Pyrotherium
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''Pyrotherium'' ('fire beast') is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
n
ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, cam ...
, of the order
Pyrotheria Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera ''Baguatherium'', ''Carolozittelia'', ''Colombitherium'', ''Griphodon'', ''Propyrotherium'', ''Proticia'', and ''Pyrotherium''. They had ...
, that lived in what is now
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
and
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
, during the
Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...
.''Pyrotherium''
at
Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...
.org
It was named ''Pyrotherium'' because the first specimens were excavated from an ancient volcanic ash deposit. Fossils of the genus have been found in the
Deseado Deseado may refer to: Geographic names and features * Deseado (crater), a crater on the planet Mars * Deseado Department, a department in Santa Cruz Province, Argentina * Deseado Massif, a geological formation in Santa Cruz Province, Argentina * De ...
and
Sarmiento Formation The Sarmiento Formation (Spanish: ''Formación Sarmiento''), in older literature described as the Casamayor Formation, is a geological formation in Chubut Province, Argentina, in central Patagonia, which spans around 30 million years from the mid- ...
s of Argentina and the Salla Formation of Bolivia. So far, two valid species have been described, ''Pyrotherium romeroi'', which lived in what it is today
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
and ''P. macfaddeni'' from
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
, at the end of
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
. ''P. romeroi'' in particular is the most recent known pyrothere in the fossil record and best known for its fossil remains, which although incomplete are the best preserved in the entire order, indicating that they are also the largest, with an estimated body length from . It is also supposed to have developed a small
trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...
, but it is not related to the current elephants (
proboscideans The Proboscidea (; , ) are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. From ...
); the resemblance is so great that when studying the fossil remains, it was attributed in the past a relationship with elephants, although the true relationship of this herbivore is still controversial today.


Discovery and naming

The original remains of ''Pyrotherium'', some molars, a premolar and an incisor, were originally identified in the
Neuquén province Neuquén () is a province of Argentina, located in the west of the country, at the northern end of Patagonia. It borders Mendoza Province to the north, Rio Negro Province to the southeast, and Chile to the west. It also meets La Pampa Province a ...
in strata dating back to the late
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
epoch, identified by the Argentine naturalist
Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...
as ''couche à Pyrotherium'' (layers of ''Pyrotherium'', in French) due to the presence of fossils of this animal that were the first to be identified there; these strata are now known as part of the
Deseadan The Deseadan ( es, Deseadense) age is a period of geologic time (29.0–21.0 Ma) within the Oligocene epoch of the Paleogene to the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification of South America. It fo ...
mammal-age (
SALMA The South American land mammal ages (SALMA) establish a geologic timescale for prehistoric South American fauna beginning 64.5 Ma during the Paleocene and continuing through to the Late Pleistocene (0.011 Ma). These periods are referred to as a ...
) in the area of the Deseado estuary, although there is the doubt whether the holotype of ''Pyrotherium romeroi'' really comes from Neuquén, it being possible that the remains actually came from Chubut. Ameghino considered that these areas corresponded to older terrains, from the
Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
and even from the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, because they were sent together with dinosaur remains; subsequent studies have shown that they actually come from the Oligocene, and in fact the ''Pyrotherium'' fossils have reached become the
guide fossil Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...
of the late Oligocene. Because the remains of this animal originally appeared in the volcanic ash beds of the Deseado Formation, they gave rise to the name of the genus, which means "fire beast". The name of the species ''P. romeroi'' is due to the captain of the Argentine army Antonio Romero who sent Ameghino the first known remains of the animal, although in several texts the erroneous spellings ''P. romeri'' or ''P. romerii'' has been used.Ameghino, F. 1889. Contribución al conocimiento de los mamíferos fósiles de la República Argentina, obra escrita bajo los auspicios de la Academia Nacional de Ciencias de la República Argentina para presentarla a la Exposición Universal de París de 1889. ''Actas Academia de Ciencias de Córdoba'' 6:1–1027. Ameghino named several species from the Deseado area such as ''P. sorondoi'' based on partial remains, mainly teeth, but later studies indicated that they are part of a single species. The first relatively complete skull did not appear until the 20th century, being discovered by Frederic B. Loomis during the
Amherst College Amherst College ( ) is a private liberal arts college in Amherst, Massachusetts. Founded in 1821 as an attempt to relocate Williams College by its then-president Zephaniah Swift Moore, Amherst is the third oldest institution of higher educatio ...
expedition in 1911-1912, and listed as specimen ACM 3207. Additional remains of the genus have appeared in
Quebrada Fiera The Agua de la Piedra Formation (FAP, Spanish names include ''Estratos de Agua de la Piedra'' and ''Complejo Volcano-sedimentario del Terciario inferior'')Combina et al., 1994, p.418 is a Late Oligocene (Deseadan in the SALMA classification) geol ...
, from the
Mendoza province Mendoza, officially Province of Mendoza, is a province of Argentina, in the western central part of the country in the Cuyo region. It borders San Juan to the north, La Pampa and Neuquén to the south, San Luis to the east, and the republic o ...
(Argentina) and in Salla, in the department of La Paz in Bolivia; the latter consist of the remains of a partial jaw, fragments of skull bones, teeth, and some limb bone such as pieces of the humerus and astragalus, which were found between the 1960s and 1980s and were initially considered part of the species ''P. romeroi'', and later they were classified as a different and smaller species, ''P. macfaddeni'', whose species name is in honor of paleontologist Bruce J. MacFadden. Molar and postcranial bone remains found in sediments from the late Oligocene of
Taubaté Taubaté is a medium-sized city in the State of São Paulo, in southeastern Brazil. Location Its strategic location between the two most important Brazilian cities (São Paulo away, and Rio de Janeiro away), connected to both by the Presiden ...
, Brazil were considered as a possible finding of ''Pyrotherium'', but it is possible that they correspond to some different genus with which it is closely related, but not yet described.


