Cambaytherium

Last updated

Cambaytherium
Temporal range: Eocene
Cambaytherium thewissi.png
Life Restoration
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
† Anthracobunia [1]
Family:
† Cambaytheriidae [2]

Bajpai et al., 2005
Genus:
†Cambaytherium [2]

Bajpai et al., 2005
Species
  • †C. thewissiBajpai et al., 2005
  • †C. gracilisSmith et al., 2016
  • †C. bidensBajpai et al., 2005

Cambaytherium is an extinct genus of placental mammals in the family Cambaytheriidae. It existed during the early Eocene approximately 55 million years ago on the Indian subcontinent. Fossils of Cambaytherium are known exclusively from the Cambay Shale Formation in western India and comprise over 200 specimens, including skulls, teeth, and postcranial elements. The genus and family were first described scientifically in 2005. Initially, placement at the base of the odd-toed ungulates was preferred, though some researchers suggested affinity with elephants within Tethytheria. Recent systematic analyses, based on abundant material, position it not at the base of odd-toed ungulates but in close relation to them. The genus's discovery on the subcontinent, then an island drifting northward toward Asia, offers insights into the origin and early evolution of the order Perissodactyla, hypothesized to have arisen in Asia.

Contents

Description

Cambaytherium was a medium-sized mammal. Smaller individuals weighed an estimated 10 to 23 kg, comparable to a modern peccary. Larger forms reached up to 99 kg. [3]

Numerous features of Cambaytherium, including dentition and sacral vertebra count, are transitional between Perissodactyla and earlier mammals, potentially reflecting the ancestral condition for all Perissodactyla. [4] These encompass a restricted nasal cavity. The nasal bones did not protrude into the frontal bones, resulting in a transverse suture with straight margins on both bones. The orbit positioned above the posterior molars, contrasting with Tethytheria's anteriorly placed eye sockets. The zygomatic arch was complete. The mandible featured a fused mandibular symphysis extending to the second premolar. Its horizontal ramus maintained uniform depth beneath the molars, tapering anteriorly to the symphysis. The condyles ascended steeply, elevating the joints above the teeth. The coronoid process angled posteriorly and was diminished in size. The angular process extended prominently at the mandible's posterior. The dental formula matched that of primitive Eutheria: . Incisors were small, spatulate or rounded. The canine extended beyond the incisors. A brief diastema separated the posterior teeth, and another occurred between the first and second premolars. Premolars lacked molarization, differing little from molars. Molars exhibited bunodont occlusal surfaces with large, conical cusps arranged in transverse pairs. This configuration precluded the lophodont pattern typical of odd-toed ungulates (transverse enamel ridges). The first two molars bore two cusp rows; the third added a third row. Molar size increased posteriorly, with the lower first molar measuring 1.1 to 1.3 cm and the third 1.5 to 1.9 cm. [2] [5] [6] [3]

The limbs display osteological traits indicating running capability, though less agile than early perissodactyls owing to its robust construction. Notable are the lumbar vertebral arches, which interarticulated robustly. The humerus was sturdy with a narrow distal end. The ulna had a robust proximal (olecranon) and mildly curved distal shaft. The olecranon constituted about 21% of bone length, aligning with early odd-toed ungulate variation. The radius lay entirely anterior to the ulna. The femur possessed a third trochanter, characteristic of odd-toed ungulates, for muscle attachment, offset proximally near the lesser trochanter's distal end. The greater trochanter was elevated, surpassing the femoral head. The tibia and fibula remained unfused. Forefeet retained at least four digits, hindfeet five with one rudimentary, unlike earliest perissodactyls limited to four digits maximally. Innermost digits (one) of fore- and hindfeet were likely shortened, known only from facets. The central digit (three) was longest, yielding the mesaxonic foot typical of odd-toed ungulates. Metapodials were robust and short overall. Terminal phalanges suggest hoof presence. Further affinity to odd-toed ungulates is evident in the talus bone's saddle-shaped distal articulation. [5] [6] [3]

Fossil record

Fossils of Cambaytherium are known solely from the Cambay Shale Formation in Gujarat, western India. This formation, 75 to 1500 m thick, is a fossiliferous deposit holding the subcontinent's oldest Cenozoic vertebrates. It outcrops mainly in Vastan and Mangrol coal mines, 40 km northeast of Surat. Composed of shales, claystones, and sandstones with two coal seams, vertebrate fossils emerged from thin clayey silt lenses, 5 m long and 30 cm thick, 1 to 3 m above the basal coal. [7] Formed in nearshore settings, these date to over 54 million years via dinoflagellates [8] and isotope analysises. [9] This aligns with the early Eocene, about 1.5 to 1 million years post-Paleocene–Eocene Thermal Maximum. Assemblage includes early mammals like primitive primates, [10] even-toed ungulates, [11] rodents, [12] and extinct groups such as Tillodontia. [13] Birds, reptiles, amphibians, and fishes are also present. [2] [14]

