Insular India
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Insular India was an isolated landmass which became the
Indian subcontinent The Indian subcontinent is a physiographic region of Asia below the Himalayas which projects into the Indian Ocean between the Bay of Bengal to the east and the Arabian Sea to the west. It is now divided between Bangladesh, India, and Pakista ...
. Across the latter stages of the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
and most of the
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
, following the breakup of
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
, the Indian subcontinent remained an isolated landmass as the
Indian Plate The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...
drifted across the
Tethys Ocean The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...
, forming the
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
. The process of India's separation from
Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...
first began 88 million years ago, but complete isolation only occurred towards the end of the
Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
, 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 Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
was established 55 million years ago. Even then, both landmasses did not become fully united until around 35 million years ago, and periods of isolation occurred as recently as 24 million years ago. 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 biota 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 Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
and
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
(then an archipelago of islands across the Tethys) occurred during this period, and a considerable
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
n influence can already been 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 Oceania ( , ) is a region, geographical region including Australasia, Melanesia, Micronesia, and Polynesia. Outside of the English-speaking world, Oceania is generally considered a continent, while Mainland Australia is regarded as its co ...
. Still, several "archaic" clades managed to survive. The vast majority of India's terrestrial
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
life was wiped out in the Cretaceous-Paleogene extinction event; only 3 extant
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
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,
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
s and
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
fauna were less affected. During the Paleogene, dispersing tetrapod lineages from Asia repopulated India, with some, such as
lagomorph The lagomorphs () are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (rabbits and hares) and the Ochotonidae ( pikas). There are 110 recent species of lagomorph, of which 109 species in t ...
s, 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 dipterocarps, which went on to become dominant tree species throughout much of tropical Asia. A significant portion of Asian mantises also originated on Insular India. The islands of the
Seychelles Seychelles (, ; ), officially the Republic of Seychelles (; Seychellois Creole: ), is an island country and archipelagic state consisting of 155 islands (as per the Constitution) in the Indian Ocean. Its capital and largest city, Victoria, ...
still retain an indigenous herpetofauna, presumably an echo of the
amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
and
reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
species seen in India as an island.


Geology

The Burma terrane or West Burma block, an isolated island arc that was present in the Tethys Sea during the Cretaceous, collided with Insular India during the Paleocene and was pushed northwards, eventually colliding with mainland Asia independent of Insular India's own collision. Much of western Myanmar consists of the former Burma Terrane.


