Labocania

Molnar, 1974 lah-boh-KAHN-ee-a

Named after the La Bocana Roja Formation in Baja California, Mexico, where the type specimen was likely recovered

100.5–72.2 million years ago Cenomanian–Campanian, Late Cretaceous

Late Cretaceous stages

Labocania is an extinct genus of theropod dinosaur of disputed affinities, known from the Late Cretaceous of Mexico. Initially regarded as an indeterminate theropod, later studies have mentioned possible affinities with tyrannosaurids, abelisaurids, or carcharodontosaurids. More recent research based on additional fossil material found support for a position within the tyrannosaurine clade Teratophoneini. Two species have been proposed: L. anomala (the type species), likely from the La Bocana Roja Formation, and L. aguillonae from the Cerro del Pueblo Formation.

Under dispute

Labocania anomala was described by Molnar (1974) as Theropoda incertae sedis — tyrannosaurid-like in some postcranial features but with cranial elements resembling other large theropods, so Molnar declined a family assignment. Its affinities remain debated; more recent material has been argued to support a tyrannosaurine position.

Diagnosis

Frontals massive and thick, with no anterior extension of supratemporal fossa onto dorsal surface
Quadrate massive, with almost cylindrical mandibular articular surface lacking the typical theropod helical groove
Mandibular condyle of quadrate inclined at about 45 degrees to the long axis of the element, implying strong posterior inclination of the suspensorium
Dentary with prominent lateral shelf (external longitudinal ridge) on its external surface
Ischium with broad plate-like triangular obturator process and relatively larger semi-circular concave tendon scar along posterior margin than in Tyrannosaurus

Species

Labocania anomala Molnar, 1974

Type species

From Latin 'anomala' meaning 'anomalous', in reference to the distinctive and unusual morphology of the type specimen that set it apart from other theropods.

Holotype: IGM 5307 , Instituto de Geología, Universidad Nacional Autónoma de México
Formerly: LACM 20877 (rehoused from Natural History Museum of Los Angeles County)
Material: Incomplete right quadrate, complete left frontal, ventral portion of left maxilla, dentary fragment, proximal portions of both ischia, central shaft of right pubis, chevron, incomplete second right metatarsal, pedal phalanx, and several loose teeth.
Horizon: La Bocana Roja Formation, Cenomanian–Campanian, Late Cretaceous , 100.5–72.2 million years ago
Locality: LACM Locality 7257, Baja California, Mexico Molnar (1974) places the type locality in the La Bocana Roja Formation. Rivera-Sylva and Longrich (2024) report that the locality data "are conflicting": LACM records merge site 6755, listed as "El Gallo Fm. (El Diseado [sic] member)", into it, and if the material comes from the El Disecado Member it would date between 75.84 Ma and 71.9 ± 1.7 Ma. The formation's own age is disputed between Turonian and Campanian.

References

Molnar, R. E. (1974). A distinctive theropod dinosaur from the Upper Cretaceous of Baja California (Mexico). Journal of Paleontology 48(5): 1009-1017. molnar1974a
Rivera-Sylva, H. E.; Longrich, N. R. (2024). A new tyrant dinosaur from the Late Campanian of Mexico reveals a tribe of southern tyrannosaurs. Fossil Studies 2(4): 245-272. doi:10.3390/fossils2040012
Reports that the type locality's records conflict, part of it listed as El Gallo Formation (El Disecado Member).
rivera-sylva2024a
Kane, I. A.; Hodgson, D. M.; Hubbard, S. M.; McArthur, A. D.; Poyatos-Moré, M.; Soutter, E. L.; Flint, S. S.; Matthews, W. (2022). Deep-water tectono-stratigraphy at a plate boundary constrained by large n-detrital zircon and micropaleontological approaches: Peninsular Ranges forearc, Baja California, Mexico. The Sedimentary Record 20(1). doi:10.2110/001c.37652
Dates the upper La Bocana Roja Formation to a maximum of 93.6 Ma (Turonian), against the Campanian age taken from Labocania.
kane2022a