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Bharattherium

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Bharattherium
Temporal range:MaastrichtianLate Cretaceous(Maastrichtian) andPaleocene[1]
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Family: †Sudamericidae
Genus: †Bharattherium
Prasad et al., 2007
Species:
†B. bonapartei
Binomial name
†Bharattherium bonapartei
Prasad et al., 2007
Synonyms[2]
  • Dakshina jederiWilson et al., 2007

Bharattheriumis amammalthat lived inIndiaduring theMaastrichtian(latestCretaceous) and possibly thePaleocene.Thegenushas a singlespecies,Bharattherium bonapartei.It is part of thegondwanatherefamilySudamericidae,which is also found in Madagascar and South America during the latest Cretaceous. The first fossil ofBharattheriumwas discovered in 1989 and published in 1997, but the animal was not named until 2007, when two teams independently named the animalBharattherium bonaparteiandDakshina jederi.The latter name is now asynonym.Bharattheriumis known from a total of eight isolated fossil teeth, including oneincisorand seven molariforms (molar-like teeth, eitherpremolarsor true molars).

Bharattheriummolariforms are high, curved teeth, with a height of 6 to 8.5 millimetres (0.24 to 0.33 in). In a number of teeth tentatively identified as fourth lower molariforms (mf4), there is a large furrow on one side and a deep cavity (infundibulum) in the middle of the tooth. Another tooth, perhaps a third lower molariform, has two furrows on one side and three infundibula on the other. Thetooth enamelhas traits that have been interpreted as protecting against cracks in the teeth. Thehypsodont(high-crowned) teeth of sudamericids likeBharattheriumare reminiscent of later grazing mammals, and the discovery of grass in Indian fossil sites contemporaneous with those yieldingBharattheriumsuggest that sudamericids were indeed grazers.

Taxonomy

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Agondwanatheretooth, catalogued as VPL/JU/NKIM/25,[Note 1]was first discovered in theMaastrichtian(latestCretaceous,about 70–66 million years ago)Intertrappean BedsofNaskal,India, in 1989, but it was not identified as such until another gondwanathere,Lavanify,was found on Madagascar in the middle 1990s. The discoveries ofLavanifyand VPL/JU/NKIM/25 were announced inNaturein 1997. Gondwanatheres were previously known only from Argentina; these discoveries extended the range of the gondwanathere familySudamericidaeacross the continents of the ancient supercontinent ofGondwana.[4]

In 2007, two teams of scientists independently named the Indian gondwanathere on the basis of new material; both teams included VPL/JU/NKIM/25 in their newly named species. Guntupalli Prasad and colleagues named the animalBharattherium bonaparteion the basis of an additional tooth, VPL/JU/IM/33,[Note 2]from another Intertrappean locality,Kisalpuri.Thegeneric name,Bharattherium,combinesBharat,Sanskritfor "India", with theAncient Greektherion,meaning "beast", and thespecific name,bonapartei,honors Argentine paleontologistJosé Bonaparte,who was the first to describe a gondwanathere fossil.[5]G.P. Wilson and colleagues namedDakshina jederion the basis of six teeth (in addition to VPL/JU/NKIM 25), and identified some additional material as indeterminate gondwanatheres.[6]Of these teeth, three (GSI/SR/PAL-G059,[Note 3]G070, and G074) are from a third Intertrappean site atGokakand three (GSI/SR/PAL-N071, N210, and N212) are from Naskal.[7]Dakshina,the generic name, derives from Sanskritdaakshinaatya"of the south", and refers both to the animal's occurrence in southern India and to the distribution of gondwanatheres in the southern continents. The specific name,jederi,honorsUniversity of MichiganpaleontologistJeffrey A. Wilson,nicknamed "Jeder", who played an important role in the project that led to the discovery ofDakshina.[7]Wilson and colleagues also described three other gondwanathere teeth from Gokak (GSI/SR/PAL-G111, G112, and G211), which they tentatively identified as a different species of gondwanathere on their small size.[8]In 2008, Prasad commented thatBharattherium bonaparteiandDakshina jederirepresented the same species and thatBharattherium,which was published first, was the correct name.[2]

