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The earliest Eocene equid Erihippus tingae gen. et sp. nov. and ceratomorph Orientolophus hengdongensis Ting, 1993 from the Lingcha Fauna of Hunan Province, China. a–fErihippus tingae, a–c left mandible with m1-3 of IVPP V 5789.1 in occlusal (a), buccal and slightly occlusal (b), and lingual views (c); d–f, left maxilla with DP4-M2 of IVPP V 5790 in occlusal (d), buccal (e), and lingual views (f); g–iOrientolophus hengdongensis, right maxilla with DP4-M2 of IVPP V 5789 in occlusal (g), buccal (h), and lingual views (i). Abbreviations: end entoconid; hy hypocone; hycd hypoconulid; mec metaconule; pac paraconule; pas parastyle; pec postentocristid; phc posthypocristid; pr protocone. Scale: 5 mm
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The earliest perissodactyls are represented by some basal equoid fossils from Euramerica near the Paleocene/Eocene boundary. Unequivocal early equoids have yet to be reported from the early Eocene of Asia, although other groups of early perissodactyls were indeed present in Asia. Here we report the earliest Eocene Asian equid, Erihippus tingae gen....
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... As a result, direct comparisons between these two species are absent, to date. A close relationship between Cambaylophus and the Asian genus Orientolophus has been suggested by independent phylogenetic research (Kapur and Bajpai 2015;Bai et al. 2018;Kapur et al. 2022). Tapiromorphs are an important component in mammalian chronology as they have allowed division of the early Eocene Bumbanian Asian Land Mammal Age (ALMA) into three interval zones namely: Orientolophus, Homogalax, and Heptodon interval zones (Ting 1998). ...
This article aims to present an overview of the Paleogene vertebrate faunal records, especially mammals, with an emphasis on research conducted within the last 5 years i.e., from 2019 to 2023. Recent developments highlight the significance of vertebrate fossil records (particularly that of mammals) in our understanding of the origin, evolution, and historical distributions close to the India-Eurasia docking phase. Overall, the fossil records of early Paleogene vertebrates indicate that India was a hotspot for biodiversity for several orders of terrestrial (such perissodactyls, primates, and artiodactyls) and marine mammals (like cetaceans and sirenians). The directions of biotic migrations between India and its surrounding continents between the ~ 66 to ~ 50 Ma time slice remains to be fully understood; however, the sweepstakes and/or island-hopping dispersal mechanisms were the most likely mode of migration for the small-and medium-sized mammals. Additionally, according to a recent study, plausible existence of corridor(s) for secular migration allowed for faunal exchanges between India and Eurasia close to ~ 56-57 Ma, particularly for the large-sized mammals (> 35 kg) (e.g., cambaythere perissodac-tyls). Further, there is now a revived interest in the early Paleogene vertebrate palaeontology of India due to recent data on biostratigraphically constrained Paleocene and early-middle Eocene vertebrate records (such as fish, reptiles, and amphibians along with associated coprolite ichnofossils) from the western and northeastern regions of India.
... The phylogenetic position of Paraphenacodus still remains obscure. On the other hand, Paraphenacodus can be distinguished from early perissodactyls in having a more bunodont dentition, much weaker cristid obliqua on the lower molars, enlarged m3 hypoconulid lobe nearly as wide as the talonid, a much smaller size, and in lacking the twinned metaconid on the lower molars (Bai et al. 2018b;Bronnert & Métais, 2023;Radinsky, 1963). Furthermore, even the tiniest perissodactyl taxa, such as Dilophodon leotanus and Selenaletes (Radinsky, 1963(Radinsky, , 1966, are larger than Paraphenacodus, which in turn is comparable to some artiodactyls in size. ...