Cambaytherium is abundant in the assemblage, with over 120 jaw and dental elements—including adult and juvenile skulls—and about 100 postcranial bones like vertebrae and limbs. Initial finds, mainly teeth and jaws, followed early 2000s detection of fossil layers, prompting extensive fieldwork. [2] [15] Subsequent excavations yielded fuller material, refining systematic placement. [16] [5]

Paleobiology

Cambaytheriums morphology combines traits of swift and slower mammals. Preserved thoracic vertebrae and tightly linked lumbar ones suggest a rigid back, less flexible than in early horses like Sifrhippus. Primitive horses exhibited flexible backs in rapid locomotion, akin to modern cheetahs. Horses' stiff galloping back evolved later with size increase; Cambaytherium prefigures this somewhat. Conversely, locomotor features imply cursorial adaptation. Forelimbs had restricted elbow rotation, shown by narrow humeral distal joint and proximal ulna-radius fusion. Hindlimbs featured a tibial distal facet fully engaging the astragalus, forming a mortise joint limiting feet to parasagittal motion. Similar orientation is indicated by elevated greater trochanter and proximally shifted third trochanter on femur. Phalangeal arrangement supports digitigrade or unguligrade stance. These cursorial traits are tempered by sturdy limbs and short distal segments, unlike elongations in specialized runners. Thus, Cambaytheriums locomotion appears more generalized than earliest odd-toed ungulates. [5] [3]

Bunodont molars with low crowns suggest omnivorous to herbivorous feeding. [5] [3] Dental analyses detail diet. Larger C. thewissi individuals display early, intense occlusal wear, with anterior molar cusps abraded by full eruption of posterior molar. Wear indicates dominant vertical over horizontal mastication, implying consumption of tough plants like hard fruits or nuts. Smaller C. gracilis shows milder wear and less robust teeth, suggesting softer vegetation. [4] Cambaytherium's robust angular process, reduced coronoid, and elevated condyle typify herbivores with pronounced masseter muscle and diminished temporalis muscle. [3]

Taxonomy

  Perissodactylamorpha  

Systematic position of Cambaytheriidae after Rose et al. (2020) [3]

Cambaytherium is a genus in the extinct family Cambaytheriidae. The genus and family were first described in 2005 by Sunil Bajpai and colleagues, based on lower and upper jaws plus isolated teeth from Gujarat's Cambay Shale Formation. The holotype (IITR/SB/VLM 505) is a mandible preserving bilateral teeth from last premolar to last molar. The name Cambaytherium derives from the Cambay Shale Formation—named for Khambhat (Cambay) and Gulf of Khambhat—and Greek θηρίον (thēríon, "beast"). Other Cambaytheriidae genera include Perissobune , described 2014 from a Pakistani Ghazij Formation jaw, [17] and Nakusia , named 1999 from a Balochistan maxilla. [18] Indobune, based on 2006 Cambay Shale maxillary fragments, [7] is now synonymous with Cambaytherium per recent studies. [16] [5] Similarly, Kalitherium, introduced 2006 with a near-complete Cambay Shale skull, [15] was synonymized with Cambaytherium in 2020. [3]

Three species of Cambaytherium are currently recognized: [5] [14] [3]

C. gracilis measures 10 to 20% smaller linearly than C. thewissi. Anterior dental and symphyseal traits exclude sexual dimorphism as cause, confirming distinct species. [14] C. marinus, the largest, was initially in Kalitherium but reassigned to Cambaytherium in 2020. [3] Originally, besides C. thewissi, C. bidens and C. minor were named, but now subsumed under C. thewissi. Thewissi honors J. G. M. "Hans" Thewissen for Indo-Pakistani fossil mammal research. (Correctly, it should be thewisseni. [19] ) [2] [5]

Originally, Cambaytherium and Cambaytheriidae were deemed primitive odd-toed ungulates, marked by bunodont molar patterns. The formation's early Eocene age supported this, as early forms like Cardiolophus or Hallensia shared similar teeth, though Cambaytherium's were simplest. Criticism noted similar patterns in Asian Anthracobunidae, with third cusp pairs on last molars; then known from teeth, they were linked to elephants. [19] [7] Thus, Indobune was later classed as Anthracobunidae. [7] Nakusia, akin to Cambaytherium, was earlier placed there. [18]