Description


Skull

The skull of ''Pyrotherium romeroi'' was long and narrow, made up of massive bones. It reaches in length from its front teeth to its occipital condyle, and has an elongated, relatively narrow snout seen from above, with retracted nostrils, a large nasal opening located between the eye sockets in the middle of the front bone, in parallel to the back of the skull, with thick bone walls for muscle support; inside there are cavities filled with air. The occipital region, in particular the condyles, was particularly high, as a consequence of the flexion of the posterior part of the skull with respect to the plane of the base, which formed an obtuse angle with that of the palatine bone; in this and other characteristics, ''Pyrotherium'' resembled proboscideans. There is a small ridge that emerges from the premaxilla and reaches the nasal bone, which appears to be broken and surrounded by a rough texture, which could be the result of erosion. How large it may have been is unknown, as it may have been only a prominence similar to that seen in the narial process of the notoungulates and rodents, or even almost a ridge; this ridge is not known in other mammals, but perhaps it served as a holding point for the muscles of a possible
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
or trunk. The brain cavity (
neurocranium In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria (skull), ...
) is damaged and surrounded by
spongy bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
tissue; Loomis considered that it indicated that in life ''P. romeroi'' had a small brain, about long and wide. Another very distinctive feature is the presence of two pairs of large front-facing incisors, in the form of tusks and arranged at a 45° angle. These showed continuous growth and were equipped with an enamel band only on the front. It lacked canines, and it also has peculiar premolars and molars, with two transverse high ridges (bilophodonts), whose general appearance is reminiscent of
tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a pig, with a short, prehensile nose trunk. Tapirs inhabit jungle and forest regions of South and Central America, with one species inhabit ...
molars. Between the incisors and the posterior teeth there was a space without teeth, the
diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...
, reaching long. The teeth in general, and particularly the posterior ones, also occupied a lot of the skull area, particularly in the palate. The auditory region is situated much higher than the palate in lateral view and curves upwards in its posterior part. In ''P. macfaddeni'' the premaxilla has an additional pair of very small alveoli, suggesting that it may have had a third pair of barely developed incisors, and their molars are distinguished by having a well-defined valley that separates the anterior and posterior lophs. The dental formula in ''P. romeroi'' is (2I/0C/3PM/3M, 1i/0c/2pm/3m) The mandible was robust and had a well-developed, long and narrow
symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together ...
extending to the second molar, a marked foramen posterior to the third molar, and a large maseteric fossa. It only has only two incisors, which protrude forward and are oriented like the upper incisors at a 45° angle, making contact with the tips of these; it has been thought that these could be the second incisors (i2), but their actual identification is uncertain. At least in ''P. macfaddeni'' have a layer of enamel that only covers the ventral part of the incisors. As in the
maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
, it has bilophodont premolars and molars; the structure of the molars is reminiscent of that found in other large archaic mammals, such as dinocerates, ''
Barytherium ''Barytherium'' (meaning "heavy beast") is a genus of an extinct family (Barytheriidae) of primitive proboscideans that lived during the late Eocene and early Oligocene in North Africa. The type species is ''Barytherium grave'', found at the begi ...
'' and deinotheriids.


