New Middle Eocene Archaeocetes (cetacea:mammalia) From The Kuldana Formation Of Northern Pakistan
artiodactyls; cetaceans; early whales; evolution; locomotion; mammalia; origin; Paleontology; time; transition
Cooper L N; Thewissen J G M; Hussain S T
Journal of Vertebrate Paleontology
2009
2009-12
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1671/039.029.0423" target="_blank" rel="noreferrer noopener">10.1671/039.029.0423</a>
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 origin and early evolution of whales: macroevolution documented on the Indian Subcontinent
Cetacea; India; evolution; energetics; Life Sciences & Biomedicine - Other Topics; artiodactyls; Eocene; pakistan; whales; cetaceans; Eocene; cetartiodactyla; locomotor evolution; dolphins; middle; semiaquatic mammals; underwater hearing
The origin of whales (order Cetacea) from a four-footed land animal is one of the best understood examples of macroevolutionary change. This evolutionary transition has been substantially elucidated by fossil finds from the Indian subcontinent in the past decade and a half. Here, we review the first steps of whale evolution, i.e. the transition from a land mammal to obligate marine predators, documented by the Eocene cetacean families of the Indian subcontinent: Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae, as well as their artiodactyl sister group, the Raoellidae. We also discuss the influence that the excellent fossil record has on the study of the evolution of organ systems, in particular the locomotor and hearing systems.
Bajpai S; Thewissen J G M; Sahni A
Journal of Biosciences
2009
2009-11
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/s12038-009-0060-0" target="_blank" rel="noreferrer noopener">10.1007/s12038-009-0060-0</a>
Evolution of dental wear and diet during the origin of whales
artiodactyls; Biodiversity & Conservation; carbon-isotope discrimination; cetaceans; Environmental Sciences & Ecology; Evolutionary Biology; mammalia; middle eocene; pakistan; Paleontology; photosynthesis; seagrasses; tooth enamel; transitions
Dental morphology changes dramatically across the artiodactyl-cetacean transition, and it is generally assumed that this reflects the evolutionary change from herbivory and omnivory to carnivory. To test hypotheses regarding tooth function and diet, we studied size and position of wear facets on the lower molars and the stable isotopes of enamel samples. We found that nearly all investigated Eocene cetaceans had dental wear different from typical wear in ungulates and isotope values indicating that they hunted similar prey and processed it similarly. The only exception is the protocetid Babiacetus, which probably ate larger prey with harder skeletons. The closest relative of cetaceans, the raoellid artiodactyl Indohyus, had wear facets that resemble those of Eocene cetaceans more than they do facets of basal artiodactyls. This is in spite of Indohyus's tooth crown morphology, which is unlike that of cetaceans, and its herbivorous diet, as indicated by stable isotopes. This implies that the evolution of masticatory function preceded that of crown morphology and diet at the origin of cetaceans.
Thewissen J G M; Sensor J D; Clementz M T; Bajpai S
Paleobiology
2011
2011
Journal Article
n/a
NEW SKELETAL MATERIAL OF ANDREWSIPHIUS AND KUTCHICETUS, TWO EOCENE CETACEANS FROM INDIA
artiodactyls; gujarat; hearing; kachchh; locomotor evolution; mammalia; Paleontology; whales
The Eocene cetacean genera Andrewsiphius and Kutchicetus are systematically revised, their anatomy described, and their phylogenetic position analyzed. Each genus contains a single species, A. sloani and K. minimus, and both are known only from the middle Eocene of the Indian Subcontinent. Andrewsiphius and Kutchicetus differ in a number of respects, the most important dental difference being that P2, P3, p2, and p3 are double-rooted in Andrewsiphius and single-rooted in Kutchicetus. Lower molars are separated by diastemata in Kutchicetus, but not in Andrewsiphius. Postcranially, Andrewsiphius has caudal vertebrae that are far more robust than those of Kutchicetus. We propose the new clade Andrewsiphiinae for these two genera, based on their unique characters: the extremely slender jaw, fused mandibular symphysis, narrow palate and rostrum, and lower molars that have a low crown with three Cusps lined tip rostro-caudally. A phylogenetic analysis indicates that andrewsiphiines are either a subfamily of Remingtonocetidae or an independent branch on the Eocene cetacean lineage. Interpreting conservatively, we classify them as remingtonocetids. Andrewsiphiines have a long, robust, dorso-ventrally flattened tail and short limbs, Suggesting that they swam using dorsoventral undulation of the tail.
