Dermotherium
Encyclopedia
Dermotherium is a genus
of fossil
mammals closely related to the living colugo
s, a small group of gliding
mammals from Southeast Asia. Two species are recognized: D. major from the Late Eocene of Thailand
, based on a single fragment of the lower jaw, and D. chimaera from the Late Oligocene of Thailand, known from three fragments of the lower jaw and two isolated upper molars
. In addition, a single isolated upper molar from the Early Oligocene of Pakistan has been tentatively assigned to D. chimaera. All sites where fossils of Dermotherium have been found probably developed in forested environments and the fossil species probably were forest dwellers like living colugos, but whether they already had the gliding adaptations of the living species is unknown.
Some features of the teeth differentiate Dermotherium from both living colugo species, but other features are shared with only one of the two. The third lower incisor
, lower canine
, and third lower premolar
at least are pectinate or comblike, bearing longitudinal rows of tines or cusps
, an unusual feature of colugos (the first two lower incisors are unknown in Dermotherium). The fourth lower premolar instead resembles the lower molars. The front part of these teeth, the trigonid, is broader in D. chimaera than in D. major, which is known only from the second and third lower molars. The two species also differ in the configuration of the inner back corner of the lower molars. The upper molars are triangular teeth bearing a number of distinct small cusps, particularly on the second upper molar, and with wrinkled enamel
.
s are a small group of Southeast Asian gliding
mammals closely related to the primate
s. Their fossil record is exceptionally poor. Although Paleogene
groups such as the Plagiomenidae are considered by some to be closely related to colugos, no fossils undoubtedly referable to the living colugo family
, Cynocephalidae, had been reported until 1992. In that year, Stéphane Ducrocq and colleagues described a jaw fragment from the Eocene
of Thailand as a new genus
and species
of colugo, Dermotherium major. In 2000, however, Brian Stafford and Frederick Szalay argued that Dermotherium might not be a colugo, since the fossil is so poorly preserved that few traits can be unambiguously recognized and some purported dermopteran features of the fossil are in fact also seen in other placental groups. Mary Silcox and colleagues reaffirmed the colugo affinities of Dermotherium in 2005 on the basis of detailed similarities in molar
morphology.
In 2006, Laurent Marivaux and colleagues described a second species of Dermotherium, D. chimaera, from material from the Oligocene
of Thailand. They gave it the specific name chimaera (Latin for "chimera") because it shares characters with both the Philippine colugo (Cynocephalus volans) and Sunda colugo (Galeopterus variegatus), the two living colugo species. In addition, they tentatively identified a fossil from the Oligocene of Pakistan as Dermotherium chimaera and regarded some fossils from the Eocene of Myanmar as indeterminate dermopterans. According to a phylogenetic analysis carried out by Marivaux and colleagues, D. chimaera, D. major, and the Myanmar dermopteran are successive sister groups of the two living colugos.
of Dermotherium chimaera is a lower jaw fragment in which remnants of the deciduous third lower premolar
are visible. X-ray microtomography reveals the unerupted
lower third incisor
(i3), canine (c1), third premolar (p3), and fourth premolar (p4) still inside the jaw. In addition, this species is known from two other jaw fragments, one bearing m1 and m2 and the other bearing m2 and m3, and two isolated molars, an upper first and second molar (M1 and M2). The tentatively referred material of this species from Pakistan includes a single M2.
The two species of Dermotherium were about as large as the Philippine colugo and larger than the Sunda colugo and differed from both in a number of characteristics of the dentition. Not enough is known of the skeleton of Dermotherium to assess whether the animal already possessed the gliding adaptations of living colugos. The two species are similar in size, but again differ in details of the dentition. In two specimens of D. chimaera, the length and width of the m2 are 5 and 4.3 mm and 5.4 and 4.8 mm respectively; this tooth is 5.4 mm long and 4.9 mm wide in the only known specimen of Dermotherium major. The Pakistani M2 of Dermotherium is 4.3 mm long and 6 mm wide, compared to 4.7 and 6.6 mm in the only known M2 of D. chimaera from Thailand.
