Kishor Kumar

Vestibular evidence for the evolution of aquatic behaviour in early cetaceans

Early cetaceans evolved from terrestrial quadrupeds to obligate swimmers, a change that is traditionally studied by functional analysis of the postcranial skeleton. 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. 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.

Early Eocene primates from Gujarat, India.

The oldest euprimates known from India come from the Early Eocene Cambay Formation at Vastan Mine in Gujarat. An Ypresian (early Cuisian) age of approximately 53Ma (based on foraminifera) indicates that these primates were roughly contemporary with, or perhaps predated, the India-Asia collision. Here we present new euprimate fossils from Vastan Mine, including teeth, jaws, and referred postcrania of the adapoids Marcgodinotius indicus and Asiadapis cambayensis. They are placed in the new subfamily Asiadapinae (family Notharctidae), which is most similar to primitive European Cercamoniinae such as Donrussellia and Protoadapis. Asiadapines were small primates in the size range of extant smaller bushbabies. Despite their generally very plesiomorphic morphology, asiadapines also share a few derived dental traits with sivaladapids, suggesting a possible relationship to these endemic Asian adapoids. In addition to the adapoids, a new species of the omomyid Vastanomys is described. Euprimate postcrania described include humeri, radii, femora, calcanei, and tali, most of which show typical notharctid features and are probably attributable to asiadapines. Anatomical features of the limb elements indicate that they represent active arboreal quadrupedal primates. At least one calcaneus is proximally shorter and distally longer than the others, resembling eosimiids in this regard, a relationship that, if confirmed, would also suggest an Asian or southeast Asian faunal connection. Isolated teeth from Vastan Mine recently attributed to a new eosimiid, Anthrasimias gujaratensis, appear to provide that confirmation. However, their attribution to Eosimiidae is equivocal. They are similar to teeth here tentatively referred to Marcgodinotius, hence A. gujaratensis may be a junior synonym of M. indicus. Corroboration of eosimiids at Vastan requires more compelling evidence. Although definitive conclusions are premature, available evidence suggests that the Vastan adapoids, at least, were derived from western European stock that reached India near the Paleocene-Eocene boundary.

Eocene evolution of whale hearing

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.

Sound Transmission in Archaic and Modern Whales: Anatomical Adaptations for Underwater Hearing

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. Anat Rec, 290:716–733, 2007.

Remingtonocetus harudiensis, new combination, a Middle Eocene archaeocete (Mammalia, Cetacea) from Western Kutch, India

ABSTRACT A new genus of archaeocete cetaceans, Remingtonocetus, is based on revision of previously described and recently collected well preserved skull material from the Middle Eocene (Lutetian) Chocolate Limestone, Babia Stage, Harudi, Kutch. Remingtonocetus harudiensis, new combination, was previously described as a species of Protocetus (Sahni and Mishra, 1975). Present studies suggest that R. harudiensis is related to Andrewsiphius kutchensis Sahni and Mishra, 1975, which is known from a slightly younger horizon, about 17 km northeast of Harudi. A. kutchensis was previously classified as an agorophiid (Odontoceti), but is here grouped with R. harudiensis in a new family Remingtonocetidae (Archaeoceti). A slightly smaller species of Remingtonocetus, R. sloani, new combination, is present in the same horizon; it was also originally referred to Protocetus. The cetacean beds are of shallow water marine origin and yield abundant foraminifers and mollusks. Catfishes also occur associated with cetacean elem...

Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India

Cambaytheres (Cambaytherium, Nakusia and Kalitherium) are recently discovered early Eocene placental mammals from the Indo-Pakistan region. They have been assigned to either Perissodactyla (the clade including horses, tapirs and rhinos, which is a member of the superorder Laurasiatheria) or Anthracobunidae, an obscure family that has been variously considered artiodactyls or perissodactyls, but most recently placed at the base of Proboscidea or of Tethytheria (Proboscidea+Sirenia, superorder Afrotheria). Here we report new dental, cranial and postcranial fossils of Cambaytherium, from the Cambay Shale Formation, Gujarat, India (~54.5 Myr). These fossils demonstrate that cambaytheres occupy a pivotal position as the sister taxon of Perissodactyla, thereby providing insight on the phylogenetic and biogeographic origin of Perissodactyla. The presence of the sister group of perissodactyls in western India near or before the time of collision suggests that Perissodactyla may have originated on the Indian Plate during its final drift toward Asia.

An ailuravine rodent from the lower Eocene Cambay Formation at Vastan, western India, and its palaeobiogeographic implications

A new ailuravine rodent, Meldimys musak sp. nov. (Mammalia: Rodentia, Ischyromyidae), is recorded from the lower Eocene lignites of western India. It is the oldest record of Rodentia from India. M. musak is more derived than the earliest Eocene ailuravine Euromys cardosoi from Portugal and more generalized than late early Eocene E. inexpectatus and Ailuravus michauxi from France. Its dental morphology closely corresponds to the middle early Eocene species M. louisi, which lived about 52 Ma in Western Europe. Meldimys was previously known only from Europe, and ailuravines were previously reported only from Europe and North America. Its occurrence in India allows the first direct correlation between the early Eocene land mammal horizons of Europe and India, and raises the possibility of a terrestrial faunal exchange between India and Eurasia close to the Palaeocene—Eocene transition.

Quercypsitta-like birds from the early Eocene of India (Aves, ?Psittaciformes)

ABSTRACT We report new avian remains from the early Eocene Cambay Formation of Vastan Lignite Mine in western India. Most of the bones belong to the as yet poorly known taxon Vastanavis, of which a new species, V. cambayensis, is described. For the first time, tarsometatarsi of Vastanavis can be identified, which show that this taxon had semi-zygodactyl feet. In overall morphology, Vastanavis closely resembles the species of the Quercypsittidae, which occur in the late Eocene of Europe and are considered stem group representatives of the parrots (Psittaciformes). Several plesiomorphic features indicate, however, that Vastanavis is outside a clade including Quercypsitta and crown group Psittaciformes, and we therefore assign it to a new family, Vastanavidae. Vastanavis corresponds well with an as yet undescribed avian species from the early Eocene London Clay in England, and we conclude that, at least concerning the arboreal taxa, the early Eocene avifauna of India shows some concordances with the much better known one from the early Eocene of Europe. We further describe a distal tarsometatarsus from Vastan Lignite Mine that superficially resembles that of extant New World vultures (Cathartidae), but comes from a roller-sized species.

Early Eocene Artiodactyls (Mammalia) from Western India

ABSTRACT The Cambay Formation at Vastan Mine in Gujarat, western India, has yielded the oldest artiodactyls and other land mammals from India, which are dated as middle Ypresian (∼53 Ma) based on foraminiferids. Here we describe new dentitions, including dentaries and upper teeth of Diacodexis indicus ( = Gujaratia indica) from Vastan. These provide better characterization of this Asian diacodexeid (Artiodactyla: Mammalia) than was available earlier. A new combination, Diacodexis indicus, is proposed in place of Gujaratia indica, and G. pakistanensis is referred back to Diacodexis. A new, very small species of Diacodexis, D. parvus, is reported based on isolated teeth. Whereas D. indicus is approximately the size of the largest known species of Diacodexis, D. parvus represents the smallest recorded species of the genus and is one of the smallest known artiodactyls. Diacodexeidae indet. from Vastan is exemplified by a fragment of a dentary and an upper molar, which are of intermediate size. Several isolated teeth represent a new genus and species, unrelated to Diacodexeidae, and are assigned to Artiodactyla indet. pending discovery of more adequate specimens. Early Eocene diacodexeid postcrania are described for the first time from India. Early Eocene artiodactyls from India are phenetically close to Euroamerican species of Diacodexis, providing further evidence of phylogenetic connections particularly with European faunas. A few postcranial features of the Vastan artiodactyls are also seen in primitive archaeocetes (Cetacea) indicating a possible relationship between Vastan artiodactyls and basal Cetacea.

Taphonomy and palaeoenvironment of the middle Eocene rodent localities of northwestern Himalaya, India

Abstract In northwestern Himalaya, the middle Eocene rodents are known from the Upper Subathu Group in Jammu and Kashmir and Himachal Pradesh (India) and from the coeval Kuldana Formation in Pakistan. Most of the localities in these areas represent more or less the same timeframe but their faunal compositions differ considerably and also some of them are lithologically dissimilar. The bone assemblages from some of the productive middle Eocene rodent localities of Jammu and Kashmir were analysed applying the standard techniques of taphonomic data collection and interpretation to reconstruct their taphonomic histories and palaeoenvironment. The petrography of the rodent-bearing matrix was also studied and used in the taphonomic analysis. The analysis has revealed markedly different taphonomic histories for two of the most prolific localities thereby partly explaining the differences in their faunal composition and demonstrating that taphonomy can be an important aid to biostratigraphic interpretations. The East Babbian Gala (EBGL) rodent assemblage was initially accumulated in the mammalian predator scats. For the accumulation of Sindkhatuti (SKL) bone assemblage, the nonpredator agents are held responsible and a catastrophic mortality is indicated. The taphonomic data from West Babbian Gala (WBGL), Chenpur (CPL), Tattapani (TTPL) and Triyath-Barakh Road (TBRL) localities is inadequate to identify with certainty mode of accumulation of their assemblages, which is best ascribed at present to an attritional mortality and fluvial accumulation. The palaeoenvironmental reconstructions suggest fluvio-deltaic conditions at the time of deposition of the rodent-yielding uppermost part of the Subathu Group. They further indicate that the shoreline of the Tethys Sea was close to the site of deposition of the Middle Eocene rodents and other land mammals. These interpretations are supported by other associated vertebrate groups which also include marine mammals, Cetacea.