Description

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Known remains ofBharattherium
Fossil Locality Tooth position References
GSI/SR/PAL-G059 Gokak Left mf3 [9]
GSI/SR/PAL-G070 Gokak Right mf4 [10]
GSI/SR/PAL-G074 Gokak Right mf4 [11]
VPL/JU/IM/33 Kisalpuri Molariform [12]
GSI/SR/PAL-N071 Naskal Left mf4 [13]
GSI/SR/PAL-N210 Naskal Left i1 [9]
GSI/SR/PAL-N212 Naskal Right mf4 [9]
VPL/JU/NKIM/25 Naskal Left mf4 [14]

Bharattherium bonaparteiis known from a total of eight isolated teeth.[15]Among the seven teeth in their sample, Wilson and colleagues tentatively identified five as fourth lower molariforms (mf4)—because gondwanatherepremolarsandmolarscannot be distinguished, they are collectively known as "molariforms" —one as a third lower molariform (mf3) and one as a lowerincisor(i1). These determinations were made on the basis of comparisons with a sample of the South American gondwanathereSudamerica ameghinoi,in which all eight molariform positions are known.[7]However, the large number of mf4s led Wilson and colleagues to suspect that the criteria used for distinguishingSudamericatooth positions may not apply directly toBharattherium.[16]Prasad and colleagues did not assign their twoBharattheriumteeth to any tooth position, but suggested that they may represent different tooth positions and that one may come from the upper and the other from the lower side of the jaw.[17]As is characteristic of sudamericids,Bharattheriummolariforms arehypsodont(high-crowned) and have a flat occlusal (chewing) surface atop a high tooth, with furrows that extend down the height of the tooth.[18]Bharattheriummolariforms are the smallest of any sudamericid; those ofLavanify,for example, are about 35% larger.[19]UnlikeSudamericamolariforms, those ofBharattheriumtaper towards the top.[20]

Molariforms

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GSI/SR/PAL-G074, a well-preserved right mf4 that Wilson and colleagues selected as theholotypeofDakshina jederi,is 7.57 mm high and has a crown of 3.66 × 2.99 mm. It is curved, with the base more distal (towards the back) than the top. The occlusal surface is rectangular. On the lingual side (towards the tongue), there is a deep furrow (filled in part withcementum) that extends from the top to near the base of the tooth. There is also a much smaller indentation on the buccal side (towards the cheeks). The occlusal surface is mostly covered withenamelsurrounding adentinelake, but there is a V-shaped islet in the middle, with the tip of the V towards the lingual side, that forms the remnant of aninfundibulum—a deep cavity in the tooth.Perikymata—wave-like bands and grooves—are visible in the enamel.[20]

The right mf4 GSI/SR/PAL-G070, which is damaged on the buccal, distal, and lingual sides, is 8.40 mm high, but has an occlusal surface of only 2.49 × 1.75 mm. Unlike in GSI/SR/PAL-G074, the dentine on the occlusal surface is not exposed, and the occlusal surface is oval in shape. Furthermore, the V-shaped islet is larger and the lingual furrow is less prominent at the occlusal surface, because it tapers near the tip of the tooth. In the heavily damaged left mf4 GSI/SR/PAL-N071 (height 7.16 mm), only the distal side is well preserved. The infundibulum is exposed internally; it extends 4.01 mm down the crown.[21]The occlusal surface is poorly preserved, but its dimensions are at least 2.14 × 2.42 mm. GSI/SR/PAL-N212, a right mf4, is damaged on the mesial side and has a height of 5.86 mm and an occlusal surface of at least 2.66 x 2.04 mm. Cementum fills the V-shaped islet.[22]

VPL/JU/NKIM/25 was the first Indian gondwanathere fossil to be described; it is damaged on one side. Wilson and colleagues identified it as a left mf4 (implying that the damaged side is buccal) with strong similarities to GSI/SR/PAL-G070, including a curved crown and a V-shaped enamel islet atop a deep infundibulum. The occlusal surface is oval. The tooth is 6 mm high and Wilson and colleagues estimate that the occlusal surface is 2.5 × 1.8 mm, close to the dimensions of GSI/SR/PAL-G070. They suggest the tooth probably had enamel on all sides of the crown,[22]but Prasad and colleagues point to a possibleenamel-dentine junctionon the damaged side as evidence that enamel may be absent there.[18]

GSI/SR/PAL-G059, identified as a left mf3, has a height of 5.97 mm at the mesial side, but only 2.02 mm at the distal side because of curvature. On the lingual side, two long furrows are visible, and on the buccal side breakage exposes three long infundibula, of which the most mesial one is the longest and the most distal one the shortest. In the occlusal surface, these three infundibula merge into a single islet. In addition, three dentine lakes are visible in the occlusal surface, which has dimensions of 4.58 × at least 2.52 mm. Although inSudamerica,mf2, mf3, and the upper molariforms MF3 and MF4 all have three lophs, like GSI/SR/PAL-G059, its curvature matches the mf3 ofSudamericabest.[22]

