INVESTIGADORES
EZCURRA Martin Daniel
artículos
Título:
An abelisauroid dinosaur from the Middle Jurassic of Laurasia and its implications on theropod palaeobiogeography and evolution
Autor/es:
EZCURRA, M. D.; AGNOLIN, F. L.
Revista:
PROCEEDINGS OF THE GEOLOGISTS ASSOCIATION
Editorial:
GEOLOGICAL SOC PUBL HOUSE
Referencias:
Lugar: Londres; Año: 2012 vol. 123
ISSN:
0016-7878
Resumen:
We review here the phylogenetic relationships of a theropod distal end of tibia (MB. R.2351) from the
Middle Jurassic Stonesfield Slate (Taunton Formation, middle Bathonian) of Oxfordshire, England. This
specimen was previously described as a small basal tetanuran, but our reinterpretation suggests that it
was an early member of the Abelisauroidea. The new assignment is supported by the presence of an
apomorphic vertical facet for the reception of the ascending process of the astragalus, sub-rectangular
anterior scar of the astragalar ascending process, median vertical ridge in the scar for the reception of the
ascending process of the astragalus, and posterolateral process not distinctly offset from the lateral
margin of the shaft. In particular, the Stonesfield specimen shares an overall morphology and a unique
combination of apomorphies with the Middle Jurassic Australian abelisauroid Ozraptor. Nevertheless,
both specimens differ in some punctual features. MB. R.2351 constitutes the oldest evidence of an
abelisauroid outside Gondwana and indicates that the group had achieved a Pangean distribution during,
at least, the Middle Jurassic. Thus, the initial diversification of abelisauroids would have occurred earlier
than previously thought. Accordingly, the Middle and Late Jurassic Pangean distribution of abelisauroids
implies that the absence of the group in Cretaceous Asiamerican assemblages would reflect a regional
extinction, in which a competitive replacement with coelurosaurs (e.g. tyrannosauroids) is surely one of
the hypotheses that should be tested in future studies.