New insights into the origins and radiation of the mid-Palaeozoic Gondwanan stem tetrapods

Abstract

The earliest tetrapodomorph fishes appear in Chinese deposits of Early Devonian age, and by the Middle Devonian they were widespread globally. Evidence for the earliest digitated tetrapods comes from largely uncontested Middle Devonian trackways and Late Devonian body fossils. The East Gondwana Provence (Australasia, Antarctica) fills vital gaps in the phylogenetic and biogeographic history of the tetrapods, with the Gondwanan clade Canowindididae exhibiting a high degree of endemism within the early part of the stem tetrapod radiation. New anatomical details of Koharalepis, from the Middle Devonian Aztec Siltstone of Antarctica, are elucidated from synchrotron scan data. These include the position of the orbit, the condition of the hyomandibular, the shape of the palate and arrangement of the vomerine fangs. Biogeographical and phylogenetic models of stem tetrapod origins and radiations are discussed.

A fresh look at Cladarosymblema narrienense, a tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous of Australia, illuminated via X-ray tomography

“…The family Megalichthyidae includes several taxa from Europe, Russia, Middle East, and North America, but there is only one taxon described from Australia. Cladarosymblema narrienense ( Fox et al, 1995 ) is known from the Lower Carboniferous (Viséan) Raymond Formation in Queensland, Australia, and is the only megalichthyid described from the Southern Hemisphere ( Long, Clement & Choo, 2018 ).…”

Early Tetrapodomorph Biogeography: Controlling for Fossil Record Bias in Macroevolutionary Analyses

“…The fastest estimated dispersal rate occurs along the branch leading to 338 Eotetrapodiformes, moving from Eastern Gondwana to Southern Euramerica (14.34x the average 339 rate). As Long et al (2018) suggest, we find evidence for an East Asian origin for Tetrapodomorpha 340 but with moderate uncertainty (average estimate ± standard deviation of posterior distribution; 341 longitudeavg = 81.5° ± 10.1°, latitudeavg = −6.4° ± 8.5°). We also reconstruct an origin for 342 "Megalichthyiformes" that borderlines East Asia and Eastern Gondwana (longitudeavg = 107.2° ± 343 14.1°, latitudeavg = −22.6° ± 8.7°), along with an Eastern Gondwana origin for the clade uniting 344 "Canowindridae" and Rhizodontida (longitudeavg = 137.1° ± 8.2°, latitudeavg = −32.0° ± 4.7°).…”