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Insular India was an isolated landmass which became the Indian subcontinent. Across the latter stages of the Cretaceous and most of the Paleocene, following the breakup of Gondwana, the Indian subcontinent remained an isolated landmass as the Indian Plate drifted across the Tethys Ocean, forming the Indian Ocean. The process of India's separation from Madagascar first began 88 million years ago, but complete isolation only occurred towards the end of the Maastrichtian, a process that has been suggested to be the creation of the Deccan Traps. Soon after, the land mass moved northward rather quickly, until contact with Asia was established 55 million years ago. Even then, both landmasses did not become fully united until around 35 million years ago,Scotese, Christopher R. (January 2001). "The collision of India and Asia (90 mya — present)". Paleomap Project. Retrieved 28 December 2004.Aitchison, Jonathan C.; Ali, Jason R.; Davis, Aileen M. (2007). "When and where did India and Asia collide?". Journal of Geophysical Research. 112 (B5). Bibcode:2007JGRB..11205423A. and periods of isolation occurred as recently as 24 million years ago.Biotic interchange between the Indian subcontinent and mainland Asia through time. Nat Commun. 2016 Jul 4;7:12132. doi: 10.1038/ncomms12132.
Thus, for a period of 53 million years India retained a degree of isolation, 11 of which it was a complete island continent. This allowed its local Biome to follow the typical patterns seen in islands and diversify in unique ways, much as in modern Madagascar, its sister landmass. Faunal interchanges with other landmasses, like Africa and Europe (then an archipelago of islands across the Tethys) occurred during this period, and a considerable influence can already be seen long before contact was made. This rendered India rather peculiar as not just an isolated continent but also a "stepping stone" in the dispersal of many animal and plant clades across Africa, Europe, Madagascar, Asia and possibly even Oceania. Still, several "archaic" clades managed to survive. The vast majority of India's terrestrial vertebrate life was wiped out in the Cretaceous-Paleogene extinction event; only 3 extant tetrapod lineages can trace their ancestry to Cretaceous India. Most of India's few other surviving Gondwanan lineages were outcompeted during the Paleogene by newly-arriving lineages. However, and invertebrate fauna were less affected.
During the Paleogene, dispersing tetrapod lineages from Asia repopulated India, with some, such as , evolving on the continent. By the time full contact was established, a large percentage of India's old and new indigenous fauna had been outcompeted by Eurasian species. However, several groups like lagomorphsRose K.D., Deleon V.B., Mmissian P., Rana R.S., Sahni A., Singh L. & Smith T. (2008). – Early Eocene lagomorph (Mammalia) from western India and the early diversification of Lagomorpha. – Proc. Royal Society B, RSPB 2007.1661.R1 have become widespread across the world, as have floral groups such as Dipterocarpaceae, which went on to become dominant tree species throughout much of tropical Asia. A significant portion of Asian Mantidae also originated on Insular India. The islands of the Seychelles still retain an indigenous herpetofauna, presumably an echo of the amphibian and reptile species seen in India as an island.
The mammalian fauna of India also bears similarities with that of Madagascar, with the gondwanathere Bharattherium, one of the most common mammals, being extremely similar to the malagasy Lavanify. The most diverse mammals in the Maastrichtian of India are eutherians, a clade normally associated with northern continents and also found in Madagascar in this epoch, which combined with their ambiguous phylogenetic positions renders them extremely important in the understanding of placental evolution. Some like Deccanolestes have been variously interpreted as ,Boyer, Doug M.; Prasad, Guntupalli V. R.; Krause, David W.; Godinot, Marc; Goswami, Anjali; Verma, Omkar; Flynn, John J. (2010). "New postcrania of Deccanolestes from the Late Cretaceous of India and their bearing on the evolutionary and biogeographic history of euarchontan mammals". Naturwissenschaften. 97 (4): 365–77. doi:10.1007/s00114-010-0648-0. . ,Smith, Thierry; Bast, Eric; Sigé, Bernard (2010). "Euarchontan affinity of Paleocene Afro-European adapisoriculid mammals and their origin in the late Cretaceous Deccan Traps of India". Naturwissenschaften. 97 (4): 417–22. doi:10.1007/s00114-010-0651-5. . or stem-,Erik R. Seiffert, The Oldest and Youngest Records of Afrosoricid Placentals from the Fayum Depression of Northern Egypt though the general consensus appears to be that they are non-placental eutherians and that there are non known Cretaceous .Halliday, Thomas J. D. (2015). "Resolving the relationships of Paleocene placental mammals". Biological Reviews. doi:10.1111/brv.12242. Kharmerungulatum, formerly interpreted as a stem-ungulate, is now known to be a representative of Zhelestidae, a herbivorous non-placental eutherian clade.James David Archibald · Alexander Olegovich Averianov, Phylogenetic analysis, taxonomic revision, and dental ontogeny of the Cretaceous Zhelestidae (Mammalia: Eutheria), Article · Feb 2012 · Zoological Journal of the Linnean Society Regardless of the phylogenetics of these eutherians, they almost certainly reached India and Madagascar through either Europe, Africa or mainland Asia;Krause, D.W., O'Connor, P.M., Rogers, K.C., Sampson, S.D., Buckley, G.A. and Rogers, R.R. 2006. Late Cretaceous terrestrial vertebrates from Madagascar: Implications for Latin American biogeography (subscription required). Annals of the Missouri Botanical Garden 93(2):178–208. later they would propagate across Gondwana as far west as Brazil.