Thewissen J G M; Bajpai S
Journal of Paleontology
2009
2009-09
Journal Article
<a href="http://doi.org/10.1666/08-045.1" target="_blank" rel="noreferrer noopener">10.1666/08-045.1</a>
The early radiations of cetacea (Mammalia): Evolutionary pattern and developmental correlations
archaeocete; artiodactyls; development; Environmental Sciences & Ecology; evolution; Evolutionary Biology; feet; fossil record; India; locomotor evolution; marine mammal; middle eocene; origin; pakistan; Stenella attenuata; time; whales
The origin and early evolution of Cetacea (whales, dolphins, and porpoises) is one of the best examples of macroevolution as documented by fossils. Early whales are divided into six families that differ greatly in their habitats, which varied from land to freshwater, coastal waters, and fully marine. Early cetaceans lived in the Eocene (55-37 million years ago), and they show an enormous morphological diversity. Toward the end of the Eocene the modem cetacean body plan originated, and this body plan remained more or less the same in the subsequent evolution. It is possible that some aspects of this body plan are rooted in constraints that are dictated by cetacean embryologic development and controlled by genes that affect many organ systems at once. It may be possible to use a study of patterns of correlations among morphological traits to test hypotheses of developmental links among organ systems.
Thewissen J G M; Williams E M
Annual Review of Ecology and Systematics
2002
2002
Journal Article
<a href="http://doi.org/10.1146/annurev.ecolysis.33.020602.095426" target="_blank" rel="noreferrer noopener">10.1146/annurev.ecolysis.33.020602.095426</a>
Vestibular evidence for the evolution of aquatic behaviour in early cetaceans
artiodactyls; bony labyrinth; feet; hearing; inner-ear; locomotor evolution; model; origin; petrosal; Science & Technology - Other Topics; whales
Early cetaceans evolved from terrestrial quadrupeds to obligate swimmers, a change that is traditionally studied by functional analysis of the postcranial skeleton(1). Here we assess the evolution of cetacean locomotor behaviour from an independent perspective by looking at the semicircular canal system, one of the main sense organs involved in neural control of locomotion(2). Extant cetaceans are found to be unique in that their canal arc size, corrected for body mass, is approximately three times smaller than in other mammals. This reduces the sensitivity of the canal system, most plausibly to match the fast body rotations that characterize cetacean behaviour. Eocene fossils show that the new sensory regime, incompatible with terrestrial competence, developed quickly and early in cetacean evolution, as soon as the taxa are associated with marine environments. Dedicated agile swimming of cetaceans thus appeared to have originated as a rapid and fundamental shift in locomotion rather than as the gradual transition suggested by postcranial evidence. We hypothesize that the unparalleled modification of the semicircular canal system represented a key 'point of no return' event in early cetacean evolution, leading to full independence from life on land.
Spoor F; Bajpal S; Hussaim S T; Kumar K; Thewissen J G M
Nature
2002
2002-05
Journal Article
<a href="http://doi.org/10.1038/417163a" target="_blank" rel="noreferrer noopener">10.1038/417163a</a>
Cranial anatomy of Pakicetidae (Cetacea, Mammalia)
artiodactyls; eocene; evolution; hearing; origin; pakistan; Paleontology; whales
The skulls and isolated tympanics are described for the earliest whales, pakicetids, from the H-GSP Locality 62 in the Ganda Kas area in Northern Pakistan. Currently three pakicetid genera are known: Pakicetus, Ichthyolestes, and Nalacetus. Ichthyolestes is smaller than the two other genera. Nalacetus and Pakicetus are similar in size, but morphologically different. Pakicetids have a nasal opening at the tip of the rostrum. Their palate retains an incisive foramen. This study reveals three characters of the cranial anatomy useful for systematic analyses. In pakicetids the orbits are orientated dorsally, and there is no supraorbital shield. The dorsal orientation of the orbits is diagnostic for the family, and the lack of supraorbital shield distinguishes pakicetids, ambulocetids, and remingtonocetids from the other Eocene archaeocetes. The intertemporal region of the pakicetid skull is very narrow, a feature that also occurs in many other Eocene cetaceans. The tympanic, which is the most abundant cranial bone (more than 30 specimens) in the pakicetid collections from H-GSP Locality 62, can be used to distinguish the species of pakicetids. In Ichthyolestes, the tympanic bulla is of the same absolute size as in Pakicetus, hence relatively larger, and the tympanic bulla of Nalacetus is larger than either of these. Morphologically, the tympanic bullae differ between the genera, and on the basis of these morphologies it is possible to recognize a fourth species of pakicetid at this locality.
Nummela S; Hussain S T; Thewissen J G M
Journal of Vertebrate Paleontology
2006
2006-09
Journal Article
<a href="http://doi.org/10.1671/0272-4634(2006)26%5B746:caopcm%5D2.0.co;2" target="_blank" rel="noreferrer noopener">10.1671/0272-4634(2006)26%5B746:caopcm%5D2.0.co;2</a>