ABSTRACT—Eocene artiodactyls from Asia were considered less diverse and abundant than the contemporary
perissodactyls, especially in the Eocene faunas from the Mongolia Plateau and Central Asia. By contrast, artiodactyls are
highly diverse and endemic from the Eocene deposits of Europe and North America. Here we report two new genera and
three new species of small- to medium-sized artiodactyls preserved by fragmentary materials from the Early and Middle
Eocene of the Erlian Basin, Inner Mongolia, China. Paraphenacodus gabuniai sp. nov. represents the first record of
artiodactyls from Arshantan Asian Land Mammal Age, and shows some more primitive characters than Paraphenacodus
solivagus from the Middle Eocene of the Zaysan Depression of Kazakhstan. Although Paraphenacodus with generally
bunodont teeth shows some similarities with both Early Eocene Tsaganohyus from Mongolia and early cebochoerid
Gervachoerus from Europe, its affinities with other artiodactyls remain obscure. Two new genera and species, Irdinodon
bicuspidata gen. et sp. nov. and Aliusuellus laolii gen. et sp. nov., from the Irdinmanhan ALMA represent new taxa of
Lantianiinae and Tapirulidae, respectively. Irdinodon is characterized by twinned metaconules and entoconids on the
upper and lower molars in lantianiines. Aliusuellus is characterized by a large size and a distinct ridge raised along the
posterolingual side of the paracone to its apex on M2. These new artiodactyl materials from the Erlian Basin, as well as
recently reported tapirulids and bunodont Erlianhyus, increase the diversity of the Eocene artiodactyls from the Mongolia
Plateau, and provide new clues on the origin and dispersal of some early artiodactyls.
... Trans-species allele sharing due to polymorphism preceding speciation has been documented in immunity-related genes as well as in several other genes in humans and other species (Klumplerova et al. 2020;Azevedo et al. 2015;Halldórsdóttir and Árnason 2015). We observed trans-species allele sharing within the Equidae, while based on the few tapir and rhino sequences available, no alleles common to equids, tapirs and rhinoceroses, which diverged approximately 56 MY ago (Bai et al. 2018), were identified. Equids diverged into horses, zebras and asses approximately 4-5 MY ago (Librado and Orlando 2021). ...
Toll-like receptors (TLRs) represent an important part of the innate immune system. While human and murine TLRs have been intensively studied, little is known about TLRs in non-model species. The order Perissodactyla comprises a variety of free-living and domesticated species exposed to different pathogens in different habitats and is therefore suitable for analyzing the diversity and evolution of immunity-related genes. We analyzed TLR genes in the order Perissodactyla with a focus on the family Equidae. Twelve TLRs were identified by bioinformatic analyses of online genomic resources; their sequences were confirmed in equids by genomic DNA re-sequencing of a panel of nine species. The expression of TLR11 and TLR12 was confirmed in the domestic horse by cDNA sequencing. Phylogenetic reconstruction of the TLR gene family in Perissodactyla identified six sub-families. TLR4 clustered together with TLR5; the TLR1-6-10 subfamily showed a high degree of sequence identity. The average estimated evolutionary divergence of all twelve TLRs studied was 0.3% among the Equidae; the most divergent CDS were those of Equus caballus and Equus hemionus kulan (1.34%) in the TLR3 , and Equus africanus somaliensis and Equus quagga antiquorum (2.1%) in the TLR1 protein. In each TLR gene, there were haplotypes shared between equid species, most extensively in TLR3 and TLR9 CDS, and TLR6 amino acid sequence. All twelve TLR genes were under strong negative overall selection. Signatures of diversifying selection in specific codon sites were detected in all TLRs except TLR8. Differences in the selection patterns between virus-sensing and non-viral TLRs were observed.
... Despite the exact geographic origin of true equids remaining somewhat contentious (Bai et al., 2018), the cradle of equid evolution lies unequivocally in North America. Throughout the Cenozoic (66 million years ago to present), North American habitats shifted from being dominated by humid rainforests in the Paleocene (66-56 Mya) and Eocene (56-40 Mya) through various stages of drying from the Oligocene (40 Mya) until the present-day Holocene (Eronen et al., 2012;Maguire & Stigall, 2008;Secord et al., 2012). ...
The evolution of the limbs of horses has fascinated scholars and laymen alike for generations. From the late 1800s until the present day, different ideas have been proposed to explain the evolution of the monodactyl (one-toed) condition in modern horse limbs. Theses such as maximal speed, stability, body mass, inertial load, and distance transport propose different selective pressures which drove the evolution of monodactyly in Equus-line equids. We posit that previous equid researchers have approached the question of monodactyly from too narrow an angle, focusing on one aspect of the story rather than treating monodactyly as the result of multiple factors. Our Equal Strength Synthesis treats intrinsic bone strength as the starting point for the evolution of monodactyly in equids and combines the biomechanical and habitual aspects of previous theses. Assuming equids have never been on the brink of failure, and that bone strength was equal in tridactyl and monodactyl equids, we demonstrate significant reductions in distal limb mass would have been possible by reducing the digit number to one. This synthesis presents a rigorous biomechanical revision to an age-old conundrum, bringing us one step closer to truly understanding one of the great transitions in vertebrate evolution.
