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Alcovasaurus

Galton & Carpenter, 2016 al-KOH-vuh-SAWR-us

Named after Alcova, Wyoming, where the holotype was discovered

154.8–143.1 million years ago Kimmeridgian–Tithonian, Late Jurassic
Late Jurassic stages

Alcovasaurus is an extinct genus of herbivorous stegosaurian dinosaurs that lived in the Late Jurassic. It was found in the Morrison Formation of Wyoming, United States. The genus contains a single species, Alcovasaurus longispinus, originally assigned to the genus Stegosaurus. Costa and Mateus (2019) referred it to Miragaia, and Sánchez-Fenollosa, Escaso and Cobos (2025) returned it to Alcovasaurus. Its subfamily is unsettled; some analyses place it in Dacentrurinae and others elsewhere within Stegosauridae.

Diagnosis

  1. All caudal vertebrae bear transverse processes, continuing to the distal caudal vertebrae
  2. Distal caudal centra anteroposteriorly short, with height exceeding length
  3. Femoral condylar articular surface confined almost exclusively to the distal surface
  4. Two pairs of greatly elongate distal dermal tail spines (~90% of femoral length) with subequal bases and slender shafts
  5. Posterior dermal tail spine pair widest at ~25% of length (constriction above base)

Species

Alcovasaurus longispinus Galton & Carpenter, 2016

Type species

From Latin 'longus' (long) and 'spina' (spine), referring to the elongate tail spines.

Holotype
UW 20503 , University of Wyoming Geological Museum
Material
Right femur and casts of the posterior pair of dermal caudal spines; original specimen largely destroyed by water damage in the 1920s.
Horizon
upper Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Reed's Stegosaurus Quarry, about 1.5 miles east of Alcova, Wyoming, United States The quarry, about 2.4 km east of Alcova near Alcova Reservoir in Natrona County, has not been found again: "efforts by the UW to relocate it were unsuccessful" (Galton and Carpenter, 2016, p. 186). Its horizon rests on photographs of the site, which by a personal communication put it "relatively high in the Morrison Formation", "equivalent to the upper Brushy Basin Member of the Colorado Plateau" (p. 186); the formal entry gives an "unknown locality high in equivalent strata to the Brushy Basin Member of the Morrison Formation (Upper Jurassic, Kimmeridgian-Tithonian)" (p. 189). Sánchez-Fenollosa and Cobos (2025) give the species as "Kimmeridgian–Tithonian, Morrison Formation, USA" (p. 182).

Synonyms

  • Natronasaurus longispinus nomen nudum

    Proposed by Roman Ulansky (2014) for "Stegosaurus" longispinus Gilmore, 1914 in a self-published electronic publication that was not archived by an independent organization and lacked an ISSN; the name is therefore ICZN-invalid under Article 8.5.3. Galton and Carpenter (2016) provided the valid replacement genus Alcovasaurus for the same material.

References

  1. Galton, P. M.; Carpenter, K. (2016). The plated dinosaur Stegosaurus longispinus Gilmore, 1914 (Dinosauria: Ornithischia; Upper Jurassic, western USA), type species of Alcovasaurus n. gen. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279(2): 185-208. Schweizerbart. doi:10.1127/njgpa/2016/0551 galton2016a
  2. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026a
  3. Sánchez-Fenollosa, S.; Cobos, A. (2025). New insights into the phylogeny and skull evolution of stegosaurian dinosaurs: an extraordinary cranium from the European Late Jurassic (Dinosauria: Stegosauria). Vertebrate Zoology 75: 165-189. doi:10.3897/vz.75.e146618

    Recovered Alcovasaurus as the earliest-diverging member of Dacentrurinae in a new data matrix, tracing its earlier position outside Eurypoda to miscoded characters.

    sánchez-fenollosa2025a
  4. Raven, T. J.; Maidment, S. C. R. (2017). A new phylogeny of Stegosauria (Dinosauria, Ornithischia). Palaeontology 60(3): 401-408. doi:10.1111/pala.12291

    Recovered Alcovasaurus outside Eurypoda, attributed to missing data and possible immaturity.

    raven2017a
  5. Gilmore, C. W. (1914). Osteology of the armored Dinosauria in the United States National Museum, with special reference to the genus Stegosaurus. United States National Museum Bulletin 89: 1-136.

    Named the species longispinus, as Stegosaurus longispinus.

    gilmore1914b
  6. Ulansky, R. E. (2014). Evolution of the stegosaurs (Dinosauria; Ornithischia). Dinologia.

    Proposed Natronasaurus as a new genus for longispinus; the name is unavailable.

    ulansky2014b
  7. Ulansky, R. E. (2014). Dinosaurs Classification. Basal Thyreophora & Stegosauria. Dinologia 1-8.

    Listed Natronasaurus longispinus as a new genus (unavailable name).

    ulansky2014a
  8. Maidment, S. C. R.; Raven, T. J.; Ouarhache, D.; Barrett, P. M. (2020). North Africa's first stegosaur: Implications for Gondwanan thyreophoran dinosaur diversity. Gondwana Research 77: 82-97. Elsevier BV. doi:10.1016/j.gr.2019.07.007

    Recovers Alcovasaurus with Tuojiangosaurus and Paranthodon, outside the clade holding Dacentrurus.

    maidment2020a
  9. Raven, T. J.; Barrett, P. M.; Joyce, C. B.; Maidment, S. C. R. (2023). The phylogenetic relationships and evolutionary history of the armoured dinosaurs (Ornithischia: Thyreophora). Journal of Systematic Palaeontology 21(1): 2205433. doi:10.1080/14772019.2023.2205433

    Recovers Alcovasaurus as the sister of Loricatosaurus, a bridge taxon between the stegosaurines and the other stegosaurids.

    raven2023a
  10. Costa, F.; Mateus, O. (2019). Dacentrurine stegosaurs (Dinosauria): A new specimen of Miragaia longicollum from the Late Jurassic of Portugal resolves taxonomical validity and shows the occurrence of the clade in North America. PLOS ONE 14(11): e0224263. Public Library of Science (PLoS). doi:10.1371/journal.pone.0224263

    Refers longispinus to Miragaia, within Dacentrurinae, on caudal vertebrae and tail spines it shares with Miragaia longicollum.

    costa2019a
  11. Sánchez-Fenollosa, S.; Escaso, F.; Cobos, A. (2024). A new specimen of Dacentrurus armatus Owen, 1875 (Ornithischia: Thyreophora) from the Upper Jurassic of Spain and its taxonomic relevance in the European stegosaurian diversity. Zoological Journal of the Linnean Society 203(3): zlae074. Oxford University Press (OUP). doi:10.1093/zoolinnean/zlae074

    Returns longispinus to Alcovasaurus, listing it in Stegosauridae without a subfamily.

    sánchez-fenollosa2024a