Abstract
The humerus is central for locomotion in turtles as quadrupedal animals. Osteological variation across testudine clades remains poorly documented. Here, we systematically describe the humerus anatomy for all major extant turtle clades based on 38 species representing the phylogenetic and ecological diversity of crown turtles. Three Late Triassic species of shelled stem turtles (Testudindata) are included to establish the plesiomorphic humerus morphology. Our work is based on 3D models, establishing a publicly available digital database. Previously defined terms for anatomical sides of the humerus (e.g., dorsal, ventral) are often not aligned with the respective body sides in turtles and other quadrupedal animals with sprawling gait. We propose alternative anatomical directional terms to simplify communication: radial and ulnar (the sides articulating with the radius/ulna), capitular (the side bearing the humeral head), and intertubercular (opposite to capitular surface). Turtle humeri show low morphological variation with exceptions concentrated in locomotory specialists. We propose 15 discrete characters to summarize osteological variation for future phylogenetic studies. Disparity analyses comparing non-shelled and shelled turtles indicate that the presence of the shell constrains humerus variation. Flippered aquatic turtles are released from this constraint and significantly increase overall disparity. Ontogenetic changes of turtle humeri are related to increased ossification and pronunciation of the proximal processes, the distal articulation areas, and the closure of the ectepicondylar groove to a foramen. Some turtle species retain juvenile features into adulthood and provide evidence for paedomorphic evolution. We review major changes of turtle humerus morphology throughout the evolution of its stem group.
Original language | English |
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Pages (from-to) | 3437-3505 |
Number of pages | 69 |
Journal | The Anatomical Record |
Volume | 307 |
Issue number | 11 |
Early online date | 8 May 2024 |
DOIs | |
Publication status | Published - 30 Nov 2024 |
Funding
We thank all researchers and institutions who make 3D data available for study via MorphoSource, as well as the MorphoSource team. We particularly thank the following people and their institutions for providing scans or access to materials for scanning: Roger Benson (AMNH), Addison Wynn, Esther Langan and Christina Sami (USNM), Patrick Campbell (NHMUK), Hilary Ketchum (OUMNH), Lo\u00EFc Costeur and Bastien Mennecart (NMB), Linda Mogk and Gunther K\u00F6hler (SMF), Rainer Schoch (SMNS), and Gabriela Cisterna (PULR), and Tomasz Sulej (ZPAL). We thank Walter Joyce for general discussions on turtle humeri. We are thankful to the editor Heather Smith, and to Walter Joyce and Juliana Sterli for insightful comments that helped improving this manuscript. TS is funded by the National Science Center, Poland (NCN) with the grant 2020/39/B/NZ8/01074. SWE is funded by an Ambizione grant of the Swiss National Science Foundation (SNSF) with the number SNF PZ00P2_202019/1. Open access funding provided by Universite de Fribourg.
Funders | Funder number |
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Narodowym Centrum Nauki | |
National Science Centre | 2020/39/B/NZ8/01074 |
National Science Centre | |
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung | PZ00P2_202019/1 |
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung |
Keywords
- disparity
- ecomorphology
- humerus
- morphological constraint
- turtle evolution
ASJC Scopus subject areas
- Biotechnology
- Anatomy
- Histology
- Ecology, Evolution, Behavior and Systematics