Search

The earliest cetaceans were interpreted as semi-aquatic based on the presence of thickened bones and stable oxygen isotopes in tooth enamel. However, the origin of aquatic behaviors in cetacean relatives (e.g., raoellids, anthracotheres) remains unclear. This study reconstructs the origins of aquatic behaviors based on long bone microanatomy and stable oxygen isotopes of tooth enamel in modern and extinct cetartiodactylans. Our findings are congruent with published accounts that microanatomy can be a reliable indicator of aquatic behaviors in taxa that are obligatorily aquatic, and also highlight that some "semi-aquatic" behaviors (fleeing into the water to escape predation) may have a stronger relationship to bone microanatomy than others (herbivory in near-shore aquatic settings). Bone microanatomy is best considered with other lines of information in the land-to-sea transition of cetaceans, such as stable isotopes. This study extends our understanding of the progression of skeletal phenotypes associated with habitat shifts in the relatives of cetaceans.

The whale ear, initially designed for hearing in air, became adapted for hearing underwater in less than ten million years of evolution. This study describes the evolution of underwater hearing in cetaceans, focusing on changes in sound transmission mechanisms. Measurements were made on 60 fossils of whole or partial skulls, isolated tympanics, middle ear ossicles, and mandibles from all six archaeocete families. Fossil data were compared with data on two families of modern mysticete whales and nine families of modern odontocete cetaceans, as well as five families of noncetacean mammals. Results show that the outer ear pinna and external auditory meatus were functionally replaced by the mandible and the mandibular fat pad, which posteriorly contacts the tympanic plate, the lateral wall of the bulla. Changes in the ear include thickening of the tympanic bulla medially, isolation of the tympanoperiotic complex by means of air sinuses, functional replacement of the tympanic membrane by a bony plate, and changes in ossicle shapes and orientation. Pakicetids, the earliest archaeocetes, had a land mammal ear for hearing in air, and used bone conduction underwater, aided by the heavy tympanic bulla. Remingtonocetids and protocetids were the first to display a genuine underwater ear where sound reached the inner ear through the mandibular fat pad, the tympanic plate, and the middle ear ossicles. Basilosaurids and dorudontids showed further aquatic adaptations of the ossicular chain and the acoustic isolation of the ear complex from the skull. The land mammal ear and the generalized modern whale ear are evolutionarily stable configurations, two ends of a process where the cetacean mandible might have been a keystone character.

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...

Anthracobunidae is an Eocene family of large mammals from south Asia that is commonly considered to be part of the radiation that gave rise to elephants (proboscideans) and sea cows (sirenians). We describe a new collection of anthracobunid fossils from Middle Eocene rocks of Indo-Pakistan that more than doubles the number of known anthracobunid fossils and challenges their putative relationships, instead implying that they are stem perissodactyls. Cranial, dental, and postcranial elements allow a revision of species and the recognition of a new anthracobunid genus. Analyses of stable isotopes and long bone geometry together suggest that most anthracobunids fed on land, but spent a considerable amount of time near water. This new evidence expands our understanding of stem perissodactyl diversity and sheds new light on perissodactyl origins.

The torsion (T) of the horn cores of Sivoreas, which was measured in degrees per 10 cm, increased with time. T-values for Sivoreas from the lower Chinji equivalent strata range from 143 to 188. The same values for Sivoreas eremita from middle and upper Chinji equivalent strata reach the maximum of 240. One Sivoreas horn core from the still younger member D of the Ngorora Formation in Kenya has a T-value of 243. Sivoreas from the Lower Chinji Formation represents a new species, S. sondaari. The T-values of Protragocerus horn cores also increased with time (lower Chinji 40≤T≤95; middle and upper Chinji 97≤T≤119). Other early Boselaphini have little torsion. Therefore, it is likely that Sivoreas and Protragocerus evolved from a boselaphine with horn cores with little torsion. In the course of evolution, the torsion in the horn cores of both genera increased at different rates.

The origin of whales (order Cetacea) is one of the best-documented examples of macroevolutionary change in vertebrates. As the earliest whales became obligately marine, all of their organ systems adapted to the new environment. The fossil record indicates that this evolutionary transition took less than 15 million years, and that different organ systems followed different evolutionary trajectories. Here we document the evolutionary changes that took place in the sound transmission mechanism of the outer and middle ear in early whales. Sound transmission mechanisms change early on in whale evolution and pass through a stage (in pakicetids) in which hearing in both air and water is unsophisticated. This intermediate stage is soon abandoned and is replaced (in remingtonocetids and protocetids) by a sound transmission mechanism similar to that in modern toothed whales. The mechanism of these fossil whales lacks sophistication, and still retains some of the key elements that land mammals use to hear airborne sound.