The lower jaw of Dermotherium major resembles that of living colugos in the presence of a strong angular process (a projecting piece of bone at the lower side of the back of the jawbone) and a retromolar space
(a flat space behind the last molars). The coronoid process
(a projecting piece of bone directly behind the molars) rises steeply, with its front wall virtually vertical.
, of which the third (counting from the front) is the largest. The p3 is similarly elongate and rounded at the front, but it is broader at the back, forming a talonid (a "heel" of cusps at the back of a tribosphenic tooth). There are six cusps on the narrow anterior part of the tooth, and the fifth (identified as the protoconid) is by far the largest. On the buccal side of the talonid is a strong cusp, the hypoconid, with a crest, the cristid obliqua, descending from it towards the front. A second, smaller cusp, the hypoconulid, is present on the lingual side of the talonid, connected to the hypoconid by a postcristid. The pectinate (comb-like) shape of the anterior teeth is a shared characteristic of the colugos and highly unusual among mammals. Dermotherium chimaera resembles the Sunda colugo in that the c1 and p3 are also pectinate; in the Philippine colugo, these teeth are not pectinate.
In Dermotherium chimaera, the p4 and m1 through m3 are similar to each other (and unlike the i3, canine, and p3) and appear to form a series of decreasing size from front to back. In D. major, only m2 and m3 are known, but they are similar in morphology and m3 is smaller than m2. In the Sunda colugo, however, the teeth get larger from p4 to m3. The p4 and molars have a distinct trigonid (a triangular group of cusps at the front of a tribosphenic tooth) and talonid. The trigonid contains strong protoconid and metaconid cusps. The metaconid is stronger than the protoconid in the molars, but it is not clear whether this is the case in the p4. In the living colugos, the protoconid is higher than the metaconid in both p4 and m1. The trigonid is longer in the p4 than in the molars. In D. chimaera, the trigonid is broader than in D. major. A low crest, the paracristid, descends from the protoconid lingually and towards the front, forming the front margin of the trigonid; there is no distinct cusp (a paraconid) at the front of the trigonid on the p4, but this cusp is present in the molars.
The talonid contains a hypoconid, hypoconulid, and entoconid and is much wider than the trigonid because the hypoconid is displaced buccally. A cristid obliqua descends from the hypoconid and reaches the protoconid. Although a crest, the postmetacristid, descends from the back side of the metaconid, ending in a small cusp, the metastylid, it is separated from the entoconid by a notch. The living colugos lack such a strong postmetacristid. The hypoconulid is near the back lingual margin of the tooth, behind the entoconid. In D. major, this cusp is further to the back than in both D. chimaera and the Sunda colugo, while the two cusps are merged in the Philippine colugo. In D. chimaera, a low crest, the post-hypoconulid cristid, reaches from the hypoconulid to the back lingual corner of the tooth, where a small cuspule, the distocuspid, is located. A long crest, the postcristid, connects the distocuspid to the hypoconid along the posterior side of the tooth. The Philippine colugo is similar, but in D. major, both the distocuspid and the post-hypoconulid cristid are absent, and the Sunda colugo has a weaker distocuspid and a postcristid that does not reach further lingually than the hypoconulid.
and metacone
, are well-developed, together forming a long W-shaped ridge. D. chimaera resembles the Philippine colugo in that the crests behind the paracone and in front of the metacone form an acute angle with each other, so that together they form a V; their shape rather resembles an U in the Sunda colugo. A cingulum
(shelf) is present on the buccal margin of the tooth, but this cingulum is rather weak in the Pakistani fossil. On the M2, smaller cusps, the paraconule and metaconule, are present on the lingual sides of the paracone and metacone, but on the M1 the paraconule is missing and the metaconule is small and ridgelike. The small cusps are better developed in the Pakistani M2. A third major cusp, the protocone
, is present on the lingual side of both upper molars. This crest is displaced towards the front in the living colugos, but less so in D. chimaera. Two strong crests descend from the front and back faces of the protocone in a buccal direction. These crests end in small cusps (protoconules) that are directly lingual to the paracone and metacone. The living colugos lack these protoconules. The enamel
is wrinkled on the flanks of the paracone and metacone and, in the Thai but not the Pakistani specimens, on the lingual side of the protocone. Enamel wrinkling is also seen in some Philippine colugos.