Cretaceous fauna

The Cretaceous fauna of India is well attested in both Coniacian and
Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
aged sites such as the Lameta Formation. Generally speaking, the local
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
ian and
crocodilian Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...
fauna is almost identical to that of
Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...
, with clades like abelisaurids,
titanosaurs Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of Sauropoda, sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with tax ...
, noasaurids and notosuchians being well represented here. A possible deviation is the presence of stegosaurs, like '' Dravidosaurus'' and '' Brachypodosaurus,'' the last remaining members of this lineage; if these aren't misidentified remains of herbivorous notosuchians and sauropods, then these relics would be the only indigenous ornithischians in the entire Indo-Malagasy landmass. Possible
ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful l ...
remains have been unearthed in India too. Another possible deviation is the presence of a troodontid, a lineage more typically associated with
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...
and thus possibly indicating interchange with
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
or even mainland
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
, but these remains are controversial and could belong either other theropods or notosuchians. Indeterminate fossils of ornithopods belonging to hypsilophodontids and iguanodontids have been unearthed in Inida. 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 The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...
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 Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...
evolution. Some like '' Deccanolestes'' have been variously interpreted as
euarchonta The Euarchonta are a proposed grandorder of mammals: the order Scandentia (treeshrews), and its sister Primatomorpha mirorder, containing the Dermoptera (colugos) and the primates (Plesiadapiformes and descendants). The term "Euarchonta" (mea ...
ns, adapisoriculids, or stem- afrotherians,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
placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...
s. '' Kharmerungulatum'', formerly interpreted as a stem-
ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...
, is now known to be a representative of Zhelestidae, a herbivorous non-placental eutherian clade. Regardless of the phylogenetics of these eutherians, they almost certainly reached India and Madagascar through either Europe, Africa or mainland Asia; later they would propagate across
Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...
as far west as
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
. Probably the most spectacular representative of India's Cretaceous fauna is '' Avashishta'', a late surviving haramiyid and the last known non-mammalian
synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...
. Non-gondwanathere multituberculates and
meridiolestida Meridiolestida is an extinct clade of mammals known from the Cretaceous and Cenozoic of South America and possibly Antarctica. They represented the dominant group of mammals in South America during the Late Cretaceous. Meridiolestidans were morph ...
ns can probably also be inferred as having lived in India during this epoch, due to the former's presence in all landmasses including Madagascar and the latter being the dominant mammals in other known Gondwannan sites. An
eutriconodont Eutriconodonta is an order (biology), order of early mammals. Eutriconodonts existed in Asia (including Insular India, pre-contact India), Africa, Europe, North America, North and South America during the Jurassic and the Cretaceous periods. The ...
, '' Indotriconodon magnus'', is also known, extending the range of this clade into the Late Cretaceous and the southern continents. The herpetofauna of India in the Cretaceous is a mosaic of indigenous groups and forms that rafted their way from Asia.
Neobatrachia The Neobatrachia (Neo-Latin ''neo-'' ("new") + ''batrachia'' ("frogs")) are a suborder of the Frog, Anura, the order (biology), order of frogs and toads. This suborder is the most advanced and apomorphic of the three anuran suborders alive toda ...
ns 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 Snakes are elongated Limbless vertebrate, limbless reptiles of the suborder Serpentes (). Cladistically Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales much like other members of ...
like '' Sanajeh'' and possibly '' Indophis'' and iguanian lizards, while anguids are from
Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...
.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. 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 Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
but are otherwise rare in Gondwanan landmasses.
Cichlids Cichlids () are a large, diverse, and widespread family of Percomorpha, percomorph fish in the family (biology), family Cichlidae, order Cichliformes. At least 1,760 species have been Binomial nomenclature, scientifically described, making ...
and other forms suspected of having had an Indian Gondwanan origin were most likely present.


Effects of the Cretaceous-Paleogene extinction event

The Cretaceous-Paleogene extinction event had a particularly catastrophic effect in India, wiping out almost all terrestrial
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
lineages on the continent. It is thought that the effects of the Deccan Traps volcanism may have compounded the extinction event's impacts, making it especially devastating there. Only three extant
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
groups have representatives that can be verified as descending from Gondwanan endemics of Insular India: one family of
frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...
s ( Nasikabatrachidae), several families of caecilians ( Grandisoniidae,
Chikilidae Chikilidae is a family of Indian caecilians, the 10th and most recent (2012) family of caecilians (legless amphibians) to be identified, although the type species, ''Fuller's caecilian, Chikila fulleri'' (formerly ''Herpele fulleri'') was first d ...
and Ichthyophiidae), and 1 family of blindsnakes ( Gerrhopilidae). Notably, all three lineages have a
fossorial A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...
mode of life, indicating that this lifestyle may have saved them from the extinction's impacts. Several mammal genera also survived the event, although they went extinct during the
Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
.
Invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
fauna, especially soil invertebrates such as
centipede Centipedes (from Neo-Latin , "hundred", and Latin , "foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', "lip", and Neo-Latin suffix , "foot", describing the forcipules) of the subphylum Myriapoda, ...
s, 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 Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails. The majority of bivalve molluscs are saltwater species that l ...
family
Unionidae The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is a ...
, are thought to have originated in East Gondwana during the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
, and survived on both Africa and Insular India throughout the Cretaceous. Several different
tribes The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...
( 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 mantises (clade Cernomantodea) are thought to have originated on the
Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...
-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.


