Most living reptile diversity is concentrated in Squamata (lizards, including snakes), which have poorly known origins in space and time. Recently, †
- Award ID(s):
- 1947094
- PAR ID:
- 10409428
- Date Published:
- Journal Name:
- Nature
- Volume:
- 614
- Issue:
- 7946
- ISSN:
- 0028-0836
- Page Range / eLocation ID:
- 102 to 107
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Cryptovaranoides microlanius from the Late Triassic of the United Kingdom was described as the oldest crown squamate. If true, this result would push back the origin of all major lizard clades by 30–65 Myr and suggest that divergence times for reptile clades estimated using genomic and morphological data are grossly inaccurate. Here, we use computed tomography scans and expanded phylogenetic datasets to re-evaluate the phylogenetic affinities of †Cryptovaranoides and other putative early squamates. We robustly reject the crown squamate affinities of †Cryptovaranoides , and instead resolve †Cryptovaranoides as a potential member of the bird and crocodylian total clade, Archosauromorpha. Bayesian total evidence dating supports a Jurassic origin of crown squamates, not Triassic as recently suggested. We highlight how features traditionally linked to lepidosaurs are in fact widespread across Triassic reptiles. Our study reaffirms the importance of critically choosing and constructing morphological datasets and appropriate taxon sampling to test the phylogenetic affinities of problematic fossils and calibrate the Tree of Life. -
Permian–Triassic rocks of the Transantarctic Basin provide an unparalleled record of high latitude paleoenvironments and terrestrial vertebrate faunas. Here we summarize the taxonomic and paleoecological implications of the approximately 1300 vertebrate fossils collected since 1968, as well as report on new geologic field observations made during the 2017–18 austral field season. The Fremouw Formation records a vertebrate assemblage taxonomically most similar to that of the Karoo Basin of South Africa, with 10 genera shared in common. However, temnospondyls form a much greater percentage of tetrapod occurrences in the Fremouw Formation, suggesting favorable conditions for these ectothermic fossil amphibians at high latitudes. Lower Triassic small reptiles (viz. Procolophon, Prolacerta) occur in slightly higher proportions than in the Karoo, but their taxonomic diversity is likely undercounted. Seven stratigraphic columns of the upper Buckley and lower–middle Fremouw formations detail fluvial depositional environments in the central Transantarctic region, recording a shift from wet swamp lands to drier floodplains, most similar to Gondwanan basins in Australia. Fremouw Formation paleosols primarily consist of Protosols, which indicate poor soil forming conditions likely due to low precipitation and high sediment supply from crevasse splays. Mineralogy from X-ray diffraction, review of igneous intrusives, and Buckley Formation coal characterization demonstrate post-pedogenic diagenetic alteration that casts doubt on the results of previous stable isotopic studies of these paleosols. Tetrapod fossils first appear in the Fremouw Formation, which has been taken as evidence for immigration to the Antarctic portion of southern Pangea around the time of the end-Permian mass extinction. However, this may be due to higher soil pH, increased base saturation, lower moisture content, and more rapid burial conditions in the Fremouw than the underlying Buckley Formation that favored bone preservation.more » « less
-
The fossil record of temnospondyl amphibians in the immediate wake of the Permo-Triassic mass extinction captures extensive taxic and ecological diversity, with most records known from high paleolatitudinal settings. In southern Pangea, the most substantial records come from South Africa and Australia, with a total of over 20 taxa presently recognized. Temnospondyls have also been known from correlated horizons in the lower Fremouw Formation of Antarctica since the late 1960s, but these records are mostly fragmentary, thereby limiting taxonomic resolution to the family level and subsequent biostratigraphic correlations and comparisons between high-latitude basins. Here we report substantial new material of the amphibamiform Micropholis stowi, a relic dissorophoid previously known only from the Katberg Formation (Lystrosaurus declivis Assemblage Zone) of South Africa, from the lower Fremouw Formation. The exceptional preservation of the recently recovered material permits not only confident taxonomic referral but also tentative association of several individuals to the broad-headed morph of the taxon. The recognition of M. stowi in Antarctica represents only the fourth geographic occurrence of a dissorophoid from southern Pangea and supports the hypothesis that high-latitude environments served as refugia for temnospondyls during the mass extinction. In the case of M. stowi, such refugia permitted the persistence of a predominantly Permo-Carboniferous clade, and the Antarctic records discussed here further hint at a poorly sampled cryptic distribution, both of amphibamiforms in southern Pangea and of small-bodied temnospondyls in early Mesozoic deposits.more » « less
-
Abstract The archaeocidarids comprise the most derived stem group echinoids and have long been regarded as closely related to the crown group. The fossil record of echinoids in the Palaeozoic is, however, poor, so details surrounding the initial divergence of crown group echinoids are not well constrained. In order to better understand the phylogenetic relationships of the most derived stem group and most basal crown group echinoids, a phylogenetic analysis was undertaken of the Archaeocidaridae, including the genera
Nortonechinus ,Devonocidaris ,Lepidocidaris ,Polytaxicidaris andArchaeocidaris and the Palaeozoic miocidarid cidaroids from the genusEotiaris . We found thatArchaeocidaris appears to be paraphyletic with respect to crown group echinoids. Furthermore, we mapped character evolution along our phylogeny and found that the diversification of archaeocidarids and miocidarids may be linked to large‐scale macroecological changes taking place in the late Palaeozoic, including increasing predation pressure and echinoid encrustation by epibionts. We compared the stratigraphical distribution of archaeocidarid and miocidarid occurrences to our resulting phylogenies, and found that the fit of our cladograms to the stratigraphic record of archaeocidarid occurrences is worse than other echinoid groups, supporting the idea that the imbricate plated archaeocidarids have a poor fossil record. In the course of carrying out these analyses, we also felt it necessary to describe a new species ofArchaeocidaris ,Archaeocidaris ivanovi sp. nov. We also provide novel descriptions and interpretations forDevonocidaris primaevus ,Archaeocidaris brownwoodensis ,Archaeocidaris apheles and revise the synonymy ofArchaeocidaris legrandensis and ?Eotiaris meurevillensis , which may be a crown group echinoid. -
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 biostratigraphymore » « less