IMPOSITION of modern worldview on very different environmental conditions of Cretaceous.

Average Polar temperature recorded in modern times = -20C considering both North and South Poles (Burgener et al., 2023)

Average Polar temperature recorded in modern times = -49C in Antarctica (Check)

Lowest Polar temperature recorded in modern times = -89.6C in Antarctica in 1983 (Check)

Average Polar temperature recorded in the Hauterivian-Barremian timeline = 4C (Burgener et al., 2023)

Average Polar temperature recorded in the Albian = 15C (Burgener et al., 2023)

Average Polar temperature recorded in the Turonian = 12C (Burgener et al., 2023)

Hypothetically: Humans will find Cretaceous conditions very hot and/or humid in various locations of the world across tropical and subtropical latitudes [if sent back in time]. Reduced seasonal climatic variability in conjunction with periodic heatwaves and very high atmospheric C0₂ levels are very likely to cause health issues including dehydration in humans across these latitudes in Cretaceous. Humans are much more likely to endure in Polar latitudes of the world in Cretaceous.

Why do YOU think Global Warming is such a matter of concern in human discourses? For the sake of chit-chat? Mankind's very existence is on the line.

www.pnas.org/doi/10.1073/pnas.2108146119

www.theguardian.com/environment/2022/aug/01/climate-endgame-risk-human-extinction-scientists-global-heating-catastrophe

www.scientificamerican.com/article/will-humans-ever-go-extinct/