Archosaurs in Zoological Journal dedicated to Alick Walker

[bh480@scn.org]

From: Ben Creisler bh480@scn.org
The new September issue of the Zoological Journal of the 
Linnean Society is devoted to archosaurs (including two 
dinosaur articles) and is dedicated to Alick Walker. Here 
are the abstracts:
September 2002 - Volume 136 Issue 1 
Gower, David and Alick D. Walker. 2002. New data on the 
braincase of the aetosaurian archosaur (Reptilia: 
Diapsida) Stagonolepis robertsoni Agassiz. Zoological 
Journal of the Linnean Society 136: 1-7. 
New data on the braincase of the aetosaurian archosaur 
Stagonolepis robertsoni Agassiz are presented, based on 
new preparation, synthetic casting, and interpretation of 
fossil material from the Triassic Elgin Sandstones, 
Scotland. The metotic fissure is not divided by bone. The 
perilymphatic foramen is completely bound by bone, and 
faces away from the otic capsule in a posterolateral 
direction. A prominent subvertical ridge on the 
anterolateral edge of the exoccipital and upper part of 
the basioccipital cannot be directly associated with the 
subcapsular process of the chondrocranium of extant 
crocodilians. This ridge projects laterally beyond the 
ventral ramus of the opisthotic, and lies anterior to the 
external foramina for the hypoglossal nerve. The overall 
structure of the braincases (especially the otic region) 
of S.robertsoni and other aetosaurians, where known, is 
more similar (in terms of derived archosaurian characters) 
to those of crocodylomorphs than are the braincases of 
other major suchian groups. This provides evidence for the 
currently unorthodox hypothesis that, among major suchian 
clades, Aetosauria and Crocodylomorpha are each others' 
closest relatives. Support for this hypothesis is found in 
features of the palatine and prefrontal that have not been 
considered in recent studies of suchian phylogeny. This 
alternative phylogenetic hypothesis demands further 
investigation but, combined with the new morphological 
data that it explains, it provides a framework for the 
understanding of the evolution of the derived and 
distinctive braincase structure of extant crocodilians
Benton, Michael J. and Alick D. Walker 2002. Erpetosuchus, 
a crocodile-like basal archosaur from the Late Triassic of 
Elgin, Scotland. Zoological Journal of the Linnean 
Society, 2002, 136: 25-47.
Erpetosuchus, a small archosaurian reptile from the Late 
Triassic of Scotland and North America, has often been 
implicated in the ancestry of crocodilians. A restudy of 
the type specimen, using new high-fidelity casts, as well 
as examinationof new, hitherto undescribed material, 
allows a detailed description and restoration of 
Erpetosuchus granti from the LossiemouthSandstone 
Formation (late Carnian, Late Triassic). This small 
reptile is known only from the front end of its body; a 
complete skull,cervical vertebral column, anterior dorsals 
and ribs, shoulder girdle, and forelimb. The skull shows a 
number of unusual features: a reducedrow of only 4-5 teeth 
on the anterior part of the maxilla, a large antorbital 
fenestra set in a deep fossa whose margins aremarked by 
distinct sharply angled ridges, a jugal that is divided 
into a lateral and a ventral portion by a sharp ridge, a 
deeplyrecessed tympanic area, the angular and surangular 
marked by a strong ridge running back from the ventral 
margin of the mandibular fenestra,and teeth oval in cross-
section and lacking anterior and posterior carinae and 
marginal serrations. The remains suggest that Erpetosuchus 
wasa light, cursorial animal that may have fed on insects. 
A cladistic analysis of crurotarsan archosaurs indicates 
that Erpetosuchus isthe closest sister group of 
Crocodylomorpha among known basal archosaurs. It shares 
with them a deep recess in the cheek region framed bythe 
quadrate and quadratojugal which slope forward side-by-
side at an angle of 45° above horizontal, and reach the 
uppermargin of the lower temporal fenestra. In 
Erpetosuchus the recess is entirely lateral, while in 
crocodylomorphs, the recesspenetrates medially as well, 
since the quadrate/quadratojugal bar meets the side wall 
of the braincase.
Gowever, David J. 2002 Braincase evolution in suchian 
archosaurs (Reptilia: Diapsida): evidence from the 
rauisuchian Batrachotomus kupferzellensis. Zoological 
Journal of the Linnean Society, 2002, 136: 49-76.