Probably the most spectacular representative of India's Cretaceous fauna is Avashishta, a late surviving haramiyid and the last known non-mammalian synapsid.Anantharaman, S.; Wilson, G. P.; Das Sarma, D. C.; Clemens, W. A. (2006). "A possible Late Cretaceous "haramiyidan" from India". Journal of Vertebrate Paleontology. 26 (2): 488–490. doi:10.1671/0272–4634(2006)26488:aplchf2.0.co;2. Non-gondwanathere multituberculates and can probably also be inferred as having lived in India during this epoch, due to the former's presence in all landmasses including MadagascarDavid W. Krause; Simone Hoffmann; Sarah Werning (2017). "First postcranial remains of Multituberculata (Allotheria, Mammalia) from Gondwana". Cretaceous Research. 80: 91–100. doi:10.1016/j.cretres.2017.08.009. and the latter being the dominant mammals in other known Gondwana sites. An eutriconodont, Indotriconodon magnus, is also known, extending the range of this clade into the Late Cretaceous and the southern continents.Bajpai, Sunil; Rautela, Abhay; Yadav, Ravi; Mantilla, Gregory P. Wilson (29 February 2024). "The first eutriconodontan mammal from the Cretaceous (Maastrichtian) of India". Journal of Vertebrate Paleongoloy. doi:10.1080/02724634.2024.2312234.
The herpetofauna of India in the Cretaceous is a mosaic of indigenous groups and forms that rafted their way from Asia. are an indigenous clade and locally well represented as they are in Madagascar in the form of ranids, hylids, leptodactylids, pelobatids and discoglossids, as are madtsoiid snakes like Sanajeh and possibly Indophis and iguanian lizards, while Anguidae are from Laurasia.Indian Cretaceous Terrestrial Vertebrates: Cosmopolitanism and Endemism in a Geodynamic Plate Tectonic Framework January 1970Lecture Notes in Earth Sciences 132:91-104 DOI: 10.1007/978-3-642-10311-7_6 In book: New Aspects of Mesozoic Biodiversity Caecillians are an indigenous Gondwanan clade, but their absence in Madagascar suggests that the Asian species have descended from African species that colonized India as it drifted north. The divergence between African and Asian groups has been estimated at 120 million years ago, indicating that this likely happened during the Cretaceous.Phylogenetic relationships of Indian caecilians (Amphibia: Gymnophiona) inferred from mitochondrial rRNA gene sequences, Department of Zoology, The Natural History Museum, London SW7 5BD, UK b Institute of Biomedical and Life Sciences, Division of Molecular Genetics, University of Glasgow, Pontecorvo Building, 56 Dumbarton Rd, Glasgow G11 6NU, Scotland, UK c Department of Zoology, University of Kerala, Kariavattom 695 581, Thiruvananthapuram, Kerala, India Received 27 June 2001; received in revised form 17 December 2001
Several fish taxa are known from estuarine locales; most are marine species, but there are also forms like lepisosteids, which do also occur in Africa but are otherwise rare in Gondwanan landmasses. Cichlids and other forms suspected of having had an Indian Gondwanan origin were most likely present.
