Purussaurus brasiliensis

[Life]

A new giant PURUSSAURUS (Crocodyliformes, Alligatoridae) from the Upper Miocene Urumaco Formation, Venezuela

Synopsis

Fossil Crocodylia are taxonomically diverse in South America, particularly in the upper Miocene Urumaco Formation (Venezuela). Among them is the giant alligatoroid Purussaurus, previously known from the upper Miocene Solimões Formation in Brasil (P. brasiliensis) and the middle Miocene of La Venta in Colombia (P. neivensis). New specimens of Crocodylia from the Urumaco Formation are described and a new species, Purussaurus mirandai, erected. This is characterised by a large, elongate and extremely flat skull, a very large narial opening comprising almost 60% of rostral length and a large incisive foramen that extends anteriorly between the fossae for the first mandibulary teeth. Purussaurus mirandai sp. nov. was the largest predator in the swampy environments and represented the top trophic level in the Urumaco assemblage. A phylogenetic analysis of 164 characters in 68 ingroup crocodile taxa supported the association of P. neivensis and P. mirandai with five synapomorphies and confirmed the sister-group relationship of the genus with the Nettosuchidae.

Link: www.tandfonline.com/doi/abs/10.1017/S147720190600188X

[Life]

Morphometry, Bite-Force, and Paleobiology of the Late Miocene Caiman Purussaurus brasiliensis

Abstract

Purussaurus brasiliensis thrived in the northwestern portion of South America during the Late Miocene. Although substantial material has been recovered since its early discovery, this fossil crocodilian can still be considered as very poorly understood. In the present work, we used regression equations based on modern crocodilians to present novel details about the morphometry, bite-force and paleobiology of this species. According to our results, an adult Purussaurus brasiliensis was estimated to reach around 12.5 m in length, weighing around 8.4 metric tons, with a mean daily food intake of 40.6 kg. It was capable of generating sustained bite forces of 69,000 N (around 7 metric tons-force). The extreme size and strength reached by this animal seems to have allowed it to include a wide range of prey in its diet, making it a top predator in its ecosystem. As an adult, it would have preyed upon large to very large vertebrates, and, being unmatched by any other carnivore, it avoided competition. The evolution of a large body size granted P. brasiliensis many advantages, but it may also have led to its vulnerability. The constantly changing environment on a large geological scale may have reduced its long-term survival, favoring smaller species more resilient to ecological shifts.

Full read: journals.plos.org/plosone/article?id=10.1371/journal.pone.0117944

[Life]

The ‘death roll’ of giant fossil crocodyliforms (Crocodylomorpha: Neosuchia): allometric and skull strength analysis

Abstract

In the evolution of crocodylomorphs, there were at least three giant-dimension genera: Deinosuchus from late Cretaceous of North America, Sarcosuchus from middle Cretaceous of Africa and South America, and Purussaurus from Miocene of South America. It has been suggested that these predators could have fed on very large prey as dinosaurs and megamammals. The ‘death roll’ is a spinning manoeuver executed to subdue and dismember large prey; therefore, it has been previously suggested that giant cocrodylomorphs may have used this manoeuver. However, this manoeuver can generate torsional stresses in the skull. We propose a biomechanical model to estimate the capability of a crocodylomorphs for withstanding this torsional stresses. Our results show a good correlation between a ‘death roll’ capability indicator and the feeding categories related with the actual use of ‘death roll’ in 16 living species. Here, for the first time, we propose a biomechanical approach of the implications of ‘death roll’ in fossil crocodylomorphs. We suggest that Deinosuchus and Purussaurus were able to execute death roll over dinosaurs and large mammals, respectively, but Sarcosuchus probably was not. We also found some allometry effects and, finally, we discuss palaeobiological implications based on our results.

