[dinosaur] Scelidosaurus (Early Jurassic thyreophoran) cranial anatomy

Ben Creisler
[email protected]

A new paper:


David B. Norman (2019)
Scelidosaurus harrisonii from the Early Jurassic of Dorset, England:
cranial anatomy.
Zoological Journal of the Linnean Society, zlz074 (advance online
publication)
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1093_zoolinnean_zlz074&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=a3aBNWe7KUCZcZRBauaCZZFtrUj5f6Jrzh1Kfwoijwg&s=Q2sTlbj4A9KxVjrpRmBRLNUqIaQJKsuT1wF7g4U9D1I&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__academic.oup.com_zoolinnean_advance-2Darticle-2Dabstract_doi_10.1093_zoolinnean_zlz074_5648050&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=a3aBNWe7KUCZcZRBauaCZZFtrUj5f6Jrzh1Kfwoijwg&s=otRtKTFDULd_5PvtXEwYW9s-krkHsLx4BkQMFKXgKHE&e= 


Scelidosaurus harrisonii is an early (Late Sinemurian) armoured
ornithischian dinosaur whose remains have, to date, only been recovered
from a restricted location on the south coast of Dorset (Charmouth),
England. This dinosaur has been known since 1859, but only on the basis of
a partial description found in two articles published in the early 1860s by
Richard Owen. The original material, discovered in 1858, comprised the
majority of the skull and its associated postcranial skeleton, and
represents the first ever, more or less complete dinosaur discovered. In
addition to the original material, a number of further discoveries have
been made at Charmouth; these latter supplement the information that can be
gleaned from the original specimen. This article describes the skull of
Scelidosaurus.

The external surface of individual skull bones in ontogenetically
relatively mature individuals displays exostoses, a patina of fibrous or
granular-textured bone that anchored an external shielding of keratinous
scales. There is a small, edentulous rostral beak, behind which is found a
row of five heterodont premaxillary teeth. There is a minimum of 22
maxillary teeth and 27 dentary teeth in jaws of the largest well-preserved
individuals known to date. Both dentitions (upper and lower) are bowed
medially and are sinuous longitudinally. Maxillary and dentary crowns are
tilted lingually on their roots, trapezoidal in outline and have crenellate
(coarsely denticulate) margins. Adjacent crowns of teeth have mesiodistally
(anteroposteriorly) expanded bases that overlap slightly and are
consequently arranged en echelon. The dentitions are flanked by deep cheek
pouches. Tooth abrasion is usually discontinuous along the dentition. In
one individual nearly all teeth seem to be fully emerged and there is
little evidence of abrasion. There is no physical evidence of a predentary,
but the presence of this (typically ornithischian) element may be inferred
from the structure of the symphyseal region of the dentary. The external
narial and antorbital fenestrae are comparatively small, whereas the orbit
and temporal fenestrae are large and open. A sclerotic ring was undoubtedly
present and supported the eyeball, but it is too poorly preserved to allow
it to be reconstructed with accuracy. A prominent supraorbital brow ridge
overhangs the orbit. There are three osteoderms: palpebral, middle
supraorbital and posterior supraorbital, sutured to the dorsal margin of
the orbit. The occiput provides an area for attachment of a pair of curved,
keratin-sheathed, osteodermal horns.

Epistyloid bones project from the ventrolateral region of the braincase;
their distal ends flank the anterolateral region of the neck. Rugose facets
on either side of the basioccipital are suggested to have provided
attachment sites for the epistyloid bones. Internally, the skull has a
deeply vaulted snout and the nasal chambers are roofed by what are here
named epivomer bones that appear to have been sutured to the dorsolateral
edges of the vomers. Unusually, among dinosaurs generally, an epipterygoid
is preserved attached to the dorsolateral surface of the pterygoid; there
is no obvious point of articulation for the epipterygoid against the
lateral wall of the braincase. A deep pit on the posterior surface of the
quadrate of an immature specimen is suggestive of the existence of a
remnant of cranial pneumatism. This pit becomes occluded in larger, more
mature specimens.