Turtle Origins: <i>Chinlechelys tenertesta</i> and Convergence in Modern Cladistic Analysis
The phylogenetic relationships of turtles (Testudines) challenge cladistics by demonstrating the inherent weaknesses of this non-Darwinian method of phylogenic reconstruction. Recent cladistic analyses have identified sauropterygians as the closest relatives of turtles and even at least one sauropte...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2023-02-01
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| Series: | Proceedings |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2504-3900/87/1/4 |
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| Summary: | The phylogenetic relationships of turtles (Testudines) challenge cladistics by demonstrating the inherent weaknesses of this non-Darwinian method of phylogenic reconstruction. Recent cladistic analyses have identified sauropterygians as the closest relatives of turtles and even at least one sauropterygian, <i>Pappochelys</i>, as a turtle. These findings are largely based on the convergence of several characteristics associated with environmental adaptation, including the relative lengths of phalanges, dense gastralia placement (assumed proto-plastron), and a well-defined intertrochanteric fossa. A lack of failure testing to identify such convergence is important in the analysis of unusual taxa because it can force a taxon into the in-group as a methodological artifact, as with the cladistic placement of <i>Eunotosaurus</i> within Testudines. <i>Eunotosaurus</i> was not placed in a wider vertebrate phylogeny, which led to its identification as a basal member of Caseidae. The characteristics shared by caseids and Testudines, including their relative head-to-body size, posterior jaw articulation, and reduced number of dorsal ribs and vertebrae, contributed to this mistake. Late Triassic <i>Chinlechelys</i> provides a useful window into these varied cladistic problems due to anatomical convergence. It demonstrates an intermediate step between a carapace with neighboring ribs and a carapace fused with ribs. This earlier state lacked the organizing role of the ribs in the carapace and had multiple rows of costals (dorsal osteoderms) arranged at an angle to the ribs, which is a condition only known in some pareiasaurs. This fits with an evo-devo model of gradual change creating a new structure (a carapace), which was followed by adaptive radiation filling the new niches opened by that structure. |
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| ISSN: | 2504-3900 |