The fossil record is replete with examples of evolutionary transitions between marine and freshwater environments, in both directions. Perhaps the most striking and best documented example of such a transition is the evolution of cetaceans (whales, dolphins, and porpoises) from the extinct group of terrestrial mammals called mesonychians. This transition, first hypothesized by Van Valen (1966), occurred in the temporally and geographically restricted setting of the Paleogene remnant Tethyan epicontinental sea (Gingerich et al., 1983) and adjacent terrestrial ecosystems. These environments lay in the zone of convergence between the Indian Plate and southern Eurasia during the early stages of the continent-continent collision that ultimately produced the Himalayas.

Microstonyx majar is described for the first time from the Nagri Formation type section. The species is compared to Hippopotamodon sivalense and Dicoryphochoerus titanoides. The latter species is found to be a junior synonym of M. major. Microstonyx and Hippopotamodon might also be synonymous but further research is needed to substantiate this hypothesis. The Indian and Eurasian suid faunas had many species and genera in common.Se describe Microstonyx major por primera vez en la sección típica de la Formación de Nagri. Se compara esta especie con Hippopotamodon sivalense y con Dicoryphochoerus titanoides. Esta última especie es un sinónimo reciente de M. major. Microstonyx y Hippopotamodon pueden ser sinónimos entre sí, pero para asegurarlo se necesita una investigación más profunda. Las faunas de suidos de la India y de Eurasia tenían muchas especies y géneros en común.

New specimens of a small, advanced catarrhine primate from the Manchar Formation in Sind, southern Pakistan, are referred to Dionysopithecus sp. Their age is biochronologically estimated to be close to the early/middle Miocene boundary. Dionysopithecus is considered closely related to, and possibly congeneric with, Micropithecus from the East African early Miocene. The Manchar Dionysopithecus is among the earliest of Eurasian catarrhines. Catarrhines may have first emigrated from Afro-Arabia around 16·5 Ma, coincident with a major short-term eustatic sea level lowering event, and with the earliest records in South Asia of certain other African mammal groups. The first appearances in Eurasia of later, more advanced catarrhine lineages also appear to correlate with episodes of global sea level lowering.

A study of the major collections of Siwalik hipparionines has resulted in the recognition of two supra-specific groups that we refer to “Cormohipparion” (Sivalhippus) and ?Hipparion s.s. The “Cormohipparion” (Sivalhippus) group is the more abundant one in the Siwaliks, and includes at least three species: “Cormohipparion” (Sivalhippus) theobaldi, “Cormohipparion” (Sivalhippus) sp. and “Cormohipparion” (Sivalhippus) perimense. The ?Hipparion group is monospecific and includes the species ?Hipparion antelopinum. In attempting to ascertain the phylogenetic relationships of these horses we have found no sound basis for falsifying the hypothesis that Old World hipparionine Groups 1–4 are monsophyletic. We derive both Groups 2 and 3 from Group 1. Group “4” is polyphyletic, with part of the original hypodigm most probably referable to Group 2. The “Cormohipparion” (Sivalhippus) group is distantly related to early Vallesian Group 1 hipparionines of probable south Asian origin, and may in turn include the...

Microstonyx major is described for the first time from the Nagri Formation type section. The species is compared to Hippopotamodon sivalense and to Dicoryphochoerus titanoides. The latter species is found to be a junior synonym of M. major. Microstonyx and Hippopotamodon might also be synonymous but further research is needed to substantiate this hypothesis. The Indian and Eurasian suid faunas had many species and genera in common., This research was partially supported by a grant from the Smithsonian Institution (No. 41007800).

SIMONS et al.1 have discussed the earliest occurrence of Hipparion, a tridactyl fossil equid, in the Tertiary of the Siwalik Hills (Pakistan and India). Their statements are confusing and they have misinterpreted one of my publications. Simons et al.1 reject a possible Chinji occurrence of the genus, partly because “Hussain has pointed out that regardless of the validity of occurrence of the Hipparion reputed to have been found near the base of the Chinji, the teeth of these specimens are very large. It is implausible that such animals should have preceded in time the small and structurally different species Hipparion nagriensis Hussain”.