Early basicranial evolution and the origins of Crocodyliformes
Publicado por Leonardo Filippi en 15:06
Diego Pol, Oliver W. M.
Rauhut, Agustina Lecuona, Juan M. Leardi, Xing Xu and James M. Clark
Extant crocodylians
have a limited taxonomic and ecological diversity but they belong to a lineage
(Crocodylomorpha) that includes basal and rather generalized species and a
highly diverse clade, Crocodyliformes. The latter was among the most successful
groups of Mesozoic tetrapods, both in terms of taxonomic and ecological
diversity. Crocodyliforms thrived in terrestrial, semiaquatic, and marine
environments, and their fossil diversity includes carnivorous, piscivorous,
insectivorous, and herbivorous species. This remarkable ecological and trophic
diversity is thought only to occur in forms with a completely akinetic skull,
characterized by a functionally integrated and tightly sutured
braincase-quadrate-palate complex. However, the patterns of evolutionary change
that led to the highly modified skull of crocodyliforms and that likely enabled
their diversification remain poorly understood. Herein, a new basal
crocodylomorph from the Late Jurassic of Patagonia is described, Almadasuchus
figarii gen. et sp. nov. The new taxon is known from a well-preserved posterior
region of the skull as well as other craniomandibular and postcranial remains.
Almadasuchus figarii differs from all other crocodylomorphs in the presence of
six autapomorphic features, including the presence of a large lateral notch on
the upper temporal bar, an otic shelf of the squamosal that is wider than long,
a deep subtriangular concavity on the posterolateral surface of the squamosal,
and an elongated pneumatopore on the ventral surface of the quadrate.
Phylogenetic analysis focused on the origin of Crocodyliformes places
Almadasuchus as the sister group of Crocodyliformes, supported by synapomorphic
features of the skull (e.g. subtriangular basisphenoid, absence of
basipterygoid process, absence of a sagittal ridge on the frontal, and a flat
anterior skull roof with an ornamented dorsal surface). New braincase
information provided by Almadasuchus and other crocodylomorphs indicates that
most of the modifications on the posterior region of the skull of
crocodyliforms, including the strongly sutured braincase, quadrate, and the
extensive secondary palate appeared in a stepwise manner, and pre-dated the
evolutionary changes in the snout, jaws, and dentition. This indicates that the
progressively increased rigidity of the skull provided the structural framework
that allowed the great ecological diversification of crocodyliforms during the
course of the Mesozoic. The phylogenetic pattern of character acquisition
inferred for the strongly sutured (akinetic) skull and the appearance of more
diverse feeding behaviours that create high mechanical loads on the skull
provides another interesting parallel between the evolution of Mesozoic
crocodyliforms and the evolutionary origins of mammals.
Pol, D., Rauhut, O.W.M., Lecuona, A., Leardi, J. M., Xu. X. and Clark, J.M. 2013
A new fossil from the Jurassic of
Patagonia reveals the early basicranial evolution and the origins of
Crocodyliformes. Biological Reviews.
doi: 10.1111/brv.12030
Subscribe to:
Enviar comentarios (Atom)
0 comentarios:
Publicar un comentario