View source for Lesothosaurus

{{Short description|Extinct genus of ornithischian dinosaur}}
{{Automatic taxobox
| fossil_range = [[Early Jurassic]], {{Fossil range|199.6|190}}
| image = Lesothosaurus sp skull 3894.jpg
| image_caption = MNHN LES 17, a skull
| display_parents = 2
| taxon = Lesothosaurus
| authority = Galton, 1978
| type_species = {{extinct}}'''''Lesothosaurus diagnosticus'''''
| type_species_authority = [[Peter Galton|Galton]], [[1978 in paleontology|1978]]
| synonyms = * ''[[Fabrosaurus australis]]''?<br/><small>Ginsburg, 1964</small>
* ''Stormbergia dangershoeki''<br/><small>Butler, 2005</small>
}}
'''''Lesothosaurus''''' is a [[Monotypic taxon|monospecific]] [[genus]] of [[ornithischia]]n [[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]].<ref name=":0">{{Cite journal |last=Sereno |first=Paul C. |date=1991-06-20 |title=''Lesothosaurus'', "Fabrosaurids," and the early evolution of Ornithischia |url=https://www.researchgate.net/publication/254313592 |journal=Journal of Vertebrate Paleontology |volume=11 |issue=2 |pages=168–197 |doi=10.1080/02724634.1991.10011386 |bibcode=1991JVPal..11..168S |issn=0272-4634}}</ref><ref name=":1">{{Cite journal |last1=Porro |first1=Laura B. |last2=Witmer |first2=Lawrence M. |last3=Barrett |first3=Paul M. |date=2015-12-21 |title=Digital preparation and osteology of the skull of ''Lesothosaurus diagnosticus'' (Ornithischia: Dinosauria) |journal=PeerJ |language=en |volume=3 |article-number=e1494 |doi=10.7717/peerj.1494 |pmid=26713245 |pmc=4690377 |s2cid=510709 |issn=2167-8359|doi-access=free }}</ref><ref name=":2">{{Cite journal |last1=Baron |first1=Matthew G. |last2=Norman |first2=David B. |last3=Barrett |first3=Paul M. |date=2017-01-01 |title=Postcranial anatomy of ''Lesothosaurus diagnosticus'' (Dinosauria: Ornithischia) from the Lower Jurassic of southern Africa: implications for basal ornithischian taxonomy and systematics |journal=Zoological Journal of the Linnean Society |volume=179 |issue=1 |pages=125–168 |doi=10.1111/zoj.12434 |issn=0024-4082|doi-access=free }}</ref> It had a simpler tooth and jaw anatomy than later ornithischians, and may have been [[omnivorous]] in some parts of the year.<ref name=":3">{{Cite journal |last1=Sciscio |first1=Lara |last2=Knoll |first2=Fabien |last3=Bordy |first3=Emese M. |last4=Kock |first4=Michiel O. de |last5=Redelstorff |first5=Ragna |date=2017-03-01 |title=Digital reconstruction of the mandible of an adult Lesothosaurus diagnosticus with insight into the tooth replacement process and diet |journal=PeerJ |language=en |volume=5 |article-number=e3054 |doi=10.7717/peerj.3054 |pmid=28265518 |pmc=5335715 |s2cid=17069570 |issn=2167-8359|doi-access=free }}</ref>