Postcranium

Some postcranial bones of ''Pyrotherium romeroi'' have been recovered, mainly from the limbs. The vertebral column is very poorly known; the remains found mainly include cervical vertebrae, including the
atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
, the
axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...
and the third and fourth vertebrae, all of which are very short. Additionally, a lumbar vertebra is known, which is massive and with a reduced spine, somewhat similar to that of ''
Astrapotherium ''Astrapotherium'' ("lightning beast") is an extinct genus of South American mammals that vaguely resembled a small elephant or large tapir. However, it was unrelated to elephants or tapirs, but was instead related to other extinct South American ...
''. A fragment of the shoulder blade indicates that it was short and strong; the glenoid cavity was twice its length and the acromion was very high. The humerus is relatively short, 497 to 500 millimeters in length, but extremely wide, with great insertions for the muscles; the ulna and radius are also known, both even shorter, about 225 millimeters, and the ulna also had a large olecranon. Likewise, two bones of the wrist have been identified, the right unciform and the left great, both being elements short but thick and trapezoidal in appearance.Cerdeño, E., & Vera, B. (2017). New Anatomical Data on ''Pyrotherium'' (Pyrotheriidae) from the Late Oligocene of Mendoza, Argentina. ''Ameghiniana'', 54(3), 290-306. A pyramidal and semilunate have also been found. Also included is an astragalus and calcaneus, and a
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
. The
pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...
was equipped with a massive iliac bone, with an acetabulum located downwards and not laterally. The femur lacked the third trochanter, with a straight head much higher than the greater trochanter, and was flattened anteroposteriorly; in this species it reached 630 millimeters in length, being greater than the only other femur known between the pyrotheres, the one of ''
Baguatherium ''Baguatherium'' is an extinct genus of herbivorous mammal, belonging to the order Pyrotheria. It lived during the Early Oligocene, and its fossilized remains were discovered in Peru. Description Although the fossils known are very partial ...
'', which reached 558 millimeters.Salas, R., Sánchez, J. and Chacaltana, C. 2006. A new pre-Deseadan pyrothere (Mammalia) from Northern Peru and the wear facets of molariform teeth of Pyrotheria. ''Journal of Vertebrate Paleontology'' 26: 760–769. The shape of the distal joint allowed the tibia to move backwards widely, which compensated for the lack of flexibility in the foot joint. The tibia was much shorter than the femur, and the fibula was very close to the tibia, except in the central part. The astragalus was strongly flattened, very simple in appearance, and neckless, with a slightly hinted tibial trochlea and a facet of the navicular located directly below the trochlea. The tarsus of ''Pyrotherium'' was characteristic: the calcaneus tubercle was compressed dorsoventrally, as was the trochlea of the astragalus; in addition, it presents an extreme reduction in the contact between the heel and the cuboid. These derived characteristics, which involve a type of graviportal and plantigrade locomotion, are not found in any other known mammal, with the significant exception of the African ''
Arsinoitherium ''Arsinoitherium'' is an extinct genus of paenungulate mammals belonging to the extinct Order (biology), order Embrithopoda. It is related to elephants, sirenians, hyraxes and the extinct desmostylians. Arsinoitheres were superficially rhinoceros ...
''.


