''Lesothosaurus'' is a monospecific

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 ...

ornithischia Ornithischia () is an extinct order 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 s ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

that lived during the Early Jurassic in what is now

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

and

Lesotho Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked country, landlocked as an Enclave and exclave, enclave in South Africa. It is situated in the Maloti Mountains and contains the Thabana Ntlenyana, highest mountains in Sou ...

. It was named by

paleontologist 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 ...

Peter Galton in 1978, the name meaning "

lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...

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.

Discovery and naming

Fossils referrable to ''Lesothosaurus'' may have been known from as early as 1959, when a right dentary (lower jawbone) fragment bearing three teeth was collected by French geologist Jean Fabre from the

Red Beds Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain ...

of the Upper Elliot Formation near Mapheteng in

, Southern Africa, dating to the Early Jurassic (199(?)-190 million years ago).Ginsburg, L., (1964), "Decouverte d’un Scelidosaurien (Dinosaure ornithischien) dans le Trias superieur du Basutoland", Comptes Rendus de l'Académie des Sciences de Paris, 258; 2366–2368. The dentary was described as the holotype of a new genus and species, '' Fabrosaurus australis'', by paleontologist Leonard Ginsburg in 1964. Ginsburg placed it in the family

Scelidosauridae ''Scelidosaurus'' (; with the intended meaning of "limb lizard", from Greek / meaning 'rib of beef' and ''sauros''/ meaning 'lizard')Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. is a gen ...

and diagnosed it based on its unusual tooth morphology when compared to the only other contemporary ornithischian '' Heterodontosaurus''. Due to its fragmentary nature, ''Fabrosaurus'' is now seen as a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium'' it may be impossible to determine whether a s ...

'', though the holotype is likely from an individual of ''Lesothosaurus''. The holotype was all that was known until expeditions by the London University College to the same site in Lesotho from 1963 to 1964 recovered scores of fossils from ''Lesothosaurus'', including a partial skeleton including a skull and another isolated partial skull (NHMUK PV RU B17 & NHMUK PV RU B23). These specimens were described in the 1970s as belonging to ''Fabrosaurus'' by geologist

Richard A. Thulborn Richard Anthony (Tony) Thulborn is a British paleontologist. He is recognized as an expert in dinosaur tracks, and as one of the most productive paleontologists of his time. In 1982, Thulborn debunked the purported plesiosaur embryos discovered by ...

. A joint expedition between the

NHMUK The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum (Lo ...

, London University College,

Yale University Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the wo ...

, and the South African Museum collected many additional specimens of ''Lesothosaurus'' from the same site in 1967-68. This included very well preserved cranial material, some of the best known, that was described in the 1991. LesothosaurusFossilDiscoveriesMap

British paleontologist Peter Galton named ''Lesothosaurus diagnosticus'' in 1968, with NHMUK PV RU B17 and NHMUK PV RU B23 as the syntypes (the series of fossils that diagnose a species). The generic name ''Lesothosaurus'' is derived from the Kingdom of Lesotho, where the fossils were discovered, and the Latin root sauros meaning “lizard”, a root commonly used in dinosaur names. The specific name ''diagnosticus'' is derived from the Greek root ''diagnostikos'' meaning “distinguished” in reference to ''Lesothosaurus'' being a distinct member of

Fabrosauridae Ornithischia () is an extinct order 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 ...

. In the material referred to ''Lesothosaurus'', Galton stated that some of it was instead from a “large fabrosaurid”. This “large fabrosaurid” was finally named in 2005, dubbed ''Stormbergia dangershoeki'', on the basis of the partial postcranial skeleton SAM-PK-K1105. This species almost certainly represents the adult form of ''Lesothosaurus''. ''Stormbergia'' was named for the

Stormberg Series 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 ...

of rocks in southern Africa, which includes the Elliot Formation, and the location (Dangerhoek Farm) in South Africa at which the type specimen was found. The type specimen consists of a partial postcranial skeleton, with two additional referred specimens assigned to the species. Fossils from Elliot Formation sites in South Africa outside of Lesotho in Jamestown were described in the 2000s, including a nearly complete skeleton of an adult preserved in articulation. A study published in 2017 by Baron, Norman & Barrett demonstrated that the differences between ''Stormbergia'' and ''Lesothosaurus'' are most likely related to the animal's growth. The authors argued that ''Stormbergia'' is a junior subjective synonym of ''Lesothosaurus'' and should be regarded as invalid. Several other skull and postcranial specimens have been discovered since, including the description of two partial skulls in 2002, which preserved signs of individual variation. Redescription of the syntypes came in 2015 and 2017, including the integration of CT technology.

