Bravoceratops

''Bravoceratops'' is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States.

Discovery and naming

''Bravoceratops'' is only known from the holotype specimen TMM 46015-1; it is housed in the collection of the Texas Memorial Museum, Austin, Texas. The skull consists of a number of fragments, altogether including: the , parts of each brow horn, the rear end of the left , assorted parts of the nasal area and horn, the , and quadratojugals from each side, a section of the and , multiple parts of the dentary, and some of the right . It was recovered from the lowermost rocks of the Javelina Formation, in Big Bend National Park; ceratopsid fossils are uncommon in this formation, giving the discovery of ''Bravoceratops'' importance in clarifying the groups' diversity. The specimen was found in sandy conglomerate sediment at the Hippiewalk geologic locality. Signs of erosion are presented in the larger bone fragments, which were found disorganized over an area of ten square metres; the site is thought to have been a lag deposit of a river, only most durable extremities able to survive preservation. The animal would have lived during the late Campanian or early Maastrichtian stage of the Cretaceous period, approximately 70 million years ago.

The genus name means "wild horn-face", and is derived from the Mexican name for the Rio Grande, " Rio Bravo del Norte" (wild river of the north), and the Greek words "keras" (κέρας) meaning "horn" and "ops" (ὤψ) referring to the "face". The specific name ''polyphemus'', refers to the giant cyclops Polyphemus confronted by Odysseus in the Greek epic poem, The Odyssey. This is in reference to the presumption that it had a single central horn on the surface of the frill, recalling the placement of a Cyclops' eye. The genus was described and named by Steven L. Wick and Thomas M. Lehman in 2013 and the type species is ''Bravoceratops polyphemus''.

Description

Two autapomorphies (unique derived traits) were originally proposed. Firstly, the median bar (which runs down the middle of the frill between its large holes) at mid-length splays out to the rear like a fan and its rear edge is not notched or embayed. Secondly, the upper surface of the bar is, at the midline, hollowed out by a symmetrical depression. It is this hollow in the form of an inverted tear that occasioned the specific name as it resembled the single eye of a cyclops, thus the allusion with Polyphemus. The authors assumed it formed the base of an epiparietal, or small horn, unpreserved in the fossil. In 2020, paleontologists Denver W. Fowler and Elizabeth A. Freedman Fowler suggested that the parietal median bar of the specimen had been reconstructed upside down, and that the genus therefore did not have any distinguishing features among chasmosaurines, making it a '' nomen dubium'', or invalid genus. However, a number of authors considered the genus valid (see classification below) and it was included as part of a southwest clade of chasmosaurines by Dalman et al., (2021).

Unlike Fowler and Freedman-Folwer, Sebastian G. Dalman and colleagues, in a 2021 paper naming the related genus '' Sierraceratops'', treated ''Bravoceratops'' as valid, noting both distinct traits and those unique to it and ''Sierraceratops''. A flange in front of its near the bones is present, large as in ''Sierraceratops'' while small or not present in other chasmosaurs. The epijugal, a small horn on the jugals, is longer than tall and sharp on its tip, as in ''Sierraceratops'' and unlike other derived chasmosaurines. The two brow horns are compressed, being taller than wide rather than conical, a trait shared with ''Sierraceratops'' and the distantly related ''Judiceratops''. The cross section of the lower bar of its parietal bar has a D-shape shared with ''Sierraceratops'' and similar but not identical to that of '' Coahuilaceratops'', but unlike other chasmosaurines. ''Bravoceratops'' is distinguishable from ''Coahuilaceratops'' in lacking enormous brow horns; it is distinguishable from ''Sierraceratops'' in having larger brow horns and a smaller epijugal horn.

Classification

''Bravoceratops'' is assigned to the Chasmosaurinae. It is an "intermediate" form of chasmosaurine; it, along with genera like ''Pentaceratops'' and '' Anchiceratops'', was distinctly more derived ("advanced") than forms like '' Chasmosaurus'' but less so than taxa like ''Triceratops''. Its position in a phylogenetic analysis performed by Wick and Lehman (2013), who first named the taxon. It was found that ''Bravoceratops'' may be the sister taxon of '' Coahuilaceratops'' (a relationship later supported by Dalman et al., 2021). The first analysis, with unmodified characters from a previous study, found the pair to be relatively basal . The second, with two added characters, instead found ''Bravoceratops'' to be a relatively derived taxon. Both positions were considered to be somewhat unintuitive; several of its derived characters would be odd for a taxon in the basal position, but the genus also possessed primitive characters would require evolutionary reversals if the more derived position was correct. Regardless, the more derived placement was considered to be somewhat more likely. The first tree is reproduced on the left, and the second on the right:

Future studies found trees showing the derived position, with ''Bravoceratops'' found related to ''Arrhinoceratops'' and Triceratopsini. However, the fragmentary nature of ''Bravoceratops'' caused it to generally be removed from phylogenetic analyses, as it was a wildcard taxon (meaning it was unstable and caused poorer results). Fowler and Freedman Fowler (2020) recovered ''Bravoceratops'' in the more basal position, and, similar to Wick and Lehman (2013), found it close to ''Pentaceratops'', and once again sister to ''Coahuilaceratops''. However, they also decided to remove it from their analysis due to their unsubstantiated conclusion the taxon was invalid. However, Dalman et al. (2021) convincingly validated the genus. They demonstrated that ''Bravoceratops'' shared a number morphological traits with other chasmosaurines from the same time and region. As a result, ''Bravoceratops'' was determined to be part of a clade endemic to the Southwestern United states. Sister taxa include ''Coahuilaceratops'' from Mexico and ''Sierraceratops'' from New Mexico.

See also

* Timeline of ceratopsian research

References

{{Taxonbar, from=Q13410268

Chasmosaurines
Dinosaurs of North America
Fossil taxa described in 2013
Maastrichtian life
Paleontology in Texas
Ornithischian genera