Acleistorhinidae
Encyclopedia
Acleistorhinidae is a family
of Early Permian-aged parareptiles
. Presently, the clade
consists of only two taxa, Colobomycter
and Acleistorhinus
, both collected from the Permian of Oklahoma
. Sister taxa include Nyctiphruretidae and Sclerosauridae.
Acleistorhinidae is notable for being the oldest-known parareptilian clade. The family is diagnosed by the presence two synapomorphies
: (1) the largest tooth
is located far anteriorly on the maxilla
; and (2) cranial ornamentation consists of sparse and shallow circular dimples.
73362 and OMNH 73364, represent a new and currently unnamed species of acleistorhinid. Fragments of arthropod
cuticle
s are present in between the many palatal
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
.
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
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.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of Early Permian-aged parareptiles
Parareptilia
Parareptilia is a subclass or clade of reptiles which is variously defined as an extinct group of primitive anapsids, or a more cladistically correct alternative to Anapsida...
. Presently, the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
consists of only two taxa, Colobomycter
Colobomycter
Colobomycter is a small parareptile known from the Early Permian of Oklahoma. The genus was first described from fossil remains in 1958, at which time it was believed to represent a synapsid , specifically, a pelycosaur. However, the discovery of new material and reexamination of the holotype led...
and Acleistorhinus
Acleistorhinus
Acleistorhinus is a genus of parareptile known from the Early Permian of Oklahoma. It is notable for being the earliest known anapsid reptile yet discovered. The morphology of the lower temporal fenestra of the skull of Acleistorhinus bears a superficial resemblance to that seen in early...
, both collected from the Permian of Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
. Sister taxa include Nyctiphruretidae and Sclerosauridae.
Acleistorhinidae is notable for being the oldest-known parareptilian clade. The family is diagnosed by the presence two synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
: (1) the largest tooth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
is located far anteriorly on the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
; and (2) cranial ornamentation consists of sparse and shallow circular dimples.
Diet
Two specimens of acleistorhinids have recently been described from the Richards Spur fissure-fill locality in Oklahoma that provide compelling evidence of the diet of acleistorhinids. These specimens, called OMNHSam Noble Oklahoma Museum of Natural History
The Sam Noble Oklahoma Museum of Natural History is a natural history museum in Norman, Oklahoma, operated by the University of Oklahoma. It is currently housed in a building on Chautauqua Avenue that opened on May 1, 2000. The museum's exhibits include a Native American gallery and collections of...
73362 and OMNH 73364, represent a new and currently unnamed species of acleistorhinid. Fragments of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
cuticle
Cuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...
s are present in between the many palatal
Palate
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 separate. The palate is divided into two parts, the anterior...
teeth of both skulls. The fragments in OMNH 73362 are thought to be the segments of an antenna
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
, while the fragments in OMNH 73364 are thought to be part of a cercus
Cercus
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons or copulation aids, or they may simply be vestigial structures.Typical cerci may appear to be...
.
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
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
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.