Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India

Abstract

For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50–52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today.

Amber fossils demonstrate deep-time stability of Caribbean lizard communities

“…The abundance of invertebrates preserved in amber from the Caribbean and other geographical regions has led to macroevolutionary and macroecological insights about some groups (28)(29)(30), but such approaches have not previously been possible for vertebrates. The Caribbean island Anolis lizards have contributed to our understanding of evolutionary processes as a well-known case of adaptive radiation.…”

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

“…They come mainly from small, thin lenses of carbonaceous shale, representing nearshore continental sediments, that occur 1-3 m above the lower of two major lignites (Lignite 2) present at Vastan and Mangrol mines 17,18,29,30 . The vertebrates are closely associated with plant fossils and amber indicating that they lived in or near a coastal tropical rainforest dominated by Dipterocarpaceae 31 . Three dinoflagellate species from the zone producing the vertebrates imply an age not older than 55 Myr; one species from about 12 m higher than the vertebrates has been interpreted as 'basal Ypresian, B54 Myr' 26 .…”

Novel Techniques to Study Ancient Micro Amber from Tropical Beach Sand Reveal a Treasurehouse of Exceptionally Well Preserved Fossilized Microfungi

“…The formation of Indian amber took place probably during Eocene period i.e. 53 million years ago [10]. Fossils records show that Coniferopsida such as Walkomiella, Searsolia and Paranocladus resin producing trees were once part of lower Gondwana [11].…”

“…The present studies showed that dimensions of Indian AMF ranged from 40-70μm and density per kilogram of sampled sand could be from 200-300 indicating their relative rarity. Larger pieces of fossiliferous amber need to be ground, polished and chemically treated [15,16,10], whereas, AMF as isolated in this work being small and thin can be easily processed, mounted in large number on a SM and could be studied using image analysis software. This work showed Keri, Arambol, Mandrem, Morjim, chapora, Baga, Miramar beach sand as most promising for retrieval of AMF possibly due to influence of turbulent currents of Tiracol estuary, Chapora river, Baga creek, and Mandovi river which could transport amber from unidentified hinterland terrestrial sources towards the sea.…”

“…The age of amber varies from 4 to 300 Million years. Size of amber ranges from sand grains to several centimeters [2]. Recent advances in spectrometry allow the development of physical characterization of amber to confirm that amber originates from various kinds of plants such as conifers and Fabaceae [3].…”