Phylogeny

Because ''Pyrotherium'' has the characteristic bilophodont posterior teeth (that is, with two ridges), tusks formed by its upper and lower incisors, a huge and robust body along with the possible presence of a trunk, it was proposed in the past that it was a close relative of the proboscideans, or even a member of that group (Ameghino 1895, 1897; Lydekker 1896; Loomis 1914).Loomis, F.B. 1914. ''The Deseado Formation of Patagonia''. Amherst College, Amherst, 232659 p. Loomis 1921 However, the mixture of characteristics of the animal is such that it has led to comparing and relating it at different times with other groups, such as the marsupial diprotodontids (Lydekker 1893; Loomis 1921), the amblipodan
pantodonts Pantodonta is an extinct suborder (or, according to some, an order) of eutherian mammals. These herbivorous mammals were one of the first groups of large mammals to evolve (around 66 million years ago) after the end of the Cretaceous. The las ...
(Zittel 1893),
perissodactyls Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) o ...
(Ameghino, 1888), the notoungulates (Osborn 1910; Loomis 1914; Scott 1913; Patterson 1977),Patterson, B. 1977. A primitive pyrothere (Mammalia, Notoungulata) from the Early Tertiary of Northwestern Venezuela. ''Fieldiana, Geology'' 33: 397–422. the
xenungulates Xenungulata ("strange ungulates") is an order of extinct and primitive South American hoofed mammals that lived from the Late Paleocene to Early Eocene (Itaboraian to Casamayoran in the SALMA classification). Fossils of the order are known f ...
(Simpson 1945; Cifelli 1983; Lucas 1986, 1993), and the
dinocerata Dinocerata (from the Greek (), "terrible", and (), "horn") is an extinct order of plant-eating hoofed mammals with horns and protuberant canine teeth. Classification A 2015 phylogenetic study recovered Dinocerata as closely related to '' ...
ns via their supposed relationship with xenungulates (Lucas 1986, 1993);Spencer, L. (1986). Pyrothere sistematics and a caribbean route for land-mammal dispersal during the Paleocene. ''Revista Geológica de América Central''. in some studies, the complete study of the tarsus of ''Pyrotherium'' fails to support a relationship with xenungulatans, instead the derived characteristics of ''Pyrotherium'' were not observed other than in other mammals examined except for the embrithopod ''Arsinoitherium'' from the Paleogene of Africa. If this is due to a common ancestor, or to the unusual mode of locomotion used by these animals ( graviportal and
plantigrade 151px, Portion of a human skeleton, showing plantigrade habit In terrestrial animals, plantigrade locomotion means walking with the toes and metatarsals flat on the ground. It is one of three forms of locomotion adopted by terrestrial mammals. T ...
) remains a mystery to be seen. However, Gaudry (1909) himself established that ''Pyrotherium'' was sufficiently different from any other group of large mammals that it should have its own order, with no clear relation to other mammals. The most recent analysis published out, like the work of Billet in 2010, suggests that pyrotheres such as ''Pyrotherium'' are a group of specialized notoungulates, related to ''
Notostylops ''Notostylops'' ("south pillar face") is a genus of extinct South American ungulates from Eocene Argentina. Fossils of the genus have been found in the Sarmiento, Casamayor, Andesitas Huancache and Koluel Kaike Formations.
'',Billet, G. 2010. New observations on the skull of ''Pyrotherium'' (Pyrotheria, Mammalia) and new phylogenetic hypotheses on South American ungulates. ''Journal of Mammalian Evolution'' 17: 21–59. although this is still a controversial idea.
Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
based on the
phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
of Cerdeño ''et al''., 2017, highlighting the location of both species of ''Pyrotherium'':