== Discovery and naming ==
[[File:Fabrosaurus australis mandible.jpg|left|thumb|Illustration of the ''[[Fabrosaurus]]'' [[holotype]] dentary.]]
Fossils referrable to ''Lesothosaurus'' may have been known from as early as 1959, when a right [[Mandible|dentary]] (lower jawbone) fragment bearing three teeth was collected by French geologist Jean Fabre from the [[Red beds|Red Beds]] of the [[Elliot Formation|Upper Elliot Formation]] near [[Mapheteng]] in [[Lesotho]], Southern Africa, dating to the [[Early Jurassic]] (199(?)-190 million years ago).<ref name=":4">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.</ref><ref>{{Cite journal |last1=Bordy |first1=E.M. |last2=Eriksson |first2=P. |date=2015 |title=Lithostratigraphy of the Elliot Formation (Karoo Supergroup), South Africa |journal=South African Journal of Geology |volume=118 |issue=3 |pages=311–316 |doi=10.2113/gssajg.118.3.311 |bibcode=2015SAJG..118..311B |hdl=2263/55739 |issn=1012-0750|hdl-access=free }}</ref><ref name=":0" /> The dentary was described as the holotype of a new genus and species, ''[[Fabrosaurus|Fabrosaurus australis]]'', by paleontologist [[Leonard Ginsburg]] in 1964.<ref name=":4" /> Ginsburg placed it in the family [[Scelidosauridae]] and diagnosed it based on its unusual tooth morphology when compared to the only other contemporary ornithischian ''[[Heterodontosaurus]]''.<ref name=":4" /><ref name=":5">{{Cite journal |last=Butler |first=Richard J. |date=2005 |title=The 'fabrosaurid' ornithischian dinosaurs of the Upper Elliot Formation (Lower Jurassic) of South Africa and Lesotho |journal=Zoological Journal of the Linnean Society |language=en |volume=145 |issue=2 |pages=175–218 |doi=10.1111/j.1096-3642.2005.00182.x |issn=1096-3642|doi-access=free }}</ref><ref name=":0" /> Due to its fragmentary nature, ''Fabrosaurus'' is now seen as a ''[[nomen dubium]]'', though the holotype is likely from an individual of ''Lesothosaurus''.<ref name=":5" /> The holotype was all that was known until expeditions by the [[University College London|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]].<ref>{{Cite journal |last=Thulborn |first=Richard A. |date=1971 |title=Tooth wear and jaw action in the Triassic ornithischian dinosaur Fabrosaurus |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1971.tb01303.x |journal=Journal of Zoology |language=en |volume=164 |issue=2 |pages=165–179 |doi=10.1111/j.1469-7998.1971.tb01303.x |issn=0952-8369|url-access=subscription }}</ref><ref>Thulborn, R. A. (1972). The postcranial skeleton of the Triassic ornithischian dinosaur Fabrosaurus australis. ''Palaeontology'', ''15''(1), 29-60.</ref><ref>Thulborn, R. A. (1970). The skull of Fabrosaurus australis, a Triassic ornithischian dinosaur. ''Palaeontology'', ''13''(3), 414-432.</ref> A joint expedition between the [[Natural History Museum, London|NHMUK]], [[University College London|London University College]], [[Yale University]], 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.<ref name=":0" />
[[File:LesothosaurusFossilDiscoveriesMap.jpg|left|thumb|Map of where ''Lesothosaurus'' fossils have been found in Lesotho and South Africa.]]
British paleontologist [[Peter Galton]] named ''Lesothosaurus diagnosticus'' in 1978, with NHMUK PV RU B17 and NHMUK PV RU B23 as the [[syntype]]s (the series of fossils that diagnose a species).<ref name=":6">{{Cite journal |last=Galton |first=Peter M. |date=1978 |title=Fabrosauridae, the basal family of ornithischian dinosaurs (Reptilia: Ornithopoda) |journal=Paläontologische Zeitschrift |language=en |volume=52 |issue=1 |pages=138–159 |doi=10.1007/BF03006735 |bibcode=1978PalZ...52..138G |s2cid=84613826 |issn=0031-0220 |eissn=1867-6812}}</ref> 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.<ref name=":6" /> The specific name ''diagnosticus'' is derived from the Greek root ''diagnostikos'' meaning "distinguished" in reference to ''Lesothosaurus'' being a distinct member of [[Ornithischia|Fabrosauridae]].<ref name=":6" /> In the material referred to ''Lesothosaurus'', Galton stated that some of it was instead from a "large fabrosaurid".<ref name=":6" /> 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''.<ref name=":2" /> ''Stormbergia'' was named for the [[Stormberg Group|Stormberg Series]] 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.<ref name=":5" /> Fossils from Elliot Formation sites in South Africa outside of Lesotho in [[Jamestown, Eastern Cape|Jamestown]] were described in the 2000s, including a nearly complete skeleton of an adult preserved in articulation.<ref name=":2" /> 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.<ref name=":2" /> 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.<ref name=":7">{{Cite journal |last=Knoll |first=Fabien |date=2002-09-01 |title=New skull of ''Lesothosaurus'' (Dinosauria: Ornithischia) from the Upper Elliot Formation (Lower Jurassic) of southern Africa |url=https://www.sciencedirect.com/science/article/pii/S0016699502000724 |journal=Geobios |language=en |volume=35 |issue=5 |pages=595–603 |doi=10.1016/S0016-6995(02)00072-4 |bibcode=2002Geobi..35..595K |issn=0016-6995|url-access=subscription }}</ref> Redescription of the syntypes came in 2015 and 2017, including the integration of CT technology.<ref name=":2" /><ref name=":1" />

