Ceratopsids are among the most
distinctive and easily recognized of Dinosaur groups, due to their large and
heavily ornamented skulls, with large neck frills and horns. Despite their
ubiquitousness in Dinosaur pop-culture they were a rather short-lived and
geographically restricted group, found only in the Late Cretaceous of North
America and parts of northeast Asia. The Ceratopsids are split taxonomically
into two groups, the Centrosaurs, which went extinct in the Early
Maastrichtian, about 5 million years before the end of the Cretaceous, and
which tended to have enlarged nasal horns (horns on their noses) and ornate
neck frills, and the Chasmosaurs, which survived till the End Cretaceous
Extinction, and which tended to have enlarged orbital horns (horns above their
eyes) and large but simple frills.
In a paper published in the
journal Current Biology on 15 June 2015, Caleb Brown and Donald Henderson of
the Royal Tyrrell Museum of Palaeontology describe a new species of Chasmosaur
from the Late Cretaceous St. Mary River Formation in the Waldron Flats area of
Alberta, close to the Oldman River and about 164 km south of Calgary.
The new specimen is named Regaliceratops peterhewsi, where ‘Regaliceratops’ means ‘Royal
Ceratopsid’, in reference to both the ornamentation of the frill and the Royal
Tyrell Museum, and ‘peterhewsi’
honours Peter Hews, who discovered the specimen from which the species is
described, a single skull, complete but for the absence of the rostral bone and
the lower jaw; the post cranial skeleton is unknown.
Photographs and Interpretive Line Drawings of the Holotype of Regaliceratops peterhewsi. (A–D) Nearly
complete cranium in right lateral (A), left lateral (B), rostral (C), and
dorsal (D) views. (A’–D’) Interpretive drawings of photographed views in
(A)–(D). Areas in shadow, (C) and (D) left, are fully illustrated at right.
Areas in white represent reconstruction (plaster/epoxy putty), and hatched
areas indicate matrix. The following abbreviations are used: cvp, caudoventral
process of premaxilla; ej, epijugal; en, external naris; isf, interseptal
fenestra; itf, infratemporal fenestra; j, jugal; jn, jugal notch; m, maxilla;
n, nasal; nhc, nasal horncore; ns, narial strut; ob, orbit; p, parietal; pf,
parietal fenestra; phc, postorbital horncore; pm, premaxilla; por, postorbital
ridge; pp, palpebral; ps, epiparietosquamosal; P#, epiparietal; s, squamosal;
stf, supertemporal fenestra; S#, episquamosal; tp, triangular process. Scale
bar represents 10 cm. Brown & Henderson (2015).
The skull morphology of Regaliceratops peterhewsi places it
firmly within the Chasmosaurinae, however it shows a number of features common
to Centrosaurs, most notably an ornate frill and a large nasal horn. These
features have been seen in Chasmosaurs before, but largely in early members of
the group, closer to the divergence between the two groups, and never to the
extent seen in Regaliceratops peterhewsi.
A phylogenetic analysis of the
Chasmosaurs carried out by Brown and Henderson suggests that they can be split
into two distinct groups, an earlier Chasmosaurus-like
group which were smaller and had features closer to those of Centrosaurs, and a
later Triceratops-like group which
were larger and had more highly developed Chasmosaur features (such as enlarged
orbital horns and large simple frills). These two groups are share a common
ancestor more recent than their common ancestor with the Centrosaurs, but
before any of the known fossil species appeared, suggesting that a long
ghost-lineage (a lineage that can be inferred from the gap in the evolutionary
record, but for which no fossils are known) for the Triceratops-like group exists. Importantly the Chasmosaurus-like group appear to go extinct at about the same time
as the Centrosaurs, suggesting that a common cause may have been responsible for
the demise of the two groups, while the Triceratops-like
group diversifies after the disappearance of the other two groups, which may
indicate they were moving into ecological niches formerly occupied by Centrosaurs
and Chasmosaurus-like Chasmosaurs.
Time-calibrated strict consensus tree of five most parsimonious trees
for Chasmosaurinae utilizing the new epiossification homology scheme. Black bars
indicate confident stratigraphic occurrence, whereas gray bars indicate less confidence.
Bottom right: oblique view of Regaliceratops
peterhewsi. Brown & Henderson (2015).
Regaliceratops peterhewsi is situated firmly within the Triceratops-like group, albeit quite
early in the known group, and is the first known member of this group to show Centrosaur-like
features. Among Mammals convergent evolution of horn ornamentation has been
linked to convergent social behaviour. This is impossible to judge in Ceratopsids,
an extinct group in which behaviour cannot be directly assessed, however it is
possible that a Chasmosaur such as Regaliceratops
peterhewsi moving into an ecological niche left vacant by the extinction of
the Centrosaurs could also have developed similar social behaviour, resulting
in convergent evolution of the skull ornamentation.
See also…
Ceratopsian Dinosaurs are thought to have originated in Asia in the Early Cretaceous, spreading to Europe and North America, and becoming the most important and diverse group of herbivorous Dinosaurs in North America by the end of the Period. Unfortunately...
Dinosaurs underwent dramatic increases in size over a number of years during their growth, and are presumed to have played a number of different ecological roles during this growth period. Numerous examples...
Ceratopsid Dinosaurs were a speciose group of large, herbivorous Dinosaurs from the Late Cretaceous of Asia and North America...
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