... In a wider sense, Baltic amber seems to preserve an essentially Holarctic harvestman fauna, potentially supported by the presence of putative land bridges allowing migration between North America and Eurasia after the Cretaceous, evidence for which has been published for vertebrates and plants (see e.g. Bai et al. 2018, Graham 2018. Already known examples of harvestmen found in Baltic amber that are restricted today to East Asia and/or North America include the genera Caddo Banks, 1892, Eumesosoma Cokendolpher, 1980 and Protolo phus Banks, 1893 (see e.g. ...
Two new laniatoreans from Eocene Baltic amber are described. Baltonychia obscura gen. et sp. nov. represents the first fossil Laniatores with a peltonychium on tarsus III–IV, implying that its closest living relatives are likely members of the extant families Cladonychiidae or Travuniidae. A second fossil is described as Insidiatores indet. as its preservation does not allow further assignment. Both fossils are substantially different to the so far only known Baltic amber laniatorean species Proholoscotolemon nemastomoides (Koch & Berendt, 1854), and suggest a more diverse Laniatores fauna in the Eocene of north-central Europe. The evolutionary history of the infraorder
Insidiatores and their development into troglomorphic species is discussed.
... The first equoids appear suddenly by dispersal at the beginning of the Eocene in North America and Europe, and probably also in Asia, coincident with the Mammalian Eocene Dispersal Event (e.g., Smith and Smith 2004;Hooker and Collinson 2012;Missiaen et al. 2013;Bai et al. 2018;Bronnert et al. 2018). The earliest equoids are represented by some basal genera ('Hyracotherium', 'Eohippus', Sifrhippus, Cymbalophus, Pachynolophus, Pliolophus) of Euramerica (Hooker 1994;Froehlich 2002;Danilo et al. 2013;Missiaen et al. 2013;Bronnert et al. 2018) and Asia (Erihippus) (Bai et al. 2018). ...
... The first equoids appear suddenly by dispersal at the beginning of the Eocene in North America and Europe, and probably also in Asia, coincident with the Mammalian Eocene Dispersal Event (e.g., Smith and Smith 2004;Hooker and Collinson 2012;Missiaen et al. 2013;Bai et al. 2018;Bronnert et al. 2018). The earliest equoids are represented by some basal genera ('Hyracotherium', 'Eohippus', Sifrhippus, Cymbalophus, Pachynolophus, Pliolophus) of Euramerica (Hooker 1994;Froehlich 2002;Danilo et al. 2013;Missiaen et al. 2013;Bronnert et al. 2018) and Asia (Erihippus) (Bai et al. 2018). Some of the most complete European mammalian fossil assemblages from the earliest Eocene (MP 7, Ypresian) come from the Belgium sites of Dormaal (the international MP 7 reference level) and Erquelinnes, and from the French site of Le Quesnoy (Smith and Smith 2004;Missiaen et al. 2013;Bronnert et al. 2018). ...
... Near the Palaeocene-Eocene boundary, mammalian dispersals seem to have occurred between Europe and Asia, via the Turgai Strait, and between Europe and Indian subcontinent, via the Kohistan-Ladakh Island arc along the Tethys shore (Smith et al. 2006;Ting et al. 2011). Asia or Indian subcontinent has been hypothesised as the main important centre of taxonomic origin in some Eocene mammalian taxa, including Perissodactyla (Hooker and Dashzeveg 2003;Rose et al. 2014;Smith et al. 2016;Bai et al. 2018). With respect to western Europe, during the earliest Eocene, there were two distinct palaeobiogeographical areas of European faunas, which were not the result of a geographic isolation between the northern and southern areas, but to a climatic barrier (Marandat et al. 2012). ...