== Description ==
[[File:Lesothosaurus_NT.jpg|left|thumb|Life restoration (reconstructed without filaments) and size compared to a human]]
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&nbsp;ft) to 2 meters (6.6&nbsp;ft) long. It was one of the earliest [[ornithischia]]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.<ref name="EoDP2">{{cite book |title=The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals |publisher=Marshall Editions |year=1999 |isbn=1-84028-152-9 |editor=Palmer, D. |location=London |page=134}}</ref><ref name=":2" /> Like all ornithischians, the tips of ''Lesothosaurus'' [[Upper jaw|upper]] and [[lower jaw]]s were horny, forming a beaklike structure. Behind the beak were leaf-shaped [[Tooth|teeth]] that lined the jaws. The teeth of the [[premaxilla]]e (six per side) are more slender and curved than the maxillary teeth.<ref name=":1" /> Analysis of its teeth has shown that ''Lesothosaurus'' sliced up its food with its beak and was not able to chew its food.<ref name="Benton, Michael J, Prehistoric Life2">{{cite book |last=Benton |first=Michael J. |title=Prehistoric Life |publisher=Dorling Kindersley |year=2012 |isbn=978-0-7566-9910-9 |location=Edinburgh, Scotland |page=271}}</ref> 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]], feeding primarily on small animals during seasons when softer plants were not available.<ref name=":3" />

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.<ref name=":1" /> Its teeth were pointed with grooved edges. The skull was mounted on a short but flexible neck.<ref name="EoDP2" />

A [[Bone bed|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.<ref>{{Cite journal |last1=Barrett |first1=P. M. |last2=Butler |first2=R. J. |last3=Yates |first3=A. M. |last4=Baron |first4=M. G. |last5=Choiniere |first5=J. N. |date=2016-03-23 |title=New specimens of the basal ornithischian dinosaur ''Lesothosaurus diagnosticus'' Galton, 1978 from the Early Jurassic of South Africa |url=https://nhm.openrepository.com/handle/10141/610870 |journal=Palaeontologia Africana |language=English |issn=0078-8554}}</ref>

