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While most early limbed vertebrates possessed a fully-roofed dermatocranium in their temporal skull region, temporal fenestrae and excavations evolved independently at least twice in the earliest amniotes, with several different variations in shape and position of the openings. Yet, the specific drivers behind this evolution have been only barely understood. It has been mostly explained by adaptations of the feeding apparatus as a response to new functional demands in the terrestrial realm, including a rearrangement of the jaw musculature as well as changes in strain distribution. Temporal fenestrae have been retained in most extant amniotes but have also been lost again, notably in turtles. However, even turtles do not represent an optimal analog for the condition in the ancestral amniote, highlighting the necessity to examine Paleozoic fossil material. Here, we describe in detail the sutures in the dermatocranium of the Permian reptileCaptorhinus aguti(Amniota, Captorhinidae) to illustrate bone integrity in an early non-fenestrated amniote skull. We reconstruct the jaw adductor musculature and discuss its relation to intracranial articulations and bone flexibility within the temporal region. Lastly, we examine whether the reconstructed cranial mechanics inC. aguticould be treated as a model for the ancestor of fenestrated amniotes. We show thatC. agutilikely exhibited a reduced loading in the areas at the intersection of jugal, squamosal, and postorbital, as well as at the contact between parietal and postorbital. We argue that these “weak” areas are prone for the development of temporal openings and may be treated as the possible precursors for infratemporal and supratemporal fenestrae in early amniotes. These findings provide a good basis for future studies on other non-fenestrated taxa close to the amniote base, for example diadectomorphs or other non-diapsid reptiles.
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Cranial anatomy and phylogenetic affinities of Bolosaurus major , with new information on the unique bolosaurid feeding apparatus and evolution of the impedance‐matching ear
Abstract Resolving the phylogenetic relationships of early amniotes, in particular stem reptiles, remains a difficult problem. Three‐dimensional morphological analysis of well‐preserved stem‐reptile specimens can reveal important anatomical data and clarify regions of phylogeny. Here, we present the first thorough description of the unusual early Permian stem reptileBolosaurus major, including the first comprehensive description of a bolosaurid braincase. We describe previously obscured details of the palate, allowing for insight into bolosaurid feeding mechanics. Aspects of the rostrum, palate, mandible, and neurocranium suggest thatB. majorhad a particularly strong bite. We additionally foundB. majorhas a surprisingly slender stapes, similar to that of the middle Permian stem reptileMacroleter poezicus, which may suggest enhanced hearing abilities compared to other Paleozoic amniotes (e.g., captorhinids). We incorporated our new anatomical information into a large phylogenetic matrix (150 OTUs, 590 characters) to explore the relationship of Bolosauridae among stem reptiles. Our analyses generally recovered a paraphyletic “Parareptilia,” and found Bolosauridae to diverge after Captorhinidae + Araeoscelidia. We also includedB. majorwithin a smaller matrix (10 OTUs, 27 characters) designed to explore the interrelationships of Bolosauridae and found all species ofBolosaurusto be monophyletic. While reptile relationships still require further investigation, our phylogeny suggests repeated evolution of impedance‐matching ears in Paleozoic stem reptiles.
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- PAR ID:
- 10527808
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- The Anatomical Record
- ISSN:
- 1932-8486
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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