Heterodontosauridae

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Heterodontosaurids
Temporal range: Early Jurassic – Early Cretaceous, 200–140  Ma
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Possible Late Triassic record
Heterodontosaurus tucki cast - University of California Museum of Paleontology - Berkeley, CA - DSC04696.JPG
Cast of specimen SAM-PK-K1332 of Heterodontosaurus tucki , University of California Museum of Palaeontology
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade:† Ornithischia
Clade:† Saphornithischia
Family:† Heterodontosauridae
Romer, 1966 (Kuhn, 1966)
Subgroups [1]
Synonyms
  • LycorhinidaeThulborn, 1971 [2]

Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group Genasauria. [3] Although their fossils are relatively rare and their group small in numbers, they have been found on all continents except Australia and Antarctica, with a range spanning the Early Jurassic to the Early Cretaceous.

Contents

Heterodontosaurids were fox-sized dinosaurs less than 2 metres (6.6 feet) in length, including a long tail. They are known mainly for their characteristic teeth, including enlarged canine-like tusks and cheek teeth adapted for chewing, analogous to those of Cretaceous hadrosaurids. Their diet was herbivorous or possibly omnivorous.

Description

Size comparison of many heterodontosaurids Heterodontosauridae Size Comparison by PaleoGeek.svg
Size comparison of many heterodontosaurids
Life restoration of Fruitadens Fruitadens.jpg
Life restoration of Fruitadens

Among heterodontosaurids, only Heterodontosaurus itself is known from a complete skeleton. Fragmentary skeletal remains of Abrictosaurus are known but have not been fully described, while most other heterodontosaurids are known only from jaw fragments and teeth. Consequently, most heterodontosaurid synapomorphies (defining features) have been described from the teeth and jaw bones. [4] [5] Heterodontosaurus measured just over 1 meter (3.3 ft) in length, [6] while the fragmentary remains of Lycorhinus may indicate a larger individual. [7]

Tianyulong from China appears to preserve filamentous integument which has been interpreted to be a variant of the proto-feathers found in some theropods. These filaments include a crest along its tail. The presence of this filamentous integument has been used to suggest that both ornithischians and saurischians were endothermic. [8]

Skull and teeth

Both Abrictosaurus and Heterodontosaurus had very large eyes. Underneath the eyes, the jugal bone projected sideways, a feature also present in ceratopsians. As in the jaws of most ornithischians, the anterior edge of the premaxilla (a bone at the tip of the upper jaw) was toothless and probably supported a keratinous beak (rhamphotheca), although heterodontosaurids did have teeth in the posterior section of the premaxilla. A large gap, called a diastema, separated these premaxillary teeth from those of the maxilla (the main upper jaw bone) in many ornithischians, but this diastema was characteristically arched in heterodontosaurids. The mandible (lower jaw) was tipped by the predentary, a bone unique to ornithischians. This bone also supported a beak similar to the one found on the premaxilla. All the teeth in the lower jaw were found on the dentary bone. [4]

Snouts of Heterodontosaurus (A), Abrictosaurus (B), and Tianyulong (C) Heterodontosaur snouts.jpg
Snouts of Heterodontosaurus (A), Abrictosaurus (B), and Tianyulong (C)

Heterodontosaurids are named for their strongly heterodont dentition. There were three premaxillary teeth. In the Early Jurassic Abrictosaurus, Heterodontosaurus, and Lycorhinus, the first two premaxillary teeth were small and conical, while the much larger third tooth resembled the canines of carnivoran mammals and is often called the caniniform or 'tusk'. A lower caniniform, larger than the upper, took the first position in the dentary and was accommodated by the arched diastema of the upper jaw when the mouth was closed. [4] These caniniforms were serrated on both the anterior and posterior edges in Heterodontosaurus and Lycorhinus, while those of Abrictosaurus bore serrations only on the anterior edge. [9] [10] In the Early Cretaceous Echinodon, there may have been two upper caniniforms, which were on the maxilla rather than the premaxilla, [11] and Fruitadens from the Late Jurassic may have had two lower caniniforms on each dentary. [12] [13]

Evolution of key masticatory specializations in heterodontosaurids, according to Sereno, 2012 Heterodontosauridae evolution.jpg
Evolution of key masticatory specializations in heterodontosaurids, according to Sereno, 2012

Like the characteristic tusks, the cheek teeth of derived heterodontosaurids were also unique among early ornithischians. Small ridges, or denticles, lined the edges of ornithischian cheek teeth in order to crop vegetation. These denticles extend only a third of the way down the tooth crown from the tip in all heterodontosaurids; in other ornithischians, the denticles extend further down towards the root. Basal forms like Abrictosaurus had cheek teeth in both maxilla and dentary that were generally similar to other ornithischians: widely spaced, each having a low crown and a strongly-developed ridge (cingulum) separating the crown from the root. In more derived forms like Lycorhinus and Heterodontosaurus, the teeth were chisel-shaped, with much higher crowns and no cingula, so that there was no difference in width between the crowns and the roots. [4]

These derived cheek teeth were overlapping, so that their crowns formed a continuous surface on which food could be chewed. The tooth rows were slightly inset from the side of the mouth, leaving a space outside the teeth that may have been bounded by a muscular cheek, which would have been necessary for chewing. The hadrosaurs and ceratopsians of the Cretaceous Period, as well as many herbivorous mammals, would convergently evolve somewhat analogous dental batteries. As opposed to hadrosaurs, which had hundreds of teeth constantly being replaced, tooth replacement in heterodontosaurids occurred far more slowly and several specimens have been found without a single replacement tooth in waiting. Characteristically, heterodontosaurids lacked the small openings (foramina) on the inside of the jaw bones which are thought to have aided in tooth development in most other ornithischians. Heterodontosaurids also boasted a unique spheroidal joint between the dentaries and the predentary, allowing the lower jaws to rotate outwards as the mouth was closed, grinding the cheek teeth against each other. Because of the slow replacement rate, this grinding produced extreme tooth wear that commonly obliterated most of the denticles in older teeth, although the increased height of the crowns gave each tooth a long life. [14]

Skeleton

Fossil of Tianyulong, muzzle, hand, feet and tail framed in red Tianyulong.jpg
Fossil of Tianyulong, muzzle, hand, feet and tail framed in red

The postcranial anatomy of Heterodontosaurus tucki has been well-described, although H. tucki is generally considered the most derived of the Early Jurassic heterodontosaurids, so it is impossible to know how many of its features were shared with other species. [4] The forelimbs were long for a dinosaur, over 70% of the length of the hindlimbs. The well-developed deltopectoral crest (a ridge for the attachment of chest and shoulder muscles) of the humerus and prominent olecranon process (where muscles that extend the forearm were attached) of the ulna indicate that the forelimb was powerful as well. There were five digits on the manus ('hand'). The first was large, tipped with a sharply curved claw, and would rotate inwards when flexed; Robert Bakker called it the 'twist-thumb'. [15] The second digit was the longest, slightly longer than the third. Both of these digits bore claws, while the clawless fourth and fifth digits were very small and simple in comparison. In the hindlimb, the tibia was 30% longer than the femur, which is generally considered an adaptation for speed. The tibia and fibula of the lower leg were fused to the astragalus and calcaneum of the ankle, forming a 'tibiofibiotarsus' convergently with modern birds. Also similarly to birds, the lower tarsal (ankle) bones and metatarsals were fused to form a 'tarsometatarsus.' There are four digits in the pes (hindfoot), with only the second, third, and fourth contacting the ground. The tail, unlike many other ornithischians, did not have ossified tendons to maintain a rigid posture and was probably flexible. [6] The fragmentary skeleton known for Abrictosaurus has never been fully described, although the forelimb and manus were smaller than in Heterodontosaurus. Also, the fourth and fifth digits of the forelimb each bear one fewer phalanx bone. [16]

Classification

Holotype jawbone of Geranosaurus Geranosaurus.png
Holotype jawbone of Geranosaurus

