''Diictodon'' (meaning "two weasel teeth") is an extinct genus of pylaecephalid

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

that lived during the Late

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 251.902 Mya. It is the s ...

period, approximately 255 million years ago. Fossils have been found in the ''Cistecephalus'' Assemblage Zone of the Madumabisa Mudstone of the Luangwa Basin in

Zambia Zambia, officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa. It is typically referred to being in South-Central Africa or Southern Africa. It is bor ...

and the ''Tropidostoma'' Assemblage Zone of the Teekloof Formation, ''Tapinocephalus'' Assemblage Zone of the Abrahamskraal Formation, ''Dicynodon'' Assemblage Zone of the Balfour Formation, ''Cistecephalus'' Assemblage Zone of the Middleton or Balfour Formation of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

and the Guodikeng Formation of

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. Roughly half of all Permian vertebrate specimens found in South Africa are those of ''Diictodon''. This small herbivorous animal was one of the most successful synapsids in the Permian period.

Characteristics

Appearance

''Diictodon'' had disproportionally large heads that ended in a horny beak. ‘There is a clear distinction between specimens having canine tusks and those lacking them, as tusked specimens are generally larger and more likely to develop a pineal boss. This probably reflects sexual dimorphism, with the tusked sex almost certainly being the male.’ ''Diictodon'' had strong arms and legs, as well as 5 sharp claws on each hand, and may have had keen senses of smell and sight. Their gait was similar to the 'high walk' of crocodiles. Their jaws were also simplified, with some of the bones dedicated instead to hearing, considered a key sign of mammalian adaptation. ''Diictodon'' also had many adaptations for digging, such as highly developed muscles, a cylindrical body, and wide hands.Ray, S., & Chinsamy, A. (2003). Functional aspects of the postcranial anatomy of the Permian dicynodont Diictodon and their ecological implications. Palaeontology, 46(1), 151–183. https://doi.org/10.1111/1475-4983.00292. Researchers Chinsmay and Rubridge analyzed seven other Dicynodonts species discovering the humeral bone microstructure in ''Diictidon'' showed no signs of growth marks indicating a variation in its growth strategy that further improved their ability to dig.

Lifestyle

As a therapsid, ''Diictodon'' shared many features with modern-day mammals. Most noticeably, they made burrows into the earth, but most reached up to in depth, suggesting that they might have been infrequent diggers and occupied abandoned burrows. Still, many scientists believe that ''Diictodon'' lived like the modern gopher. Their burrows could have been used to escape the heat of the desert, which was the dominant environment on the continent of

Pangaea 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 period approximately 335 mi ...

in the Late Permian Period. Inside these burrows, nests have been found, where ''Diictodon'' skeletons are present. They constituted of quite a gregarious lifestyle with numerous burrows in 500 square meters of space. However, their burrows were unconnected and did not form any large colonies. Many ''Diictodon'' nested close to flood plains, and some specimens may have been killed as water flowed into the nests, drowning the animals. ''Diictidon''’s primary utilization of humeral excursion rather than forearm extension aided in employing rotation thrusting when burrowing. ''Diictodon'' had no known rival species competing in its niche, so they may have competed primarily with others of their species for the little plant material available. Fossils of infant ''Diictodon'' discovered in brood chambers in some burrows suggest there was parental care in the genus, and that males seem to have been involved in raising the infants, based on the fact that some adults in said burrows had tusks.

Diet

Like all

s, ''Diictodon'' were herbivorous. They used their beaks to break off pieces of the sparse desert shrubs. Like modern desert animals, ''Diictodon'' may have had unusually efficient digestive systems, due to the lack of nutrients present in desert plants. As burrowing animals, they may have fed off of water-rich plant tubers.Cox, C. B. (1998). The jaw function and adaptive radiation of the dicynodont mammal-like reptiles of the Karoo basin of South Africa. Zoological Journal of the Linnean Society, 122(1-2), 349–384. https://doi.org/10.1111/j.1096-3642.1998.tb02534.x

Sexual dimorphism

Previously, tusked individuals were considered males, while tuskless individuals were considered females. Differences in pelvic structure may be the other evidence for sexual dimorphism.

Phylogeny

''Diictodon'' in a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

modified from Angielczyk and Rubidge (2010) showing the

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

relationships of

Dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

ia: