Open Paleo

Guemesia

Agnolín et al., 2021 gweh-MAY-see-uh

Named after Martín Miguel de Güemes, an Argentine independence hero whose death bicentenary was in 2021

83.6–66.0 million years ago Campanian–Maastrichtian, Late Cretaceous
Late Cretaceous stages

Guemesia is a genus of abelisaurid dinosaur from the Late Cretaceous Los Blanquitos Formation of Salta Province, Argentina. The type and only species is Guemesia ochoai, known from a nearly complete braincase. It is one of the smallest abelisaurids currently known.

Under dispute

Guemesia was tentatively placed in Brachyrostra by its describers, who noted a puzzling mix of majungasaurine and basal-abelisaurid features; Pol and colleagues (2024) listed it among furileusaurian abelisaurids without scoring it in their analysis, and others suggest it could represent a distinct lineage.

Diagnosis

  1. Ornamentation of frontals with median row of superficial and large pits (autapomorphy)
  2. Orbital region of each frontal highly pneumatized by a passage communicating the orbital margin of the bone with the dorsal surface of the skull roof (autapomorphy)
  3. Foramen magnum transversely wider than dorsoventrally tall, forming a subrectangular opening
  4. Basipterygoid process elongate with distal end posteroventrally oriented and projected below basal tubera level
  5. Basal tubera delicate and not thickened, distally separated from each other by a notch in the basituberal web

Species

Guemesia ochoai Agnolín et al., 2021

Type species

Named in honor of Javier Ochoa, technician of the Museo Regional 'Florentino Ameghino' in Rio Tercero (Cordoba Province, Argentina), who has worked extensively in Cretaceous outcrops of northwestern Argentina and discovered the specimen described as the holotype.

Holotype
IBIGEO-P 103 , Instituto de Bio y Geociencias del NOA
Material
Almost complete braincase with parietals, frontals, supraoccipital, basioccipital, exoccipital-opisthotic complex, basisphenoid-parasphenoid, prootics, laterosphenoids, and orbitosphenoids; ethmoidal complex not preserved
Horizon
Los Blanquitos Formation, Campanian–Maastrichtian, Late Cretaceous , 83.6–66.0 million years ago
Locality
south part of the Amblayo valley, close to Amblayo town, Salta, Argentina

References

  1. Agnolín, F. L.; Cerroni, M. A.; Scanferla, A.; Goswami, A.; Paulina-Carabajal, A.; Halliday, T.; Cuff, A. R.; Reuil, S. (2021). First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina. Journal of Vertebrate Paleontology 41(4). Informa UK Limited. doi:10.1080/02724634.2021.2002348 agnolín2021a
  2. Pol, D.; Baiano, M. A.; Černý, D.; Novas, F. E.; Cerda, I. A.; Pittman, M. (2024). A new abelisaurid dinosaur from the end Cretaceous of Patagonia and evolutionary rates among the Ceratosauria. Cladistics 40(3): 307-356. Wiley. doi:10.1111/cla.12583

    Listed Guemesia among furileusaurian abelisaurids without scoring it in the analysis.

    pol2024a