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Abstract The rapid radiation and dispersal of crown reptiles following the end‐Permian mass extinction characterizes the earliest phase of the Mesozoic. Phylogenetically, this early radiation is difficult to interpret, with polytomies near the crown node, long ghost lineages, and enigmatic origins for crown group clades. Better understanding of poorly known taxa from this time can aid in our understanding of this radiation and Permo‐Triassic ecology. Here, we describe an Early Triassic specimen of the diapsidPalacrodonfrom the Fremouw Formation of Antarctica. WhilePalacrodonis known throughout the Triassic and exhibits a cosmopolitan geographic range, little is known of its evolutionary relationships. We recoverPalacrodonoutside of crown reptiles (Sauria) but more crownward thanYoungina capensisand other late Permian diapsids. Furthermore,Palacrodonpossesses anatomical features that add clarity to the evolution of the stapes within the reptilian lineage, as well as incipient adaptations for arboreality and herbivory during the earliest phases of the Permo–Triassic recovery.
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A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondylsCitation for this article: Gee, B. M., Beightol, C. V. & Sidor, C. A. (2023) A new lapillopsid from Antarctica and a reappraisal of the phylogenetic relationships of early diverging stereospondyls. Journal of Vertebrate Paleontology . https://doi.org/10.1080/02724634.2023.2216260
Stereospondyls underwent a global radiation in the Early Triassic, including an abundance of small-bodied taxa, which are otherwise rare throughout the Mesozoic. Lapillopsidae is one such clade and is presently known only from Australia and India. This clade’s phylogenetic position, initially interpreted as micropholid dissorophoids and later as early diverging stereospondyls, remains uncertain. Although the latter interpretation is now widely accepted, lapillopsids’ specific relationship to other Early Triassic clades remains unresolved; in particular, recent work suggested that Lapillopsidae nests within Lydekkerinidae. Here we describe Rhigerpeton isbelli, gen. et sp. nov., based on a partial skull from the lower Fremouw Formation of Antarctica that is diagnosed by a combination of features shared with at least some lapillopsids, such as a longitudinal ridge on the dorsal surface of the tabular, and features not found in lapillopsids but shared with some lydekkerinids, such as the retention of pterygoid denticles and a parachoanal tooth row (as in Lydekkerina, for example). A series of phylogenetic analyses confirm the lapillopsid affinities of R. isbelli but provide conflicting results regarding the polyphyly and/or paraphyly of Lydekkerinidae with respect to lapillopsids. The position of Lapillopsidae within Temnospondyli is highly sensitive to taxon sampling of other predominantly Early Triassic temnospondyls. The occurrence of a lapillopsid in Antarctica brings the documented temnospondyl diversity more in line with historically well-sampled portions of southern Pangea but robust biogeographic comparisons remain hindered by the inability to resolve many historic Antarctic temnospondyl records to the finer taxonomic scales needed for robust biostratigraphy
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- Award ID(s):
- 1947094
- PAR ID:
- 10504951
- Publisher / Repository:
- Taylor and Francis
- Date Published:
- Journal Name:
- Journal of Vertebrate Paleontology
- Volume:
- 42
- Issue:
- 6
- ISSN:
- 0272-4634
- Subject(s) / Keyword(s):
- Antarctica Fremouw Formation Temnospondyli
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Journal Article:
- https://doi.org/10.1080/02724634.2023.2216260
