Pyrotherium (from Ancient Greek πῦρ (pûr), meaning "fire", and θηρίον (theríon), meaning "beast") is an extinct genus of South American ungulates, in the order Pyrotheria, that lived in what is now Argentina and Bolivia during the Late Oligocene.Pyrotherium at Fossilworks.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 and Sarmiento Formations of Argentina and the Salla Formation of Bolivia.
So far, two valid species have been described; Pyrotherium romeroi from Argentina, and P. macfaddeni from Bolivia, at the end of Oligocene. 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. It is also the largest, with an estimated body length from . Pyrotherium is believed to have developed a small trunk; despite its close resemblance to elephants (proboscideans), though, it is not related to them, although Pyrotherium's true relationship is still controversial today.
Discovery and naming The original remains of Pyrotherium (some molars, a premolar and an incisor) were originally discovered in the Neuquén province in strata dating back to the late Oligocene epoch, identified by the Argentine naturalist Florentino Ameghino as couche à Pyrotherium (layers of Pyrotherium, in French) due to its fossils being originally identified from them;Ameghino, F. 1894. Première contribution à la conaissance de la faune mammalogique des couches à Pyrotherium. Boletín del Instituto Geográfico Argentino 15: 603–660.Ameghino C. 1914. Le Pyrotheríum, I'étage Pyrothéréen et les couches á Notostylops. Une response á Mr. Loomis. Physis, 1: 446-460. these strata are now considered part of the Deseadan mammal-age (SALMA) in the area of the Deseado estuary, although there is doubt over whether the holotype of Pyrotherium romeroi really comes from Neuquén, with it being possible that the remains actually came from Chubut.Kramarz, A. G., Forasiepi, A. M., & Bond, M. (2011). Vertebrados cenozoicos. In Relatorio del XVIII Congreso Geológico Argentino. Geología y Recursos Naturales de la Provincia del Neuquén (pp. 557-572). Buenos Aires: Asociación Geológica Argentina. Ameghino believed that these areas corresponded to older terrains from the Paleocene and even from the Cretaceous, because they were sent together with dinosaur remains;F. Ameghino. 1897. Mammiféres crétacés de l'Argentine (Deuxième contribution à la connaissance de la fauna mammalogique de couches à Pyrotherium) [Cretaceous mammals of Argentina (second contribution to the knowledge of the mammalian fauna of the Pyrotherium Beds)]. Boletín Instituto Geográfico Argentino 18(4–9):406-521 subsequent studies have shown that they actually come from the Oligocene, with Pyrotherium itself becoming a guide fossil for the Oligocene. Because the remains of this animal originally appeared in the volcanic ash beds of the Deseado Formation, they named it Pyrotherium, which means "fire beast".
The name of the species P. romeroi comes from 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 Brewster Loomis during the Amherst College expedition in 1911-1912, and listed as specimen ACM 3207.
Additional remains of the genus have appeared in Quebrada Fiera, from the Mendoza province (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.MacFadden BJ, Frailey CD (1984) Pyrotherium, a large enigmatic ungulate (Mammalia, incertae sedis) from the Deseadan (Oligocene) of Salla, Bolivia. Palaeontol 27:867–874 Later, they were reclassified as a separate, smaller species called P. macfaddeni, named in honor of paleontologist Bruce J. MacFadden. Molar and postcranial bone remains found in sediments from the late Oligocene of Taubaté, Brazil were considered as possible remains of Pyrotherium,Couto-Ribeiro, G. and Alvarenga, H. 2009. Primeiro registro de dentes de Pyrotherium para a Formação Tremembé, Bacia de Taubaté, SP. Reunião Anual da Sociedade Brasileira de Paleontologia. Núcleo São Paulo. Abstracts: 21. but it is possible that they correspond to a different yet-to-be-described genus with which it is closely related.Ribeiro, G. D. C. Osteologia de Taubatherium paulacoutoi Soria & Alvarenga, 1989 (Notoungulata, Leontiniidae) e de um novo Pyrotheria: dois mamíferos fósseis da Formação Tremembé, Brasil (SALMA Deseadense-Oligoceno Superior). (Doctoral dissertation, Universidade de São Paulo).
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 when 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 or trunk. The brain cavity (neurocranium) is damaged and surrounded by spongy bone tissue; Loomis considered that it indicated that in life P. romeroi had a small brain, about long and wide. Later analysis by Bryan Patterson in 1977, after some additional preparation work on the only known skull, indicated some errors in earlier interpretations, and that the brain would be somewhat larger, 80 millimeters wide, more similar in size to that of notoungulates such as Homalodotherium and Nesodon.
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 molars. Between the incisors and the posterior teeth there was a space without teeth, the diastema, 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). In juvenile Pyrotherium, the dental formula is dI ?/2, dC ?/0, dP 3/3.
The mandible was robust and had a well-developed, long and narrow symphysis 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 them; 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, 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 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, the axis 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. 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 pelvis 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, 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 embrithopod Arsinoitherium.
Phylogeny