pit known as Wai Lek in Krabi Province
, southwestern Thailand. It is part of the Krabi Basin fauna, which contains at least 40 mammalian genera, mostly artiodactyls but also including some primates, such as Siamopithecus, Wailekia, and Muangthanhinius. This fauna has been dated to about 33 to 35 million years ago, during the Late Eocene.
Fossils of Dermotherium chimaera come from Phetchaburi Province
, further to the north in Thailand. The fossil deposits, located in the Cha Prong pit in a coal mine called Nong Ya Plong, are dated to the Late Oligocene. Other mammals found here include the rodent Fallomus ladakhensis, the rhinoceros Diceratherium sp. cf. D. lamilloquense
, the carnivora
n Chaprongictis phetchaburiensis, the lipotyphlan Siamosorex debonisi, and a pteropodid bat.
Paali Nala, where the M2 tentatively assigned to Dermotherium chimaera was found, is in the Bugti Hills
of Balochistan
, western Pakistan. The fossil locality, placed stratigraphically
in the Bugti Member of the Chitarwata Formation
, is thought to be Early Oligocene in age. The Paali Nala fauna also contains a diverse array of mammals, including many rodents, some primates, and rhinos.
The specializations of dermopterans are such that they are dependent on a forested habitat, and reconstructions of the paleoenvironments at Krabi, Nong Ya Plong, and Paali Nala suggest that all three fossil deposits developed in a humid, tropical forest environment. Their extinction in the Indian subcontinent may have been caused by the development of a drier climate there during the Late Oligocene.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
mammals closely related to the living colugo
Colugo
Colugos are arboreal gliding mammals found in South-east Asia. There are just two extant species, which make up the entire family Cynocephalidae and order Dermoptera. They are the most capable of all gliding mammals, using flaps of extra skin between their legs to glide from higher to lower...
s, a small group of gliding
Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
mammals from Southeast Asia. Two species are recognized: D. major from the Late Eocene of Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, based on a single fragment of the lower jaw, and D. chimaera from the Late Oligocene of Thailand, known from three fragments of the lower jaw and two isolated upper molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
. In addition, a single isolated upper molar from the Early Oligocene of Pakistan has been tentatively assigned to D. chimaera. All sites where fossils of Dermotherium have been found probably developed in forested environments and the fossil species probably were forest dwellers like living colugos, but whether they already had the gliding adaptations of the living species is unknown.
Some features of the teeth differentiate Dermotherium from both living colugo species, but other features are shared with only one of the two. The third lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
, lower canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
, and third lower premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
at least are pectinate or comblike, bearing longitudinal rows of tines or cusps
Cusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
, an unusual feature of colugos (the first two lower incisors are unknown in Dermotherium). The fourth lower premolar instead resembles the lower molars. The front part of these teeth, the trigonid, is broader in D. chimaera than in D. major, which is known only from the second and third lower molars. The two species also differ in the configuration of the inner back corner of the lower molars. The upper molars are triangular teeth bearing a number of distinct small cusps, particularly on the second upper molar, and with wrinkled enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
.
Taxonomy
ColugoColugo
Colugos are arboreal gliding mammals found in South-east Asia. There are just two extant species, which make up the entire family Cynocephalidae and order Dermoptera. They are the most capable of all gliding mammals, using flaps of extra skin between their legs to glide from higher to lower...
s are a small group of Southeast Asian gliding
Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
mammals closely related to the primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
s. Their fossil record is exceptionally poor. Although Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
groups such as the Plagiomenidae are considered by some to be closely related to colugos, no fossils undoubtedly referable to the living colugo family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, Cynocephalidae, had been reported until 1992. In that year, Stéphane Ducrocq and colleagues described a jaw fragment from the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
of Thailand as a new genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
and species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of colugo, Dermotherium major. In 2000, however, Brian Stafford and Frederick Szalay argued that Dermotherium might not be a colugo, since the fossil is so poorly preserved that few traits can be unambiguously recognized and some purported dermopteran features of the fossil are in fact also seen in other placental groups. Mary Silcox and colleagues reaffirmed the colugo affinities of Dermotherium in 2005 on the basis of detailed similarities in molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
morphology.
