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Abstract Almadasuchus figariiis a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remains. The skull of the only specimen of the monotypicAlmadasuchuswas restudied using high‐resolution computed micro tomography.Almadasuchushas an apomorphic condition in its skull shared with the closest relatives of crocodyliforms (i.e. hallopodids) where the quadrates are sutured to the laterosphenoids and the otoccipital contacts the quadrate posterolaterally, reorganizing the exit of several cranial nerves (e.g. vagus foramen) and the entry of blood vessels (e.g. internal carotids) on the occipital surface of the skull. The endocast is tubular, as previously reported in thalattosuchians, but has a marked posterior step, and a strongly projected floccular recess as in other basal crocodylomorphs. Internally, the skull ofAlmadasuchusis heavily pneumatized, where different air cavities invade the bones of the suspensorium and braincase, both on its dorsal or ventral parts.Almadasuchushas a large basioccipital recess, which is formed by cavities that excavate the basioccipital and the posterior surface of the basisphenoid, and unlike other crocodylomorphs is connected with the basisphenoid pneumatizations. Ventral to the otic capsule, a pneumatic cavity surrounded by the otoccipital and basisphenoid is identified as the rhomboidal recess. The quadrate ofAlmadasuchusis highly pneumatized, being completely hollow, and the dorsal pneumatizations of the braincase are formed by the mastoid and facial antra, and a laterosphenoid cavity (trigeminal diverticulum). To better understand the origins of pneumatic features in living crocodylomorphs we studied cranial pneumaticity in the basal members of Crocodylomorpha and found that: (a) prootic pneumaticity may be a synapomorphy for the whole clade; (b) basisphenoid pneumaticity (pre‐, postcarotid and rostral recesses) is a derived feature among basal crocodylomorphs; (c) quadrate pneumatization is acquired later in the history of the group; and (d) the rhomboidal sinus is a shared derived trait of hallopodids and crocodyliforms. The marine thallatosuchians exhibit a reduction of the pneumaticity of the braincase and this reduction is evaluated considering the two phylogenetic positions proposed for the clade.
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Helmeted hornbill cranial kinesis: Balancing mobility and stability in a high‐impact joint
Abstract Prokinesis—in which a craniofacial joint allows the rostrum to move relative to the braincase—is thought to confer diverse advantages in birds, mostly for feeding. A craniofacial joint would, however, be a weak link if cranial stability is important. Paradoxically, we have identified a craniofacial joint in helmeted hornbills (Rhinoplax vigil), birds known for violent head‐butting behavior. To understand how the helmeted hornbill balances the competing demands of kinesis and collision, we combine manual craniofacial joint manipulation, skull micro‐computed tomography (μCT) and articular raycasting, also comparing our data with μCT scans of 10 closely‐related species that do not aggressively head‐butt. The helmeted hornbill boasts a particularly massive casque, a distinctive upper mandible protrusion fronting the braincase; the craniofacial joint is immediately caudal to this, a standard prokinetic hinge joint position, at the dorsal border of braincase and upper mandible. However, whereas the craniofacial joint in all bucerotiform bird species we examined was only a slender bridge, the helmeted hornbill's joint is exceptionally reinforced. Raycasting analyses revealed high correspondence between the extremely broad joint facets, with reciprocal topographies of braincase and casque fitting like complex puzzle pieces. The result is a joint with a single degree of freedom and limited range of motion, increasing the gape when elevated, but conversely stable when depressed. With the dense network of bony trabeculae in the casque also funneling back to this joint, we infer that the damaging effects of high cranial impact are mitigated, not by dissipating impact energy, but through a skull architecture with a prodigious safety factor.
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- Award ID(s):
- 2209144
- PAR ID:
- 10577097
- 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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