The family Palaeotheriidae (Perissodactyla, Equoidea) was one of the most abundant and successful Eocene mammalian groups from western Europe. Equoid perissodactyls were diverse in the Iberian Peninsula, with the presence of six genera and 19 species (mainly palaeotheres) which are unknown elsewhere in Europe. In this work, an overview of the Eocene Iberian equoid fossil record is summarised in the context of the European palaeobiogeography, including the updating of the endemic palaeotheriid taxa. The persistence of the endemism in the western Iberian region during the late Eocene could be due to an ecological barrier. There are significant dental pattern differences between the endemic Iberian and the other European palaeotheriid taxa. These differences may be the results of dietary strategies different from those of contemporary European faunas. Some dental features might indicate that the environmental changes driven by the climatic cooling of the latest Eocene in western Europe could have started earlier in western Iberia.
... This abrupt global warming event culminated in a series of environmental changes, including intensified extreme precipitation and weathering (Schmitz and Pujalte, 2007;Chen et al., 2016Chen et al., , 2018Pujalte et al., 2019), rapid ocean acidification (Zachos et al., 2005) and mass extinction of deep-sea benthic foraminifera (Kennett and Stott, 1991). Moreover, this event greatly influenced the dispersal and evolution of terrestrial vegetation (Wing et al., 2005;Jaramillo et al., 2010;Prasad et al., 2018;Willard et al., 2019;Huurdeman et al., 2021) and mammalian fauna (Bowen et al., 2002;Smith et al., 2006;Secord et al., 2012;Bai et al., 2018). The rapid global warming during the PETM has received extensive attention because it provides an ideal analogue for understanding future rapid global warming (Zachos et al., 2008;Mcinerney and Wing, 2011). ...
Rapid global warming during the Paleocene-Eocene Thermal Maximum (PETM) profoundly affected the
marine and terrestrial environments. However, details of the climate and vegetation of subtropical and
arid regions of central China during the hyperthermal event are poorly understood. Here, we report a
palynological record from the black shale of the lowermost Yangxi Formation exposed in Songzi city,
western Jianghan Basin, central China. Biostratigraphy, magnetostratigraphy and isotope stratigraphy
indicate a PETM age for the sedimentary succession. The palynological assemblage was characterized
by high abundances of diverse tropical and subtropical broadleaved tree pollen, providing strong evidence of a dense south subtropical forest ecosystem that once existed in the arid belt of central China
during the PETM. The reconstructed climatic parameters indicate an extremely warm and humid south
subtropical climate, with mean annual temperatures (MAT) ranging from 21 to 24 �C and mean annual
precipitation (MAP) ranging from 1396 to 1997 mm. The reconstructed precipitation was surprisingly
high for such an arid setting that widespread arid climate prevailed in central China at that time.
These findings demonstrate that rapid global warming during the PETM significantly increased precipitation, leading to the growth of dense forest ecosystems as well as increasing lake eutrophication in central China. The changes to precipitation and terrestrial ecosystems during this warming event are
considerably more significant than previously reported in other mid-latitude regions, and highlighting
the need to consider regional geographic characteristics to fully understand how the environment
responds to rapid global warming.
... This date is close and only slightly younger than several molecular estimates for the initial divergence within crown Perissodactyla (e.g., Meredith et al., 2011;Foley et al., 2016). The fossil record shows that the order Perissodactyla rapidly radiated into several sub-orders and families and was then represented on all the holarctic continents (Radinsky, 1969;Hooker and Dashzeveg, 2003;Bai et al., 2018). In Western Europe, perissodactyls were represented during the early Eocene by several equoids from the localities of Abbey Wood, UK (Hooker, 2010), Silveirinha, Portugal (Estravis, 1992), Erquelinnes, Belgium (Quinet and Verlinden, 1970;Missiaen et al., 2013), and the French localities of Le Quesnoy (Bronnert et al., 2018a), Fordones (Marandat et al., 2012), Rians (Godinot, 1981) and Palette (Godinot et al., 1987). ...
... Lophiaspis maurettei is a key taxon, notably because of its early occurrence, for understanding the relationships between the lophiodontids and other perissodactyls. As such, Ls. maurettei has often been used in phylogenetic analysis (Hooker and Dashzeveg, 2004;Bai et al., 2010Bai et al., , 2018, although only one fragmentary specimen was available. Traditionally, the lophiodontids were long considered as tapiroids (Cuvier, 1822;Filhol, 1888). ...
