Intervertebral and Epiphyseal Fusion in the Postnatal Ontogeny of Cetaceans and Terrestrial Mammals
baleen; Cetacea; Evolutionary Biology; Zoology; India; skeleton; morphology; artiodactyls; Eocene; whales; locomotor evolution; body length; Epiphyseal; fusion; Intervertebral; Vertebra; vertebral osteology
In this paper we studied three related aspects of the ontogeny of the vertebral centrum of cetaceans and terrestrial mammals in an evolutionary context. We determined patterns of ontogenetic fusion of the vertebral epiphyses in bowhead whale (Balaena mysticetus) and beluga whale (Delphinapterus leucas), comparing those to terrestrial mammals and Eocene cetaceans. We found that epiphyseal fusion is initiated in the neck and the sacral region of terrestrial mammals, while in recent aquatic mammals epiphyseal fusion is initiated in the neck and caudal regions, suggesting locomotor pattern and environment affect fusion pattern. We also studied bony fusion of the sacrum and evaluated criteria used to homologize cetacean vertebrae with the fused sacrum of terrestrial mammals. We found that the initial ossification of the vertebral pedicles in the fetus may be a reliable indicator of sacral homology inmodern cetaceans. Finally, we also studied fusion of the centra of cervical vertebrae in B. mysticetus and found that it is not completed until after sexual maturity, and after 20 years of age.
Moran M M; Bajpai S; George J C; Suydam R; Usip S; Thewissen J G M
Journal of Mammalian Evolution
2015
2015-03
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/s10914-014-9256-7" target="_blank" rel="noreferrer noopener">10.1007/s10914-014-9256-7</a>
The Endocranial Cast of Indohyus (Artiodactyla, Raoellidae): The Origin of the Cetacean Brain
Eocene; Cetacea; Brain; CT scan; Endocast
We present the first description of the endocranial cast of the small raoellid artiodactyl Indohyus indirae. Raoellidae are sister group to Cetacea and the new morphological observations allow for outlining some of the early steps of the evolutionary history of the cetacean brain. The combination of primitive artiodactyl features and typical cetacean characters is unique about the Indohyus endocast. The fact that it presents the symplesiomorphic brain pattern observed in earliest Artiodactyla indicates that the cetacean brain derives from a very simple, plesiomorphic brain, with simple neocortical folding pattern, widely exposed midbrain, and concurrent small neocortex expansion. On the other hand, the Indohyus endocast shows characters that also occur in early cetaceans. These include modifications of the olfactory tract with narrow, elongated olfactory bulbs and peduncles, accompanied by a posterior location of the braincase in the cranium. The derived endocranial cast features of Indohyus mainly reflect changes in cranial architecture and these are most probably associated with modifications of the masticatory apparatus and a shift in diet. Indohyus meninges were very thin like in most terrestrial artiodactyls and it had no extensive rostral or lateral retia mirabilia. It however shows a branching pattern of ramification of intraosseous blood sinuses above the cerebellum that might represent the initial development of the caudal venous rete mirabile that would have colonized the endocranial cavity later on, in early archaeocetes.
Orliac MJ; Thewissen JGM
Journal Of Mammalian Evolution
2021
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
journalArticle
<a href="http://doi.org/10.1007/s10914-021-09552-x" target="_blank" rel="noreferrer noopener">10.1007/s10914-021-09552-x</a>
The Endocranial Cast of Indohyus (Artiodactyla, Raoellidae): The Origin of the Cetacean Brain
Orliac MJ; Thewissen J G M
Journal Of Mammalian Evolution
2021
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
journalArticle
<a href="http://doi.org/10.1007/s10914-021-09554-9" target="_blank" rel="noreferrer noopener">10.1007/s10914-021-09554-9</a>