''Anomocephalus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of primitive anomodonts and belongs to the clade

Anomocephaloidea Anomocephaloidea is a clade (evolutionary grouping) of anomodont therapsids that existed in Gondwana during the Middle Permian and includes two species, ''Anomocephalus africanus'' from South Africa and ''Tiarajudens eccentricus'' from Brazil, bo ...

. The name is said to be derived from the Greek word ''anomos'' meaning lawless and ''cephalos'' meaning head. The proper word for head in Greek is however κεφαλή (''kephalē'').Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press. It is primitive in that it retains a complete set of

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...

in both jaws, in contrast to its descendants, the

dicynodonts Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...

, whose dentition is reduced to only a single pair of

tusks Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share ...

(and in many cases no teeth at all), with their jaws covered by a horny beak similar to that of a modern

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a shell to protect from predation and other threats. The shell in tortoises is generally hard, and like oth ...

. However, they are in no way closely related. Its discovery in 1999 from the earliest terrestrial rocks of Gondwana (from Williston in the Karoo of the

Northern Cape Province The Northern Cape is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley. It includes the Kalahari Gemsbok National Park, part of the Kgalagadi ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

) has shown that this group of

herbivores A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

originated in Gondwana; not Laurasia, as had previously been supposed. It lived 260 million years ago during the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last ...

Period, in

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...

areas with

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...

s and

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s - almost like parts of modern-day

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

Botswana Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kalaha ...

. It is most closely related to ''

Tiarajudens ''Tiarajudens'' (" Tiaraju tooth") is an extinct genus of saber-toothed herbivorous anomodonts which lived during the Middle Permian period ( Capitanian stage) in what is now Rio Grande do Sul, Brazil. It is known from the holotype UFRGS P ...

'' from

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 ...

Geology and paleoenvironment

''Anomocephalus'' was discovered at the base of the

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underli ...

, which is a geographical stratum that consists of mostly sandstone and shales that have been deposited in the Karoo Basin. The Beaufort Group dominated most of the basin with fluvial sedimentation, which is carried by streams and rivers that were most likely formed by ice masses such as glaciers. The climate at this time during the Mid to

Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

became warm and semi-arid with seasonal rainfall. The central region of the basin is thought to have been drained by semi-permanent lakes and fine-grained meander belts.

History and discovery

''Anomocephalus'' was collected from a locality near Williston at the base of the Beaufort Group in the Karoo Basin, which is located within the Northern Cape Province of South Africa. It was discovered during the continued program of B. Rubidge to determine the lateral extent of the ''

Eodicynodon ''Eodicynodon'' (''eo-,'' early or primitive, dicynodont) is an extinct genus of dicynodont therapsids, a highly diverse group of herbivorous synapsids that were widespread during the middle-late Permian and early Triassic. As its name suggests, ...

'' (an extinct dicynodont therapsid) Assemblage Zone. It was first described by Modesto in 1999 and is known only by a partial skull with distinctive dentition and was preserved in hard mud rock. The discovery of ''Anomocephalus'' and its

phylogenetic 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 ...

position provided compelling evidence that anomodonts initially diversified in Gondwana. This conflicts with previous suggestions that anomodonts were freely dispersing between the northern and southern regions of the Late Permian

Pangea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

or that

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

s first evolved in Euramerica and then moved to Gondwana when climate became favorable. Additionally, the basal phylogenetic position of ''Anomocephalus'' suggests that herbivory was acquired initially by the anomodonts of Gondwana.

Description

Skull

The

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

contains a deep alveolar portion with room for two teeth and 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. T ...

is slightly elongated in comparison to other anomodonts. On the posterior portion of the maxilla, the characteristic anomodont curvature is seen in the

zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygo ...

. The nasal, prefrontal, and lacrimal resemble in both form and position those of other more basal anomodonts. Additionally, the

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

has a greater marginal exposure than other anomodonts and it tapers posteriorly. The dorsal lamella of the quadratojugal more closely resembles dicynodonts than basal anomodonts. The postorbital bone tapers ventrally and is visibly flat and curved. Like in other anomodonts, the

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 teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

is dorsoventrally deep, and the squamosal is triradiate as suggested by the ventral and anterior processes. Anomocephalus and Tiarajudens

Dentition

''Anomocephalus'' possess five upper

incisor 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, wher ...

s that have an ovoid-shaped

crown A crown is a traditional form of head adornment, or hat, worn by monarchs as a symbol of their power and dignity. A crown is often, by extension, a symbol of the monarch's government or items endorsed by it. The word itself is used, partic ...

when observed from the occlusal view. The dentition of the maxilla begins as tiny peg-like elements that become buccolingually wide and mesiodistally short. Six teeth are located on the pterygoid/ epipterygoid with four additional empty/damaged alveoli which suggests that there were at least ten teeth that made up the right palatal dentition. These palatal teeth have long, curved roots and the crowns are rectangular with an occlusal basin. There are two ''in situ'' lower incisiforms that are followed by two displaced lower teeth, the second of these teeth is transversally expanded and shows a saddle-like crown just like the palatal teeth. Additionally, there are three posterior lower teeth on the dentary with an unerupted, replacement tooth evident below the last lower tooth, which is evidence of at least a second wave of tooth replacement.

Post-cranial skeleton

Although a post-cranial skeleton was not found with the partial skull of ''Anomocephalus'', its sister taxa '' Tiarajudens eccentricus'' was discovered in 2011 with a partial left pectoral girdle and its left limb, an isolated left

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

with the pes, and foot elements. Of the axial elements, only two fragmentary ribs of parallel margin were found with no clear curvature and the most complete fragment was 8 mm wide and 86 mm long. The humerus that was found with ''T. eccentricus'' is approximately 177 mm in length and displayed well-expanded proximal and distal portions. The radius is 128 mm in length with expanded, flat proximal and distal surfaces, and the ulna is more robust than the radius and slightly longer at 137 mm. The pes showed five partial digits and they were all robust with arthrodial joints between the distal

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

and proximal phalanges as well as between the phalanges. Additionally, 15 left and three right gastralia were preserved as long, thin, and delicate bones.

Paleobiology

''Anomocephalus'' exhibits palatal teeth and the morphology of the teeth is consistent with a high-fiber herbivorous diet. Cisneros and colleagues suggested that ''Anomocephalus'' had an incipient propaliny during the occlusions due to the longitudinal dimensions of each facet of the quadrate being twice as large as the transversal dimension. They suggest that this would allow for forward and backward movement of the lower jaw during chewing. Propaliny is also suggested to be linked to improved capability for processing plant material.