Probainognathidae 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 ...

insectivorous A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...

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 varie ...

s which lived in what is now

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

during the Middle to

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

. The family was established by

Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...

in 1973 and includes two genera, ''

Probainognathus ''Probainognathus'' meaning “progressive jaw” is an extinct genus of cynodonts that lived around 235 to 221.5 million years ago, during the Late Triassic in what is now South America. ''Probainognathus'' is a member of the family Probainogna ...

'' from the

Chañares Formation The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstone ...

of Argentina and ''

Bonacynodon ''Bonacynodon'' is an extinct genus of cynodonts that lived in what is now southern Brazil during the Triassic period (Ladinian–Carnian ages). The genus is monotypic, containing only the type species ''Bonacynodon schultzi''. ''B. schultzi'' i ...

'' from the ''Dinodontosaurus'' Assemblage Zone of Brazil. Probainognathids were closely related to the clade Prozostrodontia, which includes

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s and their close relatives.

Description

Members of Probainognathidae were relatively small-bodied animals, with skull lengths of around . The temporal region (area behind the

eye socket In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , of ...

s) was rather wide, and longer than the snout. The

secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...

was well-developed compared to earlier cynodonts, and the portion made up by 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 ...

was larger than the part made from the

palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ...

. 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 ...

, the tooth-bearing bone of the lower jaw, was quite tall when seen from the side. The

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halve ...

(the joint between the two halves of the dentary) was fused in ''Probainognathus'', but unfused in ''Bonacynodon''. In addition to the ancestral quadrate-

articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...

jaw joint found in most non-mammalian cynodonts, probainognathids also had an incipient contact between the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

and

surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular. It is often a mu ...

bones. The

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened howeve ...

were large and labio-lingually compressed, and in ''Bonacynodon'' they bore a

serrated Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied p ...

edge. The postcanines had a typical "triconodont" shape, with four main cusps placed in a straight line. Unlike in other basal probainognathians like ''

Chiniquodon ''Chiniquodon'' is an extinct genus of carnivorous cynodonts, which lived during the Late Triassic (Carnian) in South America (Argentina and Brazil) and Africa (Namibia and Madagascar). ''Chiniquodon'' was closely related to the genus ''Aleodon ...

'', the cusps were not recurved. The lower postcanines bore a discontinuous cingulum which was restricted to the mesiolingual and distolingual sides of the teeth. The shape of the postcanines indicates that probainognathids most likely were

. Based on the shape of the maxillary canal, a 2020 paper by Benoit ''et al.'' suggested that ''Probainognathus'' was among the first cynodonts to possess a mobile

rhinarium The rhinarium (New Latin, "belonging to the nose"; plural: rhinaria) is the furless skin surface surrounding the external openings of the nostrils in many mammals. Commonly it is referred to as the tip of the ''snout'', and breeders of cats and ...

with

whiskers Vibrissae (; singular: vibrissa; ), more generally called Whiskers, are a type of stiff, functional hair used by mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarse ...

Classification

Probainognathidae was erected in a 1973 paper by the American palaeontologist

to contain ''

'', a cynodont from the

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...

-aged

of Argentina, which Romer had removed from the family Chiniquodontidae. The family remained

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

for a long time, until the genus ''

'', from the

Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between Ma and ~237 Ma (million years ago). The Ladinian was preceded by the Anisian and succeeded by the Carnian (part of the Upper or Late Triassic) ...

-early Carnian ''Dinodontosaurus'' Assemblage Zone of Brazil, was named in 2016.

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 ...

analyses have generally found probainognathids to be relatively early-diverging members of

Probainognathia Probainognathia is one of the two major subgroups of the clade Eucynodontia, the other being Cynognathia. The earliest forms were carnivorous and insectivorous, though some groups eventually also evolved herbivorous diets. The earliest and m ...

, a clade that includes all cynodonts closer to mammals than to

Cynognathia Cynognathia ("dog jaw") is one of two major clades of cynodonts, the other being Probainognathia. Cynognathians included the large carnivorous genus '' Cynognathus'' and the herbivorous traversodontids. Cynognathians can be identified by several ...

. The exact placement of probainognathids relative to other basal probainognathians varies between analyses. Some analyses find probainognathids to be very close relatives of Prozostrodontia, a group of advanced probainognathians that includes

s and their close relatives. Some analyses alternatively find Ecteniniidae, a group of large predatory cynodonts, to be closer to prozostrodontians than the probainognathids. Cladogram from Martinelli ''et al'' (2016) Cladogram from Stefanello ''et al.'' (2023)

References

{{Taxonbar, from=Q3068100 Prehistoric probainognathians Prehistoric therapsid families Ladinian first appearances Carnian extinctions Taxa named by Alfred Romer