Link: www.tandfonline.com/doi/abs/10.1080/08912963.2014.893300#.VPyTxvmUf1U

[Life]

Predation of the giant Miocene caiman Purussaurus on a mylodontid ground sloth in the wetlands of proto-Amazonia

Abstract

Thirteen million years ago in South America, the Pebas Mega-Wetland System sheltered multi-taxon crocodylian assemblages, with the giant caiman Purussaurus as the top predator. In these Miocene swamps where reptiles and mammals coexisted, evidence of their agonistic interactions is extremely rare. Here, we report a tibia of the mylodontid sloth Pseudoprepotherium bearing 46 predation tooth marks. The combination of round and bisected, shallow pits and large punctures that collapsed extensive portions of cortical bone points to a young or sub-adult Purussaurus (approx. 4 m in total length) as the perpetrator. Other known crocodylians of the Pebas System were either too small at adulthood or had discordant feeding anatomy to be considered. The pattern of tooth marks suggests that the perpetrator attacked and captured the ground sloth from the lower hind limb, yet an attempt of dismembering cannot be ruled out. This discovery from the Peruvian Amazonia provides an unusual snapshot of the dietary preferences of Purussaurus and reveals that prior to reaching its giant size, young individuals might have fed upon terrestrial mammals of about the size of a capybara.

Link: royalsocietypublishing.org/doi/10.1098/rsbl.2020.0239

[elosha11]

@life

(CNN)When a young crocodile-like caiman chomped down on the hind leg of a ground sloth 13 million years ago near the Napo River in Peru, it left behind 46 tooth marks as evidence.

Now, researchers have been able to reconstruct the scene of the attack after analyzing the unfortunate ground sloth's hind leg bone.
As an adult, this ancient caiman had a bite force of seven tons, more than four times the strongest bite ever measured in the animal kingdom according to previous research, study author Rodolfo Salas-Gismondi said in an email. He was not involved with the previous research. The juvenile Purussaurus that attacked the ground sloth had the bite force of a modern caiman, which was still powerful enough to break and collapse bones.
After the adult Purussaurus, the next strongest bite comes from the modern saltwater crocodile, Crocodylus porosus, which has a bite force of 1.6 tons.


The ground sloth's tibia included 46 bite marks.

"The bite was so powerful that many teeth perforated the tibia and collapsed extensive portions of the cortical bone," said Salas-Gismondi, a paleontologist at the Universidad Peruana Cayetano Heredia's BioGeoCiencias Lab in Lima, Peru. "The ground sloth did not survive."
This fossil evidence is a rare look into the relationship between predators and prey that once lived in Amazonia, or the area surrounding the Amazon River in South America, millions of years ago.
"The tibia discovered in the Peruvian Amazonia is the first one of a mammal bearing crocodylian tooth marks and therefore crucial for understanding the dynamic of ancient ecosystems," Salas-Gismondi said in an email.

"This is an unusual snapshot of the feeding behaviour of the largest non-marine predator since the extinction of non-avian dinosaurs. We have recovered thousands of fossil bones from these Amazonian localities and, up to now, the tibia of the sloth is the only bone with tooth marks that we have discovered."
The fossil of the ground sloth's damaged tibia was found in 2004 by François Pujos, study coauthor and paleontologist specializing in evolution of ground sloths at the Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales in Mendoza, Argentina.
As he explored rock outcrops in the Pebas Formation along the Napo River in Peru, Pujos discovered that the rocks were full of bones.

He collected the tibia, intrigued by the teeth marks on the bone, but he and his fellow researchers weren't sure what could have caused the damage. Little was known at the time about the animals that lived in the area during the age the ground sloth was alive.
So the fossil was stored at the department of vertebrate paleontology at the Museo de Historia Natural-UNMSM in Lima, where Salas-Gismondi is also a curator.
A research team including French, Peruvian and American scientists studied the Pebas Formation area for 15 years, learning about the animals that once lived there by studying the bones they left behind.