South African paleontologist Robert Broom created the name Geranosaurus in 1911 for dinosaur jaw bones missing all of the teeth and some partial associated limb bones. [17] In 1924, Lycorhinus was named, and classified as a cynodont, by Sidney Haughton. [18] Heterodontosaurus was named in 1962 and it, Lycorhinus and Geranosaurus were recognized as closely related ornithischian dinosaurs. [19] Alfred Romer named Heterodontosauridae in 1966 as a family of ornithischian dinosaurs including Heterodontosaurus and Lycorhinus. [20] Kuhn independently proposed Heterodontosauridae in the same year and is sometimes cited as its principal author. [21] It was defined as a clade in 1998 by Paul Sereno [22] and redefined by him in 2005 as the stem clade consisting of Heterodontosaurus tucki and all species more closely related to Heterodontosaurus than to Parasaurolophus walkeri , Pachycephalosaurus wyomingensis , Triceratops horridus , or Ankylosaurus magniventris . [23]

Heterodontosauridae includes the genera Abrictosaurus, Lycorhinus, and Heterodontosaurus, all from South Africa. While Richard Thulborn once reassigned all three to Lycorhinus, [16] all other authors consider the three genera distinct. [10] Within the family, Heterodontosaurus and Lycorhinus are considered sister taxa, with Abrictosaurus as a basal member. [5] Geranosaurus is also a heterodontosaurid, but is usually considered a nomen dubium because the type specimen is missing all its teeth, making it indistinguishable from any other genus in the family. [4] More recently, the genus Echinodon has been considered a heterodontosaurid in several studies. [11] [12] Lanasaurus was named for an upper jaw in 1975, [24] but more recent discoveries have shown that it belongs to Lycorhinus instead, making Lanasaurus a junior synonym of that genus. [7] Dianchungosaurus was once considered a heterodontosaurid from Asia, [25] but it has since been shown that the remains were a chimera of prosauropod and mesoeucrocodylian remains. [26] José Bonaparte also classified the South American Pisanosaurus as a heterodontosaurid at one time, [27] but this animal is now known to be a more basal ornithischian. [28]

Skull of Abrictosaurus Abrictosaurus.jpg
Skull of Abrictosaurus

The membership of Heterodontosauridae is well-established in comparison to its uncertain phylogenetic position. Several early studies suggested that heterodontosaurids were very primitive ornithischians. [6] [19] Due to supposed similarities in the morphology of the forelimbs, Robert Bakker proposed a relationship between heterodontosaurids and early sauropodomorphs like Anchisaurus , bridging the orders Saurischia and Ornithischia. [15] The dominant hypothesis over the last several decades has placed heterodontosaurids as basal ornithopods. [4] [5] [9] [29] However, others have suggested that heterodontosaurids instead share a common ancestor with Marginocephalia (ceratopsians and pachycephalosaurs), [30] [31] a hypothesis that has found support in some early 21st century studies. [32] [33] The clade containing heterodontosaurids and marginocephalians has been named Heterodontosauriformes. [34] Heterodontosaurids have also been seen as basal to both ornithopods and marginocephalians. [35] [36] In 2007, a cladistic analysis suggested that heterodontosaurids are basal to all known ornithischians except Pisanosaurus, a result that echoes some of the very earliest work on the family. [37] [38] However, a study by Bonaparte found the Pisanosauridae to be synonymous with the Heterodontosauridae and not a separate family in its own right, thereby including Pisanosaurus as a heterodontosaur. [39] Butler et al. (2010) found the Heterodontosauridae to be the most basal known significant ornithischian radiation. [40]

The cladogram below shows the interrelationships within Heterodontosauridae, and follows the analysis by Sereno, 2012: [41]

Heterodontosauridae 

A 2020 reworking of Cerapoda by Dieudonné and colleagues recovered the animals traditionally considered 'heterodontosaurids' as a basal grouping within Pachycephalosauria, paraphyletic with respect to the traditional, dome-headed pachycephalosaurs. This result was based on numerous skull characteristics including the dentition, and also to account for the fact that pachycephalosaur fossils are completely unknown from the Jurassic period. Modern understanding of ornithischian phylogeny implies that Jurassic pachycephalosaurs must exist, because numerous Jurassic ceratopsians have been found, yet no such pachycephalosaurs have been confidently identified. This analysis was done to elaborate on the findings of Baron and colleagues (2017), which found Chilesaurus to be a basal ornithischian. [42] The phylogenetic analysis was conducted with Chilesaurus coded as an ornithischian, which also had implications for the phylogeny of ornithopods.

