Bisticeratops

Credit: Sauriazoicillus on the WIkimedia Commons.

*Bisticeratops* is an extinct genus of chasmosaurine ceratopsid dinosaur that lived in New Mexico during the Late Cretaceous.

## History

The holotype of *Bisticeratops froesorum*, NMMNH P-50000 (originally catalogued as UALP 13342), was discovered in 1975 in the vicinity of Alamo Mesa in the Bisti/De-na-zin Federal Wilderness area. This specimen appears to have been attacked by a *Gorgosaurus* in life. It is a large, mediolaterally compressed with the posterior of the squamosals missing, a parietal absent and a right supreorbital horncore that was missing, with a a cast made of it. Previously, it was assigned to *Pentaceratops* despite being 2 million years younger, and later went unassigned by Lucas and Sullivan (2018). The name was leaked in the online description of *Sierraceratops* in 2021 (edited and physically published in 2022) and was named by Dalman et al. (2022).

## Description

* The holotype skull.
* **Credit: Skye McDavid.**
* **Credit: Skye McDavid.**
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The taxon was named from NMMNH P-50000, a nearly complete skull lacking a parietal, left squamosal, postorbital horncores (with only the cast of the right included), left jugal, left quadrate, predentary and dentaries. It was discovered in 1975 from the upper Farmington Member, Kirtland Formation, Bisti/De-Na-Zin Wilderness of the San Juan Basin, New Mexico of the Campanian age. Dalman et al. diagnose it as having a stepped margin in the lateral, a deep narrow sulcus between the triangular process base and premaxillary posteroventral process, a well-developed premaxillary posteroventral process with a robust and strong lateral-protruding ridge, the posterior of the posteroventral having two defined projections separated via a deep notch, a narrow peg-like dorsal projection, a diminutive posterior flange on the narial strut, a naris that is posteriorly expanded over the maxillary teeth, two short anterior processes differentiated by a deep notch on the maxilla, no pocket-like fossa between the ventral jugal process on the maxilla, two elongate and low parallel maxillary ridges underlying the antorbital fenestra, two small antorbital fenestrae on the maxilla, one accessory foramen on the anterodorsal margin, strong fluting on the lateroventral with large accessory mental foramina-like elements, short (and slightly extending past the teeth) ventral process/anterior process (of the premaxilla and maxilla (respectively)) contact, moderately ornamented and short palpebrals and strong anterior curving of the postorbital horncores. The frill is fenestrated and elongate similar to *Pentaceratops sternbergi*.

## Paleobiology

The holotype bears signs of tyrannosaurid predation, but shows signs of healing indicating survival. Tyrannosaurids from this formation are indeterminate or have been misclassified and actually belong to an over- or underlying formation. The holotype injuries inflicted are, bite traces on the right maxilla, right epijugal, proximal right squamosal and left premaxilla, with full penetrations on the premaxilla, maxilla and squamosal. The remodeled bone around the largest bite on the right maxilla suggested survival after the attack. However, bites on the right squamosal and left premaxilla lack this and are thus likely postmortem. The position of the bites suggests that it attacked from the right. Dalman et al. conclude that the presence of this species indicates different dinosaurian faunas in the Western Interior Basin, and that chasmosaur groups evolved in isolation as proven by *Navajoceratops* and *Terminocavus*, and evolved morphological distinction. A similar relationship between the two aforementioned is seen in *Bisticeratops* and the Almond taxon.

## Classification

   Cladistic analysis recovers *Bisticeratops* as closely related to a chasmosaurine specimen from the Almond Formation. Dalman et al. (2022) find:

## Paleoecology

The Farmington Member represents alluvial muds and overbank sand deposits created from channels draining a coastal plain in the inland seashore of North America. No other dinosaurs are known from here, but other subunits bear kritosaurins, lambeosaurines, ankylosaurids, chasmosaurs, pachycephalosaurids, dromaeosaurids, ornithomimids, tyrannosauroids, azhdarchids, crurotarsans, turtles, cartilaginous and bony fishes.

## References

* https://www.sciencedirect.com/science/article/abs/pii/S0195667121002822
* https://www.researchgate.net/publication/362680358\_A\_NEW\_CHASMOSAURINE\_CERATOPSID\_FROM\_THE\_UPPER\_CRETACEOUS\_CAMPANIAN\_FARMINGTON\_MEMBER\_OF\_THE\_KIRTLAND\_FORMATION\_NEW\_MEXICO
* https://www.researchgate.net/publication/328676803\_NEW\_EVIDENCE\_FOR\_PREDATORY\_BEHAVIOR\_IN\_TYRANNOSAURID\_DINOSAURS\_FROM\_THE\_KIRTLAND\_FORMATION\_LATE\_CRETACEOUS\_CAMPANIAN\_NORTHWESTERN\_NEW\_MEXICO
* https://en.wikipedia.org/wiki/Kirtland\_Formation#Saurischians
* https://www.researchgate.net/publication/362680358\_A\_NEW\_CHASMOSAURINE\_CERATOPSID\_FROM\_THE\_UPPER\_CRETACEOUS\_CAMPANIAN\_FARMINGTON\_MEMBER\_OF\_THE\_KIRTLAND\_FORMATION\_NEW\_MEXICO
* https://en.wikipedia.org/wiki/Bisticeratops