EARLY EOCENE SMALL MAMMAL FAUNA FROM VASTAN LIGNITE MINE, GUJARAT, WESTERN INDIA

Abstract

Until very recently, there was no record of early Eocene terrestrial mammals from India. Lack of this record has been a major hindrance in understanding India's terrestrial faunal relationships in a geodynamic framework, particularly, in the context of evolving affinities in response to the India-Asia collision around the Paleocene-Eocene boundary (ca. 55 Ma). Investigations carried out during the present doctoral work have led to the discovery of a remarkable assemblage of early Eocene terrestrial vertebrate faunas from the Cambay Shale deposits in the Vastan Lignite Mine, District Surat, Gujarat, western India. This assemblage, presently dated at 53.5 Ma on the basis of the benthic foraminifer Nummulites globulus includes members of atleast 10 placental orders: Chiroptera, Insectivora, Proteutheria, Apatotheria, Rodentia, Primates, Perissodactyla, Artiodactyla, Creodonta and Condylartha. A possible marsupial is also included in the fauna. This assemblage represents the oldest known terrestrial Cenozoic mammal fauna from South Asia. As many as 35 taxa have already been described. Most of them new at genus or even family level and the collection includes a number of dentaries and hundreds of isolated teeth. Emphasis is placed in this dissertation on small mammals from the Vastan Lignite Mine, comprising insectivores, chiropterans, proteutherians, apatotherians, rodents, primates and didelphid marsupials. Insectivores are the dominant group in the Vastan fauna, both taxonomically and numerically, followed by bats. Insectivores are represented by atleast 8 taxa, all new and pertaining to 4 families (including one new, the Vastanidae), and also record the first occurrence of the remaining three families (Geolabididae, Nyctitheriidae, Adapisoriculidae) from the Indian subcontinent. Geolabidids are being recorded for the first time outside of North America. Proteutherians, comprising two taxa (Anthraryctes and Suratilestes) also constitute the first Indian records. Apatotherians are also being reported for the first time from the subcontinent. The Vastan primates, represented atleast by 5 taxa, constitute the single largest sample of early Eocene primates from South Asia. Rodents are poorly represented, and as presently known, comprise two ctenodactyloid species. The didelphid from Vastan (Indodelphis) is the second Until very recently, there was no record of early Eocene terrestrial mammals from India. Lack of this record has been a major hindrance in understanding India's terrestrial faunal relationships in a geodynamic framework, particularly, in the context of evolving affinities in response to the India-Asia collision around the Paleocene-Eocene boundary (ca. 55 Ma). Investigations carried out during the present doctoral work have led to the discovery of a remarkable assemblage of early Eocene terrestrial vertebrate faunas from the Cambay Shale deposits in the Vastan Lignite Mine, District Surat, Gujarat, western India. This assemblage, presently dated at 53.5 Ma on the basis of the benthic foraminifer Nummulites globulus includes members of atleast 10 placental orders: Chiroptera, Insectivora, Proteutheria, Apatotheria, Rodentia, Primates, Perissodactyla, Artiodactyla, Creodonta and Condylartha. A possible marsupial is also included in the fauna. This assemblage represents the oldest known terrestrial Cenozoic mammal fauna from South Asia. As many as 35 taxa have already been described. Most of them new at genus or even family level and the collection includes a number of dentaries and hundreds of isolated teeth. Emphasis is placed in this dissertation on small mammals from the Vastan Lignite Mine, comprising insectivores, chiropterans, proteutherians, apatotherians, rodents, primates and didelphid marsupials. Insectivores are the dominant group in the Vastan fauna, both taxonomically and numerically, followed by bats. Insectivores are represented by atleast 8 taxa, all new and pertaining to 4 families (including one new, the Vastanidae), and also record the first occurrence of the remaining three families (Geolabididae, Nyctitheriidae, Adapisoriculidae) from the Indian subcontinent. Geolabidids are being recorded for the first time outside of North America. Proteutherians, comprising two taxa (Anthraryctes and Suratilestes) also constitute the first Indian records. Apatotherians are also being reported for the first time from the subcontinent. The Vastan primates, represented atleast by 5 taxa, constitute the single largest sample of early Eocene primates from South Asia. Rodents are poorly represented, and as presently known, comprise two ctenodactyloid species. The didelphid from Vastan (Indodelphis) is the second record of marsupials from the Eocene of Indo-Pakistan. A previously described didelphid (Jaegeria) is transferred here to Chiroptera. Overall, the Vastan small mammals are holarctic and are endemic at genus or even family level. Some of them share a number of primitive characters with allied taxa from the northern continents. The small mammal fauna from Vastan indicate a migration into India around the time of initiation of India-Asia collision possibly through Dras-Kohistan island arcs and the other emergent crustal blocks within the Neotethys. Of the medium/largesized mammals, however, the dentally primitive cambaythere perissodactyls may have originated in India. This possibility is consistent with the Out of India hypothesis, but can only be tested when related forms are discovered from older intervals (latest Paleocene-earliest Eocene). Summing up, the Vastan section has provided a long-awaited source of early Eocene terrestrial mammals in the subcontinent. The discoveries already made clearly point to the need for sustained work in order to fully uncover the taxonomic diversity and to understand the phylogenetic relations of the Vastan mammals based on greater anatomical coverage.