In 2006, Laurent Marivaux and colleagues described a second species of Dermotherium, D. chimaera, from material from the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
of Thailand. They gave it the specific name chimaera (Latin for "chimera") because it shares characters with both the Philippine colugo (Cynocephalus volans) and Sunda colugo (Galeopterus variegatus), the two living colugo species. In addition, they tentatively identified a fossil from the Oligocene of Pakistan as Dermotherium chimaera and regarded some fossils from the Eocene of Myanmar as indeterminate dermopterans. According to a phylogenetic analysis carried out by Marivaux and colleagues, D. chimaera, D. major, and the Myanmar dermopteran are successive sister groups of the two living colugos.
Description
Known material of Dermotherium includes a handful of jaw fragments and isolated teeth. Dermotherium major is known only from a fragment of the left lower jaw bearing the third lower molar (m3) and a poorly preserved second lower molar (m2). The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Dermotherium chimaera is a lower jaw fragment in which remnants of the deciduous third lower premolar
Premolar
The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
are visible. X-ray microtomography reveals the unerupted
Tooth eruption
Tooth eruption is a process in tooth development in which the teeth enter the mouth and become visible. It is currently believed that the periodontal ligaments play an important role in tooth eruption...
lower third incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
(i3), canine (c1), third premolar (p3), and fourth premolar (p4) still inside the jaw. In addition, this species is known from two other jaw fragments, one bearing m1 and m2 and the other bearing m2 and m3, and two isolated molars, an upper first and second molar (M1 and M2). The tentatively referred material of this species from Pakistan includes a single M2.
The two species of Dermotherium were about as large as the Philippine colugo and larger than the Sunda colugo and differed from both in a number of characteristics of the dentition. Not enough is known of the skeleton of Dermotherium to assess whether the animal already possessed the gliding adaptations of living colugos. The two species are similar in size, but again differ in details of the dentition. In two specimens of D. chimaera, the length and width of the m2 are 5 and 4.3 mm and 5.4 and 4.8 mm respectively; this tooth is 5.4 mm long and 4.9 mm wide in the only known specimen of Dermotherium major. The Pakistani M2 of Dermotherium is 4.3 mm long and 6 mm wide, compared to 4.7 and 6.6 mm in the only known M2 of D. chimaera from Thailand.
The lower jaw of Dermotherium major resembles that of living colugos in the presence of a strong angular process (a projecting piece of bone at the lower side of the back of the jawbone) and a retromolar space
Retromolar space
The retromolar space or retromolar gap is a space at the rear of a mandible, between the back of the last molar and the anterior edge of the ascending ramus where it crosses the alveolar margin....
(a flat space behind the last molars). The coronoid process
Coronoid process of the mandible
The mandible's coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size....
(a projecting piece of bone directly behind the molars) rises steeply, with its front wall virtually vertical.
Lower dentition
The i3 of Dermotherium chimaera is an elongate tooth bearing six tines (narrow, high "fingers" as in a comb) arranged from front to back. The frontmost is larger, the next four are about equal in size, and the sixth is smaller. The number of tines resembles that seen in the Sunda colugo, which has four to seven; the Philippine colugo has three to five. The c1 is also an elongate, narrow tooth; at the front, it is slightly curved towards the midline of the jaw. On the buccal (outer) side of this tooth are six cuspsCusp (dentistry)
A cusp is an occlusal or incisal eminence on a tooth.Canine teeth, otherwise known as cuspids, each possess a single cusp, while premolars, otherwise known as bicuspids, possess two each. Molars normally possess either four or five cusps...