Lakes and swamps served as the perfect habitat for ancient crocodiles and caimans between 11 million and 20 million years ago. And the research team realized that in 2019, they were "ready to know who killed this ground sloth," Salas-Gismondi said.
"We found that tooth marks in the tibia match with the anatomy and dentition of the top predator of the Pebas System, the giant caiman Purussaurus," he said.
The study published Tuesday in the journal Biology Letter

Studying the evidence
Purussaurus could reach 33 feet in length as an adult, but the researchers believe this was a young one that was about 13 feet in length. And it was in just the right place and time to lunge out from the swamp and attack the lower hind leg of an unsuspecting ground sloth likely foraging for plants along the shore.
This ground sloth was likely about 176 pounds, similar in size to modern capybaras, the largest modern living rodents in the world. Capybaras can be found in South America.

And the ancient sloth was no match for the bite force of the young Purussaurus, which left pits, scoring and deep punctures in the sloth's leg bone. If the sloth had survived, there would be evidence of bone regeneration.
The researchers haven't ruled out the possibility that the bite marks occurred shortly after death as the Purussaurus dismembered the sloth's carcass.

Purussaurus' teeth match the marks found on the fossilized bone, the researchers said. Other predators living in South America at the time included marsupials, crocodiles and giant flightless birds. The birds didn't have teeth and the bite marks from marsupial teeth don't match those on the bone. So the researchers analyzed teeth from the different types of ancient crocodiles and caimans to see which one fit best.
The strong, blunted cone-shaped teeth of Purussaurus matched the deep, large punctures on the bone. Parts of the bone had even collapsed under the force of the bite.

Portrait of an ancient predator
Purussaurus were the largest predators in this environment at the time.
Most crocodiles and alligators experience a change in diet as they grow. Newborns eat insects and spiders. As they grow, their bite force changes, meaning that juveniles and adults have the ability to capture mammals and turtles.

With its massive bite force, Purussaurus wasn't limited by size when choosing its next meal. This is evidenced, along with the ground sloth tibia, by the fossilized carapace of an ancient large turtle at the museum where Salas-Gismondi works.
This fossil shows that an adult Purussaurus took a bite of 25 inches out of the turtle's shell and amputated one of its hind legs. However, unlike the ground sloth, the turtle survived based on evidence of bone regeneration in the carapace.



Rock outcrops along the Napo River are full of bones.

Finding fossils in Amazonia is difficult because of the dense tropical rainforest environment and heavy rains, but studying areas where ancient rocks are exposed can shed light on what ancient life was like in this area.
The researchers only get a month or so during the dry season to study these rocks before torrential rains have the force to wash away the rocks and fossils.
"The good news is that every year a new window to the past opens," Salas-Gismondi said.

Clarification: The bite force of the juvenile Purussaurus in the new study was not clear in a previous version of this story.

[Life]

Giant extinct caiman breaks constraint on the axial skeleton of extant crocodylians

Abstract

The number of precaudal vertebrae in all extant crocodylians is remarkably conservative, with nine cervicals, 15 dorsals and two sacrals, a pattern present also in their closest extinct relatives. The consistent vertebral count indicates a tight control of axial patterning by Hox genes during development. Here we report on a deviation from this pattern based on an associated skeleton of the giant caimanine Purussaurus, a member of crown Crocodylia, and several other specimens from the Neogene of the northern neotropics. P. mirandai is the first crown-crocodylian to have three sacrals, two true sacral vertebrae and one non-pathological and functional dorsosacral, to articulate with the ilium (pelvis). The giant body size of this caiman relates to locomotory and postural changes. The iliosacral configuration, a more vertically oriented pectoral girdle, and low torsion of the femoral head relative to the condyles are hypothesized specializations for more upright limb orientation or weight support.

Citation: Scheyer, T. M., Hutchinson, J. R., Strauss, O., Delfino, M., Carrillo-Briceno, J. D., Sanchez, R., & Sánchez-Villagra, M. R. (2019). Giant extinct caiman breaks constraint on the axial skeleton of extant crocodylians. Elife, 8, e49972.