VPL/JU/IM/33, the holotype ofBharattherium bonapartei,is 7.33 mm high,[5]2.66 mm long, and 2.0 mm wide. The occlusal surface is about rectangular and is mostly covered by a V-shaped dentine lake, which encloses a small heart-shaped enamel islet at the top of an cementum-filled infundibulum. A vertical furrow is also present. Near the top of the tooth, enamel covers the entire crown, but further down there is no enamel on the concave face of the tooth.[18]

Incisor

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The left i1 GSI/SR/PAL-N210 is flat on the medial side (towards the middle of the head) but convex on the lateral side (towards the side of the head) and bears a shallow groove on the lateral side. At the base, the tooth is broadest on the lower end. The tooth is slightly curved upward towards the tip. Measured on the lower side, the tooth is 11.76 mm long, but breakage means the true length is probably larger. The depth of the tooth is about 3.39 mm. Wilson and colleagues identified this incisor asDakshinaon the basis of its size;[22]the upper and lower incisor that they assigned to an indeterminate gondwanathere are smaller.[23]

Enamel microstructure

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The microstructure of the enamel of VPL/JU/NKIM/25 has been studied. Unlike other gondwanatheres, it has enamel consisting of three layers—radial enamel, tangential enamel, and PLEX.[24]The rows of small, roundenamel prismsare separated byinterprismatic matrix[3]that forms crystals oriented at right angles relative to the prisms. Prisms arise at the enamel-dentine junction, run through the enamel, and meet the outer enamel at a high angle. These features of the enamel are apparently adaptations that protect the tooth from cracks.[25]

Relationships

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Relationships among gondwanatheres[26]

Bharattheriumis identifiable as a sudamericid because it has hypsodont molariforms with cementum-filled furrows.[27]Among the four known sudamericid genera—GondwanatheriumandSudamericafrom Argentina;Lavanifyfrom Madagascar; andBharattherium—it shares withSudamericaandLavanifythe presence of furrows that extend down to the base of the tooth.[28]In addition, it shares several features withLavanify,suggesting the two are closely related.[29]Wilson and colleagues list three features shared by the two: the presence of an infundibulum (seen in only one of two specimens ofLavanify), interprismatic matrix, and perikymata.[24]Prasad and colleagues also interpreted the interprismatic matrix as a shared character, but added the absence of enamel on one side of the tooth crown.[30]Wilson and colleagues identified the presence of a V-shaped enamel lake on mf4 and of three layers in the enamel asautapomorphies(uniquely derived characters) of the Indian sudamericid.[24]

Range and ecology

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Remains ofBharattheriumhave been found at three widely separated Late Cretaceous sites in peninsular India—Naskal,Andhra Pradesh;Gokak,Karnataka;and Kisalpuri,Madhya Pradesh.[31]All sites are in theIntertrappean Beds(part of theDeccan Traps) and areMaastrichtian(latestCretaceous) in age.[32]The Intertrappean Beds have yielded a variety of fossil animals, includingeutherianmammals such asDeccanolestes,Sahnitherium,andKharmerungulatum.In the perhaps slightly olderInfratrappean Beds,a possible member of the ancient and Enigma tic mammalian groupHaramiyidahas been found,Avashishta.[33]Members of the family Sudamericidae, in whichBharattheriumis classified, are also known from the Cretaceous of Argentina, Madagascar, and possibly Tanzania and from thePaleogeneof Argentina and Antarctica, and the second gondwanathere family,Ferugliotheriidae,is known with certainty only from the Cretaceous of Argentina. Thus,Bharattheriumis an example of aGondwananfaunal element in India and indicatesbiogeographicaffinities with other Gondwanan landmasses such as Madagascar and South America.[34]

In modern mammals, hypsodont teeth are often associated with diets that include abrasive vegetation such asgrasses.Hypsodonty in sudamericids has been interpreted as indicating semiaquatic, terrestrial habits and a diet with items like roots or bark, because it was thought that grasses had not yet appeared when sudamericids lived. However, grass remains have been found at Intertrappean sites contemporary with those whereBharattheriumwas found, suggesting that sudamericids likeBharattheriumwere indeed the first grazing mammals.[35]

