The first fish remains (Sarcopterygii and Actinopterygii) from the late Ladinian−earliest Carnian Chañares Formation of Argentina: a broader palaeolatitudinal distribution for early mawsoniid coelacanthiforms?

JULIA DESOJO; SOLEDAD GOUIRIC-CAVALLI; AGUSTÍN MARTINELLI; LUCAS E. FIORELLI; MARTÍN EZCURRA

Opole

Congreso; XIII Annual Meeting of the EAVP; 2015

Opole University

The amniote fossil record of the late Ladinian−earliest Carnian Chañares Formation is among the richest worldwide for the Middle Triassic. However, nonamniote osteichthyan remains were unknown from this highly fossiliferous unit, until they were collected during recent fieldwork. A specimen sampled from the lower member (~7 metres above the base), and probably late Ladinian in age, belongs to a fragment of dermal bone assignable to a coelacanthiform mawsoniid (Sarcopterygii, Actinistia) based on its ornamentation. Remains collected from the upper member (4 metres below the top; early Carnian) of the unit are represented by patches of scales thatresemble those of some pseudobeaconiid perleidiforms (Actinopterygii). The record of a putative mawsoniid in the Middle Triassic of South America is of particular interest because it represents the first evidence of the group in southern palaeolatitudes during the early evolution of the clade. The oldest unambiguous mawsoniids come from the Middle Triassic of Europe and have subsequently been recorded from North America during the Late Triassic. The specimen described here indicates a wider palaeolatitudinal distribution for mawsoniids than previously recognised, spanning from a palaeolatitude of 20ºN in the Northern Hemisphere to 45ºS in southwestern Pangaea. This distribution indicates the presence of the group in tropical to temperate/semi-aridpalaeoclimates in the north and south, respectively, and suggests a relatively broad climatic tolerance for early members of the clade. Accordingly, the probably broad geographic distribution of early mawsoniids matches the biogeographic history observed in multiple Middle Triassic vertebrates.