Probainognathidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

during the

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

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

. 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 Argentina. Together with the genus ''Bonacynodon'' from Brazil, ''Probain ...

'' 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 sandstones ...

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 Prozostrodontia is a clade of cynodonts including mammaliaforms and their closest relatives such as Tritheledontidae and Tritylodontidae. It was erected as a node-based taxon by Liu and Olsen (2010) and defined as the least inclusive clade contai ...

, which includes

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

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/hole 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 ...

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 med ...

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

maxilla In vertebrates, the maxilla (: maxillae ) 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. The two maxil ...

was larger than the part made from the

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

. The

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

, 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 ha ...

(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 o ...

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 ancestra ...

and

surangular The surangular or suprangular 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 bone, angular, splenial and articular. It is o ...

bones. The

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as '' fangs''. They can appear more fl ...

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 pr ...

edge. The

postcanine Cheek teeth or postcanines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and p ...

s 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 (Neo-Latin, "belonging to the nose"; : 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 dogs s ...

with

whiskers Whiskers, also known as vibrissae (; vibrissa; ) are a type of stiff, functional hair used by most therian mammals to sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are coarser as ta ...

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 227.3 ...

-aged

of Argentina, which Romer had removed from the family

Chiniquodontidae Chiniquodontidae is an extinct family of basal probainognathian cynodonts that lived in what is now Africa and South America during the Middle and Late Triassic. It is currently thought to include four valid genera: ''Aleodon'', '' Chiniquodon'' ...

. 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 "unisp ...

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 a 2016 paper by Martinelli ''et al.'' This paper also provided a phylogenetic definition of Probainognathidae, as "the clade including the most recent common ancestor of ''Probainognathus jenseni'' and ''Bonacynodon schultzi'', and all its descendants".

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 ...

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 most b ...

, 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 or omnivorous gomphodonts such as traversodontids. Cynogn ...

. The exact placement of probainognathids relative to other basal probainognathians varies between analyses. Some analyses find probainognathids to be very close relatives of

, a group of advanced probainognathians that includes

s and their close relatives. Some analyses alternatively find

Ecteniniidae Ecteniniidae is an extinct family of probainognathian cynodonts from the Triassic of South America. They are notable for their large size, as well as for being among the first synapsids with specializations towards cursoriality. Phylogeny Be ...

, 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 Probainognathia Prehistoric therapsid families Ladinian first appearances Carnian extinctions Taxa named by Alfred Romer