The cladogram below is an abridged version of Dieudonne and colleagues' findings: [43]

Ornithischia

Distribution

Biogeographic distribution of heterodontosaurids in time Heterodontosauridae biogeography.jpg
Biogeographic distribution of heterodontosaurids in time

While originally known only from the Early Jurassic of southern Africa, heterodontosaurid remains are now known from four continents. Early in heterodontosaurid history, the supercontinent Pangaea was still largely intact, allowing the family to achieve a near-worldwide distribution. [11] The oldest known possible heterodontosaurid remains are a jaw fragment and isolated teeth from the Laguna Colorada Formation of Argentina, which dates back to the Late Triassic. These remains have a derived morphology similar to Heterodontosaurus, including a caniniform with serrations on both anterior and posterior edges, as well as high-crowned maxillary teeth lacking a cingulum. [44] Irmis et al. (2007) tentatively agreed that this fossil material represents a heterodontosaurid, but stated that additional material is needed to confirm this assignment because the specimen is poorly preserved, [45] while Sereno (2012) only stated that this material may represent an ornithischian or even specifically a heterodontosaurid. [1] Olsen, Kent & Whiteside (2010) noted that the age of the Laguna Colorada Formation itself is poorly constrained, and thus it wasn't conclusively determined whether the putative heterodontosaurid from this formation is of Triassic or Jurassic age. [46] The most diverse heterodontosaurid fauna comes from the Early Jurassic of southern Africa, where fossils of Heterodontosaurus, Abrictosaurus, Lycorhinus, and the dubious Geranosaurus are found. [4]

Undescribed Early Jurassic heterodontosaurids are also known from the United States [47] and Mexico, [48] respectively. In addition, beginning in the 1970s, a great deal of fossil material was discovered from the Late Jurassic Morrison Formation near Fruita, Colorado in the United States. [12] Described in print in 2009, this material was placed in the genus Fruitadens . [13] Heterodontosaurid teeth lacking a cingulum have also been described from Late Jurassic and Early Cretaceous formations in Spain and Portugal. [49] The remains of Echinodon were redescribed in 2002, showing that it may represent a late-surviving heterodontosaurid from the Berriasian stage of the Early Cretaceous in southern England. [11] Dianchungosaurus from the Early Jurassic of China is no longer considered a heterodontosaurid; though one Middle-Late Jurassic Asian form is known ( Tianyulong ). [8] Indeterminate cheek teeth possibly representing heterodontosaurids are also known from the Barremian aged Wessex Formation of southern England, which if confirmed would represent the youngest record of the group. [50]

Paleobiology

Restoration of Pegomastax Pegomastax africana reconstruction.jpg
Restoration of Pegomastax

Most heterodontosaurid fossils are found in geologic formations that represent arid to semi-arid environments, including the Upper Elliot Formation of South Africa and the Purbeck Beds of southern England. [5] It has been suggested that heterodontosaurids underwent seasonal aestivation or hibernation during the driest times of year. Due to the lack of replacement teeth in most heterodontosaurids, it was proposed that the entire set of teeth was replaced during this dormant period, as it seemed that continual and sporadic replacement of teeth would interrupt the function of the tooth row as a single chewing surface. [16] However, this was based on a misunderstanding of heterodontosaurid jaw mechanics. [51] It was thought that heterodontosaurids actually did replace their teeth continually, though more slowly than in other reptiles, but CT scanning of skulls from juvenile and mature Heterodontosaurus shows no replacement teeth. [52] There is currently no evidence that supports the hypothesis of aestivation in heterodontosaurids, [4] but it cannot be rejected, based on the skull scans. [52]

While the cheek teeth of heterodontosaurids are clearly adapted for grinding tough plant material, their diet may have been omnivorous. The pointed premaxillary teeth and sharp, curved claws on the forelimbs suggest some degree of predatory behavior. It has been suggested that the long, powerful forelimbs of Heterodontosaurus may have been useful for tearing into insect nests, similarly to modern anteaters. These forelimbs may have also functioned as digging tools, perhaps for roots and tubers. [4]

