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Archosauriform remains from Late Triassic of San Luis province, Argentina



Ben Creisler
bcreisler@gmail.com

A new paper:

Federico A. Gianechini, Laura Codorniú, Andrea B. Arcucci, Gabriela
Castillo Elías & David Rivarola (2015)
Archosauriform remains from the Late Triassic of San Luis province,
Argentina, Quebrada del Barro Formation, Marayes–El Carrizal Basin.
Journal of South American Earth Sciences (advance online publication)
doi:10.1016/j.jsames.2015.12.012
http://www.sciencedirect.com/science/article/pii/S0895981115301073

Highlights

We describe archosauriform remains from San Luis province, Argentina.
The fossils come from levels of the Quebrada del Barro Formation (Late
Triassic).
These beds represent the southernmost outcrops of the Marayes–El Carrizal Basin.
The remains present affinities with ‘rauisuchians’, sauropodomorphs
and theropods.
This record adds to a recently reported fauna from northern beds of this basin.

Abstract

Here we present archosauriform remains from ‘Abra de los Colorados’, a
fossiliferous locality at Sierra de Guayaguas, NW San Luis Province.
Two fossiliferous levels were identified in outcrops of the Quebrada
del Barro Formation (Norian), which represent the southernmost
outcrops of the Marayes–El Carrizal Basin. These levels are composed
by massive muddy lithofacies, interpreted as floodplain deposits. The
specimens consist of one incomplete maxilla (MIC-V718), one caudal
vertebra (MIC-V719), one metatarsal (MIC-V720) and one indeterminate
appendicular bone (MIC-V721). The materials can be assigned to
Archosauriformes but the fragmentary nature and lack of unambiguous
synapomorphies preclude a more precise taxomic assignment. The maxilla
is remarkably large and robust and represents the posterior process.
It preserved one partially erupted tooth with ziphodont morphology.
This bone shows some anatomical traits and size match with
‘rauisuchians’ and theropods. MIC-V719 corresponds to a proximal
caudal vertebra. It has a high centrum, a ventral longitudinal furrow,
expanded articular processes for the chevrons, a posteriorly displaced
diapophysis located below the level of the prezygapophyses, and short
prezygapophyses. This vertebra would be from an indeterminate
archosauriform. MIC-V720 presents a cylindrical diaphysis, with a
well-developed distal trochlea, which present resemblances with
metatarsals of theropods, pseudosuchians, and silesaurids, although
the size matches better with theropods. MIC-V721 has a slender
diaphysis and a convex triangular articular surface, and corresponds
to an indeterminate archosauriform. Despite being fragmentary, these
materials indicate the presence of a diverse archosauriforms
association from Late Triassic beds of San Luis. Thus, they add to the
faunal assemblage recently reported from this basin at San Juan
Province, which is much rich and diverse than the coeval paleofauna
well known from Los Colorados Formation in the Ischigualasto–Villa
Union Basin.