=== Skull and dentition ===
[[File:Lesothosaurus_skull_diagram.png|left|thumb|Skull diagram]]
The skull and teeth of ''Lesothosaurus'' are more generalized than the heavily specialized and unusual anatomies of the contemporary [[Thyreophora|scelidosaurid]] and [[Heterodontosauridae|heterodontosaurid]] ornithischians, which exhibit traits like [[osteoderm]]s and extreme [[heterodont]]y.<ref name=":1" /><ref name=":0" /> 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 (anatomical term)|caudal]] half was boxy while the anterior half was tapered and elongated. The height apex of the cranium is just behind the [[Orbit (anatomy)|orbit]] (eye socket) in [[Lateral (anatomy)|lateral]] view and the [[skull roof]] ([[Frontal bone|frontals]], [[Parietal bone|parietals]]) are gently rounded in lateral view. The snout is smoothly tapered to the [[premaxilla]] (snout tip bone). The skull lacks a break in slope along the snout [[Anatomical terms of location|anterior]] 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 (anatomy)|posterior]] margin of the [[Basilar part of occipital bone|basioccipital]]). 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]]e are anteroposteriorly longer than mediolaterally wide, with a sub-ovary to sub-triangular outline in dorsal view. In contrast, the [[infratemporal fenestra]]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 [[Nostril|naris]] (nostril) had several small, sub-ovate openings along its length. The craniomandibular [[Joint (anatomy)|joint]] (where the skull contacts the [[Mandible|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]]''<nowiki />' (a Late Triassic [[Dinosauromorpha|dinosauriform]] that may be an ornithischian). There are 20 tooth positions in the dentary of ''Lesothosaurus,'' but only 15 are preserved in ''Pisanosaurus.'' The [[Alveolus|alveolar foramina]] are on the medial wall of the maxilla and dentary, one per tooth position, and represent the area where the [[Neurovascular unit|neurovascular]] supply accesses the dental [[Dental lamina|lamina]].<ref name=":1" /> 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.<ref>Knoll, F. (2008). Buccal soft anatomy in Lesothosaurus (Dinosauria: Ornithischia). ''Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen'', ''248''(3), 355-364.</ref><ref>{{Cite journal |last=Nabavizadeh |first=Ali |date=2020 |title=New Reconstruction of Cranial Musculature in Ornithischian Dinosaurs: Implications for Feeding Mechanisms and Buccal Anatomy |journal=The Anatomical Record |language=en |volume=303 |issue=2 |pages=347–362 |doi=10.1002/ar.23988 |pmid=30332723 |s2cid=52986589 |issn=1932-8486|doi-access=free }}</ref> The cranium is widest across the [[Postorbital bone|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 [[Quadrate bone|quadrates]] in occipital view.<ref name=":1" /><ref name=":8">Norman, D. B., Witmer, L. M., & Weishampel, D. B. (2004). Basal ornithischia. ''The dinosauria'', ''2'', 325-334.</ref>

The [[mandible]] (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 [[Ornithischia#Predentary|predentary]]. The predentary is shaped like an arrowhead in [[Anatomical terms of location|ventral]] view, with one elongated central keel with smaller lateral processes jutting off the sides. The [[Mouth|oral]] margin is smooth and straight in lateral view, with an uncurved anterior tip. Two [[Foramen|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 [[Process (anatomy)|processes]] (projection of bone) like in advanced Ornithischians like ''[[Triceratops]]'' and ''[[Zalmoxes]].''<ref>{{cite book | first1 = Peter | last1 = Dodson | first2 = Catherine A. | last2 = Foster | first3 = Scott D. | last3 = Sampsom | chapter = Ceratopsidae | page = 494 | editor-last=Weishampel | editor-first=David B. | editor-last2=Dodson | editor-first2=Peter | editor-last3=Osmo´lska | editor-first3=Halszka | title=The Dinosauria | publisher=University of California Press | publication-place=Berkeley, Calif. | date=2004 | isbn=978-0-520-94143-4 | oclc=801843269 | title-link = The Dinosauria | edition = Second }}</ref><ref>{{Cite journal |last1=Weishampel |first1=David B. |last2=Jianu |first2=Coralia-Maria |last3=Csiki |first3=Zoltan |last4=Norman |first4=David B. |date=2003-01-01 |title=Osteology and phylogeny of Zalmoxes (n. g.), an unusual Euornithopod dinosaur from the latest Cretaceous of Romania |journal=Journal of Systematic Palaeontology |volume=1 |issue=2 |pages=65–123 |doi=10.1017/S1477201903001032 |bibcode=2003JSPal...1...65W |s2cid=86339025 |issn=1477-2019}}</ref> 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 bone|angular]], and [[Surangular|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 [[Mandibular symphysis|symphysis]] is preserved.<ref name=":8" /><ref name=":1" />