It is among the two Indian mammal taxa that are inferred to have survived theKT eventinIndia,alongsideDeccanolestes.[1]

Notes

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  1. ^This tooth is stored in the collection of mammals from theNaskalfossil site in the Vertebrate Palaeontology Laboratory at theUniversity of Jammu,numbered 25.[3]
  2. ^This tooth is stored in the collection of mammals from the Intertrappean Beds in the collections of Jammu University's Vertebrate Palaeontology Laboratory, numbered 33.[5]
  3. ^Like the others described by Wilson and colleagues, this tooth is stored in the collections of the Palaeontology Division of the Southern Region of theGeological Survey of India.[7]

References

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  1. ^abWilson, G. P.; Widdowson, M.; Anantharaman, S.; Das Sarma, D. C.; Wilson, J. A.; Renne, P. R. (October 27, 2016). "New mammalian fossils from the intertrappean beds of the southern part of the Deccan Volcanic Province and the Cretaceous-Paleogene transition in India".SVP 2016 Program Book.Vol. 6. Society of Vertebrate Paleontology. p. 252.
  2. ^abPrasad 2008,p. 91.
  3. ^abKrause et al. 1997,p. 505.
  4. ^Krause et al. 1997,p. 504.
  5. ^abcPrasad et al. 2007,p. 19.
  6. ^Wilson, Das Sarma & Anantharaman 2007,p. 521.
  7. ^abcdWilson, Das Sarma & Anantharaman 2007,p. 522.
  8. ^Wilson, Das Sarma & Anantharaman 2007,pp. 526–527.
  9. ^abcWilson, Das Sarma & Anantharaman 2007,pp. 522, 525.
  10. ^Wilson, Das Sarma & Anantharaman 2007,pp. 522, 524.
  11. ^Wilson, Das Sarma & Anantharaman 2007,pp. 522–524.
  12. ^Prasad et al. 2007,pp. 19–20.
  13. ^Wilson, Das Sarma & Anantharaman 2007,pp. 522, 524–525.
  14. ^Krause et al. 1997,pp. 505–506;von Koenigswald, Goin & Pascual 1999,pp. 290–293;Prasad et al. 2007,pp. 19–20;Wilson, Das Sarma & Anantharaman 2007,pp. 522, 525.
  15. ^Prasad et al. 2007,p. 17;Wilson, Das Sarma & Anantharaman 2007,p. 522.
  16. ^Wilson, Das Sarma & Anantharaman 2007,pp. 525–526.
  17. ^Prasad et al. 2007,p. 22.
  18. ^abcPrasad et al. 2007,p. 20.
  19. ^Wilson, Das Sarma & Anantharaman 2007,p. 526;Prasad et al. 2007,pp. 19, 21.
  20. ^abWilson, Das Sarma & Anantharaman 2007,p. 523.
  21. ^Wilson, Das Sarma & Anantharaman 2007,p. 524.
  22. ^abcdWilson, Das Sarma & Anantharaman 2007,p. 525.
  23. ^Wilson, Das Sarma & Anantharaman 2007,p. 527.
  24. ^abcWilson, Das Sarma & Anantharaman 2007,p. 526.
  25. ^Prasad et al. 2007,p. 24.
  26. ^Krause et al. 1997,fig. 3;Wilson, Das Sarma & Anantharaman 2007,p. 526;Prasad et al. 2007,p. 23.
  27. ^Wilson, Das Sarma & Anantharaman 2007,p. 526;Prasad et al. 2007,p. 20.
  28. ^Wilson, Das Sarma & Anantharaman 2007,p. 526;Prasad et al. 2007,p. 21.
  29. ^Wilson, Das Sarma & Anantharaman 2007,p. 526;Prasad et al. 2007,p. 23.
  30. ^Prasad et al. 2007,p. 21.
  31. ^Wilson, Das Sarma & Anantharaman 2007,pp. 521–522;Prasad et al. 2007,p. 19.
  32. ^Wilson, Das Sarma & Anantharaman 2007,p. 522;Prasad et al. 2007,p. 19.
  33. ^Prasad & Sahni 2009,pp. 370, 373.
  34. ^Wilson, Das Sarma & Anantharaman 2007,pp. 521, 528.
  35. ^Prasad et al. 2007,pp. 23–24;Prasad et al. 2005,pp. 1179–1180;Wilson, Das Sarma & Anantharaman 2007,p. 521.

Literature cited

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