Expanded fossils, including postcrania, enable refined positioning of Cambaytherium and Cambaytheriidae as perissodactyl relatives, shown by astragalar navicular notch—a perissodactyl apomorphy—and mesaxonic hands/feet with elongated central ray. Skull traits like nasal-frontal transverse suture connect them. Primitive features absent in perissodactyls include pentadactyl limbs. Earliest perissodactyls had tetradactyl fore- and tridactyl hindlimbs (like modern tapirs). Only Sifrhippus , earliest Equidae, retained reduced hind outer digit. These suggest descent from "Condylarthra" lineages. Molars lack transverse crests for bilophodonty, typical of perissodactyls. Hence, Cambaytheriidae and Cambaytherium are perissodactyl sister group, with Anthracobunidae closely related. [5] A concurrent cranial-mandibular study concurs, viewing Cambaytheriidae as "stem perissodactyls". It includes Anthracobunidae and semiaquatic Desmostylia—usually tethytherian—in close kinship. [20] A 2020 analysis united Cambaytheriidae and Anthracobunidae as Anthracobunia, sister to perissodactyls, forming Perissodactylamorpha. This removes Anthracobunidae from elephant affinity. [3]

Perissodactyls were among the most diverse Eutheria historically, emerging abruptly in early Eocene ~56 million years ago in North America and Eurasia. Asian origin was often proposed. Cambay Shale perissodactyl relatives support this, localizing to South Asia. Early Eocene India was an island post-Madagascar separation, drifting north to Asia, colliding ~50 million years ago or later. Possible island arcs may have linked it to Afro-Arabia, allowing perissodactyl ancestor dispersal. This accounts for European-like early primates and rodents in Cambay Shale. Contemporaneous Ghazij Formation in Balochistan yields early perissodactyls resembling Cambaytherium alongside advanced Tapiromorpha and Hippomorpha. Balochistan was a separate island, seaway-divided from India. [16] [21] [17] [14] Paleocene fossils are absent in both areas, hindering hypothesis verification. [5]