''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 [[Beak|rhampthotheca]] (beak) made of [[keratin]]. A neck and slight swelling divides the base of the [[Crown (tooth)|tooth crown]] from the long, subcylindrical [[Tooth root|roots]]. The [[Anatomical terms of location|lingual]] 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 [[Denticle (tooth feature)|denticles]]. The posterior process of the premaxilla lacks alvelovi, creating a small [[diastema]] (gap) in between the premaxillary and maxillary tooth rows. The maxillary and dentary teeth are low, triangular, and "leaf-shaped" with a distinct neck and [[Cingulum (tooth)|cingulum]]. The denticles are coarse on the medial and distal tooth borders, with sporadically developed high-angled marginal [[tooth wear]]ing. This suggests rapid [[tooth replacement]] in these teeth.<ref name=":8" /><ref name=":1" />

=== Postcrania ===
Although many specimens are known, some elements of ''Lesothosaurus'<nowiki />'' postcranial anatomy are poorly known, especially in the axial skeleton which is incomplete in all specimens. The [[Cervical vertebrae|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 (anatomy)|axis]], in articulation with the 3rd cervical vertebra. The [[Vertebra|centrum]] of the axis is spool-shaped without a ventral keel. The [[Vertebra|neural arch]] is very large and well-developed, greatly extending posterodorsally past the [[Articular processes|postzygapophyses]]. The 3rd cervical is also amphicoelus but has a trapezoidal centrum shape. The [[Vertebra|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 [[Thoracic vertebrae|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. [[Tendon|Ossified tendons]] are preserved attached to the neural spines of anterior dorsals, suggesting they were arranged longitudinally as in ''Heterodontosaurus, Scelidosaurus,'' and ''Hypsilophodon.''<ref name=":2" /> This feature probably countered stress caused by bending forces acting on the spine during bipedal locomotion.<ref>{{cite journal | last = Luca | first = A. P. Santa | title = The Postcranial Skeleton of Heterodontosaurus tucki (Reptilia, Ornithischia) from the Stormberg of South Africa | journal = Annals of the South African Museum | volume = 79 |issue = 7 | year = 1980 | pages = 159–211 | issn = 0303-2515 | oclc = 11886969}}</ref> The [[Sacrum|sacral vertebrae]] series had 5 vertebrae with [[Rib cage|sacral ribs]] and a sacrodorsal with a short sacral rib. The sacrals notably had large [[transverse processes]] that were muscle attachments to the sacral ribs. The number of [[Vertebra|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.<ref name=":8" /><ref name=":2" /> 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.<ref name=":2" />

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|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.<ref name=":2" />

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 [[Humerus|deltopectoral crest]] 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 an 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.<ref name=":5" /><ref name=":0" /><ref name=":2" />

The hindlimbs were long and slender, similar to those of most other small basal ornithischians. The [[femur]] (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 {{Convert|273.70|mm|in}} 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 (bone)|astragalus]] and [[Calcaneus|calcaneum]] 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 {{Convert|57.7|mm|in}}. 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.<ref name=":5" /><ref name=":8" /><ref name=":2" />
[[File:Lesothosaurus_diagnosticus.png|right|thumb|Life restoration (reconstructed with filaments) of ''Lesothosaurus'']]

== 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]]'' (from the Lower Cretaceous of England), and ''Fabrosaurus'' (which Galton considered distinct from ''Lesothosaurus'' but only included the holotype). However, a 1991 redescription by [[Paul Sereno]] 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).<ref name=":0" /> 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.''<ref name=":2" /> Alternatively, this dinosaur may be a very early [[thyreophora]]n, a member of the group including the armored [[stegosauria]]ns and [[ankylosauria]]ns.<ref name="BUN08">{{cite journal |last=Butler |first=Richard J. |author2=Upchurch, Paul |author3=Norman, David B. |author3-link=David B. Norman |year=2008 |title=The phylogeny of the ornithischian dinosaurs |journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |pages=1–40 |doi=10.1017/S1477201907002271 |bibcode=2008JSPal...6....1B |s2cid=86728076}}</ref>

