The Narial Anatomy of Extinct and Extant Sloths (Xenarthra, Folivora): Osteological Anomalies in the Extant Two-Toed Sloth Choloepus

Gaudin, Timothy J.; Smith, Kelsea; Wible, John R.

doi:10.1007/s10914-021-09562-9

Cited by 3 publications

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References 27 publications

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“…Except for the entotympanic in the auditory bulla, all neomorphic skull bones reported to date were found in the muzzle, i.e., the extended neomorphic region of the mammalian head, as proposed by Higashiyama et al [66]. Generally, the muzzle of mammals contains no skeletal structure, but the rare exceptions include the rostral bone in suids, os proboscidis of Hispaniolan solenodon ( Solenodon paradoxus ), os internasale of two-toed sloths ( Choloepus didactylus and Choloepus hoffmanni ), os nariale of xenarthrans, and mineralization of the external nasal cartilages in several species of bats [73,141,142]. Multiple ossifications are also found rostral to the nasal bones in various species of elephant shrew ( Rhynchocyon ) [143].…”

Section: Novel Bones and Conservatism Of The Mammalian Skullmentioning

confidence: 99%

Evolution, conservatism and overlooked homologies of the mammalian skull

Koyabu

2023

Phil. Trans. R. Soc. B

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In the last decade, studies integrating palaeontology, embryology and experimental developmental biology have markedly altered our homological understanding of the mammalian skull. Indeed, new evidence suggests that we should revisit and restructure the conventional anatomical terminology applied to the components of the mammalian skull. Notably, these are classical problems that have remained unresolved since the ninteenth century. In this review, I offer perspectives on the overlooked problems associated with the homology, development, and conservatism of the mammalian skull, aiming to encourage future studies in these areas. I emphasise that ossification patterns, bone fusion, cranial sutures and taxon-specific neomorphic bones in the skull are virtually unexplored, and further studies would improve our homological understanding of the mammalian skull. Lastly, I highlight that overlooked bones may exist in the skull that are not yet known to science and suggest that further search is needed. This article is part of the theme issue ‘The mammalian skull: development, structure and function’.

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Section: Novel Bones and Conservatism Of The Mammalian Skullmentioning

confidence: 99%

Evolution, conservatism and overlooked homologies of the mammalian skull

Koyabu

2023

Phil. Trans. R. Soc. B

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Cranial osteology of a juvenile specimen ofAcratocnus ye(Mammalia, Xenarthra, Folivora) and its ontogenetic and phylogenetic implications

Gaudin

Scaife

2022

The Anatomical Record

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The present study comprises a description of the skull and jaw anatomy of a juvenile specimen of the Antillean sloth Acratocnus ye, from the Holocene of Haiti. Detailed descriptions and illustrations are provided of the skull bones and their sutural connections, which normally fuse in adults. Descriptions are also provided for the mandible and ear ossicles, as well as endocranial surfaces and sinuses exposed by breaks. The anatomy of our juvenile A. ye is compared to that of adult A. ye to assess ontogenetic changes in the skull. Several of these ontogenetic features are significant new observations that impact the relationships within Xenarthra as a whole, or between Xenarthrans and other placental mammals, most notably, the presence of a separate mesethmoid element, the presence of alveoli for a lower deciduous canine and anterior incisor, and the presence of separate rostral and caudal entotympanic elements. A full list of such changes are provided. In addition, the specimen provides information on phylogenetically relevant characters, including features unique to the genus Acratocnus, and features of the clade Choloepodini, including Acratocnus, the smaller extinct Antillean sloth Neocnus, and the extant two-toed sloth Choloepus. Contrary to previous studies, Acratocnus shares as many features with Choloepus as it does with its fellow Antillean form Neocnus in the present study, which is consistent with current morphology-based phylogenetic hypotheses regarding the relationships within Choloepodini. The current study highlights the need for further anatomical and phylogenetic investigations of Antillean sloths (Megalocnidae/Megalonychidae), and juvenile sloths in general.

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The history and homology of the os paradoxum or dumb-bell-shaped bone of the platypus Ornithorhynchus anatinus (Mammalia, Monotremata)

Wible¹

2022

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The os paradoxum or dumb-bell-shaped bone is a paired bone occurring in the middle of the specialized bill of the platypus Ornithorhynchus anatinus. It has been variously considered as a neomorph of the platypus, as the homologue of the paired vomer of sauropsids, or as a part of the paired premaxillae. A review of the near 200-year history of this element strongly supports the os paradoxum as a remnant of the medial palatine processes of the premaxillae given its ontogenetic continuity with the premaxillae and association with the vomeronasal organ and cartilage, incisive foramen, and cartilaginous nasal septum. In conjunction with this hypothesis, homologies of the unpaired vomer of extant mammals and the paired vomer of extant sauropsids are also supported. These views are reinforced with observations from CT scans of O. anatinus, the Miocene ornithorhynchid Obdurodon dicksoni, and the extant didelphid marsupial Didelphis marsupialis. At the choanae, Obdurodon has what appears to be a separate parasphenoid bone unknown in extant monotremes.

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The Narial Anatomy of Extinct and Extant Sloths (Xenarthra, Folivora): Osteological Anomalies in the Extant Two-Toed Sloth Choloepus

Cited by 3 publications

References 27 publications

Evolution, conservatism and overlooked homologies of the mammalian skull

Evolution, conservatism and overlooked homologies of the mammalian skull

Cranial osteology of a juvenile specimen ofAcratocnus ye(Mammalia, Xenarthra, Folivora) and its ontogenetic and phylogenetic implications

The history and homology of the os paradoxum or dumb-bell-shaped bone of the platypus Ornithorhynchus anatinus (Mammalia, Monotremata)

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