... The familial status of Lophiaspis has been uncertain since then. Lophiodontids have been successively assigned to Ceratomorpha or Ancylopoda in the latest phylogenetic analyses (Hooker and Dashzeveg, 2004;Holbrook, 2009), and the position of Lophiaspis within the lophiodontids has often been challenged (Hooker, 1989;Bai et al., 2010Bai et al., , 2018. ...
The Lophiodontidae are endemic perissodactyls from Europe that flourished during the Eocene. Despite their preponderance in the European fossil record, their exact origin and relationships within the perissodactyls remain unknown due to the rare and fragmentary material in the early Ypresian, the time of their earliest radiation. Lophiaspis maurettei is the oldest and earliest diverging lophiodontid known to date but is unfortunately poorly known. We describe here the results of new excavations of the type locality of Palette. Important new material including complete skulls, mandibles, post-cranial elements and juvenile specimens lead us to revise Lophiaspis maurettei from Palette and other localities and to describe novel morphology for this species. According to an original phylogenetic analysis, based on a revised matrix of dental, cranio-mandibular and postcranial characters, Ls. maurettei is an early diverging lophiodontid morphologically close to Protomoropus and Paleomoropus, two basal chalicotheres, known from Asia and North America, respectively. Our
resulting topology does not support the previously proposed inclusion of the lophiodontids within the Ceratomorpha and supports a position within the suborder Ancylopoda, close to some Eomoropidae representatives. These results imply that Ls. maurettei was restricted to Southern Europe during the early Eocene, which would be compatible with an Asian origin for lophiodontids in accordance with the evolutionary history of other perissodactyls and placental mammals.
... The early Eocene was an extremely warm interval during the Cenozoic (Zachos et al., 2001(Zachos et al., , 2008, and was a critical period for the evolution of mammals: the modern mammalian orders of Primates, Artiodactyla, and Perissodactyla and the family Hyaenodontidae appeared almost simultaneously on the Holarctic continents (Asia, Europe and North America) (Bowen et al., 2002;Bai et al., 2018). The early Eocene greenhouse period is crucial in understanding the climate of China before the significant Tibetan Plateau uplift, proto-Paratethys Sea retreat and global cooling. ...
... The Hengyang Basin, located in the central-southern Hunan Province, southern China (Fig. 1a), is located in a key geographical location filled with a continuous succession of Paleocene to early Eocene sediments. Mammalian fossils, as well as paleomagnetic and isotopic analysis (Li et al., 1979;Ting and Li, 1987;Bowen et al., 2002;Ting et al., 2003;Ting et al., 2004;Ni et al., 2004;Tong et al., 2006;Bai et al., 2018) have enabled a reliable chronological framework to be established, thus providing an exceptional opportunity to study early Eocene climate and vegetation landscape. ...
... The Limuping Fm. is composed of purplish-red to brownish-red argillaceous sandstone and sandy mudstone, interbedded with variegated mudstones and marlstone, while the Lingcha Fm. consists of purplish-red to brownish-red argillaceous sandstone and sandy mudstone, interbedded with greyish-green, yellowish-green to greyish-yellow mudstone and marlstone, and is rich in calcareous concretions. Previous studies based on fossils of mammals (Li et al., 1979;Ting and Li, 1987;Ting et al., 2004;Ni et al., 2004;Bai et al., 2018) and ostracods (Zhang and Li, 2010), as well as paleomagnetic and carbon isotopic evidence (Bowen et al., 2002;Ting et al., 2003), all support an early Eocene age for the upper Lingcha Fm. (refer to the Lingcha Fm in the text). The base of the Lingcha Fm. records the first transient Asian continental carbon isotope excursion, associated with the first appearance of mammals such as perissodactyls, artiodactyls, primates and ctenodactyloid rodents, and has been suggested to represent the Paleocene/Eocene boundary (Bowen et al., 2002;Ting et al., 2003;Ting et al., 2004;Tong et al., 2006;Wang et al., 2011Wang et al., , 2019. ...