Paleobiology

The ''Pyrotherium'''s bilophodont molariform teeth were examined to determine their
dental enamel Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, ...
type, using an electronic microscope to examine their prisms. Examinations showed that its enamel follows a strange keyhole pattern, also known as Boyde pattern, in which the prisms are densely clustered with no interprismatic matrix between them. This type of prism in the enamel is characteristic of pyrotheres and is not known in the other orders of native South American ungulates (xenungulates, astrapotheres, litopterns, and notoungulates). In ''P. romeroi'', the enamel also has a distinctive kind, just called "''Pyrotherium'''s enamel" in which the enamel bands are arranged vertically with the prisms in a decoupled way (that is, forming patterns in "X").Koenigswald, W 647 . von, Martin, T. and Billet, G. 2015. Enamel microstructure and mastication in ''Pyrotherium romeroi'' (Pyrotheria, Mammalia). ''Paläontologische Zeitschrift'' 89: 611–634. This analysis also made it possible to infer the chewing patterns of ''Pyrotherium''. This would be dominated by the so-called phase 1, in which the mandible is tilted and directed mesially, while the cutting ridges of the molars were compressing the food bolus. Then a phase 2 was developed, in which the jaw moved laterally; this move seems to have been less significant. This type of chewing and molars resembles that observed in some other mammals, such as the ''
Macropus ''Macropus'' is a marsupial genus in the family Macropodidae. It has two extant species of large terrestrial kangaroos. The term is derived from the Ancient Greek μάκρος, ''makros'' "long" and πους, ''pous'' "foot". Thirteen known exti ...
'' kangaroos, the perissodactyl ''
Lophiodon ''Lophiodon'' (from el, λόφος , 'crest' and el, ὀδούς 'tooth') is an extinct genus of mammal related to chalicotheres. It lived in Eocene Europe Europe is a large peninsula conventionally considered a continent in its own r ...
'', the marsupial ''
Diprotodon ''Diprotodon'' (Ancient Greek: "two protruding front teeth") is an extinct genus of marsupial from the Pleistocene of Australia, containing one species, ''D. optatum''. The earliest finds date to 1.77 million to 780,000 years ago, but most speci ...
'' and the proboscidean ''
Deinotherium ''Deinotherium'' was a large elephant-like proboscidean that appeared in the Middle Miocene and survived until the Early Pleistocene. Although superficially resembling modern elephants, they had notably more flexible necks, limbs adapted to a mo ...
'', but in these animals their enamel (and molar lophs) wear out quickly into adulthood, leaving a flat surface for grinding, whereas in ''Pyrotherium'' the lophs are much more resistant and can be clearly seen even in elderly individuals, in whom the worn molars still have sharp ridges. A similar condition is only seen in embrithopods such as ''Arsinoitherium'', which also has vertically arranged enamel and in '' Namatherium'', which closely resembles ''Pyrotherium'' in this respect by having enamel and highly inclined enamel facets. Due to the robust structure of the animal, it was most likely a graviportal quadruped, that is, an animal weighing more than a ton whose physical structure is prepared to support that great mass, but not for speed.Johnson, S. C. (1984). ''Astrapotheres from the Miocene of Colombia, South America''. University of California, Berkeley. With a weight of in ''P. macfaddeni'' to in ''P. romeroi'' based on estimates of its molars, and in ''P. macfadeni'' at for ''P. romeroi'' with base in equations derived from the head-body ratios, ''Pyrotherium'' was among the largest native mammals in South America. Its bones are extremely dense, even more than in other large meridiungulates such as the notoungulate
toxodonts Toxodontia. Retrieved April 2013. is a suborder of the meridiungulate order Notoungulata. Most of the members of the five included families, including the largest notoungulates, share several dental, auditory and tarsal specializations. The gr ...
and astrapotheres, which implies an extreme specialization towards graviportality; X-ray
microtomography X-ray microtomography, like tomography and X-ray computed tomography, uses X-rays to create cross-sections of a physical object that can be used to recreate a virtual model (3D model) without destroying the original object. The prefix ''micro-'' ...
analysis of the bone density of its humerus and femur indicate that its medullary area was particularly compact, almost comparable to the
pachyostosis Pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (osteosclerosis), reducing inner ca ...
of aquatic or semiaquatic mammals, with thick trabeculae and very small intratrabecular cavities, although they resemble externally the bones of proboscideans or rhinos, which would help it better absorb the impact energy on the bones. It is also inferred that its posture would have been semi-plantigrade, since the fingers of the hands would support its weight, but instead the feet they would have been plantigrade, as inferred from the ankle bones.


