''Pentasaurus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...

of the family

Stahleckeriidae Stahleckeriidae is a family of dicynodont therapsids whose fossils are known from the Triassic of North America, South America, Asia and Africa. Classification Phylogeny Below is a cladogram A cladogram (from Greek ''clados'' "branch" and ...

, closely related to the well known ''

Placerias ''Placerias'' (meaning 'broad body') is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (230–220 million years ago). ''Placerias'' belongs to a group of dicynodonts called Kannemeyeriiforme ...

''. It was found in the Lower

Elliot Formation The Elliot Formation is a geological formation and forms part of the Stormberg Group, the uppermost geological Stratigraphic unit, group that comprises the greater Karoo Supergroup. Outcrops of the Elliot Formation have been found in the northern ...

of South Africa, dated to the

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

of the

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 ...

period. The genus contains the type and only

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''Pentasaurus goggai''. ''Pentasaurus'' is named after the

ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon based on the fossilized work of an organism", i.e. the non-human equivalent of an artifact. ''Ichnotaxa'' comes from the Greek ίχνος, ''ichnos'' meaning ''track'' and ταξις, ''taxis'' meaning ...

'' Pentasauropus'',

fossil footprints A fossil track or ichnite (Ancient Greek, Greek "''ιχνιον''" (''ichnion'') – a track, trace or footstep) is a fossilized footprint. This is a type of trace fossil. A fossil trackway is a sequence of fossil tracks left by a single organism ...

that were originally described from the lower Elliot Formation in 1970 decades before the body fossils of ''Pentasaurus'' itself were recognised. ''Pentasauropus'' footprints were likely made by dicynodonts, and in South Africa ''Pentasaurus'' itself was the likely trackmaker. The name reflects the fact that a large dicynodont was predicted to have existed in the lower Elliot Formation before any body fossils were recognised, and so ''Pentasaurus'' was named after its probable footprints. This is a reversal of the more typical occurrence where fossil footprints are named after their presumed trackmakers. The name of the species honours its collector Alfred Brown, nicknamed "Gogga", which means "bug" in

Afrikaans Afrikaans (, ) is a West Germanic language that evolved in the Dutch Cape Colony from the Dutch vernacular of Holland proper (i.e., the Hollandic dialect) used by Dutch, French, and German settlers and their enslaved people. Afrikaans gra ...

. ''Pentasaurus'' is also unique for being one of the only known dicynodonts to have coexisted with large-bodied

sauropodomorph Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...

dinosaurs. Prior to its discovery, large sauropodomorphs and dicynodonts were thought to have never ecologically coexisted, with dicynodonts either going extinct prior to large sauropodomorphs evolving or being outcompeted and driven to extinction by the herbivorous dinosaurs. ''Pentasaurus'' challenges these assumptions, suggesting that dicynodonts and large sauropodomorphs could be contemporaneous, and may instead have been separated through habitat and dietary preferences. Furthermore, ''Pentasaurus'' expands the range of stahleckeriid dicynodonts in the Late Triassic into South Africa, refuting ideas that dicynodonts were geographically restricted by the Late Triassic.

Description

The fossil remains of ''Pentasaurus'' are fragmented and very incomplete, so its overall morphology is poorly understood. However, it was similarly sized to other large Late Triassic dicynodonts, such as the closely related ''Placerias'', and likely resembled them in appearance.

Skull and mandible

The only known bones from the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

of ''Pentasaurus'' is a portion from the roof of the skull, specifically the front end of the intertemporal region consisting of both

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...

s, the left

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

and the preparietal (a bone unique to dicynodonts and some other therapsids). There are two depressed regions of the skull piece, one along the bottom left side and another cut into the back end, interpreted as representing a site for jaw muscle attachments at the edge of the

temporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets, ...

and for the

pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhythm ...

, respectively. Otherwise, the skull is notably rough and strongly textured, particularly on a pair of mound-like rugosities at the back edge of the frontals. Frontal rugosities are absent in other kannemeyeriiforms and may be unique to ''Pentasaurus'', although the bones around the eyes of ''Placerias'' are similarly rugose.. Only the very front of the

mandible 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 tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

of ''Pentasaurus'' is known, mostly consisting of the fused

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 halves ...

