Wednesday 7 January 2015

An Allodaposuchian Crocodylian from the Late Cretaceous of the southeast Pyrenees.

All modern Crocodylomorphs are assigned to a single suborder, the Eusuchia, which appeared in the Early Cretaceous in Europe and North America (which were then connected), and underwent a major radiation in the Late Cretaceous, when the modern Crocodylians (defined as all living Crocodiles, Alligators and Gavials, there most recent common ancestor, and everything descended from that ancestor) appeared and rapidly diversified. The Late Cretaceous of Europe had a highly diverse Crocodylomorph diversity, includingCrocodiles, Alligators, Gavails, the non-Crocodylian Eusuchian Hylaeochampsids and non-Eusuchian groups such as Dyrosaurids, Pholidosaurids, Notosuchians, Atoposaurids and Goniopholidids. This fauna also includes a number of enigmatic taxa, of uncertain affinities, such as the genus Allodaposuchus, which currently contains two described species, Allodaposuchus precedens, which is known from fragmentary material from Romania, France and Spain (some of which is disputed and assigned to other taxa by some experts) and Allodaposuchus subjuniperus, which is known from a single, almost complete, skull from Huesca in northeast Spain. Allodaposuchus is considered to be a Eusuchian, but its position within that group is unclear.

In a paper published in the journal PLoS One on 31 December 2014, Alejandro Blanco of the Institut Català de Paleontologia Miquel Crusafont at the Universitat Autònomade Barcelona, Eduardo Puértolas-Pascual of the Área de Paleontología at the Universidadde Zaragoza, Josep Marmi, also of the Institut Català de Paleontologia Miquel Crusafont at the Universitat Autònoma de Barcelona, Bernat Vila also of the Área de Paleontología at the Universidad de Zaragoza and Albert Sellés, again of the the Institut Català de Paleontologia Miquel Crusafont at the Universitat Autònoma de Barcelona describe a new species of Allodaposuchus from the Late Cretaceous Tremp Formation in the southeast Pyrenees.

The new species is named Allodaposuchus palustris, from the Latin ‘palus’, meaning ‘swamp’, the specimen was recovered from a layer of grey organic mudstones interpreted as having been laid down in a swampy lagoon environment. The species is described from a fragmentary and disarticulated skull and jaw, plus numerous isolated vertebrae and limb bones. While the remains are disarticulated, they were all found in close association, often touching, and were in approximately the correct life position (i.e. head at one end, tail at the other etc.), were all from an animal or animals of similar size, and there were no duplicate bones, leading Blanco et al. to conclude that this was the disarticulated remains of a single animal rather than a bone assemblage, and that they had probably been disarticulated due to exposed decomposition rather than transportation or scavenging.

Mapping of the Crocodylian bones at the Fumanya Sud locality and their anatomical location. (A) Distribution of the fossils along a 2.3 m-long accumulation with indication of the type of bone. Grid square is 10 centimeters. (B) Anatomical location of the recovered bones. Abbreviations: a, astragalus; ar, articular; ca, calcaneum; cdv, caudal vertebra; cr, cervical rib; cv, cervical vertebra; d, dentary; dr, dorsal rib; dv, dorsal vertebra; eo, exoccipital; ept, ectopterygoid; f, frontal; fi, fibula; fm, femur; h, humerus; il, ilium; lv, lumbar vertebra; ost, osteoderm; pa, parietal; pf, prefrontal; ph, phalanx; q, quadrate; r, radius; rb, rib; sf: skull fragment; sq, squamosal; t, tooth; ti, tibia; ul, ulna. Blanco et al. (2014).

All of the remains are black in colour, indicative of a high hydrocarbon content in the sediments which buried them, which is typical of swampy environments. A layer of coal was located about 60 cm below the remains, suggesting a peat-forming environment, and the deposits also contained remains of the Cheirolepidiaceous Conifer Frenelopsis, the Palm Sabalites longirhachis and a variety of Ferns, all of which are typical of wetlands with shrubby vegetation; Turtle remains have also been found nearby, as have Oysters, Saccostrea, which are typical of brackish environments, and Unionid Bivalves (Freshwater Mussels) which are found in freshwater. Blanco et al. interpret this as representing a system of freshwater lakes and marshes near the edge of a system of brackish mudflats.

Mandibular bones and teeth of Allodaposuchus palustris from the Fumanya locality. (A, C, E)Anterior tip of the left dentary in occlusal, lingual and ventral views; (B, D, F) interpretative drawings of (A, C and E); (G) articular; (H) interpretative drawing of (G); (I) a tooth in labial, lingual and lateral views and a detail of the ornamentation of the crown surface (scale 1 mm). Abbreviations: an, angular; dt1-7, tooth alveoli1-7; de, dentary; fim, foramen intermandibularisoralis; fo, foramen; glfo, glenoid fossa; mc, Meckelian canal; re pro, retroarticular process; spcs, splenial scar; sym, symphysis. Blanco et al. (2014).

The large size of the lumbar vertebrae of Allodaposuchus palustris combined with the well-developed ligament attachments on its limb-bones suggests that it was a powerful muscular animal. Its teeth are robust but pointed rather than bulbous, indicative of a generalist predator. The living animal is calculated to have weighed about 211 kg, and to have been capable of biting down with a force of 6788.63 Newtons, comparable to large modern Crocodiles. Small Sauropod Dinosaurs have been found in nearby, associated deposits, which would have made ideal prey for such an animal.

While the remains of Allodaposuchus palustrisare somewhat fragmentary, they do add considerably to our understanding of the morphology of the genus, and its relationships to other Eusuchians. Blanco et al. conclude that these were members of the Crocodylia, more closely related to Crocodiles and Alligators than to Gavials. They also suggest that Allodaposuchus is closely related to another enigmatic European Crocodylian, Arenysuchus gascabadiolorum, known from Late Cretaceous fluvial (river) deposits in the Pyrenees, and erect the name ‘Allodaposuchians’ to include the three species of Allodaposuchus plus Arenysuchus gascabadiolorum.

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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...

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