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

DESOJO, J. B.; GOUIRIC-CAVALLI, S.; MARTINELLI, A.; FIORELLI, L. E.; EZCURRA, M. D.

Congreso; 3th Annual Meeting of the European Association of Vertebrate Palaeontologists; 2016

The amniote fossil record of the late Ladinian−earliest Carnian Chañares Formation is among the richest worldwide for the Middle Triassic. However, non-amniote osteichthyan remains were unknown from this highly fossiliferous unit until they were collected in recent fieldworks. A specimen sampled from the lower member (~7 metres above the base), and probably late Ladinian, belongs to a fragment of dermal bone probably assigned to the 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 that resemble 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 are subsequently recorded in North America during the Late Triassic. The specimen described here indicates a broader palaeolatitudinal distribution for mawsoniids than previously recognized, 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/semiarid palaeoclimates in the north and south, respectively, and suggesting a relatively broad climatic tolerance for the early members of the clade. Accordingly, the probable broad geographic distribution of early mawsoniids matches the biogeographic history observed in multiple Middle Triassic vertebrates.