Paleoecology

The ''Pyrotherium'' fossils recovered from both Salla, Deseado and Quebrada Fiera correspond to relatively dry environments, with
xerophytic A xerophyte (from Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or places in the Alps or th ...
vegetation and periods of drought;Croft, D. A. (2016). ''Horned armadillos and rafting monkeys: the fascinating fossil mammals of South America''. Indiana University Press. this would contradict the hypothesis that they were semiaquatic animals, similar to
hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
es, while the remains of astrapotheres (another group of large, tusked native ungulates) are in fact found in areas associated with bodies of water, which would imply that they would live in humid environments and were able to spend some time in the water.Houssaye, A., Fernández, V., and Billet, G. 2016. Hyperspecialization in some South American endemic ungulates revealed by long bone microstructure. ''Journal of Mammalian Evolution'' 23: 221–235. ''Pyrotherium'' would have used its incisors and trunk in order to collect food such as leaves and branches of the trees, in a similar way to black rhinos and African forest elephants. ''Pyrotherium'' cohabited with several other mammals, several of them large that are typical of the Deseadan fauna of places like La Flecha in Argentina. The presence of predatory
sparassodonts Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now thoug ...
such as ''
Pharsophorus ''Pharsophorus'' is an extinct genus of borhyaenoid sparassodont that inhabited South America during the Middle to Late Oligocene epoch.
'', '' Notogale'' and the enormous '' Proborhyaena'' is noteworthy, and other ungulates which were mainly notoungulates, such as ''
Trachytherus ''Trachytherus'' is an extinct genus of mesotheriid notoungulate that lived from the Late Oligocene to the Early Miocene in what is now South America. Description ''Trachytherus'' had a relatively low, compact skull with an elongated snout, l ...
'', ''
Leontinia ''Leontinia'' is an extinct genus of leontiniid notoungulate. Fossils have been found in the Deseado and Sarmiento Formations in Argentina and Trembembé Formation of Brazil, and are the most abundant remains of any animal found there. The genu ...
'', ''
Rhynchippus ''Rhynchippus'' ("Snout Horse") is an extinct genus of notoungulate mammals from the Late Oligocene ( Deseadan in the SALMA classification) of South America. The genus was first described by Florentino Ameghino in 1897 and the type species is ' ...
'', ''
Propachyrucos ''Propachyrucos'' is an extinct genus of hegetotheriid notoungulate. It lived from the Late Oligocene to the Early Miocene, in what is today South America. Description This animal was the size of a large hare, with a 10 centimeter long skull. ...
'', '' Argyrohyrax'', '' Archaeohyrax'', and ''
Prohegetotherium ''Prohegetotherium'' is an extinct genus of Hegetotheriidae, hegetotheriid Notoungulata, notoungulates from the Oligocene, Late Oligocene to Miocene, Early Miocene (Deseadan-Santacrucian in the South American land mammal age, SALMA classificatio ...
''.Marani, H. A. (2005). ''Los Rhynchippinae de Edad Mamífero Deseadense de la Localidad Cabeza Blanca''. Doctoral dissertation, Universidad Nacional de la Patagonia San Juan Bosco, Chubut-Argentina.


References


Bibliography

*F. Ameghino. 1894. Sur les oiseaux fossiles de Patagonie; et la faune mammalogique des couches à ''Pyrotherium''. ''Boletín del Instituto Geographico Argentino'' 15:501-660 *F. Ameghino. 1901. Notices préliminaires sur des ongulés nouveaux des terrains crétacés de Patagonie reliminary notes on new ungulates from the Cretaceous terrains of Patagonia ''Boletín de la Academia Nacional de Ciencias de Córdoba'' 16:349-429 {{Taxonbar, from=Q2606712 Meridiungulata Oligocene mammals of South America Deseadan Paleogene Argentina Fossils of Argentina Paleogene Bolivia Fossils of Bolivia Fossil taxa described in 1888 Taxa named by Florentino Ameghino Prehistoric placental genera Golfo San Jorge Basin Sarmiento Formation