, of which the third (counting from the front) is the largest. The p3 is similarly elongate and rounded at the front, but it is broader at the back, forming a talonid (a "heel" of cusps at the back of a tribosphenic tooth). There are six cusps on the narrow anterior part of the tooth, and the fifth (identified as the protoconid) is by far the largest. On the buccal side of the talonid is a strong cusp, the hypoconid, with a crest, the cristid obliqua, descending from it towards the front. A second, smaller cusp, the hypoconulid, is present on the lingual side of the talonid, connected to the hypoconid by a postcristid. The pectinate (comb-like) shape of the anterior teeth is a shared characteristic of the colugos and highly unusual among mammals. Dermotherium chimaera resembles the Sunda colugo in that the c1 and p3 are also pectinate; in the Philippine colugo, these teeth are not pectinate.
In Dermotherium chimaera, the p4 and m1 through m3 are similar to each other (and unlike the i3, canine, and p3) and appear to form a series of decreasing size from front to back. In D. major, only m2 and m3 are known, but they are similar in morphology and m3 is smaller than m2. In the Sunda colugo, however, the teeth get larger from p4 to m3. The p4 and molars have a distinct trigonid (a triangular group of cusps at the front of a tribosphenic tooth) and talonid. The trigonid contains strong protoconid and metaconid cusps. The metaconid is stronger than the protoconid in the molars, but it is not clear whether this is the case in the p4. In the living colugos, the protoconid is higher than the metaconid in both p4 and m1. The trigonid is longer in the p4 than in the molars. In D. chimaera, the trigonid is broader than in D. major. A low crest, the paracristid, descends from the protoconid lingually and towards the front, forming the front margin of the trigonid; there is no distinct cusp (a paraconid) at the front of the trigonid on the p4, but this cusp is present in the molars.
The talonid contains a hypoconid, hypoconulid, and entoconid and is much wider than the trigonid because the hypoconid is displaced buccally. A cristid obliqua descends from the hypoconid and reaches the protoconid. Although a crest, the postmetacristid, descends from the back side of the metaconid, ending in a small cusp, the metastylid, it is separated from the entoconid by a notch. The living colugos lack such a strong postmetacristid. The hypoconulid is near the back lingual margin of the tooth, behind the entoconid. In D. major, this cusp is further to the back than in both D. chimaera and the Sunda colugo, while the two cusps are merged in the Philippine colugo. In D. chimaera, a low crest, the post-hypoconulid cristid, reaches from the hypoconulid to the back lingual corner of the tooth, where a small cuspule, the distocuspid, is located. A long crest, the postcristid, connects the distocuspid to the hypoconid along the posterior side of the tooth. The Philippine colugo is similar, but in D. major, both the distocuspid and the post-hypoconulid cristid are absent, and the Sunda colugo has a weaker distocuspid and a postcristid that does not reach further lingually than the hypoconulid.
Upper dentition
The upper molars of Dermotherium chimaera are triangular in overall shape and much broader than long, with the narrow end of the triangle pointing lingually. The M2 from Pakistan that was tentatively placed in D. chimaera is slightly smaller than Thai fossils of the species, but otherwise very similar. The crest in front of and behind the major cusps on the buccal side of the tooth, the paraconeParacone
An atmospheric reentry or spaceflight mission abort concept using an inflatable cone.A notable feature of the paracone concept is that it facilitates an abort throughout the entire flight profile....
and metacone
Metacone
thumb|500px|left|Right upper molar showing the four main upper molars cusps.The metacone is a cusp on the molars of the upper dentition in hominids. It is found at the buccal distal area of the tooth...
, are well-developed, together forming a long W-shaped ridge. D. chimaera resembles the Philippine colugo in that the crests behind the paracone and in front of the metacone form an acute angle with each other, so that together they form a V; their shape rather resembles an U in the Sunda colugo. A cingulum
Cingulum (tooth)
In dentistry, cingulum refers to an anatomical feature of the anterior teeth . It refers to the portion of the teeth, occurring on the lingual or palatal aspects, that forms a convex protuberance at the cervical third of the anatomic crown. It represents the lingual or palatal developmental lobe...