The India–Asia collision and subsequent uplift of the Tibetan Plateau during the Cenozoic were the main drivers of Asian monsoon development and evolution. However, the climate and possible existence of a desert landscape in southern China prior to the significant uplift of the Tibetan Plateau remain uncertain, because of a lack of reliable proxies or direct geological evidence. The well–preserved early Eocene palynomorphs recovered from the Hengyang Basin, southern China, provide an ideal opportunity to address this problem. The palynological record suggests that the Hengyang Basin was dominated by xerophytic shrubs and an open forest vegetation landscape, confirming that a typical arid desert environment prevailed in the Hengyang Basin during the early Eocene. The high proportion of thermophilic and xerophytic taxa implies a hot and arid climate. The estimated mean annual precipitation (<230 mm) of the early Eocene in the Hengyang Basin was significantly lower than that of present (1354 mm). We propose that, prior to the significant uplift of the Tibetan Plateau, the combined effects of a strong subtropical anticyclone associated with the extremely warm climate and a rain–shadow effect caused by coastal mountains, were the primary factors responsible for the extreme arid climate and desert–like landscape of inland southern China during the early Eocene.
... At present, the only close phylogenetic link seems to be with anthracobunids. The age of Cambaytherium-early Eocene but younger than the demonstrably oldest perissodactyls on Laurasian continents (Gingerich, 1989;Hooker and Collinson, 2012;Bai et al., 2018)-eliminates it from direct ancestry. Nevertheless, as the earliest anthracobunian and the most primitive known perissodactylamorph, it provides the best current anatomical model for the last common ancestor of Perissodactyla. ...
... On the northern continents, perissodactyls appear suddenly, just after the beginning of the PETM (e.g., Gingerich, 1989;Bowen et al., 2002;Missiaen et al., 2013;Bronnert et al., 2017). Bai et al. (2018) recently argued that all four earliest perissodactyl lineages (equids, brontotheres, chalicotheres, and ceratomorphs) were already present in the earliest Eocene of China and thereby suggested that all diverged near the Paleocene-Eocene boundary, the last three originating in non-Indian Asia. This proposal, however, was based not on new discoveries but on reinterpretation of fragmentary fossils previously allocated to two species: the basal ceratomorph Orientolophus hengdongensis and the early equoid 'Propachynolophus' hengyangensis. ...
... Although he came to the same conclusion regarding perissodactyl origins, Hooker (2005) rejected close perissodactyl affinities for Radinskya and questioned the reliability of the stratigraphic information on the Bayan Ulan perissodactyls. Hooker and Dashzeveg (2003) further speculated that equoids evolved in Europe in the latest Paleocene (see also Hooker, 2015;Bai et al., 2018), following dispersal of a basal perissodactyl from Asia across the Turgai Straits during an episode of lower sea level (Iakovleva et al., 2001). Their hypothesis included "dispersal to the Indian subcontinent sometime in the early Eocene" (Hooker and Dashzeveg, 2003:491). ...
The anatomy of Cambaytherium, a primitive, perissodactyl-like mammal from the lower Eocene Cambay Shale Formation of Gujarat, India, is described in detail on the basis of more than 350 specimens that represent almost the entire dentition and the skeleton. Cambaytherium combines plesiomorphic traits typical of archaic ungulates such as phenacodontids with derived traits characteristic of early perissodactyls. Cambaytherium was a subcursorial animal better adapted for running than phenacodontids but less specialized than early perissodactyls. The cheek teeth are bunodont with large upper molar conules, not lophodont as in early perissodactyls; like perissodactyls, however, the lower molars have twinned metaconids and m3 has an extended hypoconulid lobe. A steep wear gradient with heavy wear in the middle of the tooth row suggests an abrasive herbivorous diet. Three species of Cambaytherium are recognized: C. thewissi (∼23 kg), C. gracilis (∼10 kg), and C. marinus (∼99 kg). Body masses were estimated from tooth size and long bone dimensions. Biostratigraphic and isotopic evidence indicates an age of ca. 54.5 Ma for the Cambay Shale vertebrate fauna, the oldest Cenozoic continental vertebrate assemblage from India, near or prior to the initial collision with Asia. Cambaytheriidae (also including Nakusia and Perissobune) and Anthracobunidae are sister taxa, constituting the clade Anthracobunia, which is sister to Perissodactyla. We unite them in a new higher taxon, Perissodactylamorpha. The antiquity and occurrence of Cambaytherium—the most primitive known perissodactylamorph—in India near or before its collision with Asia suggest that Perissodactyla evolved during the Paleocene on the Indian Plate or in peripheral areas of southern or southwestern Asia.