(including the

splenial The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular The suprangular or surangular is a jaw bone found in most land verteb ...

) and part of the left

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 tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

and angular, although the tip of the beak is missing. The mandible is robust, and like other dicynodonts was fused into a toothless beak. The beak was relatively short in ''Pentasaurus'', with a steep front edge drawn into a mid-line ridge like those of other placeriines, although it is relatively shorter and lacks a pair of grooves typically found on either side of the ridge in other stahleckeriids. The beak is proportionately broader than that of ''Placerias'', and its edges are smoothly rounded and curve towards the tip, unlike the sharp edged, flattened surfaces on the beaks of ''Placerias'' or ''

Stahleckeria ''Stahleckeria'' is an extinct genus of Middle Triassic (Ladinian) dicynodonts. The lateral dentary shelf, a characteristic ridge on the jaws of dicynodonts for attaching jaw muscles, is unusual in ''Pentasaurus''. It is remarkably robust and prominent, and the shelf sits uniquely far forward on the jaw compared to all other dicynodonts. Further unlike other dicynodonts, the shelf does not extend back to meet the

mandibular fenestra The skull is a bone protective Cranial cavity, cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible ...

either, instead curving up at its end from an otherwise horizontal position. Features such as the shape of the beak and lateral dentary shelf likely influenced the feeding style of dicynodonts, although the significance of the unusual morphology in ''Pentasaurus'' is currently unknown.

Postcranial skeleton

The postcranial skeleton of ''Pentasaurus'' is mostly represented by the

appendicular skeleton The appendicular skeleton is the portion of the skeleton of vertebrates consisting of the bones that support the appendages. There are 126 bones. The appendicular skeleton includes the skeletal elements within the limbs, as well as supporting shou ...

, including parts of the

limb Limb may refer to: Science and technology *Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...

shoulders The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...

and

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

, with only a single poorly preserved

cervical vertebra In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sau ...

from the neck representing the

axial skeleton The axial skeleton is the part of the skeleton that consists of the bones of the head and trunk (anatomy), trunk of a vertebrate. In the human skeleton, it consists of 80 bones and is composed of six parts; the human skull, skull (22 bones), als ...

The shoulder is only known from the

glenoid The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sha ...

region of the fused

scapulocoracoid The scapulocoracoid is the unit of the pectoral girdle that contains the coracoid and scapula. The coracoid itself is a beak-shaped bone that is commonly found in most vertebrates with a few exceptions. The scapula is commonly known as the ''shoulde ...

and is typical for stahleckeriid dicynodonts, including a relatively large glenoid opening for the shoulder joint directed back and out to the side, indicating a sprawled forelimb posture. The forelimb itself is only known from the end of the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

and the proximal portion of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

. The humerus is largely typical of kannemeyeriiform dicynodonts in shape, however, the distal end is unusually large and thickened compared to other stahleckeriids. The

capitulum capitulum (plural capitula) may refer to: *the Latin word for chapter ** an index or list of chapters at the head of a gospel manuscript ** a short reading in the Liturgy of the Hours *** derived from which, it is the Latin for the assembly known ...

(part of the elbow) in the only known specimen is unossified and would have been

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...

, suggesting the specimen may be immature compared to similarly sized specimens of ''Placerias''. The known portion of ulna is badly worn, but the roundness of its tip suggests that ''Pentasaurus'' had a separated

olecranon The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon ...

process of the elbow, similar to ''Placerias'' and ''

Ischigualastia ''Ischigualastia'' is an extinct genus of large dicynodont therapsids that lived during the Late Carnian age and the Early Norian age of the Late Triassic Period. The genus was found in and named after the Ischigualasto Formation (Cancha de Boc ...

