Acleistorhinidae is an extinct

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Late Carboniferous 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, ...

and Early Permian-aged ( Moscovian to

Kungurian In the geologic timescale, the Kungurian is an age or stage of the Permian. It is the latest or upper of four subdivisions of the Cisuralian Epoch or Series. The Kungurian lasted between and million years ago (Ma). It was preceded by the Ar ...

stage)

parareptile Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids (reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near th ...

s. Acleistorhinids are most diverse from the

Richards Spur Richards Spur is a Permian fossil locality located at the Dolese Brothers Limestone Quarry north of Lawton, Oklahoma. The locality preserves clay and mudstone fissure fills of a karst system eroded out of Ordovician limestone and dolomite (rock), d ...

locality of the Early Permian of Oklahoma. Richards Spur acleistorhinids include '' Acleistorhinus'', '' Colobomycter'', and possibly '' Delorhynchus'' and '' Feeserpeton''. Other taxa include ''

Carbonodraco ''Carbonodraco'' is an extinct genus of acleistorhinid parareptile known from the Late Carboniferous of Ohio. It contains a single species, ''Carbonodraco lundi''. It was closely related to ''Colobomycter'', a parareptile from the early Permian ...

'' from the

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

and '' Karutia'' from the Early Permian of

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 ...

. Acleistorhinidae is commonly considered a subgroup of lanthanosuchoids, related to taxa such as '' Chalcosaurus'', '' Lanthaniscus'' and '' Lanthanosuchus''. However, a re-examination of parareptile phylogeny conducted by Cisneros ''et al.'' (2021) argued that lanthanosuchids were not closely related to acleistorhinids. The phylogenetic analysis conducted by these authors recovered acleistorhinids as the sister group of the clade

Procolophonia The Procolophonia are a suborder of herbivorous reptiles that lived from the Middle Permian till the end of the Triassic period. They were originally included as a suborder of the Cotylosauria (later renamed Captorhinida Carroll 1988) but are ...

, while lanthanosuchids were recovered within the procolophonian subgroup

Pareiasauromorpha Pareiasauromorpha is a group of parareptilian amniotes from the Permian. It includes genera found all over the world, with many genera from Asia and South Africa. The clade was first used as a group by Linda A. Tsuji in 2011, in order to grou ...

. Acleistorhinidae is notable for being the oldest-known parareptilian clade. The family is diagnosed by the presence two synapomorphies: (1) the largest

tooth 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 ...

is located far anteriorly on 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 ...

; and (2)

cranial Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

ornamentation consists of sparse and shallow circular dimples.

Diet

Two specimens of acleistorhinids described from the

fissure-fill locality in Oklahoma have provided compelling evidence of the diet of acleistorhinids. One specimen, OMNH 73362, was later referred to ''

Delorhynchus cifellii ''Delorhynchus'' is an extinct genus of lanthanosuchoid parareptile known from the late Early Permian (Artinskian age) Garber Formation of Comanche County, Oklahoma. It contains three species: the type species ''D. priscus'' is based on a series ...

'', a species named in 2014. The other specimen, OMNH 73364, has not been formally described. Fragments of

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...

cuticles are present in between the many

palatal The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...

teeth of both skulls. The fragments in OMNH 73362 are thought to be the segments of an antenna, while the fragments in OMNH 73364 are thought to be part of a

cercus Cerci (singular cercus) are paired appendages on the rear-most segments of many arthropods, including insects and symphylans. Many forms of cerci serve as sensory organs, but some serve as pinching weapons or as organs of copulation. In many in ...

. In acleistorhinids, the marginal teeth, which are small and recurved, are suggestive of an insectivorous diet, as they probably were used for gripping and piercing arthropod cuticle. The denticulated palate, with three pairs of tooth fields and smaller teeth in between the fields, is seen as an adaptation for holding food in the oral cavity. The teeth, which possess cutting edges, may also have been suitable for a carnivorous diet in which vertebrate flesh may have been consumed. It is possible that acleistorhinids would have preyed on

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s that were small enough to swallow whole. It is likely that one acleistorhinid, ''Colobomycter pholeter'', specialized either on invertebrates with hard cuticles or on small tetrapods.

References

Procolophonomorphs Prehistoric reptile families {{permian-reptile-stub