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Lesothosaurus

Galton, 1978 le-SOH-toh-SAWR-us

Named after Lesotho, the country in southern Africa where it was found, combined with Greek 'sauros' (lizard); meaning 'lizard from Lesotho'

201.4–192.9 million years ago Hettangian–Sinemurian, Early Jurassic
Early Jurassic stages

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.

Under dispute

Lesothosaurus is one of the most unstable basal ornithischians. It has been recovered as the most basal thyreophoran (Butler and colleagues, 2008; Boyd, 2015), as the basalmost neornithischian (Herne and colleagues, 2019; Manitkoon and colleagues, 2023, followed by Jones, 2026), and as an ornithischian outside Genasauria (Baron and colleagues, 2017; Fonseca and colleagues, 2024). Because these placements straddle Genasauria, it is placed at the least-inclusive uncontested node.

Diagnosis

  1. Anterior premaxillary foramen piercing the premaxilla near the alveolar margin, opening onto the premaxillary palate just anterior to the first premaxillary tooth.
  2. Thin, tongue-shaped maxillary process at the apex of the antorbital fossa receiving the lacrimal in a narrow slot (a configuration unknown elsewhere in Ornithischia).
  3. Forelimb very short, less than 40% of hind-limb length.
  4. Brevis surface on the postacetabular process of the ilium broadly exposed in lateral view (medial wall of the brevis fossa extending ventrally below the lateral wall).
  5. Groove on the dorsal margin of the proximal ischial shaft, passing onto the medial side of the blade.
  6. Pedal digit I reduced, with metatarsal I splint-shaped proximally and the ungual extending just beyond the second metatarsal.

Species

Lesothosaurus diagnosticus Galton, 1978

Type species

From Greek 'diagnostikos' meaning 'distinguished', in reference to Lesothosaurus being a distinct member of Fabrosauridae.

Syntypes
NHMUK PV RU B 17, NHMUK PV RU B 23, NHMUK PV R 11956 , Natural History Museum
Material
Syntype assemblage from at least two individuals — mostly disarticulated remains including one articulated skull (with stapes, ceratohyals, and anterior cervical vertebrae), additional postcranial material, and a separate partial skull.
Horizon
upper Elliot Formation, Hettangian–Sinemurian, Early Jurassic , 201.4–192.9 million years ago
Locality
Likhoele Mountain, Mafeteng, Lesotho

Synonyms of the genus

Name Type Reason
Stormbergia junior subjective Now generally treated as a junior synonym of Lesothosaurus.

References

  1. Galton, P. M. (1978). Fabrosauridae, the basal family of ornithischian dinosaurs (Reptilia: Ornithopoda). Paläontologische Zeitschrift 52(1-2): 138-159. Springer Science and Business Media LLC. doi:10.1007/bf03006735 galton1978a
  2. Sereno, P. C. (1991). Lesothosaurus, 'fabrosaurids,' and the early evolution of Ornithischia. Journal of Vertebrate Paleontology 11(2): 168-197. doi:10.1080/02724634.1991.10011386

    Rediagnoses Lesothosaurus diagnosticus on autapomorphies, treats Fabrosauridae as invalid (Fabrosaurus a nomen dubium), and places it as a basal ornithischian.

    sereno1991a
  3. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the mass estimate.

    paul2024a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate.

    jones2026a
  5. Butler, R. J.; Upchurch, P.; Norman, D. B. (2008). The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1): 1-40. doi:10.1017/S1477201907002271

    Recovered Lesothosaurus as the most basal thyreophoran, on a single unambiguous character.

    butler2008b
  6. Herne, M. C.; Nair, J. P.; Evans, A. R.; Tait, A. M. (2019). New small-bodied ornithopods (Dinosauria, Neornithischia) from the Early Cretaceous Wonthaggi Formation (Strzelecki Group) of the Australian-Antarctic rift system, with revision of Qantassaurus intrepidus Rich and Vickers-Rich, 1999. Journal of Paleontology 93(3): 543-584. Cambridge University Press (CUP). doi:10.1017/jpa.2018.95

    Recovered Lesothosaurus as the basalmost neornithischian.

    herne2019a
  7. Manitkoon, S.; Deesri, U.; Khalloufi, B.; Nonsrirach, T.; Suteethorn, V.; Chanthasit, P.; Boonla, W.; Buffetaut, E. (2023). A New Basal Neornithischian Dinosaur from the Phu Kradung Formation (Upper Jurassic) of Northeastern Thailand. Diversity 15(7). MDPI AG. doi:10.3390/d15070851

    Recovered Lesothosaurus as basalmost neornithischian, following Herne.

    manitkoon2023a
  8. Fonseca, A. O.; Reid, I. J.; Venner, A.; Duncan, R. J.; Garcia, M. S.; Müller, R. T. (2024). A comprehensive phylogenetic analysis on early ornithischian evolution. Journal of Systematic Palaeontology 22: 2346577. doi:10.1080/14772019.2024.2346577

    Comprehensive ornithischian phylogeny placing Lesothosaurus among early ornithischians.

    fonseca2024a
  9. Baron, M. G.; Norman, D. B.; Barrett, P. M. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543(7646): 501-506. doi:10.1038/nature21700

    Included Lesothosaurus in the analysis recovering Ornithischia and Theropoda as sister clades

    baron2017a
  10. Boyd, C. A. (2015). The systematic relationships and biogeographic history of ornithischian dinosaurs. PeerJ 3: e1523. PeerJ. doi:10.7717/peerj.1523

    Recovered Lesothosaurus as the most basal thyreophoran.

    boyd2015a