Tianyulong restoration Tianyulong BW.jpg
Tianyulong restoration

The length of the forelimb compared to the hindlimb suggests that Heterodontosaurus might have been partially quadrupedal, and the prominent olecranon process and hyperextendable digits of the forelimb are found in many quadrupeds. However, the manus is clearly designed for grasping, not weight support. Many features of the hindlimb, including the long tibia and foot, as well as the fusion of the tibiofibiotarsus and tarsometatarsus, indicate that heterodontosaurids were adapted to run quickly on the hindlegs, so it is unlikely that Heterodontosaurus moved on all four limbs except perhaps when feeding. [6]

The short tusks found in all known heterodontosaurids strongly resemble tusks found in modern musk deer, peccaries and pigs. In many of these animals (as well as the longer-tusked walrus and Asian elephants), this is a sexually dimorphic trait, with tusks only found in males. The type specimen of Abrictosaurus lacks tusks and was originally described as a female. [16] While this remains possible, the unfused sacral vertebrae and short face indicate that this specimen represents a juvenile animal. A second, larger specimen originally proposed to belong to Abrictosaurus clearly possesses tusks, which was used to support the idea that tusks are found only in adults, rather than being a secondary sexual characteristic of males. These tusks could have been used for combat or display with members of the same species or with other species. [4] The absence of tusks in juvenile Abrictosaurus could also be another characteristic separating it from other heterodontosaurids as well, as tusks are known in juvenile Heterodontosaurus. Other proposed functions for the tusks include defense and use in an occasionally omnivorous diet. [52] However, this specimen was alternatively reassigned to Lycorhinus by Sereno in 2012, which is already known to have possessed tusks and therefore their absence in Abrictosaurus may not have been a result of age. [1]

In 2005 a small complete fossilized heterodontosaurid skeleton more than 200 million years old was discovered in South Africa. In July 2016 it was scanned by a team of South African researchers using the European Synchrotron Radiation Facility; the scan of the dentition revealed palate bones less than a millimeter thick. [53]

Related Research Articles

<span class="mw-page-title-main">Ornithischia</span> Extinct clade of dinosaurs

Ornithischia is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name Ornithischia, or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- (ὀρνιθ-), meaning "bird", and ischion (ἴσχιον), meaning "hip". However, birds are only distantly related to this group as birds are theropod dinosaurs. Ornithischians with well known anatomical adaptations include the ceratopsians or "horn-faced" dinosaurs, the pachycephalosaurs or "thick-headed" dinosaurs, the armored dinosaurs (Thyreophora) such as stegosaurs and ankylosaurs, and the ornithopods. There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous pelts, and there is much debate over whether these filaments found in specimens of Tianyulong, Psittacosaurus, and Kulindadromeus may have been primitive feathers.

<i>Lesothosaurus</i> Extinct genus of ornithischian dinosaur

Lesothosaurus is a monospecific genus of ornithischian dinosaur that lived during the Early Jurassic in what is now South Africa and Lesotho. It was named by paleontologist Peter Galton in 1978, the name meaning "lizard from Lesotho". The genus has only one valid species, Lesothosaurus diagnosticus. Lesothosaurus is one of the most completely-known early ornithischians, based on numerous skull and postcranial fossils from the Upper Elliot Formation. It had a simpler tooth and jaw anatomy than later ornithischians, and may have been omnivorous in some parts of the year.

<span class="mw-page-title-main">Pachycephalosauria</span> Extinct clade of dinosaurs

Pachycephalosauria is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephalosaurs lived during the Late Cretaceous Period, dating between about 85.8 and 66 million years ago. They are exclusive to the Northern Hemisphere, all of them being found in North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls. Skulls can be domed, flat, or wedge-shaped depending on the species, and are all heavily ossified. The domes were often surrounded by nodes and/or spikes. Partial skeletons have been found of several pachycephalosaur species, but to date no complete skeletons have been discovered. Often isolated skull fragments are the only bones that are found.