'' but unlike some specimens of ''Stahleckeria''. An unidentified long bone may represent a

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

. The pelvis is known from a partial left pubis and

ischium The ischium () form ...

and is typical of kannemeyeriiforms, including notable 'twisting' of the pubic shaft. The only known hindlimb element is the proximal end of a right

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

, and likewise it is typical of kannemeyeriiform dicynodonts. Although similar in construction to

dinosaurs, the internal structure visible at the broken end shows extensive

trabecular bone A trabecula (plural trabeculae, from Latin for "small beam") is a small, often microscopic, tissue element in the form of a small beam, strut or rod that supports or anchors a framework of parts within a body or organ. A trabecula generally has ...

, characteristic of Triassic dicynodonts.

History of discovery

The only known fossil remains of ''Pentasaurus'' were collected in the late 19th century by amateur

palaeontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Alfred "Gogga" Brown, an Englishman

recluse A recluse is a person who lives in voluntary seclusion from the public and society. The word is from the Latin ''recludere'', which means "shut up" or "sequester". Historically, the word referred to a Christian hermit's total isolation from th ...

who lived for much of his life in

Aliwal North Aliwal North (officially Maletswai) is a town in central South Africa on the banks of the Orange River, Eastern Cape Province. It is a medium-sized commercial centre in the northernmost part of the Eastern Cape. History Sir Harry Smith, then ...

in the

Eastern Cape Province The Eastern Cape is one of the provinces of South Africa. Its capital is Bhisho, but its two largest cities are East London and Gqeberha. The second largest province in the country (at 168,966 km2) after Northern Cape, it was formed in 1994 ...

, South Africa. His first fossil discoveries began in the 1860s, and his collections largely consisted of

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 theraps ...

fossils from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underlie ...

and Late Triassic–

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

Stormberg Group The Stormberg Group is one of the four geological groups that comprises the Karoo Supergroup in South Africa. It is the uppermost geological group representing the final phase of preserved sedimentation of the Karoo Basin. The Stormberg Group roc ...

. After initially corresponding with and sending a crate of fossils to the geologist

Sir Roderick Murchison Sir Roderick Impey Murchison, 1st Baronet, (19 February 1792 – 22 October 1871) was a Scottish geologist who served as director-general of the British Geological Survey from 1855 until his death in 1871. He is noted for investigating and ...

in London, Brown's relationships with English and later Parisian scientists soured. However, he later accepted an invitation to have his fossils shipped to the

Imperial Natural History Museum The Imperial Natural History Museum or Imperial-Royal Natural History Court Museum of Austria-Hungary was created by (Kaiser) Emperor Franz Joseph I during an extensive reorganization of the museum collections, from 1851 to 1876, and opened to th ...

, now a part of the

Natural History Museum, Vienna The Natural History Museum Vienna (german: Naturhistorisches Museum Wien) is a large natural history museum located in Vienna, Austria. It is one of the most important natural history museums worldwide. The NHM Vienna is one of the largest museum ...

in Austria. The fossils of ''Pentasaurus'' were part of a lot accessioned in 1876 that was determined to have been collected from a single locality in the Norian aged lower Elliot Formation, based on the shared brown-grey colour of the bones and brown

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...

surrounding them, as well as the association with fossils of the exclusively lower Elliot dinosaur ''

Eucnemesaurus ''Eucnemesaurus'' (; meaning "good tibia lizard", for its robust tibiae) is a basal sauropodomorph dinosaur genus usually considered to be a synonym of ''Euskelosaurus''. Recent study by Yates (2006), however, indicates that it is valid and the ...

''. Prior to the recognition of ''Pentasaurus'' body fossils, dicynodonts were inferred to have been present in the lower Elliot Formation from preserved footprints and track ways attributed to them. These

ichnofossil A trace fossil, also known as an ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, ...

s were described in 1970 as ''Pentasauropus incredibilis'', and were determined to have most likely been produced by dicynodonts from their large size and five short toes (

pentadactyly In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος (''dáktylos'') = "finger". Sometimes the ending "-dactylia" is used ...