Description

Due to the great quantity and quality of specimens known from ''Lesothosaurus'', information about its anatomy is known in detail. ''Lesothosaurus'' was a lightly built, bipedal animal that varied between 1 (3.3 ft) to 2 meters (6.6 ft) long. It was one of the earliest

ns. Its long slender legs, small arms with hands that would not have been able to grasp properly, and slender tail all suggest that it was a fast runner. Like all ornithischians, the tips of ''Lesothosaurus'' upper and lower jaws were horny, forming a beaklike structure. Behind the beak were leaf-shaped

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

that lined the jaws. The teeth of the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

e (six per side) are more slender and curved than the maxillary teeth. Analysis of its teeth has shown that ''Lesothosaurus'' sliced up its food with its beak and was not able to chew its food. Studies of the tooth wear have shown much less abrasion on the teeth than would be expected of a plant-eater feeding mainly on tough, arid-climate plants, and concluded that ''Lesothosaurus'' was probably an opportunistic

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutr ...

, feeding primarily on small animals during seasons when softer plants were not available. The small skull of ''Lesothosaurus'' was narrow and pointed, with large eye sockets. It had large cavities for the eye and jaw muscles. The tip of the snout likely ended in a small beak, based on a blade-like predentary bone (at the tip of the lower jaw) and a roughly-texture front end of the cranium. Its teeth were pointed with grooved edges. The skull was mounted on a short but flexible neck. A bonebed of ''Lesothosaurus'' described in 2016 includes material from three large individuals. This association suggest that this early ornithischian dinosaur may have lived in groups.

Skull and dentition

The skull and teeth of ''Lesothosaurus'' are more generalized than the heavily specialized and unusual anatomies of the contemporary scelidosaurid and

heterodontosaurid 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 ...

ornithischians, which exhibit traits like

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...

s and extreme

heterodont In anatomy, a heterodont (from Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology. In vertebrates, heterodont pertains to animals where teeth are differentiated into different forms. For example, ...

y. The best preserved skull is NHMUK PV RU B23, though it is missing some elements. The skull was unlike the triangular skull of '' Heterodontosaurus'' in that the

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

half was boxy while the anterior half was tapered and elongated. The height apex of the cranium is just behind the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

(eye socket) in lateral view and the

skull roof The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In comparati ...

( frontals, parietals) are gently rounded in lateral view. The snout is smoothly tapered to the

(snout tip bone). The skull lacks a break in slope along the snout

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

to the orbit, as in the contemporary ''Heterodontosaurus''. The orbits are round and large relative to the skull size (making up 36% of the basal skull length i. e. from the premaxilla tip to the posterior margin of the

basioccipital The basilar part of the occipital bone (also basioccipital) extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined t ...

). The skulls bears a relatively small, sub-triangular antorbital fenestra (a large gap of bone) with an apex pointing dorsally and a length that is circa 13% of basal skull length. The

supratemporal fenestra 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 ...

e are anteroposteriorly longer than mediolaterally wide, with a sub-ovary to sub-triangular outline in dorsal view. In contrast, the

infratemporal 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, ...

e are sub-rectangular in lateral view and extend for most of the skull’s height. The infratemporal fenestra is oblong with an oblique axis, while the supratemporal fenestra is oval in outline. The anterior

naris A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

(nostril) had several small, sub-ovate openings along its length. The craniomandibular joint (where the skull contacts the jaw bone) is depressed relative to the margin of the maxillary alveoli. There are 15-16 tooth positions in the maxilla, in contrary to the 11 preserved in ''

Pisanosaurus ''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 long. Onl ...

''’ (a Late Triassic

dinosauriform Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...

that may be an ornithischian). There are 20 tooth positions in the dentary of ''Lesothosaurus,'' but only 15 are preserved in ''Pisanosaurus.'' The alveolar foramina are on the medial wall of the maxilla and dentary, one per tooth position, and represent the area where the neurovascular supply accesses the dental lamina. This condition is similar to that in the extant Lepidosaurs, which have lizard lips, leading some paleontologists to suggest that ''Lesothosaurus'' had cheeks and lips covering its teeth. The cranium is widest across the postorbitals in dorsal view. It tapers anteriorly to the premaxillae, which creates a short, strongly pointed muzzle. The skull is widest at the midshafts of the quadrates in occipital view.Norman, D. B., Witmer, L. M., & Weishampel, D. B. (2004). Basal ornithischia. ''The dinosauria'', ''2'', 325-334. 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 ...