<i>Abrictosaurus</i> Extinct genus of dinosaur from the early Jurassic of southern Africa

Abrictosaurus is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic in what is now in parts of southern Africa such as Lesotho and South Africa. It was a bipedal herbivore or omnivore and was one of the most basal heterodontosaurids. It was approximately 1.2 metres (3.9 ft) long and weighed between 0.68 and 3 kilograms.

<i>Echinodon</i> Extinct genus of dinosaurs

Echinodon is a genus of heterodontosaurid dinosaur that lived during the earliest Cretaceous of southern England and possibly western France in the Berriasian epoch. The first specimens were jaw bones named Echinodon becklesii by Sir Richard Owen in 1861, and since their original description only additional teeth have been discovered. The specific name honours collector Samuel Beckles who discovered the material of Echinodon and many other taxa from across England, while the genus name translates as "prickly tooth" in reference to the dental anatomy of the taxon.

<i>Heterodontosaurus</i> Extinct genus of dinosaur from the early Jurassic of South Africa

Heterodontosaurus is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic, 200–190 million years ago. Its only known member species, Heterodontosaurus tucki, was named in 1962 based on a skull discovered in South Africa. The genus name means "different toothed lizard", in reference to its unusual, heterodont dentition; the specific name honours G. C. Tuck, who supported the discoverers. Further specimens have since been found, including an almost complete skeleton in 1966.

<i>Alocodon</i> Extinct genus of dinosaurs

Alocodon is a genus of ornithischian dinosaur known from multiple teeth from the Middle or Late Jurassic Cabaços Formation of Portugal, and also the Forest Marble and Chipping Norton Formations of England. A single species is known, A. kuehnei.

Trimucrodon is a genus of ornithischian dinosaur from the Late Jurassic Lourinhã Formation of Portugal. The type, and currently only, species is T. cuneatus.

<i>Pisanosaurus</i> Extinct genus of dinosauriforms

Pisanosaurus is an extinct genus of early dinosauriform, likely an ornithischian or silesaurid, from the Late Triassic of Argentina. It was a small, lightly built, ground-dwelling herbivore, that could grow up to an estimated 1 m (3.3 ft) long. Only one species, the type, Pisanosaurus mertii, is known, based on a single partial skeleton discovered in the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. This part of the formation has been dated to the late Carnian, approximately 229 million years ago.

Gongbusaurus is a genus of ornithischian, perhaps ornithopod, dinosaur that lived between about 160 and 157 million years ago, in the Late Jurassic period. A small herbivore, it is very poorly known. Two species have been assigned to it, but as the original name is based on teeth, there is no concrete evidence to connect the two species. Its fossils have been found in China.

<i>Lycorhinus</i> Extinct genus of dinosaur from the early Jurassic of South Africa

Lycorhinus is a genus of heterodontosaurid ornithischian dinosaur from the Early Jurassic strata of the Elliot Formation located in the Cape Province, South Africa.

<i>Yinlong</i> Extinct genus of dinosaurs

Yinlong is a genus of basal ceratopsian dinosaur from the Late Jurassic Period of central Asia. By far the earliest known ceratopsian, it was a small, primarily bipedal herbivore.

<i>Eocursor</i> Extinct genus of dinosaur from early Jurassic South Africa

Eocursor is genus of basal ornithischian dinosaur that lived in what is now South Africa during the Early Jurassic. Remains of this animal have been found in the Upper Elliot Formation and it is among the most completely known early ornithischians, shedding new light on the origin of the group.

<span class="mw-page-title-main">Genasauria</span> Extinct clade of dinosaurs

Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word gena meaning ‘cheek’ and the Greek word saúra (σαύρα) meaning ‘lizard.’ It is hypothesized that Genasauria had diverged from Lesothosaurus by the Early Jurassic. Cranial features that characterize Genasauria include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous anterior portion of the premaxilla. A distinguishing postcranial feature of Genasauria is a pubic peduncle of the ilium that is less robust than the ischial peduncle. Genasauria is commonly divided into Neornithischia and Thyreophora. Neornithischia is characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischia includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophora is characterized by body armor and includes stegosaurs, ankylosaurs, Scelidosaurus, and Scutellosaurus.