Link: elifesciences.org/articles/49972

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Scheyer et al., however, now report that one extinct caiman called Purussaurus mirandai had a spine that was structured unlike any other known crocodylian. Weighing almost three tons (~2,600 kg), the 10-meter-long Purussaurus was more than twice as heavy as the largest living crocodylian, the saltwater crocodile. When Scheyer et al. examined fossilized remains from Venezuela that are estimated to be between 7–5 million years old, they found an extra vertebra in the creature's pelvic area and one less in its trunk. Scheyer et al. speculate that this unusual arrangement may have helped the extinct creature to support its massive weight and compensate for the strain imposed on its skeleton.

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Figure 2 with 1 supplement

Selected pectoral bones of AMU-CURS-541 and UNEFM-CIAAP-1367 of Purussaurus from the Urumaco Formation of Venezuela.

(A) Interpretative reconstruction of the complete body outline of P. mirandai (AMU-CURS-541) showing the preserved and assembled postcranial bones and the lower jaw in tentative live position. Osteoderms (in upper part of trunk) and ribs (in lower part of trunk) are not in life position. The second author (OS) serves as scale (see Figure 2—figure supplement 1). (B) Left scapula of AMU-CURS-541 in lateral, medial, and posterior view. (C) Right scapula of Purussaurus cf. P. mirandai (UNEFM-CIAAP-1367) in medial view. (D) Right coracoid (UNEFM-CIAAP-1367) in dorsomedial, ventrolateral, and anterior view. Abbreviations: cor.f, coracoid foramen; dc, deltoid crest of scapula; gl, glenoid fossa.

Figure 3 with 2 supplements 

Selected pelvic and sacral bones of AMU-CURS-541 and other specimens of Purussaurus from the Urumaco Formation of Venezuela.

(A) Left ischium (AMU-CURS-541) in posterior, anterior, dorsal (above), and ventral (below) view. (B) Right pubis (AMU-CURS-541) in ventral and dorsal view. (C) Articulated left ilium and ischium (non-holotype, additional bones accessioned under UNEFM-CIAAP-1369) in lateral and medial view. Note the three large depressions separated by ridges, that is attachment sites for three sacral ribs (a.s1-a.s3). (D) Right ilium (AMU-CURS-541) in lateral, medial, and ventral view. (E) Right ilium (UNEFM-CIAAP-1367) in lateral, medial, and ventral view. Stippled white lines indicate the weathered ridges separating the articulation facets for the sacral ribs. (F) Sacral region (non-holotype, additional bones accessioned under UNEFM-CIAAP-1369) consisting of three sacrals in articulation in dorsal, ventral, and posterior view. Note the right pubis (in dorsal view) attached ventrally to the sacrals. Abbreviations: ac, acetabulum; a.s1-a.s3, attachment sites for three sacral ribs; as.is, anterior articular surface for ilium; posp, postacetabular process; prep, preacetabular process; prz, prezygapophysis; ps.is, posterior articular surface for ischium; pu, pubis; s1-s3: sacral vertebrae/ribs 1–3; sac, supraacetabular crest.

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Conclusions

The pectoral and pelvic regions of Purussaurus mirandai show a peculiar morphology in comparison to extant taxa, including a narrow scapulocoracoid contact, wide and prominent deltoid crest on the scapula serving as a muscle origin, more vertically oriented pectoral girdle, and autapomorphic ‘three sacral’ condition in the pelvis, interpreted herein to be linked to the giant body size. We infer that the underlying developmental mechanisms, especially an earlier timing of expression of Hox11 and partial suppression of Hox10 (Wellik and Capecchi, 2003), resulting in shifted domains of Hoxc8 and Hox11, led to the formation of the dorsosacral in P. mirandai. Discovery and examination of additional specimens of Purussaurus with exceptional preservation to document genus variation, and of other giant crocodylians would lead to a better understanding of the anatomical peculiarities of these taxa. Such studies should inspect the medial side of the ilium to provide indirect information on the sacral count.

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