). Similar trace fossils were identified on other continents, including

South South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...

and North America, where they were more confidently attributed to large dicynodonts. However, the absence of dicynodont fossils in some localities known to produce ''Pentasauropus'', as well as their younger age compared to known dicynodont genera, led palaeontologists Adrian Hunt and

Spencer Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils ...

to question this identification. Re-examination of Brown's collections in the 21st century revealed that a number of bones belonged to a large dicynodont, and in 2018 they were described by palaeontologist Christian Kammerer as a new genus and species, ''Pentasaurus goggai''. The generic name was derived from the

''Pentasauropus'' due to the likely association between the tracks and their track maker. Such

nomenclatural Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally ag ...

associations are not uncommon in palaeontology (e.g. '' Anchisauripus'', '' Megalosauropus''). However, typically the ichnofossil is named after the presumed track maker, whereas this situation is reversed in ''Pentasaurus''. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

is named in honour and recognition of Alfred Brown and his work, derived from his nickname 'Gogga' (pronounced ), an Afrikaan word loosely translated to "bug" that the local villagers nicknamed him for this unusual habits. ''Pentasaurus'' is only known from several isolated fragments of bone, of which a partial mandible (NHMW 1876-VII-B-114) was made the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen. However, because the bones were collected from one locality and that none of them are duplicated, as well as their similar sizes, it is possible that they all belong to only a single individual. Although disarticulated from each other, the known bones are characteristic of dicynodonts and cannot be referred to other large animals known from the Elliot Formation, such as '

rauisuchia "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilia ...

ns' or

dinosaurs. The inferred association between ''Pentasaurus'' and ''Pentasauropus incredibilis'' tracks cannot be definitively proven, as there are no known bones from the hands and feet to compare with the shape of the tracks. However, ''Pentasaurus'' is the only known candidate dicynodont track-maker in the Elliot Formation, and as other Norian localities are only ever known to have supported one species of dicynodont, it is almost certain that ''Pentasaurus'' produced the ''Pentasauropus'' tracks originally identified from the Elliot Formation.

Classification

Although fragmentary, the known remains of ''Pentasaurus'' are clearly dicynodont and are consistent with belonging to the only known

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

of Late Triassic dicynodonts, the

. Furthermore, a number of features of the lower jaw and humerus support its position in the stahleckeriid

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

Placeriinae, and so as a close relative of the North American ''

'', Moroccan '' Moghreberia'' and the giant Polish ''

Lisowicia ''Lisowicia'' is an extinct genus of giant dicynodont synapsid that lived in what is now Poland during the late Norian or earliest Rhaetian age of the Late Triassic Period, about 210–205 million years ago. ''Lisowicia'' is the largest known di ...

''. A

phylogenetic analysis 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 o ...

performed by Kammerer (2018) supported this relationship, however, it could not resolve the relationships within Placeriinae beyond a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

containing ''Pentasaurus'' and all other placeriines, as shown in the cladogram reproduced below. Later phylogenetic analyses including ''Pentasaurus'' produced the same results. Stahleckeriid mandibles

The precise relationships of ''Pentasaurus'' to other placeriines cannot be determined

cladistically Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived chara ...

due to the incompleteness of the known remains, nonetheless, it can still be readily distinguished from other placeriines. Particularly, ''Pentasaurus'' is characterised by the rounder shape of the beak on its lower jaw, compared to the more angular, straight edged beaks of ''Placerias'' and ''Moghreberia''. The robustness and position of the lateral dentary shelf far forward on the lower jaw is also unique to ''Pentasaurus'' among dicynodonts, as well as the thickness of its distal humerus. The paired mound-like rugosities over its frontals may also be a diagnostic trait of ''Pentasaurus''.

Palaeoecology

The lower Elliot Formation consists mostly of red-purple

mudstones Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' ...

and thick, stacked layers of sandstone deposited by

meandering river A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex bank w ...

channels on a

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

. The relatively narrow width (10s of metres) of the sandstone channels indicate that the river channels were stable and did not

migrate Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...

across the floodplain, and sedimentary structures preserved within the sandstone indicate that the rivers were slow-moving and perennial. The stability of the channels suggests that

riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...

forests were present along the banks of these rivers, which is further supported by the relatively high abundance of fossilised wood fragments found in the lower Elliot Formation. These riparian environments were separated by extensive floodplains that were less well vegetated, but likewise they show little evidence for desiccation. Overall, the evidence is consistent with a humid to semi-arid climate in the lower Elliot Formation, and was a wetter environment than the dry, arid upper Elliot Formation of the proceeding

. The fauna of the lower Elliot Formation is poorly known compared to the upper Elliot Formation, but they show some similarities to other Norian-aged faunas globally. Only two others

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...

are known from the lower Elliot Formation, the large herbivore '' Scalenodontoides'', a

traversodontid Traversodontidae is an extinct family of herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe and eastern North America. Tra ...

