Arcusaurus
Early Jurassic sauropodomorph dinosaur from South Africa.
Arcusaurus is a genus of sauropodomorph dinosaur that lived during the Early Jurassic (Pliensbachian age) in what is now South Africa. In 2011, Adam Yates, Matthew Bonnan, and Johann Neveling gave it the name Arcusaurus pereirabdalorum. The genus name comes from the Latin word for "rainbow," a nod to the Rainbow Nation, while the species name honors Lucille Pereira and Fernando Abdala, who found the fossils. A phylogenetic study placed Arcusaurus as a basal sauropodomorph, making it the sister taxon of Efraasia and all more derived sauropodomorphs. Since Efraasia is known from the Late Triassic (Norian stage), this close relationship suggests a 35-million-year ghost lineage of sauropodomorphs stretching from the Late Triassic to Arcusaurus. However, Arcusaurus also has many features unique to more advanced groups within Plateosauria, which casts doubt on the results of that analysis.
The fossils were collected in March 2006 at the Spion Kop Heelbo site in the upper Elliot Formation near Senekal in Free State. The site may be Pliensbachian in age. The holotype (specimen BP/1/6235) is a partial skull. About 50 cm around this skull, additional bones of similar size were found, and overlapping material confirms they belong to the same species. But two right nasal bones were discovered, meaning at least two individuals were present. Since each specimen should only include bones from one individual, every bone except the holotype was given its own specimen number. The holotype was found disarticulated, like all other bones, and includes the nasal, postorbital, dentary, coronoid, and teeth from the maxilla. A single tail vertebra may also belong to this individual. Other specimens include a second right nasal, another dentary, a premaxilla, a laterosphenoid, several phalanges and unguals, a humerus, and fragments of the sacrum and ilium. The individuals were probably juveniles, based on their small size and open bone sutures. Detailed features led the describers to conclude they were not juveniles of *Aardonyx* or *Massospondylus*.
The snout was likely relatively deep, as in plateosaurians, shown by the square shape of the premaxilla. The nostril opening was near the snout tip, and the eye socket was proportionally large and circular, similar to that of *Eoraptor*. The premaxilla held four teeth on each side.
Quick Facts
- Taxon
- Arcusaurus
Facts from the source article.
Lore & Background
Arcusaurus was discovered in March 2006 at the Spion Kop Heelbo site in Senekal, Free State, from the upper Elliot Formation. The holotype (BP/1/6235) consists of a partial skull, including the nasal, postorbital, dentary, coronoid, and maxillary teeth. Additional bones found within 50 cm of the skull, such as a second right nasal, indicate at least two individuals were present. Each bone apart from the holotype was given its own specimen number. The small size and open bone sutures suggest the individuals were juveniles, and the describers concluded they were not juveniles of Aardonyx or Massospondylus.
Reader's Guide
Arcusaurus is significant for its phylogenetic position as a basal sauropodomorph, placed as the sister taxon of Efraasia and all more derived sauropodomorphs. This relationship implies a 35-million-year ghost lineage from the Late Triassic (Norian) to the Early Jurassic. However, Arcusaurus possesses many features unique to more advanced groups within Plateosauria, raising doubts about the results of the phylogenetic analysis. Its discovery provides insight into early sauropodomorph diversity in the Early Jurassic of southern Africa and highlights the incomplete nature of the fossil record for this group.
Did You Know?
- The generic name Arcusaurus is derived from Latin arcus, meaning 'rainbow', a reference to the Rainbow Nation.
- The specific epithet pereirabdalorum honors Lucille Pereira and Fernando Abdala, who discovered the fossils.
- Two right nasal bones were found, indicating at least two individuals were present at the site.
- The holotype skull was found disarticulated, with bones not in their original anatomical positions.
Frequently Asked Questions
What is Arcusaurus?
Arcusaurus is a basal sauropodomorph dinosaur from the Early Jurassic of South Africa. Its type species, A. pereirabdalorum, was formally named in 2011 by Yates, Bonnan, and Neveling on the basis of a partial skull and postcranial elements recovered from the Free State region.
What does the name Arcusaurus mean?
The genus name comes from the Latin word for 'rainbow,' a deliberate nod to South Africa's 'Rainbow Nation' identity. The species epithet pereirabdalorum honors Lucille Pereira and Fernando Abdala, the two people who originally uncovered the fossil material.
Where and when did Arcusaurus live?
Arcusaurus is known from Pliensbachian-age (Early Jurassic) deposits in the Free State province of South Africa. This places it slightly later in time than the Late Triassic Efraasia, its closest known relative.
How does Arcusaurus fit into sauropodomorph evolution?
Phylogenetic analyses position Arcusaurus as a basal sauropodomorph sitting just outside the clade that contains Efraasia and all more derived sauropodomorph lineages. In practical terms, it is the sister taxon to Efraasia plus every later sauropodomorph, making it one of the earliest known members of the group.
What fossils of Arcusaurus are known?
The known material consists of a partial skull along with assorted postcranial bones, which is relatively limited compared to better-documented sauropodomorphs. Despite this incomplete preservation, the specimen was sufficient for the 2011 description and phylogenetic placement of the genus.
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