The Butler ''et al''., 2005 analysis placed ''Lesothosaurus'' at the base of Neornithischia:
{{clade|''[[Euparkeria]]''|{{clade
   |1=''[[Marasuchus]]''
   |2={{clade
      |1=''[[Herrerasaurus]]''
      |label2=[[Ornithischia]]
      |2={{clade
         |1=''[[Pisanosaurus]]''
         |2={{clade
            |1=[[Heterodontosauridae]]
            |2={{clade
               |1=''[[Eocursor]]''
               |2={{clade
                  |1=[[Thyreophora]]
                  |label2=[[Neornithischia]]
                  |2={{clade
                     |1='''''Lesothosaurus'''''
                     |2={{clade
                        |1=''[[Agilisaurus]]''
                        |2={{clade
                           |1=''[[Hexinlusaurus]]''
                           |2={{clade
                              |1=''[[Othnielosaurus]]''
                              |2=[[Cerapoda]]
}} }} }} }} }} }} }} }} }} }}}}
Basal neornithischians like ''Lesothosaurus'' are known from several time periods and regions, with ''Nanosaurus'' fossils coming from the [[Late Jurassic|Upper Jurassic]] [[Morrison Formation]] (155–148 mya) of the western United States,<ref name=":9">{{Cite journal |last1=Carpenter |first1=Kenneth |last2=Galton |first2=Peter |date=2018-08-17 |title=A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA |url=https://giw.utahgeology.org/giw/index.php/GIW/article/view/30 |journal=Geology of the Intermountain West |language=en |volume=5 |pages=167–207 |doi=10.31711/giw.v5.pp167-207 |s2cid=73691452 |issn=2380-7601|doi-access=free }}</ref> ''Hexinlusaurus'' from the [[Shaximiao Formation]], dating to the [[Middle Jurassic]] (170–168 mya), in southern China,<ref>{{Cite journal |last1=Barrett |first1=Paul M. |last2=Butler |first2=Richard J. |last3=Knoll |first3=Fabien |date=2005-12-30 |title=Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China |url=https://www.tandfonline.com/doi/abs/10.1671/0272-4634%282005%29025%5B0823%3ASODFTM%5D2.0.CO%3B2 |journal=Journal of Vertebrate Paleontology |volume=25 |issue=4 |pages=823–834 |doi=10.1671/0272-4634(2005)025[0823:SODFTM]2.0.CO;2 |s2cid=85892620 |issn=0272-4634|url-access=subscription }}</ref> and ''[[Hypsilophodon]]'' from the [[Early Cretaceous]] (130–125 mya) of England.<ref>{{cite journal |last=Galton |first=P. M. |year=1974 |title=The ornithischian dinosaur Hypsilophodon from the Wealden of the Isle of Wight |journal=Bulletin of the British Museum (Natural History), Geology Series |volume=25 |issue=1 |pages=1–152 |doi=10.5962/p.313819 |doi-access=free }}</ref>{{verify inline|reason=details added without access|date=October 2025}} 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.<ref>{{Cite journal |last1=Madzia |first1=Daniel |last2=Boyd |first2=Clint A. |last3=Mazuch |first3=Martin |date=2018-09-02 |title=A basal ornithopod dinosaur from the Cenomanian of the Czech Republic |journal=Journal of Systematic Palaeontology |volume=16 |issue=11 |pages=967–979 |doi=10.1080/14772019.2017.1371258 |bibcode=2018JSPal..16..967M |s2cid=90008574 |issn=1477-2019 |url=https://figshare.com/articles/dataset/A_basal_ornithopod_dinosaur_from_the_Cenomanian_of_the_Czech_Republic/5436457 }}</ref><ref name=":9" /><ref name=":2" />

