Ichnotaxonomy of bird-like footprints: an example from the Late Triassic-Early Jurassic of Northwest Argentina

DE VALAIS, S. Y MELCHOR, R. N

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Año: 2008 vol. 28 p. 145 - 159

0272-4634

The ichnotaxobases previously used to classify avian-like footprints, at ichnogeneric, ichnospecific and ichnofamily level, are varied and contrasting. In consequence, an agreement upon the most adequate taxobases to be used in classification those vertebrate trace fossils is necessary. The authors follow an ichnotaxonomy treatment independent to the age and locality provenance of the trace fossils, and the possible trackmarker. The ichnotaxobases used to classify tracks with avian affinities at ichnogeneric and ichnospecific levels are evaluated and a proposal is made of a set considered most useful and appropriate. Also the criteria to distinguish avian footprints from non-avian theropod or ornithischian tracks are analysed and modified from those suggested by previous authors. These concepts are applied to the avian footprints from the upper part of the Late Triassic-Early Jurassic Santo Domingo Formation from La Rioja Province, northwest Argentina, which has yielded a diverse assemblage of vertebrate trace fossils. The most conspicuous avian footprints is named as Gruipeda dominguensis isp. nov. The ichnogenus Gruipeda Panin and Avram, 1962 is revised and an emendation of its diagnosis is suggested. Trisauropodiscus Ellenberger, 1972, from South Africa, and Antarctichnus Covacevich and Lamperein, 1970, from Antarctica, are considered as junior synonyms of Gruipeda. There are other three morphotypes of avian footprints, one assigned as cf. Alaripeda isp., and two left under open nomenclature: bird-like footprints type C, and bird-like footprint with elongated drag marks. The specimens from Santo Domingo could be related to avian origin, but the possibility of a case of convergence with birds is not discarded. In those tracks with a wide total divarication, an environment with shallow ponds and ephemeral fluvial systems associated, the muddy plains would favour the attainment of a convergent avian-form feet to improve the control of movements.