Transitional evolutionary forms in chasmosaurine ceratopsid dinosaurs: evidence from the Campanian of New Mexico

Denver W Fowler; Elizabeth A Freedman Fowler

doi:10.7717/peerj.9251

Transitional evolutionary forms in chasmosaurine ceratopsid dinosaurs: evidence from the Campanian of New Mexico

PeerJ. 2020 Jun 5:8:e9251. doi: 10.7717/peerj.9251. eCollection 2020.

Authors

Denver W Fowler^{1

2}, Elizabeth A Freedman Fowler^{1

2

3}

Affiliations

¹ Badlands Dinosaur Museum, Dickinson Museum Center, Dickinson, ND, USA.
² Museum of the Rockies, Montana State University, Bozeman, MT, USA.
³ Department of Natural Sciences, Dickinson State University, Dickinson, ND, USA.

Abstract

Three new chasmosaurines from the Kirtland Formation (~75.0-73.4 Ma), New Mexico, form morphological and stratigraphic intermediates between Pentaceratops (~74.7-75 Ma, Fruitland Formation, New Mexico) and Anchiceratops (~72-71 Ma, Horseshoe Canyon Formation, Alberta). The new specimens exhibit gradual enclosure of the parietal embayment that characterizes Pentaceratops, providing support for the phylogenetic hypothesis that Pentaceratops and Anchiceratops are closely related. This stepwise change of morphologic characters observed in chasmosaurine taxa that do not overlap stratigraphically is supportive of evolution by anagenesis. Recently published hypotheses that place Pentaceratops and Anchiceratops into separate clades are not supported. This phylogenetic relationship demonstrates unrestricted movement of large-bodied taxa between hitherto purported northern and southern provinces in the late Campanian, weakening support for the hypothesis of extreme faunal provincialism in the Late Cretaceous Western Interior.

Keywords: Anagenesis; Anchiceratops; Ceratopsidae; Chasmosaurinae; Cretaceous; Dinosaur; Diversity; Pentaceratops.

Grants and funding

This work was supported by the Jurassic Foundation, and the Horner Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.