TAXONOMY OF THE ARCHOSAUR ORNITHOSUCHUS: REASSESSING ORNITHOSUCHUS WOODWARDI NEWTON 1894 AND DASYGNATHOIDES LONGIDENS (HUXLEY 1877)

BACZKO, M. B.; EZCURRA, M. D.

Capital Federal

Congreso; XXX Jornadas Argentinas de Paleontología de Vertebrados; 2016

Museo Argentino de Ciencias Naturales

Ornithosuchidae is a group of terrestrial carnivorous archosaurs registered in Upper Triassic rocks of Argentina and Scotland. The pseudosuchian archosaur Ornithosuchus, from the Lossiemouth Sandstone Formation (early Late Triassic), Scotland, was the first ornithosuchid to be discovered and the only one recorded in the northern hemisphere. The hypodigm of Ornithosuchus is based on eleven juvenile to adult specimens, generally preserved as natural moulds and in a few cases three-dimensional bones. In 1894, Newton erected the species Ornithosuchus woodwardi based on a fairly complete, though juvenile, individual. Broom (1913) coined the species Ornithosuchus taylori based on two new large specimens. In 1964, Walker synonymized Ornithosuchus woodwardi and Ornithosuchus taylori with ?Dasygnathoides longidens?, a species erected by Huxley in 1877 and based on a few partial moulds, erecting the combination ?Ornithosuchus longidens?. ?Dasygnathoides longidens? is composed of the natural moulds of a partial maxilla, partial vertebra, and phalanx (EM1), pterygoid and haemal arch (EM15), articular (EM29), and osteoderm (EM unnumbered). None of the diagnostic features of Ornithosuchus, listed by Sereno in 1991, can be recognized in ?Dasygnathoides longidens?. Thus, their synonymy is here rejected and the latter genus and species are considered nomina dubia. EM1 represented the largest ornithosuchid specimen, but under this new interpretation, the body size of Ornithosuchus is reduced to 40%, resembling the size of its Argentinean relatives Riojasuchus and Venaticosuchus. The pseudosuchian EM1 does not belong to any of the named archosauriform species from the Lossiemouth Sandstone Formation and represents the largest predatory tetrapod of this unit.