[Paleontology • 2015]
Hualianceratops wucaiwanensis • A New Taxon of Basal Ceratopsian from China and the Early Evolution of Ceratopsia
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| Hualianceratops wucaiwanensis
Han, Forster, Clark & Xu, 2015
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Abstract
Ceratopsia is one of the best studied herbivorous ornithischian clades, but the early evolution of Ceratopsia, including the placement of Psittacosaurus, is still controversial and unclear. Here, we report a second basal ceratopsian, Hualianceratops wucaiwanensis gen. et sp. nov.,
from the Upper Jurassic (Oxfordian) Shishugou Formation of the Junggar
Basin, northwestern China. This new taxon is characterized by a
prominent caudodorsal process on the subtemporal ramus of the jugal, a
robust quadrate with an expansive quadratojugal facet, a prominent notch
near the ventral region of the quadrate, a deep and short dentary, and
strongly rugose texturing on the lateral surface of the dentary. Hualianceratops shares several derived characters with both Psittacosaurus and the basal ceratopsians Yinlong, Chaoyangsaurus, and Xuanhuaceratops.
A new comprehensive phylogeny of ceratopsians weakly supports both Yinlong and Hualianceratops as chaoyangsaurids (along with Chaoyangsaurus and Xuanhuaceratops), as well as the monophyly of Chaoyangosauridae + Psittacosaurus. This analysis also weakly supports the novel hypothesis that Chaoyangsauridae + Psittacosaurus is
the sister group to the rest of Neoceratopsia, suggesting a basal split
between these clades before the Late Jurassic. This phylogeny and the
earliest Late Jurassic age of Yinlong and Hualianceratops imply that at least five ceratopsian lineages (Yinlong, Hualianceratops, Chaoyangsaurus + Xuanhuaceratops, Psittacosaurus, Neoceratopsia) were present at the beginning of the Late Jurassic.
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| the reconstructed skull of the holotype specimen of Hualianceratops wucaiwanensis (IVPP V18641).
Abbreviations: an, angular; d, dentary; j, jugal; ma, maxilla; pd, predentary;
po, postorbital; q, quadrate; sa, surangular; sq, squamosal DOI: 10.1371/journal.pone.0143369 |
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| An artist's interpretation of Hualianceratops wucaiwanensis, a dinosaur that lived about 160 million years ago.
illustration: Portia Sloan Rollings || facebook.com/PortiaRollings
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Systematic Paleontology
Dinosauria Owen, 1842
Ornithischia Seeley, 1887
Ceratopsia Marsh, 1890
Chaoyangsauridae Zhao et al., 2006
Type Genus: Chaoyangsaurus Zhao et al., 1999
Definition: A stem-based taxon defined as all ceratopsians more closely related to Chaoyangsaurus youngi than to Psittacosaurus mongoliensis or Triceratops horridus.
Revised Diagnosis: Chaoyangsaurids may be distinguished from
other ceratopsians by the following synapomorphies: semicircular ventral
process near the medial face of the mandibular glenoid [3], expanded,
flat dorsal surface of the squamosal with a stalked quadrate process,
deep sulcus dividing the quadrate condyles, ventral margin of the
angular extending laterally to form a ridge with a distinct concavity
formed above the ridge, predentary reduced and much shorter than
premaxillary oral margin, dorsal and ventral margin of the dentary
converged rostrally more than 20% of the depth.
Hualianceratops gen.nov.
urn:lsid:zoobank.org:act:D96319BA-6380-47D6-9512-5BDA15221A00
Type Species: Hualianceratops wucaiwanensis gen. et sp. nov.
urn:lsid:zoobank.org:act:DEEB3095-CB69-47CD-91FC-2D01D9F429D5
Etymology: “Hualian” means ornamental face, referring to the texture found on most part of the skull, combined with ceratops (horned face) from the Greek, a common suffix for horned dinosaurs; “wucaiwan” (Chinese: five color bay) for the area where the specimen was discovered.