<i>Fruitadens</i> Extinct genus of dinosaurs

Fruitadens is a genus of heterodontosaurid dinosaur. The name means "Fruita teeth", in reference to Fruita, Colorado (USA), where its fossils were first found. It is known from partial skulls and skeletons from at least four individuals of differing biological ages, found in Tithonian rocks of the Morrison Formation in Colorado. Fruitadens is one of the smallest known ornithischian dinosaur, with young adults estimated at 65 to 75 cm in length and 0.5 to 0.75 kg in weight. It is interpreted as an omnivore and represents one of the latest-surviving heterodontosaurids.

<i>Manidens</i> Extinct genus of dinosaurs

Manidens is an extinct genus of heterodontosaurid dinosaur from the Early Jurassic of Patagonia. It is a sister taxon of the closely related Pegomastax from South Africa. Fossils have been found in the Cañadón Asfalto Formation in Chubut Province, Argentina, dating to the Toarcian.

<i>Pegomastax</i> Extinct genus of dinosaurs

Pegomastax is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic of South Africa. The only known specimen was discovered in a 1966-1967 expedition in Transkei District of Cape Province, but wasn't described until 2012 when Paul Sereno named it as the new taxon Pegomastax africana. The genus name is derived from the Greek for "strong jaw", and the species name describes the provenance of Africa; it was originally spelled africanus, was corrected to africana to align with the gender of the genus name.

<span class="mw-page-title-main">Heterodontosaurinae</span> Extinct subfamily of dinosaurs

Heterodontosaurinae is an extinct subfamily of heterodontosaurid ornithischian dinosaurs from the earliest to the mid Middle Jurassic of Africa and South America. Currently, the basalmost known heterodontosaurine is Lycorhinus angustidens from the Early Jurassic of Cape Province, South Africa. Heterodontosaurines are small-bodied ornithischians characterized by their cheek tooth crowns that are taller than wide, and jaw joint set below the axis of occlusion between maxillary and dentary teeth. Heterodontosaurinae was implicitly named in 1966 by Oskar Kuhn as he is the author of the family Heterodontosauridae. It is a stem-based taxon defined phylogenetically for the first time by Paul Sereno in 2012 as "the most inclusive clade containing Heterodontosaurus tucki but not Tianyulong confuciusi, Fruitadens haagarorum, Echinodon becklesii."

<i>Laquintasaura</i> Extinct genus of dinosaurs

Laquintasaura is a genus of Venezuelan ornithischian dinosaur containing only the type species Laquintasaura venezuelae. The species was the first dinosaur to have been identified from Venezuela. It is known from extensive remains, all from a singular bonebed locality which has been sampled for specimen blocks over the course of several expeditions, largely led by Marcelo R Sánchez-Villagra. A small, very primitive animal, it is known for its distinct dental anatomy and for being one of the earliest and most primitive ornithischians in the fossil record. Taxonomic uncertainty has led to conflicting theories that it is either as the base of Ornithischia or at the base of the subgroup Thyreophora. In either model, its dating to around 200 million years ago, at the start of the Jurassic, existence in equatorial latitudes, and primitive nature make it a key view into early ornithischian evolution. It's thought that Laquintasaura would've lived in groups and had a possible omnivorous diet, living on a seasonal alluvial plain and being preyed about by the contemporary Tachiraptor.

References

  1. 1 2 3 Sereno, Paul C. (2012). "Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs". ZooKeys (226): 1–225. doi: 10.3897/zookeys.226.2840 . PMC   3491919 . PMID   23166462.
  2. ↑ R.A. Thulborn, 1971, "Origins and evolution of ornithischian dinosaurs", Nature234(5324): 75-78
  3. ↑ Madzia, Daniel; Arbour, Victoria M.; Boyd, Clint A.; Farke, Andrew A.; Cruzado-Caballero, Penélope; Evans, David C. (2021-12-09). "The phylogenetic nomenclature of ornithischian dinosaurs". PeerJ. 9: e12362. doi: 10.7717/peerj.12362 . ISSN   2167-8359. PMC   8667728 . PMID   34966571.
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