Open Paleo

Oxalaia

Kellner et al., 2011 Disputed

From 'Oxalá', the most respected masculine deity of the African pantheon, whose worship was brought to Brazil during slavery, with Latin '-ia'.

100.5–93.9 million years ago Cenomanian, Late Cretaceous
Late Cretaceous stages

Oxalaia is a genus of spinosaurid dinosaur that lived in what is now the Northeast Region of Brazil during the Cenomanian stage of the Late Cretaceous period, sometime between 100.5 and 93.9 million years ago. Its fossils were found in 1999 on Cajual Island in the rocks of the Alcântara Formation, which is known for its abundance of fragmentary, isolated fossil specimens. The remains of Oxalaia were described in 2011 by Brazilian paleontologist Alexander Kellner and colleagues, who assigned the specimens to a new genus containing one species, Oxalaia quilombensis. The species name refers to the Brazilian quilombo settlements. Oxalaia quilombensis is the eighth officially named theropod species from Brazil and the largest carnivorous dinosaur discovered there. One study suggested that this taxon is a junior synonym of the closely related African genus Spinosaurus, but some subsequent studies consider the genus to be diagnostic.

Under dispute

The validity of Oxalaia is contested, and the argument runs through its diagnosis rather than through phylogeny. Kellner and colleagues (2011) erected the genus on fused premaxillae with four proposed autapomorphies. Sales and Schultz (2017) reassessed those characters individually, rejected the thin anteromedial maxillary processes as not distinguishable from other spinosaurids once ontogeny is allowed for, and issued a revised diagnosis retaining two: the paired replacement teeth at the third premaxillary alveolus and the strongly sculptured palatal surface, both held tentatively against the possibility that they are intraspecific variation. Smyth and colleagues (2020) rejected every proposed character — noting that the maximum premaxillary expansion varies between the left and right sides of the holotype itself — and concluded that Oxalaia quilombensis is a junior synonym of Spinosaurus aegyptiacus pending more diagnostic material. Lacerda and colleagues (2022) rejected that synonymy in turn, finding no overlapping structures that would allow the direct comparison it requires and treating the genus as a valid name-bearing taxon. The species is marked disputed and the genus retained at Spinosaurinae.

Diagnosis

  1. Two replacement teeth associated with the functional third premaxillary alveolus
  2. Palatal portion of the fused premaxillae bears a strongly sculptured surface forming a convex secondary palate

Species

Oxalaia quilombensis Kellner et al., 2011 Disputed

Type species

From Portuguese 'quilombo', a settlement founded by escaped slaves; Cajual Island, where the specimens were collected, was one such place.

Holotype
MN 6117-V , Museu Nacional
Material
Fused premaxillae of a very large individual.
Horizon
Alcântara Formation, Cenomanian, Late Cretaceous , 100.5–93.9 million years ago
Locality
Laje do Coringa, Cajual Island, Maranhão, Brazil

References

  1. Kellner, A. W. A.; Azevedo, S. A. K.; Machado, E. B.; Carvalho, L. B.; Henriques, D. D. R. (2011). A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil. Anais da Academia Brasileira de Ciências 83(1): 99-108. FapUNIFESP (SciELO). doi:10.1590/s0001-37652011000100006

    Erects the genus and species on fused premaxillae and proposes four autapomorphies.

    kellner2011b
  2. Sales, M. A. F.; Schultz, C. L. (2017). Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil. PLOS ONE 12(11): e0187070. doi:10.1371/journal.pone.0187070

    Reassesses the proposed autapomorphies individually and issues a revised diagnosis retaining two of them.

    sales2017a
  3. Smyth, R. S. H.; Ibrahim, N.; Martill, D. M. (2020). Sigilmassasaurus is Spinosaurus: a reappraisal of African spinosaurines. Cretaceous Research 114: 104520. Elsevier BV. doi:10.1016/j.cretres.2020.104520

    Rejects every proposed autapomorphy and treats the species as a junior synonym of Spinosaurus aegyptiacus.

    smyth2020a
  4. Lacerda, M. B. S.; Grillo, O. N.; Romano, P. S. R. (2022). Rostral morphology of Spinosauridae (Theropoda, Megalosauroidea): premaxilla shape variation and a new phylogenetic inference. Historical Biology 34(11): 2089-2109. Informa UK Limited. doi:10.1080/08912963.2021.2000974

    Rejects that synonymy and treats the species as a valid name-bearing taxon.

    lacerda2022a