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Article: Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest‐known crocodylomorphs

Papers in Palaeontology - Volume 2 Part 4 - Cover
Publication: Palaeontology
Volume: 2
Part: 4
Publication Date: November 2016
Page(s): 585 622
Author(s): Agustina Lecuona, Martín D. Ezcurra, and Randall B. Irmis
DOI: 10.1002/spp2.1056
Addition Information

How to Cite

LECUONA, A., EZCURRA, M.D., IRMIS, R.B. 2016. Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest‐known crocodylomorphs. Papers in Palaeontology, 2, 4, 585-622. DOI: 10.1002/spp2.1056

Author Information

  • Agustina Lecuona - Museo Paleontológico Egidio Feruglio Trelew Chubut Argentina (Email: alecuona@mef.org.ar)
  • Martín D. Ezcurra - Sección Paleontología de Vertebrados Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’ Buenos Aires Argentina (Email: martindezcurra@yahoo.com.ar)
  • Martín D. Ezcurra - School of Geography, Earth & Environmental Sciences University of Birmingham Edgbaston Birmingham UK
  • Randall B. Irmis - Natural History Museum of Utah and Department of Geology & Geophysics University of Utah Salt Lake City UT USA (Email: irmis@umnh.utah.edu)

Publication History

  • Manuscript Accepted: 28 August 2016
  • Manuscript Received: 23 January 2016

Funded By

FONCYT – PICT. Grant Number: 925
H.D. Montgomery
Jurassic Foundation
University of Utah

Online Version Hosted By

Wiley Online Library
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Abstract

Trialestes romeri (Reig) is an early crocodylomorph from the Ischigualasto Formation (late Carnian – early Norian; Ischigualasto – Villa Unión Basin, Argentina) and one of the oldest‐known members of this clade. Two specimens of this species are known, the holotype (PVL 2561) and a referred specimen (PVL 3889), both consisting of associated cranial and postcranial remains. These specimens are incomplete and poorly preserved thus leading previous authors to propose different phylogenetic hypotheses for the species. Trialestes romeri was originally interpreted as a basal dinosaur, subsequently considered to be a crocodylomorph with some dinosaurian characters (e.g. mesotarsal ankle joint, functionally tridactyl pes), and even proposed as a chimera representing two different genera. Some recent workers have mentioned and discussed Trialestes, but none have described it in detail or included it in a quantitative phylogenetic analysis. Here, we describe in detail all the material assignable to the species and test its phylogenetic relationships using a comprehensive data matrix focused on early archosaurs. We support the referral of PVL 3889 to Trialestes and reject the presence of a mesotarsal ankle joint in this specimen. We recovered Trialestes within Crocodylomorpha, closer to Crocodyliformes than Pseudhesperosuchus, Hesperosuchus, Dromicosuchus and Sphenosuchus. Several stratigraphical units worldwide approximately coeval with the Ischigualasto Formation, have also yielded early crocodylomorph remains, such as the upper Santa María (Brazil), Pekin (USA), and lower Maleri (India) formations. However, the crocodylomorph specimens recovered from those units are more incomplete, possess uncertain phylogenetic affinities, or are part of chimaerae. Therefore, Trialestes represents the most completely known of the earliest non‐crocodyliform crocodylomorph taxa known to date.

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