== Paleoenvironment ==
''Lesothosaurus'' is known from fossils found in formations of the [[Karoo Supergroup]], including the [[Upper Elliot Formation]] and the Clarens Formation, which date to the [[Hettangian]] and [[Sinemurian]] ages of the [[Lower Jurassic]], around 200–190&nbsp;[[Annum|million years ago]]. Originally, ''Lesothosaurus'' was thought to be from the [[Upper Triassic]] period. The Upper Elliot Formation consists of red/purple [[mudstone]] and red/white [[sandstone]], 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.<ref name="sereno2012 4–17">Sereno, P.C. (2012). pp. 4–17.</ref><ref name="Crompton Charig 1962">{{Cite journal|doi=10.1038/1961074a0|title=A new ornithischian from the Upper Triassic of South Africa|journal=Nature|volume=196|issue=4859|pages=1074–1077|year=1962|last1=Crompton|first1=A.W.|last2=Charig|first2=A.J.|bibcode=1962Natur.196.1074C|s2cid=4198113}}</ref> 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]] [[amphibians]], turtles, [[lepidosaurs]], [[aetosaurs]], [[crocodylomorphs]], and non-mammal [[cynodonts]].<ref name="Crompton Charig 1962" /><ref name=knoll2005>{{Cite journal|doi=10.2113/176.1.81|title=The tetrapod fauna of the Upper Elliot and Clarens formations in the main Karoo Basin (South Africa and Lesotho)|journal=Bulletin de la Société Géologique de France|volume=176|pages=81–91|year=2005|last1=Knoll|first1=F.}}</ref>

Other dinosaurs from these formations include the heterodontosaurid ''Heterodontosaurus'', the basal sauropodomorph ''Massospondylus'', and the theropod ''[[Megapnosaurus]]''. The Upper 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]]).<ref name="porro2010">{{Cite journal|doi=10.1017/S175569101102010X|issn=1755-6929|volume=101|issue=Special Issue 3–4|pages=351–366|last1=Porro|first1=L.B.|last2=Butler|first2=R.J.|last3=Barrett|first3=P.M.|last4=Moore-Fay|first4=S.|last5=Abel|first5=R.L.|title=New heterodontosaurid specimens from the Lower Jurassic of southern Africa and the early ornithischian dinosaur radiation|journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh|year=2011|s2cid=128636991|url=http://rosslab.uchicago.edu/Members/laura-porro/porro_et_al_south_african_heterodontosaurids.pdf/at_download/porro_et_al_south_african_heterodontosaurids.pdf|access-date=2015-12-30|archive-url=https://web.archive.org/web/20170811120238/http://rosslab.uchicago.edu/Members/laura-porro/porro_et_al_south_african_heterodontosaurids.pdf/at_download/porro_et_al_south_african_heterodontosaurids.pdf|archive-date=2017-08-11}}</ref><ref name="butler2012">{{cite journal |doi=10.1371/journal.pone.0031556 |pmid=22509242 |pmc=3324477 |title=Anatomy and Cranial Functional Morphology of the Small-Bodied Dinosaur ''Fruitadens haagarorum'' from the Upper Jurassic of the USA |journal=PLOS ONE |volume=7 |issue=4 |article-number=e31556 |year=2012 |last1=Butler |first1=Richard J |last2=Porro |first2=Laura B |last3=Galton |first3=Peter M |last4=Chiappe |first4=Luis M |bibcode=2012PLoSO...731556B |doi-access=free }}</ref>

== References ==
{{Reflist}}

=== 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.

{{Portal bar|Dinosaurs|South Africa}}
{{Ornithischia|H.}}
{{Geology of South Africa|paleontology}}
{{Taxonbar|from=Q131088}}

[[Category:Ornithischia]]
[[Category:Dinosaur genera]]
[[Category:Hettangian dinosaurs]]
[[Category:Sinemurian dinosaurs]]
[[Category:Elliot Formation]]
[[Category:Fossil taxa described in 1978]]
[[Category:Taxa named by Peter Galton]]
[[Category:Dinosaurs of South Africa]]