(lower jaw) of ''Lesothosaurus'' has a nearly straight ventral margin and bears only a slight upturn at its anterior tip. The mandible is made up mostly of the dentary, which is 50% of its length in lateral view. Characteristically of Ornithischians, there is a small beak-like bone at the tip of the dentary known as the predentary. The predentary is shaped like an arrowhead in ventral view, with one elongated central keel with smaller lateral processes jutting off the sides. The

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or oral ...

margin is smooth and straight in lateral view, with an uncurved anterior tip. Two foramina are preserved on and near the lateral processes, suggesting that this element was well-supplied with blood and nerves. There is a well-developed coronoid eminence, but it does not expand dorsally into the tall, distinct processes (projection of bone) like in advanced Ornithischians like ''

Triceratops ''Triceratops'' ( ; ) is a genus of herbivore, herbivorous Chasmosaurinae, chasmosaurine Ceratopsidae, ceratopsid dinosaur that first appeared during the late Maastrichtian stage of the Late Cretaceous Period (geology), period, about 68 m ...

'' and ''

Zalmoxes ''Zalmoxes'' is an extinct genus of rhabdodontid ornithopod dinosaur from the Maastrichtian of Romania. The genus is known from specimens first named as the species '' Mochlodon robustum'' in 1899 by Franz Nopcsa before being reclassified as ...

.'' The jaw joint is slightly depressed relative to the alveolar bar that takes up most of the mandible. The mandible preserves an anteroposteriorly elongated fenestra between the dentary, angular, and surrangular, similar to the ones in the skull, that would make the mandible lighter. The mandible differentiates from those of other Ornithischians greatly in that an inturned, ‘spout-like’ mandibular symphysis is preserved. ''Lesothosaurus'' has two types of teeth preserved: long, curved, sharp premaxillary teeth at the front of the mouth; wide, short, robust maxillary and dentary teeth. There are 6 premaxillary teeth on the left and right sides of the premaxilla which are preceded by a small edentulous (tooth-lacking) section that shows signs of preserving a large rhampthotheca (beak) made of

keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...

. A neck and slight swelling divides the base of the

tooth crown In dentistry, crown refers to the anatomical area of teeth, usually covered by tooth enamel, enamel. The crown is usually visible in the mouth after tooth development, developing below the gingiva and then tooth eruption, erupting into place. ...

from the long, subcylindrical

roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...

. The

lingual Lingual may refer to: * Tongue, a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication * Lingual, in palaeontology, the side of the teeth that faces the tongue * Lingual artery arises from the e ...

surface of the more medial premaxillary teeth have a vertical furrow and an adjacent sharp ride that extends towards the crown’s mesial edge. The last two teeth crowns in the series acquire distal and medial denticles. The posterior process of the premaxilla lacks alvelovi, creating a small

diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...

(gap) inbetween the premaxillary and maxillary tooth rows. The maxillary and dentary teeth are low, triangular, and “leaf-shaped” with a distinct neck and cingulum. The denticles are coarse on the medial and distal tooth borders, with sporadically developed high-angled marginal tooth wearing. This suggests rapid

tooth replacement Tooth loss is a process in which one or more teeth come loose and fall out. Tooth loss is normal for deciduous teeth (baby teeth), when they are replaced by a person's adult teeth. Otherwise, losing teeth is undesirable and is the result of injur ...

in these teeth.

Postcrania

Although many specimens are known, some elements of ''Lesothosaurus’'' postcranial anatomy are poorly known, especially in the axial skeleton which is incomplete in all specimens. The cervical (neck) vertebrae were only 9 in number, but no full cervical series are known. The cervical series of the syntype NHMUK PV R11004 preserves the 2nd cervical, known as the axis, in articulation with the 3rd cervical vertebra. The

centrum (Latin for ''center'') may refer to: Places In Greenland * Nuuk Centrum, a district of Nuuk, Greenland * Centrum Lake, Greenland In the Netherlands * Amsterdam-Centrum, the inner-most borough of Amsterdam, Netherlands * Rotterdam Centrum, a borou ...

of the axis is spool-shaped without a ventral

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

. The neural arch is very large and well-developed, greatly extending posterodorsally past the

postzygapophyses The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...