Further reading

References

  1. ↑ Rose, K.D.; Holbrook, L.T.; et al. (2019). "Anatomy, relationships, and paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the Lower Eocene of western India". Journal of Vertebrate Paleontology. 39 (sup1): 1–147. Bibcode:2019JVPal..39S...1R. doi:10.1080/02724634.2020.1761370. S2CID   226263139.
  2. 1 2 3 4 5 6 S. Bajpai; V. V. Kapur; D. P. Das; B. N. Tiwari; N. Saravanan; R. Sharma (2005). "Early Eocene land mammals from Vastan Lignite Mine, District Surat (Gujarat), Western India". Journal of the Palaeontological Society of India. 50 (1): 101–113.
  3. 1 2 3 4 5 6 7 8 9 10 11 Rose, Kenneth D.; Holbrook, Luke T.; Kumar, Kishor; Rana, Rajendra S.; Ahrens, Heather E.; Dunn, Rachel H.; Folie, Annelise; Jones, Katrina E.; Smith, Thierry (2019-11-11). "Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India" . Journal of Vertebrate Paleontology. 39 (sup1): 1–147. doi:10.1080/02724634.2020.1761370. ISSN   0272-4634.
  4. 1 2 von Koenigswald, Wighart; Rose, Kenneth D.; Holbrook, Luke T.; Kumar, Kishor; Rana, Rajendra S.; Smith, Thierry (2018-12-01). "Mastication and enamel microstructure in Cambaytherium, a perissodactyl-like ungulate from the early Eocene of India" . PalZ. 92 (4): 671–680. Bibcode:2018PalZ...92..671V. doi:10.1007/s12542-018-0422-8. ISSN   1867-6812. S2CID   133969194.
  5. 1 2 3 4 5 6 7 8 9 10 Rose, Kenneth D.; Holbrook, Luke T.; Rana, Rajendra S.; Kumar, Kishor; Jones, Katrina E.; Ahrens, Heather E.; Missiaen, Pieter; Sahni, Ashok; Smith, Thierry (2014-11-20). "Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India". Nature Communications. 5 (1): 5570. doi:10.1038/ncomms6570. ISSN   2041-1723.
  6. 1 2 Kenneth D. Rose, Luke T. Holbrook, Rajendra S. Rana, Kishor Kumar, Katrina E. Jones, Heather E. Ahrens, Pieter Missiaen, Ashok Sahni und Thierry Smith: Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications 5 (5570), 2014 (suppl.)
  7. 1 2 3 4 Kenneth D. Rose, Thierry Smith, Rajendra S. Rana, Ashok Sahni, H. Singh, Pieter Missiaen und A. Folie: Early Eocene (Ypresian) continental vertebrate assemblage from India, with description of a new anthracobunid (Mammalia, Tethytheria). Journal of Vertebrate Paleontology 26 (1), 2006, S. 219–225
  8. ↑ Rahul Garg, Khowaja-Ateequzzaman, Vandana Prasad, S. K. M. Tripathi, I. B. Singh, A. K. Jauhri und S. Bajpai: Age-diagnostic dinoflagellate cysts from lignite-bearing sediments of the Vastan lignite mine, Surat District, Gujarat, western India. Journal of the Palaeontological Society of India 53 (1), 2008, S. 99–105
  9. ↑ Mark Clementz, S. Bajpai, V. Ravikant, J. G. M. Thewissen, N. Saravanan, I. B. Singh und V. Prasad: Early Eocene warming events and the timing of terrestrial faunal exchange between India and Asia. Geology 39 (1), 2011, S. 15–18
  10. ↑ Kenneth D. Rose, Rajendra S. Rana, Ashok Sahni, Kishor Kumar, Pieter Missiaen, Lachham Singh und Thierry Smith: Early Eocene Primates from Gujarat, India. Journal of Human Evolution 56, 2009, S. 366–404
  11. ↑ Kishor Kumar, Kenneth D. Rose, Rajendra S. Rana, Lachham Singh, Thierry Smith und Ashok Sahni: Early Eocene Artiodactyls (Mammalia) from Western India. Journal of Vertebrate Paleontology 30 (4), 2010, S. 1245–1274
  12. ↑ Rajendra S. Rana, Kishor Kumar, Gilles Escarguel, Ashok Sahni, Kenneth D. Rose, Thierry Smith, Hukam Singh und Lachham Singh: An Ailuravine Rodent from the Lower Eocene Cambay Formation at Vastan, Western India, and Its Palaeobiogeographic Implications. Acta Palaeontologica Polonica 53 (1), 2008, S. 1–14
  13. ↑ Kenneth D. Rose, Kishor Kumar, Rajendra S. Rana, Ashok Sahni und Thierry Smith: New Hypsodont Tillodont (Mammalia, Tillodontia) from the Early Eocene of India. Journal of Paleontology 87 (5), 2013, S. 842–853
  14. 1 2 3 4 Smith, Thierry; Kumar, Kishor; Rana, Rajendra S.; Folie, Annelise; Solé, Floréal; Noiret, Corentin; Steeman, Thomas; Sahni, Ashok; Rose, Kenneth D. (2016-11-01). "New early Eocene vertebrate assemblage from western India reveals a mixed fauna of European and Gondwana affinities". Geoscience Frontiers. 7 (6): 969–1001. doi:10.1016/j.gsf.2016.05.001. hdl: 1854/LU-8522812 . ISSN   1674-9871.
  15. 1 2 Sunil Bajpai, Vivesh Kapur, J. G. M. Thewissen, Debasis P. Das und B. N. Tiwari: New Early Eocene cambaythere (Perissodactyla, Mammalia) from the Vastan Lignite Mine (Gujarat, India) and an evaluation of cambaythere relationships. Journal of the Palaeontological Society of India 51 (1), 2006, S. 101–110
  16. 1 2 3 Pieter Missiaen, Kenneth Rose, Heather Ahrens, Kishor Kumar und Thierry Smith: Revision of Indobune and Cambaytherium from the early Eocene of Vastan (India), and their affinities with anthracobunid and perissodactyl mammals. Journal of Vertebrate Paleontology 31 (suppl.), 2011, S. 159
  17. 1 2 Pieter Missiaen und Philip D. Gingerich: New basal Perissodactyla (Mammalia) from the Lower Eocene Ghazij Formation of Pakistan. Contributions from the Museum of Paleontology, University of Michigan 32 (9), 2014, S. 139–160
  18. 1 2 Léonard Ginsburg, Khadim Hussain Durrani, Akhtar Mohammad Kassi und Jean-Loup Welcomme: Discovery of a new Anthracobunidae (Tethytheria, Mammalia) from the Lower Eocene lignite of the Kach-Harnai area in Baluchistan (Pakistan). Comptes Rendus de l'Académie des Sciences – Series IIA – Earth and Planetary Science 328 (3), 1999, S. 209–213
  19. 1 2 Kishor Kumar: Comments on ‘Early Eocene land mammals from Vastan Lignite Mine, District Surat (Gujarat), western India’ by Bajpai, S. et al. published in Journal of the Palaeontological Society of India 50, 1: 101-113, 2005. Palarch 1 (2), 2006, S. 7–13
  20. ↑ Lisa Noelle Cooper, Erik R. Seiffert, Mark Clementz, Sandra I. Madar, Sunil Bajpai, S. Taseer Hussain und J. G. M. Thewissen: Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PlosONE 9 (10), 2014, S. e109232
  21. ↑ Pieter Missiaen and Philip D. Gingerich: New Early Eocene Tapiromorph Perissodactyls from the Ghazij Formation of Pakistan, with Implications for Mammalian Biochronology in Asia. Acta Palaeontologica Polonica 57 (1), 2012, S. 21–34
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.