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ABSTRACT Crocodylians evolved some of the most characteristic skulls of the animal kingdom with specializations for semiaquatic and ambush lifestyles, resulting in a feeding apparatus capable of tolerating high biomechanical loads and bite forces and a head with a derived sense of trigeminal‐nerve‐mediated touch. The mandibular symphysis accommodates these specializations being both at the end of a biomechanical lever and an antenna for sensation. Little is known about the anatomy of the crocodylian mandibular symphysis, hampering our understanding of form, function, and evolution of the joint in extant and extinct lineages. We explore mandibular symphysis anatomy of an ontogenetic series ofAlligator mississippiensisusing imaging, histology, and whole mount methods. Complex sutural ligaments emanating about a midline‐fused Meckel's cartilage bridge the symphysis. These tissues organize during days 37–42 ofin ovodevelopment. However, interdigitations do not manifest until after hatching. These soft tissues leave a hub and spoke‐like bony morphology of the symphyseal plate, which never fuses. Interdigitation morphology varies within the symphysis suggesting differential loading about the joint. Neurovascular canals extend throughout the mandibles to alveoli, integument, and bone adjacent to the symphysis. These features suggest theAlligatormandibular symphysis offers compliance in an otherwise rigid skull. We hypothesize a fused Meckel's cartilage offers stiffness in hatchling mandibles prior to the development of organized sutural ligaments and mineralized bone while offering a scaffold for somatic growth. The porosity of the dentaries due to neurovascular tissues likely allows transmission of sensory and proprioceptive information from the surroundings and the loaded symphysis. Anat Rec, 302:1696–1708, 2019. © 2019 American Association for Anatomy
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Rostral neurovasculature indicates sensory trade‐offs in Mesozoic pelagic crocodylomorphs
ABSTRACT Metriorhynchoid thalattosuchians were a marine clade of Mesozoic crocodylomorphs that evolved from semi‐aquatic, “gharial”‐like species into the obligately pelagic subclade Metriorhynchidae. To explore whether the sensory and physiological demands of underwater life necessitates a shift in rostral anatomy, both in neurology and vasculature, we investigate the trigeminal innervation and potential somatosensory abilities of metriorhynchoids by digitally segmenting the rostral neurovascular canals in CT scans of 10 extant and extinct crocodyliforms. The dataset includes the terrestrial, basal crocodyliformProtosuchus haughtoni, two semi‐aquatic basal metriorhynchoids, four pelagic metriorhynchids and three extant, semi‐aquatic crocodylians. In the crocodylian and basal metriorhynchoid taxa, we find three main neurovascular channels running parallel to one another posteroanteriorly down the length of the snout, whereas in metriorhynchids there are two, and inP. haughtonionly one. Crocodylians appear to be unique in their extensive trigeminal innervation, which is used to supply the integumentary sensory organs (ISOs) involved with their facial somatosensory abilities. Crocodylians have a far higher number of foramina on the maxillary bones than either metriorhynchoids orP. haughtoni, suggesting that the fossil taxa lacked the somatosensory abilities seen in extant species. We posit that the lack of ISO osteological correlates in metriorhynchoids is due to their basal position in Crocodyliformes, rather than a pelagic adaptation. This is reinforced by the hypothesis that extant crocodyliforms, and possibly some neosuchian clades, underwent a long “nocturnal bottleneck”—hinting that their complex network of ISOs evolved in Neosuchia, as a sensory trade‐off to compensate for poorer eyesight.
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- Award ID(s):
- 1902242
- PAR ID:
- 10371054
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- The Anatomical Record
- Volume:
- 305
- Issue:
- 10
- ISSN:
- 1932-8486
- Format(s):
- Medium: X Size: p. 2654-2669
- Size(s):
- p. 2654-2669
- Sponsoring Org:
- National Science Foundation
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