''Alemoatherium'' 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 ...

prozostrodontia Prozostrodontia is a clade of cynodonts including mammaliaforms and their closest relatives such as Tritheledontidae and Tritylodontidae. It was erected as a node-based taxon by Liu and Olsen (2010) and defined as the least inclusive clade cont ...

cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...

which lived in the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

. It contains a single

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''A. huebneri'', named in 2017 by Agustín Martinelli and colleagues. The genus is based on

UFSM The Federal University of Santa Maria ( pt, Universidade Federal de Santa Maria, UFSM) is a Brazilian public university located in Santa Maria, in the state of Rio Grande do Sul, funded by the federal government of Brazil. It was founded in ...

11579b, a left lower jaw (

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

) found in the Alemoa Member of the

Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age (Late Triassic), and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and oth ...

, preserving the late

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

-age ''Hyperodapedon'' Assemblage Zone. ''Alemoatherium'' was among the smallest species of cynodonts found in the rich

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes reptil ...

fauna of the Santa Maria Formation. Its blade-like four-cusped

postcanine Cheek teeth or post-canines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...

teeth show many similarities with those of dromatheriids, an obscure group of early prozostrodontians.

Description

The

is similar in shape to that of many other prozostrodontians, with an overall slender form that abruptly changes angle near the front of the jaw. This distinct change in angle separates the dentary into two main regions, the horizontal ramus behind the level of the first postcanine tooth, and the upwards-tilted anterodorsal process in front of the first postcanine. Seen in medial (inside) view, the dentary has a faint groove along the tooth row and a much more prominent

Meckelian groove The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.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 ...

, where the left and right jaws connect to each other at the chin.

Dentition

''Alemoatherium'' has five

incisors Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...

, one canine, and at least seven postcanines on its lower jaw. Though none of the incisors are fully preserved, the largest would have been the first incisor (i1), indicated by an

alveolus Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * Mam ...

(tooth socket) which was strongly procumbent (oriented forwards) and circular in cross section. The second incisor (i2) was smaller and strongly worn on the labial (cheek) side. The third, fourth, and fifth incisors (i3-i5) are similar but smaller still. The single canine tooth (c1) is quite small, with a straight distal (rear) edge and no apparent serrations. The first postcanine tooth (pc1) is similar to the canine but larger, with a tiny second

cusp A cusp is the most pointed end of a curve. It often refers to cusp (anatomy), a pointed structure on a tooth. Cusp or CUSP may also refer to: Mathematics * Cusp (singularity), a singular point of a curve * Cusp catastrophe, a branch of bifurca ...

behind the main cusp. The second postcanine (pc2) is not preserved but it would have been slightly larger than pc1. The third postcanine (pc3) has four main cusps: the large main cusp (a), preceded by a small cusp (b), and followed by two more small cusps (c and d). This tooth is a fairly typical cynodont sectorial (flesh-slicing tooth), with a continues sharp cutting surface from cusp a back to cusp c. Cusp b is set slightly more labial (towards the cheek) and separated by a groove, while the tiny cusp d is set low and has a straight lingual (towards the tongue) edge. The fourth postcanine (pc4) is significantly larger, with a tall cusp a with a convex labial surface. Cusp b is small and set low on the crown. An additional

cingular AT&T Mobility LLC, also known as AT&T Wireless and marketed as simply AT&T, is an American telecommunications company. It is a wholly owned subsidiary of AT&T Inc. and provides wireless services in the United States. AT&T Mobility is the th ...

cusp is positioned below the lingual surface of cusp b. Cusp c is the second-largest in the tooth, separated from cusp a by a sharp notch. Cusp d is very small and leans back. There is a vertical groove on the side of the

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

, the predecessor condition to a bifurcated root. The even larger fifth postcanine (pc5) is similar to the fourth, though cusp b is taller, cusp d curves further, and two cingular cusps are positioned below cusp b rather than just one. The sixth postcanine (pc6) is similar to its predecessors and is the largest preserved tooth in the jaw, though it has only one cingular cusp. The seventh postcanine (pc7) is not preserved, but its alveolus indicates that it was around the size of pc3.

Classification

The unfused mandibular symphysis and constricted roots of the lower postcanines support the placement of ''Alemoatherium'' within

Prozostrodontia Prozostrodontia is a clade of cynodonts including mammaliaforms and their closest relatives such as Tritheledontidae and Tritylodontidae. It was erected as a node-based taxon by Liu and Olsen (2010) and defined as the least inclusive clade cont ...

, a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of cynodonts including

mammaliaforms Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recen ...

and many of their Late Triassic relatives, from ''

Prozostrodon ''Prozostrodon'' is an extinct genus of advanced cynodonts that was closely related to the ancestors of mammals. The remains were found in Brazil and are dated middle to late Triassic. It was originally described as a species of ''Thrinaxodon' ...

'' crownwards. Among its Brazilian contemporaries, ''Alemoatherium'' shares some similarities with probainognathids (postcanine tooth shape), ''

Protheriodon ''Protheriodon'' is an extinct genus of probainognathian cynodonts which existed in the Santa Maria Formation of the Paraná Basin in southeastern Brazil during the middle Triassic period. It contains the species ''Protheriodon estudianti''. It ...

'' (slender jaw, high number of incisors), '' Santacruzgnathus'' (slender jaw, distinct Meckelian groove), and brasilodontids (overall jaw and tooth shape). However, all of these taxa also possess traits contradicting the remains of ''Alemoatherium''. The teeth of ''Alemoatherium'' share many similarities to those of dromatheriids, a poorly-known group of cynodonts found in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

, and

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

. Its dentary was also very similar to those of dromatheriids such as '' Microconodon'' and '' Dromatherium'', supporting their connection further. Below is a

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 ...

showing the results of Martinelli ''et al.'' (2017)'s

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 ...

(excluding ''Santacruzgnathus'', ''Microconodon'', and ''

Charruodon ''Charruodon'' is an extinct genus of cynodonts which existed in the ''Hyperodapedon'' Assemblage Zone of the Santa Maria Formation in the Paraná Basin in southeastern Brazil during the Late Triassic. The genus contains only the type species ...

'').

References

{{Taxonbar, from=Q39050742 Prehistoric prozostrodonts Prehistoric cynodont genera Fossil taxa described in 2017