THE POSTCRANIAL SKELETON OF EARLY EOCENE PAKICETID CETACEANS

A comparative analysis of the postcranial skeletal morphology of three species of pakicetid cetaceans provides new insights into their locomotor behavior. In gross morphology, they are similar to their smaller early artiodactyl relatives, lacking obvious signs of their transition to an aquatic niche...

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Bibliographic Details
Published in:Journal of paleontology 2007-01, Vol.81 (1), p.176-200
Main Author: MADAR, S. I
Format: Article
Language:English
Subjects:
Animal morphology
Asia
Bone density
Bones
Canals
Cenozoic
Cetacea
Cetaceans
Chordata
Eocene
Eutheria
Femur
Flat surfaces
Fossils
functional morphology
Ganda Kas Pakistan
Ichthyolestes pinfoldi
Indian Peninsula
locomotion
lower Eocene
Mammalia
morphology
Nalacetus ratimitus
Niches
osteology
Pakicetidae
Pakicetus attocki
Pakistan
Paleogene
Paleontology
Phalanges
phylogeny
Skeleton
skeletons
Tarsus
Taxa
Tertiary
Tetrapoda
Theria
Vertebrata
vertebrate
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Summary:A comparative analysis of the postcranial skeletal morphology of three species of pakicetid cetaceans provides new insights into their locomotor behavior. In gross morphology, they are similar to their smaller early artiodactyl relatives, lacking obvious signs of their transition to an aquatic niche. Features linking them are related to a cursorial adaptation centered in the reduction of joint mobility to the parasagittal plane, evident in both the elbow and the ankle. In addition to cursorial features of the limbs, the earliest whales and early artiodactyls both possess a long, stable lumbus and robust tails. The three pakicetid genera can be distinguished by size, proportion, and details of articular morphology. However, all pakicetid postcrania bear microstructural specializations commensurate with aquatic locomotion, and incompatible with cursoriality. The most striking modification is the presence of systemic increased bone density, likely used as skeletal ballast. When both postcranial morphology and microstructure are considered, it can be concluded that pakicetid cetaceans were highly adapted for an aquatic niche. As in several extant semiaquatic taxa, the pakicetid tail undoubtedly contributed to its locomotor repertoire, whether in propulsion or stabilization.
ISSN:0022-3360
1937-2337
DOI:10.1666/0022-3360(2007)81[176:TPSOEE]2.0.CO;2