(shelf) is present on the buccal margin of the tooth, but this cingulum is rather weak in the Pakistani fossil. On the M2, smaller cusps, the paraconule and metaconule, are present on the lingual sides of the paracone and metacone, but on the M1 the paraconule is missing and the metaconule is small and ridgelike. The small cusps are better developed in the Pakistani M2. A third major cusp, the protocone
Protocone
thumb|500px|right|Right upper molar showing the four main upper molars cusps.The protocone is a cusp of the molars of the upper dentition in Placental and Marsupial vertebrates .It is found at the mesiolingual area of the tooth...
, is present on the lingual side of both upper molars. This crest is displaced towards the front in the living colugos, but less so in D. chimaera. Two strong crests descend from the front and back faces of the protocone in a buccal direction. These crests end in small cusps (protoconules) that are directly lingual to the paracone and metacone. The living colugos lack these protoconules. The enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
is wrinkled on the flanks of the paracone and metacone and, in the Thai but not the Pakistani specimens, on the lingual side of the protocone. Enamel wrinkling is also seen in some Philippine colugos.
Range and ecology
Dermotherium major was found in a ligniteLignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...
pit known as Wai Lek in Krabi Province
Krabi Province
Krabi is one of the southern provinces of Thailand, at the shore of the Andaman Sea. Neighbouring provinces are Phang Nga, Surat Thani, Nakhon Si Thammarat and Trang. The Phuket province to the west is also neighbouring, but without any land boundary...
, southwestern Thailand. It is part of the Krabi Basin fauna, which contains at least 40 mammalian genera, mostly artiodactyls but also including some primates, such as Siamopithecus, Wailekia, and Muangthanhinius. This fauna has been dated to about 33 to 35 million years ago, during the Late Eocene.
Fossils of Dermotherium chimaera come from Phetchaburi Province
Phetchaburi Province
Phetchaburi is one of the central provinces of Thailand. Neighboring provinces are Ratchaburi, Samut Songkhram and Prachuap Khiri Khan...
, further to the north in Thailand. The fossil deposits, located in the Cha Prong pit in a coal mine called Nong Ya Plong, are dated to the Late Oligocene. Other mammals found here include the rodent Fallomus ladakhensis, the rhinoceros Diceratherium sp. cf. D. lamilloquense
Diceratherium
Diceratherium is an extinct genus of rhinoceros endemic to North America, Europe, and Asia during the Oligocene through Miocene living from 33.9—11.6 mya, existing for approximately .-Taxonomy:...
, the carnivora
Carnivora
The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...
n Chaprongictis phetchaburiensis, the lipotyphlan Siamosorex debonisi, and a pteropodid bat.
Paali Nala, where the M2 tentatively assigned to Dermotherium chimaera was found, is in the Bugti Hills
Bugti Hills
Bugti Hills are a range of hills in eastern Balochistan, Pakistan. It includes the tribal tract called Bugti country.30 million years ago the Haplorrhinies: Bugtipithecus inexpectans, Phileosimias kamali and Phileosimias brahuiorum, similar to today's lemurs, lived in rainforests on the Bugti...
of Balochistan
Balochistan
Balochistan or Baluchistan is a region which covers parts of Afghanistan, Iran and Pakistan. It can also refer to one of several modern and historical territories within that region:...
, western Pakistan. The fossil locality, placed stratigraphically
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
in the Bugti Member of the Chitarwata Formation
Chitarwata Formation
The Chitarwata Formation is a geological formation in western Pakistan, made up of Oligocene and early Miocene terrestrial facies. It is dominated by coastal paleoenvironments ....
, is thought to be Early Oligocene in age. The Paali Nala fauna also contains a diverse array of mammals, including many rodents, some primates, and rhinos.
The specializations of dermopterans are such that they are dependent on a forested habitat, and reconstructions of the paleoenvironments at Krabi, Nong Ya Plong, and Paali Nala suggest that all three fossil deposits developed in a humid, tropical forest environment. Their extinction in the Indian subcontinent may have been caused by the development of a drier climate there during the Late Oligocene.