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Juvenile chasmosaurine from Dinosaur Park Formation, Alberta, Canada



Ben Creisler
bcreisler@gmail.com

A new paper:

Philip J. Currie, Robert B. Holmes, Michael J. Ryan & Clive Coy (2016)
A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from
the Dinosaur Park Formation, Alberta, Canada.
Journal of Vertebrate Paleontology (advance online publication)
DOI:10.1080/02724634.2015.1048348
http://www.tandfonline.com/doi/full/10.1080/02724634.2015.1048348


An articulated, 1.5 m long skeleton of a juvenile Chasmosaurus,
lacking only the front limbs, pectoral girdles, and terminal caudal
vertebrae, was collected from the Dinosaur Park Formation in Dinosaur
Provincial Park, Alberta. The short, tall skull has a narrow frill
that lacks a posterior embayment. Many of the cranial bones are
co-ossified in spite of the small size of the specimen. The nasals
form an incipient horncore, and the short, knob-like postorbital
horncore lacks sinuses. The palpebral is not fused to the rest of the
skull. The frontal fontanelle is keyhole-shaped. The triangular
squamosal extends to the back of the parietals. Epiossifications are
lacking, although the squamosal margin is thick and scalloped. The
parietal has a pronounced midline sagittal crest. Parietal fenestrae,
if present, would have been narrow and elongate. There are only 18
maxillary tooth positions. The syncervical comprises three
co-ossified, but distinct vertebrae. Anterior caudal vertebrae support
unfused caudal ribs. Ossified tendons in the neck, trunk, and sacrum
do not extend into the tail. Hind limb proportions are comparable to
those of adult ceratopsids. The pedal unguals are distally acute. Skin
impressions are similar to those of mature chasmosaurines.
Phylogenetic analysis, if all characters are coded as they are seen,
suggests that the specimen is a basal chasmosaurine. When size or age
dependent characters are recoded as ‘?,’ the specimen groups with
other Chasmosaurus. These characters should only be used in
phylogenetic analyses when all specimens are mature.