Mariliasuchus

Animalia

Mariliasuchus ("Marilia crocodile") is an extinct genus of Late Cretaceous notosuchian mesoeucrocodylian found near Marilia, Brazil. It was described in 1999 by Brazilian palaeontologists Ismar de Souza Carvalho and Reinaldo J. Bertini.

Its type species is M. amarali, in honour of Sérgio Estanislaw do Amaral, Brazilian naturalist. A second species, M. robustus, was named in 2007.^[1]

Material

Several specimens of M. amarali have been found to date:

• UFRJ DG 50-R (holotype): a partially complete and articulated skeleton, including a nearly complete skull and partially preserved axial and appendicular skeletons. It belongs to a juvenile specimen.
• UFRJ DG 105-R
• UFRJ DG 106-R
• MZSP-PV 50
• MZSP-PV 51
• MN 6298-V
• MN 6756-V

All of these specimens have been recovered in a road cut near the town of Marilia. They come from the upper part of the Adamantina Formation, indicating a Late Cretaceous (possibly Campanian/Maastrichtian) age.

Systematics

A phylogenetic analysis done by Zaher et al. (2006) found Mariliasuchus amarali to share a close relationship with Comahuesuchus. Andrade et al. (2006), while studying the palate and choanae of some mesoeucrocodylians, reached this same conclusion. Though no name was given to this clade in either publication, it is referred in this article as Comahuesuchidae.

Palaeobiology

Mariliasuchus, unlike modern crocodylians, was an animal of terrestrial habits. Its nostrils were located on the front of the skull, unlike modern crocodiles, in which the nostrils face upwards, to help the animal breathe while its almost completely submerged. Furthermore, the eyes in M. amarali are faced laterally (in modern crocodiles they face upwards). It had a very modified dentition, differentiated in incisiforms, caniforms and molariforms. Strangelly, in particular, were the anterior-most teeth, which were directed horizontally rather than vertically. The function of this strange arrangement is not yet clear, but Vasconcellos et al. (2002) made comparisons with the dentition of pigs, indicating that their dietary preferences may be convergent. It also had strong jaw muscles, indicating a good degree of mandibular activity.

There seems to be a significant degree of variation between specimens of M. amarali. Some of this is related to ontogenetic variation, but some may also suggest sexual dimorphism, or even that some of the specimens assigned to this species belong to a different animal.

Ontogenetic studies done by Vasconcellos and Carvalho (2005) concluded that during its growth, the skull of M. amarali individuals becomes shorter and the skull more resistant, while being laterally compressed. In adulthood, the orbit has a less circular arrangement than in younger individuals.

References

• Andrade, M.B.; Bertini, R. J.; Pinheiro, A. E. P. (2006). "Observations on the palate and choanae structures in Mesoeucrocodylia (Archosauria, Crocodylomorpha): phylogenetic implications". Revista Brasileira de Paleontologia, Sociedade Brasileira de Paleontologia 9 (3): 323–332. 
• Vasconcellos, F.M. & Carvalho, I.S. (2006). Inferências morfofuncionais e ontogenéticas sobre o crânio de Mariliasuchus amarali Carvalho & Bertini 1999, Crocodylomorpha cretácico da Formação Araçatuba/Adamantina, Bacia Bauru, Brasil. Paleontologia de Vertebrados: Grandes Temas e Contribuições Científicas: 229-239.
• Vasconcellos, F.M.; Carvalho, I.S.; Nobre, P.H. (2002). "Aspectos ecológicos de Mariliasuchus amarali (Crocodylomorpha) do". Cretáceo Superior da Bacia Bauru. Paleontologia em Destaque 40: 43–44. 
• Zaher, H.; Pol, D.; Carvalho, A. B.; Riccomini, C.; Campos, D.; Navas, W. (2006). "Re-description of the cranial morphology of Mariliasuchus amarali, and its phylogenetic affinities (Crocodyliformes, Notosuchia)". American Museum Novitates 3512: 1–40. doi:10.1206/0003-0082(2006)3512[1:ROTCMO]2.0.CO;2. ISSN 0003-0082. 

External links

• Andrade et al. (2006)
• Vasconcellos & Carvalho (2006)
• Vasconcellos et al. (2002)
• Zaher et al. (2006)