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Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara).

Jones ME, Anderson CL, Hipsley CA, Müller J, Evans SE, Schoch RR - BMC Evol. Biol. (2013)

Bottom Line: A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid.Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora.The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Department of Cell and Developmental Biology, Anatomy Building, UCL, University College London, Gower Street, London WCIE 6BT, UK. marc.jones@adelaide.edu.au.

ABSTRACT

Background: Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g. Brachyrhinodon), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole.

Results: Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238-240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238-249.5), and crown-group Squamata originated around 193 Mya (176-213).

Conclusion: A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.

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Maximum clade credibility tree (BEAST) with constrained nodes labelled according to Table2. Tectonic maps were redrawn from Blakey [58]. CPE indicates the Carnian Pluvial Event [61]. Calibrated nodes are numbered X and 1–12 as in Table 1 but Y, crown Archosauria, is not shown. For results from the MrBayes analysis, including posterior probabilities of separate nodes, see Additional file 5.
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Figure 4: Maximum clade credibility tree (BEAST) with constrained nodes labelled according to Table2. Tectonic maps were redrawn from Blakey [58]. CPE indicates the Carnian Pluvial Event [61]. Calibrated nodes are numbered X and 1–12 as in Table 1 but Y, crown Archosauria, is not shown. For results from the MrBayes analysis, including posterior probabilities of separate nodes, see Additional file 5.

Mentions: The topology obtained from our molecular divergence dating in the BEAST analysis (Figure 4: maximum clade credibility tree) is generally the same as that found by previous studies based on molecular data (e.g. [41,51,145]): Lepidosauria is monophyletic, Gekkota is the sister taxon to all other Squamata, amphisbaenians are nested within Lacertoidea, and Iguania is sister group to Serpentes + Anguimorpha. However, there are there are areas of disagreement some with two recent major studies: Townsend et al. [146] and Pyron et al. [2].


Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara).

Jones ME, Anderson CL, Hipsley CA, Müller J, Evans SE, Schoch RR - BMC Evol. Biol. (2013)

Maximum clade credibility tree (BEAST) with constrained nodes labelled according to Table2. Tectonic maps were redrawn from Blakey [58]. CPE indicates the Carnian Pluvial Event [61]. Calibrated nodes are numbered X and 1–12 as in Table 1 but Y, crown Archosauria, is not shown. For results from the MrBayes analysis, including posterior probabilities of separate nodes, see Additional file 5.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4016551&req=5

Figure 4: Maximum clade credibility tree (BEAST) with constrained nodes labelled according to Table2. Tectonic maps were redrawn from Blakey [58]. CPE indicates the Carnian Pluvial Event [61]. Calibrated nodes are numbered X and 1–12 as in Table 1 but Y, crown Archosauria, is not shown. For results from the MrBayes analysis, including posterior probabilities of separate nodes, see Additional file 5.
Mentions: The topology obtained from our molecular divergence dating in the BEAST analysis (Figure 4: maximum clade credibility tree) is generally the same as that found by previous studies based on molecular data (e.g. [41,51,145]): Lepidosauria is monophyletic, Gekkota is the sister taxon to all other Squamata, amphisbaenians are nested within Lacertoidea, and Iguania is sister group to Serpentes + Anguimorpha. However, there are there are areas of disagreement some with two recent major studies: Townsend et al. [146] and Pyron et al. [2].

Bottom Line: A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid.Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora.The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: Research Department of Cell and Developmental Biology, Anatomy Building, UCL, University College London, Gower Street, London WCIE 6BT, UK. marc.jones@adelaide.edu.au.

ABSTRACT

Background: Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g. Brachyrhinodon), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole.

Results: Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238-240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238-249.5), and crown-group Squamata originated around 193 Mya (176-213).

Conclusion: A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.

Show MeSH
Related in: MedlinePlus