. The 3rd cervical is also amphicoelus but has a trapezoidal centrum shape. The neural arch is expanded dorsoventrally, but has a small neural spine. As for the dorsal (back) vertebrae, ''Lesothosaurus'' has no complete dorsal columns preserved but likely had 12-15 dorsal (back) vertebrae. The dorsals also had spool-shaped centra, ventral keels (though they are lost in more caudal centra), and neural spines that are short and rectangular. The neural spines of the anterior dorsals are also larger than those of the posterior ones. Ossified tendons are preserved attached to the neural spines of anterior dorsals, suggesting they were arranged longitudinally as in ''Heterodontosaurus, Scelidosaurus,'' & ''Hypsilophodon.'' This feature probably countered stress caused by bending forces acting on the spine during bipedal locomotion. The

sacral vertebrae The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...

series had 5 vertebrae with sacral ribs and a sacrodorsal with a short sacral rib. The sacrals notably had large

transverse processes The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

that were muscle attachments to the sacral ribs. The number of caudal (tail) vertebrae is unknown, but the proximal caudals are well preserved. The centra of these caudals became more cylindrical as they became located distally, in contrast to the spool-shaped dorsal centra. The chevrons are Y-shaped in anterior and posterior view and attached to the ventral side of the caudal centra, with larger attachment points on the proximal caudals. The scapula (shoulder blade) is not fused to the coracoid and is longer than the humerus (upper arm bone). The dorsal surface develops a large, bar-like acromion process that extends further dorsally than in many other ornithischians. The distal end of the scapula is greatly expanded and has a convex margin. The coracoid is disc-shaped and subcircular in lateral and medial views. No sternal ribs are preserved in ''Lesothosaurus,'' but based on related taxa, the sternal plates were connected to the rib cage by elements known as sternal ribs. The pelvis was long and expanded dorsally on the ilium, with a long pubis that had a stub-like prepubis connected to it. The ischium had a large proximal end with a curved, thin shaft. The forelimbs were small relative to the rest of the body. The humerus was elongate and straight in anterior and lateral views, with expanded proximal and distal ends linked by a long, slender shaft. The proximal end had a large

deltopectoral crest Deltopectoral may refer to; * Clavipectoral triangle, also known as the deltopectoral triangle * Deltopectoral groove * Deltopectoral lymph nodes One or two deltopectoral lymph nodes (or infraclavicular nodes) are found beside the cephalic vein, b ...

which was asymmetrical and C-shaped in dorsal view. The humeral shaft has a rounded, transverse cross-section. The humerus length was only 63.3% as long as the femur length, which is much shorter than other basal ornithischians. The radius is mostly straight except for transversely expanded proximal and distal ends, the proximal end having two small, rounded condyles. The ulna is also straight, but is slightly longer with a ovoid cross-section. There is only a single, incomplete manus known from ''Lesothosaurus.'' The manus has 5 metacarpals and 5 phalanxes, though only the second phalanx is fully preserved. The unguals are small and triangular in dorsal view. The hindlimbs were long and slender, similar to those of most other small basal ornithischians. The

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

(thigh bone) was long and bowed anteriorly, with a large 4th trochanter for muscle attachments. The femoral head at the proximal end was large, while the distal end terminated with two condyles where the tibia would interlock. The largest known femur is from NMQR 3076, which measures in length. The tibia (shin bone) has a very similar morphology, but it is 25% longer than the femur and more slender. The fibula has an expansion at the proximal end and a thin shaft that is sub-oval in cross-section. The astragalus and

calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. St ...

are small, though the latter is the smaller of the two, and only preserved in one specimen. The metatarsals are thin, long, and tightly fit together. The metatarsals have great expansions at the distal ends where the pedal phalanges would articulate with the rest of the leg. Metatarsal III is the longest of them all and has the greatest transverse width distally and at the mid-shaft. The metatarsal I is truncated and less than half the length of metatarsal II. Notably, ''Lesothosaurus'' lacks a metatarsal V, a distinct trait of the taxon. The pedal digits (toes) are long, with pedal phalanges (toe bones) that are spool-shaped, with large proximal and distal ends but thin shafts. Digit I was a hallux, with one small phalange ending in a large ungual (claw). Digit II had two large, thick phalanges ending in a large, wide ungual. Digit III was the longest digit by length and had a combined length of . It was composed of 3 pedal phalanges and an ungual. Digit IV had the most pedal phalanges, with 4 preserved and a small ungual. The ungual bones of the toes were claw-like, and not hoof-like as in more advanced ornithischians. Lesothosaurus_diagnosticus

Classification

Peter Galton considered ''Lesothosaurus'' to be a basal ornithopod in the family Fabrosauridae, which included several other ornithischians such as '' Nanosaurus'' (from the Late Jurassic of North America), ''

Echinodon ''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 Ric ...