Invertebrate fauna, especially soil invertebrates such as , were likely less affected by the extinction, and several lineages that persist today are thought to have Gondwanan ancestry. The Parreysiinae, a subfamily of the freshwater mussel family Unionidae, are thought to have originated in East Gondwana during the Jurassic, and survived on both Africa and Insular India throughout the Cretaceous. Several different tribes (Indochinellini, Lamellidentini, and Parreysiini) of the Parreysiinae evolved in isolation on Insular India. These endemic tribes managed to survive the K-Pg extinction, and colonized mainland Asia via both Insular India and the Burma terrane, the latter of which collided with and was pushed north by Insular India during the Paleogene. They are now found throughout much of India and Southeast Asia. Similarly, numerous lineages of Mantidae (clade Cernomantodea) are thought to have originated on the Antarctica-Indian landmass after the breakup of Gondwana, and persisted on Insular India after it broke away. This massive diversity of mantises survived the K-Pg extinction and invaded mainland Asia following the collision of Insular India with Asia.
It was previously thought that several major families of Neobatrachia (True frog, Dicroglossidae, Rhacophoridae) originated in India from an ancestor that colonized the continent from Africa during the Cretaceous. This was supported by closely related families (Nyctibatrachidae, Ranixalidae, Micrixalus) being endemic to India. However, more recent studies hypothesize that these families have a mainland Asian origin and colonized India during the Paleogene.
During this epoch, unambiguous placental mammals make their way into India in spite of its isolation, probably by rafting like the many placental groups in Madagascar, or perhaps brief connections with Africa and Europe (the latter still an archipelago). Hyaenodonts are an endemic African clade, first showing outside of the continent in the Paleocene of India and Europe.Floréal Solé & Thierry Smith, Dispersals of placental carnivorous mammals (Carnivoramorpha, Oxyaenodonta & Hyaenodontida) near the Paleocene-Eocene boundary: a climatic and almost worldwide story, GEOLOGICA BELGICA (2013) 16/4: 254-261 Glires evolved in Asia, but a lineage became isolated in India, where it gave rise to the lagomorphs.
For a while it was theorised that ostriches evolved in India during this epoch, under the assumption that European ratites like Palaeotis represented recent Asiatic migrations. However, the first unambiguous ostriches are now thought to have evolved in Africa, with Eogruiidae having occupied their ecological niche in Asia; likewise, European ratites are now thought to be among the oldest known,Buffetaut, E.; Angst, D. (November 2014). "Stratigraphic distribution of large flightless birds in the Palaeogene of Europe and its palaeobiological and palaeogeographical implications". Earth-Science Reviews. 138: 394–408. doi:10.1016/j.earscirev.2014.07.001. and probably evolved independently there, being unrelated to ostriches. Still, India probably had a thriving paleognath fauna; the volant ancestors of kiwis and elephant birds presumably flew from there to Oceania and Madagascar respectively,Mitchell, K. J.; Llamas, B.; Soubrier, J.; Rawlence, N. J.; Worthy, T. H.; Wood, J.; Lee, M. S. Y.; Cooper, A. (2014-05-23). "Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution". Science. 344 (6186): 898–900. doi:10.1126/science.1251981. . while the mysterious Hypselornis may represent an indigenous clade.
During this time, lagomorphs and hyaenodonts disperse out of India, establishing their cosmopolitan ranges.
The Gecarcinucidae, a family of widespread throughout much of tropical Asia, is thought to have originated in India, despite not being of ancient Gondwanan origins themselves. Divergence estimates indicate that the Gecarcinucidae originate from ancestors that dispersed to Insular India and diverged there during the middle Eocene, before India collided with Asia. As India drifted northwards, it may have come into close enough proximity to Southeast Asia to allow for dispersing lineages to colonize it. Notably, as the Gecarcinucidae are a freshwater group that could not disperse via marine habitats, this indicates that temporary may have formed in the Eocene between India and Southeast Asia, allowing for the dispersal of freshwater organisms to India while it was still isolated. Following the India-Asia collision, the Gecarcinucidae dispersed back into mainland Asia.
The giant Madtsoiidae snake Vasuki indicus was likely the apex predator of this time and environment.
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