Conference Agenda

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Session Overview
3.11-2 Triassic Revolution
Monday, 04/Sept/2023:
3:30pm - 5:00pm

Session Chair: Michael J. Benton, University of Bristol
Location: Wiwi 104a


3:30pm - 3:45pm
Topics: 3.11 Triassic Revolution

New insights into the Dinocephalosauridae, a recently recognised clade of Triassic marine archosauromorphs, including the identification of its first European member

Stephan N.F. Spiekman

Naturkunde Museum Stuttgart, Germany

The diversification of marine reptiles played a major part in the Triassic Revolution and represented the first large-scale return of tetrapods to an aquatic environment. Recently, a new marine archosauromorph clade, Dinocephalosauridae, was recognised, considerably increasing the known diversity of Triassic marine reptiles, particularly among the generally terrestrial Archosauromorpha. Its best-known member, Dinocephalosaurus orientalis, superficially resembles plesiosaurs, possessing a hyperelongate neck composed of many cervical vertebrae, an elongate torso, and flipper-like limbs. The osteology of Dinocephalosaurus is virtually completely described based on newly discovered specimens. Up to six metres long, it is characterised by its long tail and even longer neck. The appendicular skeleton exhibits a high degree of skeletal paedomorphosis recalling that of many sauropterygians, but the skull and neck are completely inconsistent with sauropterygian affinities. Its cranial morphology, including the presence of narial fossae, is very similar to that seen in another long-necked archosauromorph, Tanystropheus hydroides, which largely represents a convergence related to an aquatic piscivorous lifestyle. Chinese discoveries such as Dinocephalosaurus merit a re-evaluation of historical European collections. Based on such a revision, we also redescribe Trachelosaurus fischeri, known from a single, disarticulated specimen collected in the 1800s from the Solling Formation (Buntsandstein) of Bernburg, Germany. It possesses short, bifurcating cervical ribs, which are unique among archosauromorphs. Trachelosaurus is confidently recognised as the first European dinocephalosaurid based on a wide range of character states, including its highly presacral vertebral count, wide dorsal transverse processes, holocephalous dorsal ribs, an ilium lacking a preacetabular process, and a rod-like femur.

3:45pm - 4:00pm
Topics: 3.11 Triassic Revolution



Hefei University of Technology

Sauropterygia was a taxonomically and ecomorphologically diverse clade of Mesozoic marine reptiles spanning the Early Triassic to the Late Cretaceous. Sauropterygians are traditionally divided into two groups representing two markedly different body plans – the short-necked, durophagous Placodontia and the long-necked Eosauropterygia – whereas Saurosphargidae, a small clade of armoured marine reptiles, is considered as the sauropterygian sister-group. However, the early evolutionary history of sauropterygians and their phylogenetic relationships with other groups within Diapsida are still incompletely understood. Here, we report a new saurosphargid from the Early Triassic of South China, representing the earliest known occurrence of the clade. An updated phylogenetic analysis focussing on the interrelationships within diapsid reptiles recovers saurosphargids as nested within sauropterygians, forming a clade with eosauropterygians to the exclusion of placodonts. Furthermore, a clade comprising Eusaurosphargis and Palatodonta is recovered as the sauropterygian sister-group. The phylogenetic position of several Early and Middle Triassic sauropterygians of previously uncertain phylogenetic affinity, such as Atopodentatus, Hanosaurus, Majiashanosaurus and Corosaurus, is also clarified, elucidating the early evolutionary assembly of the sauropterygian body plan. Finally, our phylogenetic analysis recovers Testudinata and Archosauromorpha within Archelosauria, a result strongly supported by molecular data, but until now rarely recovered by any phylogenetic analysis using a morphology-only data set. Our study provides evidence for the rapid diversification of sauropterygians in the aftermath of the Permo-Triassic mass extinction event and emphasises the importance of broad taxonomic sampling in reconstructing phylogenetic relationships among extinct taxa.

4:15pm - 4:30pm
Topics: 3.11 Triassic Revolution

Puberty in a Mesozoic reptile

Qiang Li1,2, Jun Liu1,2, Nicole Klein2, Yasuhisa Nakajima3, P. Martin Sander1,2,4

1Division of Geology, School of Resources and Environmental Engineering, Hefei University of Technology, 230009 Hefei, China; 2Section Paleontology, Institute of Geosciences, University of Bonn, 53115 Bonn, Germany; 3Department of Natural Sciences, Faculty of Science and Engineering, Tokyo City University, 1588557 Tokyo, Japan; 4The Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, 90007 CA, USA

The histology of bone can be preserved virtually unaltered for hundreds of millions of years in fossils from all environments and all vertebrate taxa, giving rise to the flourishing field of paleohistology. The shafts of long bones are formed by the apposition of periosteal bone tissue, similar to the growth of wood, and preserve (an often cyclical) record of the growth of the individual and events in its life history. One such event is sexual maturation or puberty, during which hormonal changes transform the juvenile into a sexually mature adult. Puberty has been well studied in humans and some other living vertebrates. Here we describe puberty in Keichousaurus, a small sexually dimorphic and live-bearing marine reptile from Middle Triassic rocks of SW China, about 240 million years old. Using a combination of bone histology and morphology, we detected puberty as one of four life stages (the others being foetus, juvenile, and adult). Adult Keichousaurus males have a more robust humerus than females with pronounced muscle attachment sites and a triangular shaft cross section. Mid-shaft sections of the humeri of the males show the transition from the rounded juvenile cross section to the triangular adult cross section, as reflected in the contour of the growth marks. This shape change is produced by differential bone apposition of the periosteum, presumably triggered by sex hormones, as in humans, and influenced by changes in loading regime during puberty. This is the first report of puberty in a fossil amniote.

4:30pm - 5:00pm
Invited Session Keynote
Topics: 3.11 Triassic Revolution

Novel insights into the end-Triassic extinction from contemporaneous southern African sedimentary basins

Kimberley Chapelle

University of the Witwatersrand, South Africa

The end-Triassic Extinction Event (ETE) lead to the demise of ~76% of species, as well as major biotic transitions in terrestrial vertebrate faunas. These include the shift from a mainly synapsid- and pseudosuchian-dominated ecosystem in the Triassic (e.g. dicynodont and cynodont therapsids) to dinosaur-dominated ecosystem in the Jurassic. Our understanding of this crucial time in Earth’s history is hindered by the lack of sedimentary deposits that record the Triassic–Jurassic boundary and bear informative vertebrate fossils across this interval. Several southern African basins are infilled by uninterrupted Carnian–Pliensbachian sediments. These include the Stormberg Group of the main Karoo Basin of southern Africa, as well as the Mid-Zambezi and Tuli basins of Zimbabwe. Surprisingly, the paucity of the current known fossil record recovered from these southern African deposits limits their use in understanding the ETE. This is in part because, to date, the Late Triassic vertebrates known to pertain from these units are much less abundant and diverse than those from the Early Jurassic units. Over the last decade, increased field work targeting these areas, combining excavations with high-resolution dating and biostratigraphy, has yielded multiple new fossil-bearing localities that add crucial new data to our understanding of ETE faunal change. Here, I present an overview of these novel sites. One notable location includes the late Norian quarries from near the village of Qhemegha in the Eastern Cape of South Africa which preserve a diversity of vertebrates such as: large-bodied late-branching pseudosuchians; large- and small-bodied sauropodomorphs and theropods; non-dinosaurian avemetatarsalians; and synapsids.