Monday 15 December 2014

A Baurusuchid Crocodyliforme with preserved stomach contents from the Late Cretaceous of Brazil.

The Adamantina Formation from the Late Cretaceous of southern Brazil produces a wide variety of Crocodyliformes, including semi-aquatic Trematochampsids and Peirosaurids and terrestrial forms such as the large, predatory Baurusuchids, which often reached four meters in length, and smaller forms such as the Notosuchids and Sphagesaurids, which are thought to have been omnivorous or even fully herbivorous. The deposits are unusual in that they are almost completely lacking in Dinosaurs, with only Sauropods being common, Theropods represented only by isolated and fragmentary bones and Ornithischians completely absent. This is quite different from deposits from Argentina from roughly the same time period, which had a diverse Dinosaurian fauna, and is thought to be indicative of the Brazilian ecosystem being somehow isolated from that of Argentina.

In a paper published in the journal PLoS One on 8 May 2014, Pedro Godoy of the Departamento de Biologia at the Universidade de São Paulo and the Division of Paleontology at the American Museum of Natural History, Felipe Montefeltro of the Departamento de Zoologia at the Universidade Estadual Paulista, Mark Norell of the Division of Paleontology at the American Museum of Natural History and Max Langer of the Departamento de Biologia at the Universidade de São Paulo describe a new species of Baurusuchid Crocodyliforme from the Adamantina Formation in São Paulo State, Brazil, from a single specimen preserved with stomach contents intact.

The new species is named Aplestosuchus sordidus, where ‘Aplestosuchus’ means ‘greedy Crocodile’and ‘sordidus’ means ‘filthy’, in reference to the animals apparently voracious eating habits. The specimen is preserved on two blocks as a partially disarticulated skeleton on its side with the tail and ends of the hindlimbs missing.

Fossil Crocodyliformes showing predator-prey interaction.(A) Aplestosuchus sordidus skeleton. Scale bar, 10 cm. (B) Area highlighted in (A) with details of the abdominal content, including sphagesaurid remains. Scale bar, 5 cm. C, Reconstructed predator and prey. Reconstruction by Rodolfo Nogueira. Scale bar, 50 cm. Godoy et al. (2014).

Aplestosuchus sordidus has a short snout (for a Crocodyleforme), with a low number of teeth, four on each premaxilla and five on each maxilla (elements of the upper jaw); the dentary (lower jaw) is less well preserved, but it is thought unlikely that the living animal had more than nine lower teeth on each side. The teeth at the front of the jaws are rounded in profile (conical) and curve backwards slightly, those at the back are flattened and serrated and curve backwards more strongly (conical teeth are good for gripping and holding prey, flattened, blade-like teeth good for cutting).

Skull of Aplestosuchus sordidus in lateral (right) view.(A) Photograph. (B) Interpretative drawing. Abbreviations: a, angular; ap, anterior palpebral; ar, articular; d, dentary; d4, dentary tooth 4; f, frontal; j, jugal; m, maxilla; ma, mandibular fenestra; m3, maxillary tooth 3; pa, parietal; pm, premaxilla; po, postorbital; pp, posterior palpebral; q, quadrate; sa, surangular. Scale bar equals 10 cm. Godoy et al. (2014).

The stomach contents include the frontal, parietal, palpebral, and jugal bones, and three isolated teeth, of a small Sphagesaurid Crocodyliforme, as well as other isolated bones of uncertain origin, held within the preserved articulated gastralia of the Baurusuchid. These remains are thought to have come from an animal about 60 cm in length, which, if Aplestosuchus sordidus fed in a similar way to modern Crocodilians, would have been small enough to have been swallowed whole. Preserved stomach contents are more-or-less unknown in Crocodyliformes (despite their habit of swallowing prey whole), with this being only the second instance reported (the first being an Eocene fossil from the Green River Formation of Wyoming). This is almost certainly due to high acidity in the digestive system of the living animals (extant Crocodilians have the most acidic forgut contents of any known Vertebrate), which aids rapid digestion of bone. As such almost everything we know about the diet of extinct Crocodyliformes comes from analysis of their teeth and jaws and from marks on presumed prey animals.

Details of the preserved remains of the prey Crocodyliforme. (A, B) Teeth of in lateral view. The red arrow in (A) indicates one of the basiapical keels, typical for Sphagesauridae. (C) Detail of the teeth of another Sphagesaurid, Caryonosuchus pricei. (D) Cranial bones preserved. Abbreviations: f, frontal; j, jugal; p, parietal; pl, palpebral. Scale bars, 10 mm.Godoy et al. (2014).

See also…

The Tethysuchians were a group of largely marine Crocodyliforms that are reasonably well known from the Middle and Late Cretaceous, with one group, the Dyrosauridae surviving the End Cretaceous extinction...

The Rosso Ammonitico Veronese is a red nodular limestone found on the Trento Plateau in northern Italy, and Middle to Late Jurassic in age. It is noted for its numerous Ammonite fossils, but also produces occasional Marine Reptiles, notably Thalattosuchian Crocodylomorphs and Plesiosaurians. The earliest recorded discovery of such a Reptile is a Crocodylian...

The Sebecosuchians were the only group of Crocodylomorphs other than the modern Crocodyliforms to survive the end Cretaceous extinction, radiating in South America and Europe during the Palaeogene, then going extinct later in the Tertiary. A variety of South American forms have been described, and the group is reasonably well...

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