'' (from the Lower Cretaceous of England), and ''Fabrosaurus'' (which Galton considered distinct from ''Lesothosaurus'' but only included the holotype). However, Fabrosauridae is now considered an invalid family and many of its members are instead basal ornithischians. However, a 1991 redescription by

Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago and a National Geographic "explorer-in-residence" who has discovered several new dinosaur species on several continents, including at sites ...

suggested that ''Lesothosaurus'' and many other "fabrosaurids" were actually basal members of Ornithischia, one of the two main orders of Dinosauria (the other being Saurischia). This opinion has been supported by later cladistic studies of basal Ornithischia, which have also found it as the basalmost member of Neornithischia (a group that includes pachycephalosaurs, ceratopsians, and ornithopods) and related to ''Agilisaurus, Hexinulsaurus,'' and ''Nanosaurus.'' Alternatively, this dinosaur may be a very early thyreophoran, a member of the group including the armored

stegosauria Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...

ns and ankylosaurians. The Butler ''et al''., 2005 analysis placed ''Lesothosaurus'' at the base of Neornithischia: Basal neornithischians like ''Lesothosaurus'' are known from several time periods and regions, with ''Nanosaurus'' fossils coming from the

Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Morrison Formation The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...

(155-148 mya) of the western United States, ''Hexinlusaurus'' from the

Shaximiao Formation The Shaximiao Formation () is a Middle Jurassic, Middle to Late Jurassic aged geological formation in Sichuan, China, most notable for the wealth of dinosaurs fossils that have been excavated from its strata. The Shaximiao Formation is exposed in ...

, dating to the

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

(170-168 mya), in southern China, and '' Hypsilophodon'' from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

(130-125 mya) of England. However, the phylogenetic status of basal neornithischians is constantly in a flux and some analyses have recovered these taxa as basal ornithopods or in other groups.

Paleoenvironment

''Lesothosaurus'' is known from fossils found in formations of the

Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a perio ...

, including the Upper Elliot Formation and the Clarens Formation, which date to the

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (My ...

and Sinemurian ages of the Lower Jurassic, around 200–190

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

. Originally, ''Lesothosaurus'' was thought to be from the Upper Triassic period. The Upper Elliot Formation consists of red/purple

mudstone 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 red/white

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) ...

, whereas the slightly younger Clarens Formation consists of white/cream-coloured sandstone. The Clarens Formation is less rich in fossils than the Upper Elliot Formation; its sediments also often form cliffs, restricting accessibility for fossil hunters.Sereno, P.C. (2012). pp. 4–17. The Upper Elliot Formation is characterised by animals that appear to be more lightly built than those of the Lower Elliot Formation, which may have been an adaptation to the drier climate at this time in southern Africa. Both formations are famous for their abundant vertebrate fossils, including

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 ...

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

, turtles,

lepidosaurs The Lepidosauria (, from Greek meaning ''scaled lizards'') is a subclass or superorder of reptiles, containing the orders Squamata and Rhynchocephalia. Squamata includes snakes, lizards, and amphisbaenians. Squamata contains over 9,000 species ...

aetosaurs Aetosaurs () are heavily armored reptiles belonging to the extinct order Aetosauria (; from Greek, (aetos, "eagle") and (, "lizard")). They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs ...

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 ...

, and non-mammal

cynodonts 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 ...

. Other dinosaurs from these formations include the heterodontosaurid ''Heterodontosaurus'', the basal sauropodomorph ''Massospondylus'', and the theropod '' Megapnosaurus''. The Lower Elliot Formation shows the largest known heterodontosaurid diversity of any rock unit; besides ''Heterodontosaurus'', it contained ''Lycorhinus'', ''Abrictosaurus'', and ''Pegomastax''. Yet another member of the family, ''Geranosaurus'', is known from the Clarens Formation. The high heterodontosaurid diversity have led researchers to conclude that different species might have fed on separate food sources in order to avoid competition ( niche partitioning).

References

Bibliography

* P. M. Galton. 1978. Fabrosauridae, the basal family of ornithischian dinosaurs (Reptilia: Ornithischia). Paläontologische Zeitschrift 52(1/2):138-159 * Butler, R.J., 2005. "The 'fabrosaurid' ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho." ''Zoological Journal of the Linnean Society'' 145: 175–218. {{Taxonbar, from=Q131088 Ornithischian genera Early Jurassic dinosaurs of Africa Fossil taxa described in 1978 Taxa named by Peter Galton Paleontology in Lesotho Paleontology in South Africa