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 variety ...

and the small trithelodontid

Elliotherium ''Elliotherium'' is an extinct genus of cynodonts which existed in South Africa during the upper Triassic period. The type species is ''Elliotherium kersteni'', named after the Elliot Formation The Elliot Formation is a geological formation a ...

''.

Archosaurs Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avi ...

are better represented, though mostly by several species of herbivorous sauropodomorph dinosaurs. ''Eucnemesaurus'' was collected together with ''Pentasaurus'', and so very likely coexisted with it, but ''Pentasaurus'' may also have occurred with ''

Blikanasaurus ''Blikanasaurus'' is a genus of sauropodomorph dinosaur from the late Triassic of South Africa. The generic name ''Blikanasaurus'' is derived from Greek, meaning "lizard from Blikana". The species name ''cromptoni'' is taken from the surname of ...

'', ''

Sefapanosaurus ''Sefapanosaurus'' was an early, herbivorous sauropodomorph dinosaur occurring in the southern regions of Gondwana some 200 million years ago in the Late Triassic or Early Jurassic. The sauropodomorphs were the dominant terrestrial herbivores th ...

'' and ''

Meroktenos ''Meroktenos'' is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period of what is now Lesotho. Discovery and naming In 1959, François Ellenberger, Paul Ellenberger, Jean Fabre and Leonard Ginsburg discovere ...

'', as well as perhaps ''

Melanorosaurus ''Melanorosaurus'' (meaning "Black Mountain Lizard", from the Greek ''melas/'', "black", ''oros/'', "mountain" + ''/'', "lizard") is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. A herbivore from South Af ...

'' and ''

Plateosauravus ''Plateosauravus'' ("grandfather of ''Plateosaurus''") is a basal plateosaurian of uncertain affinities from the Late Triassic Elliot Formation of South Africa. Sidney Haughton named ''Plateosaurus cullingworthi'' in 1924 from a partial skeleto ...

'' depending on their

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostrati ...

positions. Predatory archosaurs are less well known, but include probable '

rauisuchian "Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians ...

' remains, including portions of jaws and teeth that were collected with ''Pentasaurus''. Predatory

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaurs were also present, but are only known from isolated teeth and footprints.

Temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

s are also known from the lower Elliot Formation, but consist of only of

chigutisaurids Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. ...

. The footprint record from the lower Elliot Formation records a similar set of fauna to those known from body fossils, although a singular footprint may indicate that

crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...

were also present.

Biogeography

The coexistence of ''Pentasaurus'' with large sauropodomorph dinosaurs including as ''Eucnemesaurus'' in the Elliot Formation is significant, as dicynodonts and large sauropodomorphs are otherwise not known to have coexisted anywhere else in world. Prior to the discovery of ''Pentasaurus'', it was even suggested that the two groups of herbivores never even coexisted at all, and that sauropodomorphs replaced dicynodonts as large herbivores in most Late Triassic ecosystems, either through ecological turnover or by direct competition. The coexistence of ''Pentasaurus'' and large sauropodomorphs in the lower Elliot Formation suggests that this may not be the case, and that the two groups may have instead been segregated by habitat preference, and may have fed upon different types of vegetation. ''Pentasaurus'' also represents the southernmost example of a placeriine in the world, refuting prior suggestions that placeriine dicynodonts were mostly restricted to the northern hemisphere and demonstrating instead that the group had a more global distribution.

References

{{Taxonbar, from=Q55392106 Kannemeyeriiformes Anomodont genera Late Triassic synapsids Norian genera Triassic South Africa Fossils of South Africa Fossil taxa described in 2018