[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Gryposaurus monumentensis & Cryolophosaurus ellioti
One's a hadrosaurid, one's a basal theropod. They're detectives...
Or rather, they are both in the latest issue of Zoological Journal of the
TERRY A. GATES, SCOTT D. SAMPSON (2007) A new species of Gryposaurus
(Dinosauria: Hadrosauridae) from the late Campanian Kaiparowits Formation,
southern Utah, USA. Zoological Journal of the Linnean Society 151 (2),
Abstract: A new species of the hadrosaurine hadrosaurid Gryposaurus was
discovered in the late Campanian Kaiparowits Formation of southern Utah.
Gryposaurus monumentensis, sp. nov. is distinguished from other Gryposaurus
species by possessing a more robust skull, enlarged clover-shaped prongs on
the predentary oral margin, an anteroposteriorly narrow infratemporal
fenestra, and other autapomorphies plausibly associated with feeding
adaptations. The derived morphology revealed in G. monumentensis
necessitates revision of the generic diagnosis of Gryposaurus, including the
addition of synapomorphies that further aid in distinguishing this taxon
from Kritosaurus. A revised phylogenetic analysis places Gryposaurus within
a monophyletic clade that includes Brachylophosaurus and Maiasaura.
Gryposaurus monumentensis represents the most southern example of
Gryposaurus, and underlines the remarkable diversification and long duration
of this genus. Based on the phylogenetic, geographical, and stratigraphic
evidence at hand, Gryposaurus was the most diverse genus within
Hadrosaurinae; it also possessed one of the largest geographical and
stratigraphic distributions, spanning more than five million years of the
Campanian, and ranging from Alberta in the north to Utah (and possibly
Texas) in the south.
NATHAN D. SMITH, PETER J. MAKOVICKY, WILLIAM R. HAMMER, PHILIP J. CURRIE
(2007) Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the
Early Jurassic of Antarctica and implications for early theropod evolution.
Zoological Journal of the Linnean Society 151 (2), 377-421.
Abstract: Cryolophosaurus ellioti Hammer and Hickerson, 1994, from the Early
Jurassic Hanson Formation of the Central Transantarctic Mountains,
represents a theropod dinosaur from a period of time and geographical area
that are poorly sampled with respect to dinosaur taxa. An in-depth
morphological description of Cryolophosaurus is presented here, along with a
rigorous phylogenetic analysis of theropod relationships consisting of 347
characters and 56 taxa, in an attempt to clarify the relationships of
Cryolophosaurus and to provide insight into questions surrounding early
theropod evolution. Cryolophosaurus is characterized by a unique cranial
crest, formed primarily by the lacrimals, a pronounced constriction of the
squamosal and jugal bones across the infratemporal fenestra, and extremely
elongate cranial processes on the cervical ribs. Several shared characters,
including the presence of a slot-shaped foramen at the base of the nasal
process of the premaxilla, nasolacrimal crests and erect tab-like dorsal
processes on the articular, suggest affinities between Cryolophosaurus and a
clade of medium-bodied Early Jurassic theropods that includes
'Dilophosaurus' sinensis, Dracovenator regenti and Dilophosaurus wetherilli.
This clade is recovered as sister-taxon to a Neoceratosauria + Tetanurae
clade, rendering both a traditional Coelophysoidea and Ceratosauria
non-monophyletic. Cryolophosaurus represents the largest known Early
Jurassic theropod, and marks the beginning of theropod occupation of the
dominant predator niche in the Mesozoic.
This is the reference coming VERY SOON I mentioned on the
weekend. Truly good stuff, and I strongly suspect that they have better
captured the actual phylogeny of basal theropods than most previous studies.
Beyond the discovery of the dilophosaur clade, they find that
Piatnitzkysaurus and Condorraptor are sister taxa and lie outside of
Spinosauroidea + Avetheropoda; that Megaraptor is a carcharodontosaurid (but
only weakly supported, with some definite spinosauroid traits); that
Monolophosaurus is outside Avetheropoda (a non-crazy hypothesis). The heart
of the paper, however, is the osteology of the beast.
Congrats to Terry, Nathan, and their co-authors on these papers.
Oh, and for the furry fans, the same issue has:
PER CHRISTIANSEN (2007) Comparative bite forces and canine bending strength
in feline and sabretooth felids: implications for predatory ecology.
Zoological Journal of the Linnean Society 151 (2), 423-437.
Abstract: The sabretooth felids were widespread across much of the world in
the Late Tertiary, and appear to have been an important group of large
predators. Owing to the substantially different skull morphology of derived
sabretooths compared with extant felids, there has been considerable debate
over the killing mode, bite forces, and bending strength of the large upper
canines, and over the implications of these characteristics on feeding
ecology. Debates have, however, usually been based on indirect comparisons
of force vectors. In this paper, I provide assessments of the estimated
force output from the jaw adductor muscles, based on estimates of muscle
cross-sectional areas and force vectors, along with canine bending
strengths, in a variety of sabretooth felids, in comparison with extant
felids. In general, sabretoothed felids had moderately powerful bites,
albeit with less jaw adductor power for their body sizes compared with
extant felids, sometimes markedly so. Less derived sabrecats appear to have
had proportionally higher bite forces than derived forms. The length of the
upper canines seemingly compromised their bending strength at any given body
size, and again this was most marked in derived forms. However, compared
with estimated jaw adductor forces, the canines of sabrecats appear, if
anything, to have been stronger than those of extant conical-toothed felids.
It has previously been suggested that large sabretoothed felids hunted large
prey with a canine shearing bite, powered in part by the jaw adductors and
in part by the muscles of the upper neck-occipital region. The present
results of canine bending strengths versus the predicted bite force from the
jaw adductors supports this suggestion.
Thomas R. Holtz, Jr.
Email: firstname.lastname@example.org Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Earth, Life & Time Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA