Spinosaurus aegyptiacus

[elosha11]

Spinosaurus aegyptiacus


Life reconstruction of S. aegyptiacus, accounting for all known evidence as of January 2021. © @ Chris Masna

Temporal range: Cretaceous; Cenomanian (99-93.5 million years ago)

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Cephalochordata
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Clade: Euteleostomi
Clade: Sarcopterygii
Clade: Rhipidistia
Clade: Tetrapodomorpha
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Class: Reptilia or Clade: Sauropsida
Clade: Eureptilia
Clade: Romeriida
Clade: Diapsida
Clade: Neodiapsida
Clade: Archelosauria
Clade: Archosauromorpha
Clade: Archosauriformes
Clade: Crurotarsi
Clade: Archosauria
Clade: Avemetatarsalia
Clade: Ornithodira
Clade: Dinosauromorpha
Clade: Dinosauriformes
Clade: Dinosauria
Order: Saurischia
Clade: Eusaurischia
Suborder: Theropoda
Clade: Neotheropoda
Clade: Averostra
Clade: Tetanurae
Clade: Orionides
Clade: Avetheropoda
Superfamily: †Megalosauroidea
Clade: †Megalosauria
Family: †Spinosauridae
Genus: †Spinosaurus
Species: †S. aegyptiacus

Spinosaurus is an extinct genus of theropod dinosaur that lived in North Africa from 99-93.5 million years ago.

Locality:
Spinosaurus remains (or remains comparable to it) have been uncovered in Algeria, Tunisia, Egypt, Morocco, and Niger.[1]

Taxonomy:
Two Spinosaurus species have been named based on the region where they were discovered: Spinosaurus aegyptiacus (Egyptian spine lizard) and Spinosaurus maroccanus (Moroccan spine lizard). The latter is nowadays regarded as a junior synonym of Sigilmassasaurus brevicollis.[2]

Description and paleobiology:
Spinosaurus was named for the elongated neural spines that protruded from its back, forming a sail. One recent hypothesis proposes that the sail was used to improve maneuverability while swimming underwater, while providing hydrodynamic fulcrum needed to make powerful neck and tail blows (akin to those made by sailfish and thresher sharks) to stun, injure, or kill prey. The sail may also have served to help herd shoals of prey.[3] This hypothesis was rejected by a more recent paper, which claims that the torso and sail were too inflexible to function akin to that of a sailfish (which are flexible, collapsable, and mediolaterally thin).[4]

Spinosaurus exhibits a number of adaptations to a semiaquatic lifestyle[5][6]. There is still debate as to whether Spinosaurus was a shoreline generalist or an aquatic pursuit specialist.[4][5][6]

S. aegyptiacus is one of the largest known theropods, with a body length estimated to reach 15 meters.[5] Specimen FSAC-KK 11888 in particular was estimated to weigh anywhere between 3,219-4,173 kg.[6 supp. info] The non-specific gravity of Spinosaurus was estimated to be similar to that of crocodilians, at 1.05, making it slightly more dense than water.[7]

The cranial anatomy of Spinosaurus has also received attention from paleontologists. The anterior rostrum of Spinosaurus and Baryonyx both absolutely outperform modern crocodilian taxa in their ability to withstand stress, due to their large size. Despite differences in size and morphology, the anterior rostra of both Spinosaurus and Baryonyx perform similarly, suggesting similar feeding methods between the two. When the effects of size are removed, Baryonyx still outperforms all other taxa in dorsoventral bending, but Spinosaurus' performance falls between that of the alligator and gharial. In mediolateral bending, Baryonyx performs intermediately between the alligator and gharial, while Spinosaurus performs worse than all crocodilian taxa (a later study found that the anterior rostrum of Baryonyx performs similarly in bending to that of a Nile crocodile[8] with a total skull length of 50.1 cm[9]). In torsion, Baryonyx performs intermediately between the alligator and all other crocodilians, while Spinosaurus performs equal to or worse than the gharial and the slender-snouted crocodile. It should be noted that only the anterior rostrum was tested, and the results must be considered in this context.[10]

As a result, Spinosaurus and its kin seem to have been more apt to kill smaller prey via dorsoventral shaking. The deeply-rooted teeth and near vertical-sided teeth rows of spinosaurids are ideal for withstanding large dorsoventral bite forces and dissipating the resulting forces throughout the skull. The ability of Spinosaurus to prey on larger, struggling prey was not conferred by a snout specialized in withstanding stress, but by simple size-related advantages.[10]

The mandibular ramus of Spinosaurus was able to move laterally thanks to a mobile mandibular symphysis, which allowed the pharynx to widen. This is similar to jaw mechanics in some pterosaurs and pelicans. Hence, it is thought that Spinosaurus had the ability to swallow large fish and other prey items, with the ability to prey upon pterosaurs and juvenile dinosaurs.[11]

Isotope analysis and taphonomic evidence both support the use of aquatic resources by Spinosaurus.[12][13]


Carved reconstructed of the cranium of Spinosaurus, held by paleoartist Tyler Keillor.

Competition:
Interestingly, large crocodylomorph remains (e.g. Sarcosuchus) dominate Aptian beds in Africa and South America, but are unknown from the Cenomanian of North Africa. The largest crocodylomorph from the latter beds is Elosuchus; with a skull ~100 cm long, it would have been smaller than the giant spinosaurids. Larger crocodylomorphs seem rare in the Kem Kem Beds and Bahariya fauna. This suggests that spinosaurids became freshwater apex predators in North Africa as giant crocodylomorphs declined. Spinosaurids may have either replaced a vacant niche left behind by these crocodylomorphs or actively outcompeted them into extinction.[14]

References:

[1] paleobiodb.org/classic/basicTaxonInfo?taxon_no=53372
[2] Evers SW, Rauhut OWM, Milner AC, McFeeters B, Allain R. 2015. A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of Morocco. PeerJ 3:e1323 doi.org/10.7717/peerj.1323
[3] GIMSA, J., SLEIGH, R., & GIMSA, U. (2016). The riddle of Spinosaurus aegyptiacus’ dorsal sail. Geological Magazine, 153(3), 544-547. doi:10.1017/S0016756815000801
[4] Hone, D., & Holtz, T. (2021). Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist?. Palaeontologia Electronica.
[5] Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S., Myhrvold, N., & Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science (New York, N.Y.), 345(6204), 1613–1616. doi.org/10.1126/science.1258750
[6] Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature 581, 67–70 (2020). doi.org/10.1038/s41586-020-2190-3
[7] Larramendi, A., Paul, G. S., & Hsu, S. Y. (2020). A review and reappraisal of the specific gravities of present and past multicellular organisms, with an emphasis on tetrapods. Anatomical record (Hoboken, N.J. : 2007), 10.1002/ar.24574. Advance online publication. doi.org/10.1002/ar.24574
[8] Foffa, D., Cuff, A. R., Sassoon, J., Rayfield, E. J., Mavrogordato, M. N., & Benton, M. J. (2014). Functional anatomy and feeding biomechanics of a giant Upper Jurassic pliosaur (Reptilia: Sauropterygia) from Weymouth Bay, Dorset, UK. Journal of anatomy, 225(2), 209–219. doi.org/10.1111/joa.12200
[9] Lemanis, R., Jones, A. S., Butler, R. J., Anderson, P. S., & Rayfield, E. J. (2019). Comparative biomechanical analysis demonstrates functional convergence between slender-snouted crocodilians and phytosaurs (No. e27476v1). PeerJ Preprints.
[10] Cuff, A. R., & Rayfield, E. J. (2013). Feeding mechanics in spinosaurid theropods and extant crocodilians. PloS one, 8(5), e65295. doi.org/10.1371/journal.pone.0065295
[11] Hendrickx, C., Mateus, O., & Buffetaut, E. (2016). [url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144695Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa[/url]. PloS one, 11(1), e0144695. doi.org/10.1371/journal.pone.0144695
[12] Amiot, R., Buffetaut, E., Lécuyer, C., Wang, X., Boudad, L., Ding, Z., ... & Zhou, Z. (2010). Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods. Geology, 38(2), 139-142.[13] Beevor, T., Quigley, A., Smith, R. E., Smyth, R. S. H
[13] Ibrahim, N., Zouhri, S., & Martill, D. M. (2021). Taphonomic evidence supports an aquatic lifestyle for Spinosaurus. Cretaceous Research, 117, [104627]. doi.org/10.1016/j.cretres.2020.104627
[14] Arden, T. M., Klein, C. G., Zouhri, S., & Longrich, N. R. (2019). Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurids. Cretaceous Research, 93, 275-284.

[Life]

NEW INFORMATION REGARDING THE HOLOTYPE OF SPINOSAURUS AEGYPTIACUS STROMER, 1915

IN THE autumn of 1912, the fossil collector Richard Markgraf, with financial support and direction from Bavarian paleontologist Ernst Freiherr Stromer von Reichenbach and the Bavarian Academy of Sciences, discovered the partial skeleton of a bizarre predatory dinosaur in Upper Cretaceous (early Cenomanian, ;97 Ma, see Ismail et al., 1989; Barakat et al., 1993; El Beialy, 1994, 1995; Nabil and Hussein, 1994; Ismail and Soliman, 2001; Ibrahim, 2002; Gradstein et al., 2005) rocks of the Bahariya Formation exposed in the Bahariya Oasis of western Egypt (Fig. 1, see also Sereno et al., 1998; Nothdurft et al., 2002). This gigantic theropod, Spinosaurus aegyptiacus Stromer, 1915, possessed highly derived cranial and vertebral features sufficiently distinct for it to be designated as the nominal genus of the clade Spinosauridae (Stromer, 1915, 1936). Spinosaurids, currently definitively known only from Europe, South America, and Africa, are important because of the scarcity of Cretaceous Gondwanan tetrapod fossils (see Krause et al., 1999, 2003; Carrano et al., 2002; Lamanna et al., 2002). Moreover, fossils of Spinosaurus Stromer, 1915 and other spinosaurids are significant because of controversy surrounding the postulated paleoecology of these taxa (see discussions in Charig and Milner, 1997; Sereno et al., 1998; Sues et al., 2002). Questions related to spinosaurid paleoecology are particularly important in the Bahariya Formation, where Spinosaurus appears to have shared its habitat (see Stromer, 1936; Smith et al., 2001) with at least two other theropods in the size range of Tyrannosaurus Osborn, 1905 (Bahariasaurus Stromer, 1934 and Carcharodontosaurus Stromer, 1931). Unfortunately, the holotype and only known indisputable specimen of S. aegyptiacus (BSP 1912 VIII 19) was lost during the night of 24/25 April 1944 in a British bombing raid of Munich (Nothdurft et al., 2002). The attack severely damaged the building (dating to ca. 1583, No¨hbauer, 1987) that housed the Pala¨ontologische Staatssammlung Mu¨nchen and destroyed most of Stromer’s Bahariya collection (see Appendix 1). Since 1944, new spinosaurid taxa have been described (see Charig and Milner, 1986; Martill et al., 1996; Sereno et al., 1998; Sues et al., 2002) and additional material has been referred to Spinosaurus (e.g., Buffetaut, 1989, 1992; Russell, 1996; Taquet and Russell, 1998; Benton et al., 2000; Buffetaut and Ouaja, 2002), some of it questionably. However, definitive S. aegyptiacus material, or information regarding the original specimen of Spinosaurus, has not been forthcoming. We report here on two photographs of the holotype of Spinosaurus aegyptiacus as it was reposited in the Pala¨ontologische Staatssammlung Mu¨nchen prior to 1944, which we ‘‘rediscovered’’ in the archives of the Pala¨ontologisches Museum in June 2000, after they were donated to the museum by Ernst Stromer’s son, Wolfgang Stromer, in 1995 (Figs. 2, 3). These are, to our knowledge, the only surviving photographs of this, the one irrefutable specimen of S. aegyptiacus, which, prior to the initial print releases, which we authorized, of the photograph in Figure 3 (Prendergast, 2001; Glut and Chiappe, 2003), has been represented only by Stromer’s (1915, 1936) drawings (it has recently been suggested that BSP 1912 VIII 19 may represent a chimera of more than one dinosaurian taxon [Rauhut, 2003], but examining that idea is beyond the scope of this paper). Aside from their historical significance, these images are important in that they permit a direct comparison of several of Stromer’s (1915) illustrations with actual photographs of BSP 1912 VIII 19, thereby providing new insight into the skeleton. This is of note because Stromer’s (1915) text and illustrations have been used as sources of character data for Spinosaurus and the Spinosauridae in several theropod phylogenetic analyses (e.g., Sereno et al., 1998; Holtz et al., 2004). It is thus beneficial to be able to determine how closely these illustrations correspond to the actual anatomy of BSP 1912 VIII 19 as reproduced by the photographs, an effort which holds implications for the use of published drawings as sources of systematic information.

For full details: click here. (PDF download warning)

[Life]

NEW INFORMATION ON THE SKULL OF THE ENIGMATIC THEROPOD SPINOSAURUS, WITH REMARKS ON ITS SIZE AND AFFINITIES

ABSTRACT—New specimens of the unusual theropod Spinosaurus cf. S. aegyptiacus from the Late Cretaceous (early Cenomanian) of Morocco reveal new information about the structure of the snout and the very large adult body size attained by the species. The external naris is retracted farther caudally on the snout than in other spinosaurids and is bordered exclusively by the maxilla and nasal. The fused nasals preserve a longitudinal, fluted crest. The size of the snout suggests that Spinosaurus may well have exceeded the maximum adult body size of other large Cretaceous theropods such as Tyrannosaurus and Giganotosaurus. The new material also supports the monophyly of the Spinosaurinae and the separation of Spinosaurus and Irritator.

For full details: click here (PDF download warning)

[theropod]

one note: the lenght of 1,65m for the spinous processes is for the holotype IPHG 1912 VIII 19 which is regarded as a subadult (for example by Mickey Mortimer) most sources regard MSNM V4047 as much larger (with the exception of Hartman, whose skeletal shows remains of both individuals in the same animal, but his spinous processes don't fit when adjusting for the dentary size), hence its spines could have been longer too.

Also, S. marocannus is at best a nomen dubium, mostly it is regarded as synonymous with S. aegyptiacus

I have seen some pictures of supposed relatively complete private juvenile and subadult skeletons from northern Africa, whose skull shape varies quite a bit from the parts we know from Dal Sasso and Stromer's descriptions, so I'm cautious but it should be noted.

-------------------
(private coll.) (multiple individuals) partial skull (1.05 m), partial mandibles (Hendrickx, online)
(private coll.) (~8 m; multiple individuals) partial skull, partial skeleton (Hendrickx, online)
(private coll.) (multiple individuals) premaxillae, quadrate, posterior mandible, cervical vertebrae, caudal vertebrae (Hendrickx, pers. comm.)
(private coll.) premaxillae, dentary (Hendrickx, pers. comm.)
(private coll.) anterior dentary (Hendrickx, pers. comm.)
-------------------------
This is from the theropod database; these might be the same specimens
You can see some pictures of them on carnivora.

[theropod]

dml.cmnh.org/2007Mar/msg00292.html

Comments on the Therrien & Henderson metod, why it is not reliable for spinosaurs and spinosaurus skull lenght.

[creature386]

Known to everyone, but someone has to update the profile:


We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is downsized, the hind limbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal “sail” may have been enveloped in skin that functioned primarily for display on land and in water.

www.sciencemag.org/content/early/2014/09/10/science.1258750

And broly, I stole your new reconstruction in case that's OK.

[Infinity Blade]

The riddle of Spinosaurus aegyptiacus’ dorsal sail
Jan Gisma, Robert Sleigh, and Ulrike Gisma (2015)

"Spinosaurus aegyptiacus was probably the largest predatory dinosaur of the Cretaceous period. A new study shows that it was a semiaquatic hunter. The function of Spinosaurus’ huge dorsal ‘sail’ remains unsolved, however. Three hypotheses have been proposed: (1) thermoregulation; (2) humpback storage; or (3) display. According to our alternative hypothesis, the submerged sail would have improved manoeuvrability and provided the hydrodynamic fulcrum for powerful neck and tail movements such as those made by sailfish or thresher sharks when stunning or injuring prey. Finally, it could have been employed as a screen for encircling prey underwater."

Link

[Infinity Blade]

Morphofunctional Analysis of the Quadrate of Spinosauridae (Dinosauria: Theropoda) and the Presence of Spinosaurus and a Second Spinosaurine Taxon in the Cenomanian of North Africa.
Christophe Hendrickx, Octávio Mateus, Eric Buffetaut (2016)

"Six quadrate bones, of which two almost certainly come from the Kem Kem beds (Cenomanian, Upper Cretaceous) of south-eastern Morocco, are determined to be from juvenile and adult individuals of Spinosaurinae based on phylogenetic, geometric morphometric, and phylogenetic morphometric analyses. Their morphology indicates two morphotypes evidencing the presence of two spinosaurine taxa ascribed to Spinosaurus aegyptiacus and? Sigilmassasaurus brevicollis in the Cenomanian of North Africa, casting doubt on the accuracy of some recent skeletal reconstructions which may be based on elements from several distinct species. Morphofunctional analysis of the mandibular articulation of the quadrate has shown that the jaw mechanics was peculiar in Spinosauridae. In mature spinosaurids, the posterior parts of the two mandibular rami displaced laterally when the jaw was depressed due to a lateromedially oriented intercondylar sulcus of the quadrate. Such lateral movement of the mandibular ramus was possible due to a movable mandibular symphysis in spinosaurids, allowing the pharynx to be widened. Similar jaw mechanics also occur in some pterosaurs and living pelecanids which are both adapted to capture and swallow large prey items. Spinosauridae, which were engaged, at least partially, in a piscivorous lifestyle, were able to consume large fish and may have occasionally fed on other prey such as pterosaurs and juvenile dinosaurs."

Link

[creature386]

Donald Henderson disagrees with the semi-aquatic Spinosaurus hypothesis, stating that it was not more adapted towards buoyancy or floating than other large theropods:

A recent interpretation of the fossil remains of the enigmatic, large predatory dinosaur Spinosaurus aegyptiacus proposed that it was specially adapted for an aquatic mode of life – a first for any predatory dinosaur. A detailed, three-dimensional, digital model of the animal was generated and the flotation potential of the model was tested using specially written software. It was found that Spinosaurus would have been able to float with its head clear of the water surface. However, a similarly detailed model of Tyrannosaurus rex was also able to float in a position enabling the animal to breathe freely, showing that there is nothing exceptional about a floating Spinosaurus. The software also showed that the centre of mass of Spinosaurus was much closer to the hips than previously estimated, implying that this dinosaur would still have been a competent walker on land. With regional body densities accounting for pneumatized skeletons and system of air sacs (modelled after birds), both the Spinosaurus and Tyrannosaurus models were found to be unsinkable, even with the air sacs substantially deflated. The conclusion is that Spinosaurus would still have been a competent terrestrial animal.

Testing the buoyancy of an immersed Spinosaurus (Dinosauria: Theropoda) with a digital model. by Donald M. Henderson (2016)

[Infinity Blade]

My college displays a few Spinosaurus teeth in one part of its science wing. Here are a few pictures. By the way, I don't know if you guys can see (probably better in the second and third pictures), but some of these teeth actually had carinae on them (notice how some teeth have an eerily straight, "sharp-looking" edges that are sometimes clearly broken/worn at points; those I'm pretty sure are carinae). They were smooth and sometimes worn, probably by taphonomy. The presence of some smooth carinae may not be too surprising, seeing as how Spinosaurus teeth had to puncture prey to grip them first.

[Infinity Blade]

Tail-propelled aquatic locomotion in a theropod dinosaur
Nizar Ibrahim, Simone Maganuco, Cristiano Dal Sasso, Matteo Fabbri, Marco Auditore, Gabriele Bindellini, David M. Martill, Samir Zouhri, Diego A. Mattarelli, David M. Unwin, Jasmina Wiemann, Davide Bonadonna, Ayoub Amane, Juliana Jakubczak, Ulrich Joger, George V. Lauder & Stephanie E. Pierce

Abstract

In recent decades, intensive research on non-avian dinosaurs has strongly suggested that these animals were restricted to terrestrial environments. Historical proposals that some groups, such as sauropods and hadrosaurs, lived in aquatic environments were abandoned decades ago. It has recently been argued that at least some of the spinosaurids—an unusual group of large-bodied theropods of the Cretaceous era—were semi-aquatic, but this idea has been challenged on anatomical, biomechanical and taphonomic grounds, and remains controversial. Here we present unambiguous evidence for an aquatic propulsive structure in a dinosaur, the giant theropod Spinosaurus aegyptiacus. This dinosaur has a tail with an unexpected and unique shape that consists of extremely tall neural spines and elongate chevrons, which forms a large, flexible fin-like organ capable of extensive lateral excursion. Using a robotic flapping apparatus to measure undulatory forces in physical models of different tail shapes, we show that the tail shape of Spinosaurus produces greater thrust and efficiency in water than the tail shapes of terrestrial dinosaurs and that these measures of performance are more comparable to those of extant aquatic vertebrates that use vertically expanded tails to generate forward propulsion while swimming. These results are consistent with the suite of adaptations for an aquatic lifestyle and piscivorous diet that have previously been documented for Spinosaurus. Although developed to a lesser degree, aquatic adaptations are also found in other members of the spinosaurid clade, which had a near-global distribution and a stratigraphic range of more than 50 million years, pointing to a substantial invasion of aquatic environments by dinosaurs.

Fig. 1: Reconstructed skeleton and caudal series of FSAC-KK 11888. a, b, Caudal series (preserved parts shown in colour) in dorsal view (a) and left lateral view (b). c–e, Reconstructed sequential cross-sections through the tail show proximal-to-distal changes in the arrangement of major muscles. f, Sequential cross-sections through the neural spine of caudal vertebra 23 (Ca23) to show apicobasal changes. g, Skeletal reconstruction. Scale bars, 50 cm (a–e), 10 cm (f), 1 m (g).

www.nature.com/articles/s41586-020-2190-3

[elosha11]

^Really cool findings. I'm going to try to read it in full when I have the time.

[Infinity Blade]

EDIT: the actual paper is now available. www.sciencedirect.com/science/article/abs/pii/S019566712030313X

Journal pre-proof with further evidence of an aquatic lifestyle in Spinosaurus.

Taphonomic evidence supports an aquatic lifestyle for Spinosaurus

A new locality near Tarda on the northern margin of the Tafilalt, south eastern Morocco exposes extensive sequences of the Ifezouane and Aoufous formations of the fluvial Kem Kem Group (Cretaceous, ?Albian-Cenomanian) on the south western flank of Ikfh n’Oufza escarpment of the Hamada du Meski. The stratigraphic sequence here differs significantly from better known exposures of the Kem Kem Group in the southern Tafilalt, and includes a heterolithic sequence of alternating grey mudstones and fine sandstones and a thin (~1.5 m) marine limestone. The locality is noteworthy for three vertebrate-bearing horizons within the upper part of the Ifezouane Formation. The upper two (Sites 1 and 2 in ascending order) are dominated by dental remains of the sawfish Onchopristis and the aquatic theropod dinosaur Spinosaurus. Significantly, the remains of terrestrial dinosaurs constitute less than 1 % of the total dental assemblage at Site 1 and 5.6% at Site 2. At Site 2 teeth of Spinosaurus outnumber the rostral “teeth” of Onchopristis. The remarkably high abundance of spinosaur teeth compared to remains of terrestrial dinosaurs, and even some aquatic animals strongly supports Spinosaurus being an aquatic animal spending much of its life in water where its teeth were shed and preserved.

drive.google.com/file/d/1Gm2CbdsoXcCbJq0-MB6_6mU9pImYHb_T/view

[Infinity Blade]

The most recent Spinosaurus paper that doubts the swimming hypothesis put forward for its ecology. Won't be the last Spinosaurus paper for this year, though.

Evaluating the ecology of Spinosaurus: Shoreline generalist or aquatic pursuit specialist?

The giant theropod Spinosaurus was an unusual animal and highly derived in many ways, and interpretations of its ecology remain controversial. Recent papers have added considerable knowledge of the anatomy of the genus with the discovery of a new and much more complete specimen, but this has also brought new and dramatic interpretations of its ecology as a highly specialised semi-aquatic animal that actively pursued aquatic prey. Here we assess the arguments about the functional morphology of this animal and the available data on its ecology and possible habits in the light of these new finds. We conclude that based on the available data, the degree of adaptations for aquatic life are questionable, other interpretations for the tail fin and other features are supported (e.g., socio-sexual signalling), and the pursuit predation hypothesis for Spinosaurus as a “highly specialized aquatic predator” is not supported. In contrast, a ‘wading’ model for an animal that predominantly fished from shorelines or within shallow waters is not contradicted by any line of evidence and is well supported. Spinosaurus almost certainly fed primarily from the water and may have swum, but there is no evidence that it was a specialised aquatic pursuit predator.

palaeo-electronica.org/content/2021/3219-the-ecology-of-spinosaurus

[creature386]

Not sure if anyone is interested, but I recently held a talk on Hone's and Holtz's paper as to whether Spinosaurus was a shoreline generalist or an aquatic pursuit predator. The below is NOT a recording of the talk itself, but rather of one of the many practice sessions I made beforehand.

I made a few factual mistakes (such as presenting Spinosaurus' level of pneumatization as a fact rather than a hypothesis by the authors. I might also have represented the fauna and flora of the Kem Kem beds inaccurately, but I think I rectified that in the talk itself.
A link to the paper itself:
palaeo-electronica.org/content/2021/3219-the-ecology-of-spinosaurus

And here a transcript:

SPOILER: Click to show

Hello and welcome everyone. My name is Petar Arsic and I studied geology at the Free University of Berlin and now I study OEP here in Bonn. Unfortunately, I don't have much in the way of research yet, so, I can't really present my own work or anything. I can, however, present something I found really interesting. I'd like to talk about a dinosaur I'm sure all of you know, the Spinosaurus. Spinosaurus was a big African Cretaceous theropod known for its crocodile-like snout, its sail-like back structure and for having slayed the Tyrannosaurus in the third Jurassic Park movie. Well, T. rex fanboys haven't forgiven it that one.
As anyone who has been following academic discussions about it can tell you, there have been a lot of battles about this animal. Specifically, it's locomotion and it's lifestyle. Over the last few years, there have been basically two camps. One said, "It lived in the water, don't believe what Jurassic Park III told you", while the other claimed it was for the most part a land-based predator.
The thing that really sparked this debate was a paper by Nizar Ibrahim et al. whose title you can see here. First of all, you have to know that Spinosaurus is a really poorly known animal.
We had a really good holotype specimen described by Ernst Stromer, but it became a war casualty in World War II. Most of what we know from it is very fragmentary. One of the best known fossils for a long time has been a single upper jaw bone described by Dal Sasso et al.
All of this suddenly changed in the year 2014. There, Nizar Ibrahim and colleagues had a very interesting discovery to present to the world. They had found a partial Spinosaurus skeleton in the Kem Kem beds that belonged to a subadult individual. It included fragments of the skull, the vertebral column, the ribcage and, most importantly of all, the legs. Yeah, the legs are gonna be really important here especially their proportions are a little... off compared to those of other theropods.
The hindlimbs are unusually short, just a bit longer than the forelimbs. Hence, we got funny reconstructions like this one where the Spinosaurus' arms almost touch the ground.
Or this one, where Spinosaurus literally walks on all fours. So, for a while, people thought it was basically a prehistoric hippo. An animal who spent most of its time in the water because it needed the water to support itself and that, whenever it moved out, moved like a hippo. To say that this caused controvery would be an understatement.
Scott Hartman called the new Spinosaurus "fishy" and disagreed with the reconstruction. He thought that its hindlimbs were way too short and that, in reality, our favorite fish-eating mega carnivore did walk on land quite well.
www.skeletaldrawing.com/home/theres-something-fishy-about-spinosaurus9112014
Likewise, Donald Henderson published a paper in which he argued that Spinosaurus was effectiely incapable of diving down and that it couldn't have swam without toppling over thanks to its sail. He concluded that it was likely a perfectly capable terrestrial animal.
Other papers supported the aquatic interpretation. In 2015, Gimsa and colleagues for example suggested that Spinosaurus used its sail like sailfish do to trap large swarms of fish and devour them from all sides. You see, this is a very difficult debate here that won't end anytime soon. It only became more complicated once we learned that Spinosaurus had a paddle-like tail like a crocodile, but more on that later.
Unfortunately, looking at Spinosaurus' closest relatives isn't the easy way out either. Many other spinosaurids have a similarly scant fossil record and all the evidence suggests that Spinosaurus was a weird animal even compared to its family full of weird animals. There is at least a general consensus that Spinosaurus spent a lot of time in the water and ate a lot of fish, as simple analysis of its bones' isotope ratios show.
So, after this overlong introduction, let's get to the paper I wanted to talk about. In January 2021, Thomas R. Holtz and David Hone have published a paper about Spinosaurus and it's ecology. As you can see from the title, they're looking at two possibilities:
First, there is the wading model under which Spino was a generalist who lived at the shore, waited at the shoreline and took the fish when they came to it like a bear with salmons. This model is the upper one of the two. Don't worry about the letters and arrows and all. I'll explain them later when we get to them. This model is assumed to be the general condition for spinosaurids like Suchomimus and Baryonyx, too. The second model is the pursuit predator model under which Spinosaurus went after the fish in the rivers and caught its prey in the water column like a crocodile. Look at the second of the two reconstructions down below to see what it looks like. This model, if true, is assumed to be unique to Spinosaurus, though a note of caution, most other spinosaurids aren't quite as complete as it, so, there might have been other highly aquatic species in the family. So, which of these two models is it gonna be?
In their study, the authors selected various cranial and postcranial features of Spinosaurus and compared them to extinct and extant reptiles of various lineages. If you count the letters over the arrows, A, B, C, D, E, they go until the letter W. So, there's 24 traits that are being analyzed. The skull of Spinosaurus, for example, got compared to theropods and to crocodiles. They gathered data about crtieria like how flattened the skull is, and how the nose and the eyes are placed to see if it had them stick out of the water like a crocodile. Another part of the body they looked at a lot was the shape of its claws. In previous works, they have been described as flattened and well-suited for swimming. For the sake of this analysis, the authors compared them to claws of other theropods.
So, what did they find out? Well, for the skull, they ran a Principal Component Analysis, since they had a lot of data. They found two principal components to which the skull parameters could be scaled.
One is parameters related to length which is PC 1 here, the X axis and it explains more than 80% of the variance. The other parameters, the PC 2, are all related to the position of the orbit.
The red point here shows Spinosaurus. Now, here, you have a crocodile, here, you have a varanid, here, you have some aquatic reptiles and here, you have other theropods. As you can see, Spinosaurus is surrounded by theropods. Lots of theropods.
The marine reptiles aren't all that similar to it, after all. For example, noted aquatic or semi-aquatic reptiles seem to have dorsally flattened skulls and Spino, well, does not. Also, the nose is not dorsally positioned like we would expect it to be in an aquatic reptile. Aquatic reptiles, as you know, like to stick their noses out to breathe.
­Here is a comparison between the skulls of Spinosaurus and Baryonyx. Their skulls as well as their eye and nose placement are very similar, so, the idea that one was a strongly specialized aquatic predator and the other just strolled at the coasts seems unlikely.
What their skulls have in common is that the eyes and the nose are retracted posteriorly, but not dorsally. The lack of dorsal placement means they couldn't have their noses or eyes stick out of the water, but the posterior placement meant they could still see and breathe with their snouts underwater. Thus, the skull suggests a semi-aquatic, but not fully aquatic animal.
This is something you can see in this figure. You see, option A is the most comfortable one for Spino where it stands at the coast, puts its snout in the water and has eyes and nares free. Swimming like in C would be a bit hard. Swimming like in B would leave large sections of its head exposed.
By contrast, the next figure shows what it looks like when a croc has its head submerged. You see, due to the dorsal placement of the nose and the fact that it has this little bulge in the nostrum, much more of the crocodile's skull is covered by water than of Spinosaurus. Spino would have basically everything between its eyes and snout exposed. Here's a stork skull and you can see that it, like Spinosaurus, has its nares and its eyes very posteriorly placed, but they aren't elevated like in the crocodile. The scalebar in both skulls is 100 mm by the way. Just so that you don't think a crocodile and a stork have the same skull size.
The teeth are similar to those of aquatic predators like mosasaurs or crocodiles as they are fairly thin, compressed and lack serrations. However, this only shows that their prey was aquatic, not that Spinosaurus itself was an aquatic animal. The authors cite a paper according to which spinosaurids had unusually fast tooth replacement rates. It seems likely that they preyed on rather hard-scaled fish as well as prey with armor slash shells like crustaceans or ammonites. The high tooth replacement rate is backed up by the high number of teeth we find overall, although it should be noted that we could simply have a very good tooth preservation rate, as Spinosaurus lived near the water and that's where its teeth fell in.
Now, one last bit of evidence the authors looked at were little pores in the rostrum of Spinosaurus. It has been suggested that Spinosaurus had little pressure sensors like those crocodiles have to sense motion in the water. Those of you who watched BBC's excellent documentary Planet Dinosaurs might already know what I'm talking about. For those of you who didn't, I'll just show you.
youtu.be/VTzfaY2kx0U?t=172
(Start at 2:52)
Now, the authors are highly skeptical that these types of holes and sinuses are unique to Spinosaurus. But they believe that even if they were, they would neither argue for the pursuit predator nor for the wading predator model. Even if Spinosaurus had pressure sensors, it would have been enough to just briefly put the snout in the water, no need to live like a crocodile as the pursuit predator model postulates.
All in all, the authors believe that the evidence from skull morphology speaks strongly in favor of the wading and not in favor of the pursuit predator model.
Now, I wanted to jump from cranial to post-cranial evidence, but there's something at the border of the two, namely the neck. Thankfully, we now have neck bones thanks to the neotype. First, the neck was really long and gracile. Aquatic pursuit predators normally have short and stocky necks so that they could swim faster, however, a long neck could also help it to catch a lot of fish at once, so, this part is a bit ambiguous. What is less ambiguous are those neck bones though. They have been described as extremely long and have elongated cervical ribs similar to those of Suchomimus. They probably stabilized the neck against gravity and against lateral movement. When you want to swim really fast underwater, a strong and stiff neck is advantageous. However, it also meant that it couldn't move its neck to the side so well. A neck that moves up and down more easily than it moves to the side would support the wading model. Because if it hunted fish from above the water, it only had to strike down and pull out, whereas if it hunted from within the water, it had to move in all directions if necessary. So, the neck probably supports the wading model more than the pursuit predator model, but it's not 100% clear.
Now we are going to look at the controversional hindlimbs. As I mentioned in the introduction, the neotype had unusually short hindlimbs for a theropod. The ungals turned out to be much flatter than in other theropods, which liked their foot claws to be curved. However, ungal shape is a rather poor predictor of ecology. You see, ducks have flat feet and they're swimmers, but flamingos also have flattened feet and they're waders. Also, many terrestrial theropods like Sinraptor or Majungasaurus had similarly flat claws. If flat feet indicated anything, they likely showed that the animal in question was very large and didn't need its feet for predation or running. It's also not really clear if the legs were suitable for swimming. Really fast swimmers, which are what the pursuit predator model implies, don't really use their feet while swimming so much. Even crocodiles just push themselves off of the ground with them. About the length of the hindlimbs, the authors wrote that, while the femur was really short by theropod standards, the muscle distribution was fairly normal and its limbs would likely have been even shorter if it was an underwater pursuit predator. It likely walked like most theropods, and since it only had to walk from one river to the next instead of chasing down prey like other theropods, the short hindlimbs likely didn't bother it. So, the evidence from the limbs seems to be rather inconclusive.
Now, the authos also looked at the function of the mysterious sail, you know, the body part Spinosaurus is most famous for. What gives Spinosaurus its name are those elongated dorsal spines on its back that most people believe had skin in between to form a sail.
However, last year, scientists found that it had very similar spines on its tail. These caudal spines likely made its tail look like that of a crocodile or a newt. Computer simulations have shown that it could have used that tail like a paddle to propel itself. You can read more about this finding on the German news portal Geohorizon. And look at who wrote that article.
geohorizon.de/2020/05/31/koerper-eines-theropoden-schwanz-eines-molchs-wie-der-spinosaurus-sich-im-wasser-fortbewegte/
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Given that this paddle tail existed, did it maybe use it along with the tail as some sort of fins?
There are some extant analogues which we could use, like, say, the basilisk. Basilisks are semi-aquatic animals and they have pretty impressive dorsal sails along with a caudal sail not connected to it. However, while they spend a lot of time in the water, they do not use that sail for swimming usually. Also, even modern newts rather use their tails for sexual display than for swimming.
Plus, we have fossils of reptiles with very similar tails to Spinosaurus that likely didn't live in the water at all. This is a drepanosaurid, you can see its kinda fin-like tail, but it was likely a terrestrial animal.
It's also worth noting that the chevrons, that is, the bones on the lower part of the tail are noticably shorter and thicker than the neural spines, that is, the upper portion of the tail. This doesn't make much sense when you think about it, because if it was used as a paddle, both sides of the tail must have been subject to the same pressures. The tail was most likely used for the same purposes as the dorsal sail, that is, sexual display, thermoregulation or fat storage. Of course, what the dorsal sail did is a whole other can of worms, so, we'll just leave it at saying that this tail "fin" it had does not necessarily prove it was a swimmer.
Now, I'll talk about something that's not a body part this time. Namely, how well was Spinosaurus able to swim overall? The authors dedicated a whole section to this question. They referred to the data from their principle component analysis and made statements about the body types of various aquatic predators. They found out that the bodies of most aquatic pursuit predators had the features of being long, stiff, short-limbed and having a long, muscular tail for propelled swimming. Now, Spinosaurus had a somewhat less muscular tail than most crocodiles, but its body is otherwise not dissimilar to that of underwater swimmers that can swim fast in very short bursts, like crocodiles, nothosaurs, or mosasaurs, even if that's not quite pursuit predation.
However, there's a factor that's very important for swimming animals of its size and that's drag. Unfortunately, with its sail and large forelimbs, both of which it couldn't retract, Spinosaurus was very likely to encounter drag. There's also the issue that Spinosaurus, much like most theropods, had pneumatic bones which made its density very low. Therefore, it'd have needed a lot of energy to actually dive. Surface swimming is much more energetically costly than submerged swimming, so, if Spinosaurus was a pursuit predator, it had to dive. Moreover, there's the issue of tipping over. As Henderson pointed out in a previous paper, the sail, the legs and the pneumatic bones and all meant that Spinosaurus center of mass wasn't where its center of buoyancy. As this figure shows, Spinosaurus likely had to dive into depths of 6 meters or deeper if it wanted to swim in a stable manner. It's not so clear whether waters deep enough for that were common in Spinosaurus' habitat. Either way, the authors concluded that Spino likely couldn't compete with crocodiles in terms of pursuit predation.
Last, but not least, before we conclude this, we'll look at environmental factors. Particularly the sort of biota Spinosaurus lived in, the animals it coexisted with and its presumed diet. Now, most Spinosaurus remains come from a locality in Morroco known as the Kem Kem beds. The Kem Kem beds show fluvial deposits full of aquatic life and with lots of mega carnivores, but surprisingly few terrestrial herbivores. This lack of herbivores, some authors argued, is what drove Spinosaurus into the water in the first place because there, it could prey on large fish such as Onchopristis and afford itself to grow to such a big size. By contrast, if it spent most of its time on land, it wouldn't have found enough herbivores to feed its massive body and it'd have starved to death.
However, it's possible that Spinosaurus had a varied diet that sometimes included fish and sometimes dinosaurs. Isotope analyses of various specimens showed that, while some individuals fed almost exclusively on fish, others were more varied in their diet. Likewise, it is possible that Spinosaurus existed in far more localities than in the Kem Kem beds, especially considering that a lot of spinosaurids in Africa might have been synonyms of Spinosaurus aegypticus. While this predator undoubtably ate more fish than most other theropods, that didn't mean that it necessarily only ate them. It could have been a generalist like a grizzly that in some locations specialized in fish and in other locations ate something else.
What can we say in summary?
It's probably no surprise that the authors strongly favor the wading model over the pursuit predator model, though even they implicitly note in their summary that they won't be able to settle the debate once and for all. More future findings can hopefully tell us what the situation was like in other spinosaurids. While Spinosaurus was weird among them, it is nonetheless the most well-known and most well-preserved taxon of its group, so, there's still more to learn about that family as a whole. Thank you for listening.