Holotype: IVPP V18641, articulated right maxilla, jugal,
postorbital and partial squamosal, articulated right quadrate and
partial quadratojugal, articulated left partial jugal, quadratojugal and
quadrate, left partial squamosal, most of the mandible, and postcranial
fragments including a nearly complete left pes (Figs 1–9; also see S1
File).
Discussion and Conclusion:
Hualianceratops (IVPP V18641) represents the second species of
basal ceratopsian present in the upper part of the Shishugou Formation
at the Wucaiwan locality. Though Yinlong possesses a number of
autapomorphies, the incompleteness of the Hualianceratops material
does not allow all of these characters to be evaluated. While two
characters have been recognized that are uniquely shared by these taxa
(a deep sulcus on the ventral surface of the quadratojugal for
articulation with the jugal, and a squamosal with a flat dorsal surface
that expands both laterally and caudally), neither unambiguously define a
sister-group relationship between these taxa (see above). Hualianceratops is distinct from Yinlong in
possessing the following characters: a prominent dorsal process on the
infratemporal ramus of the jugal, a robust quadrate with an expanded
rostral margin above the quadratojugal facet, an expansive quadratojugal
facet, a deep notch on the ventral jugal wing of the quadrate, a
shallow sulcus between the quadrate condyles, and strongly rugose
sculpturing on the lateral surface of the dentary. None of these
characters occur in individuals of Yinlong of any size, suggesting they are not ontogenetically dependent.
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| “New” family tree for horned dinosaurs [simplified] |
Yinlong downsi shares some derived feature with both Psittacosaurus and neoceratopsians. Interestingly, Hualianceratops shares more derived characters with Psittacosaurus than
with basal neoceratopsians. This includes the divergent quadratojugal
process and the flattened ventral surface of the jugal, the
caudodorsally curved quadrate head, the deep and short dentary. However,
the large antorbital fossa, preserved squamosal and sculpture lateral
surface of most bones are quite different from that of Psittacosaurus. Additionally, the wide jugal-postorbital bar is more like basal neoceratopsians.
The age of the two Shishugou species within the dating error for the
beginning of the Oxfordian coupled with the most parsimonious
phylogenies imply that at least five lineage of ceratopsians were
present at the beginning of the Late Jurassic (Fig 11), including the
two Shishugou species. The grouping of Psittacosaurus with chaoyangsaurids (Fig 11) implies long ghost lineages for Psittacosaurus and
Neoceratopsia. By comparison, if there are no morphological constraints
on the phylogeny then only two ceratopsian lineages are minimally
necessary at the beginning of the Oxfordian, the two Shishugou species.
Furthermore, all of the alternative MPTs indicate at least three
lineages of chaoyangsaurids were present (assuming the autapomorphies of
the two Shishugou taxa debar them from being direct ancestors to any
other taxa). Three lineages are implied when the two Shishugou taxa are
sister-taxa with a Chaoyangsaurus-Xuanhuaceratops clade or when the former are paraphyletic with the latter, but four lineages are implied when Chaoyangsaurus and Xuanhuaceratops are paraphyletic to a Yinlong-Hualianceratops clade.
The presence of at least five lineages at the beginning of the Late
Jurassic contrasts with the previous published analyses indicating only a
minimum of two lineages at this time, Yinlong and all other
ceratopsians, and prior to 2006 no ceratopsians were known from the
beginning of the Late Jurassic. In any case, this phylogeny implies that
ceratopsian phylogenetic diversification was well established by the
beginning of the Late Jurassic.
Fenglu Han, Catherine A. Forster, James M. Clark and Xing Xu. 2015. A
New Taxon of Basal Ceratopsian from China and the Early Evolution of
Ceratopsia. PLoS ONE. DOI: 10.1371/journal.pone.0143369
Warty-Faced Wonder Reconfigures Horned Dinosaur Family Tree http://blogs.plos.org/paleocomm/2015/12/09/warty-faced-wonder-reconfigures-horned-dinosaur-family-tree/
New Triceratops Cousin Had a Gnarly, Bumpy Skull http://on.natgeo.com/1U6Abch via @NatGeo