Paleogene fauna

Following the near-total extirpation of vertebrate life from India during the K-Pg extinction, India's vertebrate fauna was successively rebuilt by dispersing lineages primarily from Asia, first over water during its period of isolation, and later via land when it collided with Asia. Some of India's surviving tetrapod Gondwanan vertebrate lineages were outcompeted by these new arrivals. It was previously thought that several major families of Neobatrachia ( Ranidae, 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, Micrixalidae) being endemic to India. However, more recent studies hypothesize that these families have a mainland Asian origin and colonized India during the
Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
.


Paleocene fauna

The fossil record of the Paleocene of India, when the continent was a fully isolated landmass, is dubious and thus most inferrals about its fauna are somewhat speculative. It is known for certain that '' Deccanolestes'' and '' Bharattherium'' survived the K-Pg event,WILSON, Gregory P, NEW MAMMALIAN FOSSILS FROM THE INTERTRAPPEAN BEDS OF THE SOUTHERN PART OF THE DECCAN VOLCANIC PROVINCE AND THE CRETACEOUS–PALEOGENE TRANSITION IN INDIA, October 27, 2016 though for how further long did non-placental eutherians and gondwanatheres live in India is unknown, and by the time the landmass makes contact with Asia they are most likely extinct. 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. 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 Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...
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 eogruiids having occupied their ecological niche in Asia; likewise, European ratites are now thought to be among the oldest known, 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, while the mysterious '' Hypselornis'' may represent an indigenous clade.


Eocene fauna

By this time India already has an extensive placental fauna (as well as
metatherians Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...
like '' Indodelphis''), but in its isolation there are still high degrees of endemism, with some clades like anthracobunids not being found elsewhere. A study on '' Cambaytherium'' suggests that
Perissodactyla Perissodactyla (, ), or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They t ...
might have had an insular origin in India. The most notable endemic mammals are
cetaceans Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...
, which are in fact restricted to the Indian Subcontinent until the evolution of the marine " protocetids". Eocene India is also rich in
bat Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...
remains, including many representatives of modern groups, though its unclear if this Indian chiropteran fauna represents an adaptive radiation or simply that bat fossils elsewhere are rare. During this time, lagomorphs and hyaenodonts disperse out of India, establishing their cosmopolitan ranges. The Gecarcinucidae, a family of
freshwater crab Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight family (biology), families. They show direct development and maternal care of a small number of offspring, in contrast to marine c ...
s 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
Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
n 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
land bridge In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea le ...
s 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 madtsoiid snake '' Vasuki indicus'' was likely the apex predator of this time and environment.


Flora

The Dipterocarpoideae, the largest subfamily of the
Dipterocarpaceae Dipterocarpaceae is a family (biology), family of flowering plants with 22 genera and about 695 known species of mainly lowland tropical forest trees. Their distribution is pantropical, from northern South America to Africa, the Seychelles, India ...
, is thought to originate from ancestors that dispersed from
Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
to India during the Late Cretaceous. Surviving the K-Pg extinction event, the Dipterocarpoideae were isolated on Insular India (aside from some representatives in the
Seychelles Seychelles (, ; ), officially the Republic of Seychelles (; Seychellois Creole: ), is an island country and archipelagic state consisting of 155 islands (as per the Constitution) in the Indian Ocean. Its capital and largest city, Victoria, ...
) until India's collision with Asia, after which they migrated out of the continent and diversified. The Dipterocarpaceae are now among the most widespread and dominant tree groups in tropical Asia. Fossil evidence indicates that the other subfamily of Dipterocarpaceae, the Monotoideae (presently found in Africa, Madagasar, and
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
), also colonized India and was present until the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, but ultimately went extinct in India and thus did not disperse to other parts of Asia.


References

{{reflist Historical continents