The osteology of an almost complete braincase of the 
rauisuchian archosaur Batrachotomus kupferzellensis Gower 
from the Middle Triassic of Germany is described. There is 
a possibly discrete epiotic ossification, the metotic 
fissure is undivided by bone (i.e. there is a metotic 
foramen), the medial wall of the otic capsule is mostly 
ossified, the cerebral branch of the internal carotid 
artery entered the lateral surface of the 
parabasisphenoid, the ventral ramus of the opisthotic is 
more prominent laterally than a strong subvertical ridge 
on the exoccipital and basioccipital that lies posterior 
to the external foramen for the hypoglossal nerve, and the 
perilymphatic foramen faces away from the otic capsule in 
a posterior direction. Braincase morphology in the 
rauisuchians Saurosuchus galilei, Postosuchus 
kirkpatricki, and Tikisuchus romeri is reviewed. A matrix 
of 27 braincase characters for 12 archosaurian taxa is 
analysed. The most parsimonious hypothesis is consistent 
with the currently orthodox view of archosaurian 
phylogeny, except in that aetosaurians are more closely 
related to crocodylomorphs than is any rauisuchian. This 
phylogeny is used in a brief interpretation of the 
evolution of derived braincase features present in extant 
crocodilians. 
Clark,  James M. and Hans-Dieter Sues. 2002Two new basal 
crocodylomorph archosaurs from the Lower Jurassic and the 
monophyly of the Sphenosuchia. Zoological Journal of the 
Linnean Society, 2002, 136: 77-95.
We report on and name two new taxa of basal crocodylomorph 
archosaurs from the Lower Jurassic, Litargosuchus 
leptorhynchus gen. et sp. nov., from the upper Elliot 
Formation (Stormberg Group) of South Africa, and 
Kayentasuchus walkeri gen. et sp. nov., from the Kayenta 
Formation (Glen Canyon Group) of Arizona, USA. Examination 
of this material led to a reconsideration of basal 
crocodylomorph interrelationships. A phylogenetic analysis 
found no support for the monophyly of Sphenosuchia.. 
Small, Bryan J. 2002 .Cranial anatomy of Desmatosuchus 
haplocerus (Reptilia: Archosauria: Stagonolepididae). 
Zoological Journal of the Linnean Society, 2002, 136: 97-
111.
New skull material of the Triassic aetosaur Desmatosuchus 
haplocerus (Archosauria: Stagonolepididae) from the Cooper 
Canyon Formation (Late Triassic: early Norian) of Texas is 
described. This is the most complete description of the 
skull of Desmatosuchus to date, shedding light on the 
edentulous premaxilla, laterally exposed splenial on the 
mandible, reduced external mandibular fenestra, dentition 
(small denticles and wear facets), and variability of the 
hemispherical fontanelle. The quadratojugal/postorbital 
contact, a synapomorphy supposedly shared by the 
Stagonolepididae and Rauisuchia (sensu Parrish), is absent 
in Desmatosuchus. The interesting convergence in cranial 
and postcranial morphology of aetosaurs and certain living 
edentates (armadillos) suggests the possibility of 
insectivory or omnivory, instead of herbivory as a feeding 
strategy. This new description is intended to provide 
detailed information for future studies on the 
interrelationships of the Stagonolepididae (which are 
plagued by incomplete material), and their phylogenetic 
position among the archosaurs.
 Norman, David B. 2002. On Asian ornithopods (Dinosauria: 
Ornithischia). 4. Probactrosaurus Rozhdestvensky, 1966. 
Zoological Journal of the Linnean Society, 2002, 136: 113-
144.
The genus Probactrosaurus was first established for 
material discovered by a joint Russian/Chinese expedition 
to the Chinese autonomous region of Neimongol (Inner 
Mongolia). Fossils were collected at a site named Maorty 
(= Maortu). Material attributable to ornithopod dinosaurs 
was considered sufficiently distinct to permit the 
definition of two species of the new genus: 
Probactrosaurus gobiensis and P.alashanicus. The former 
species was based on a considerable quantity of skeletal 
material, much of which is still to be found in the 
collections of the Palaeontological Institute (PIN), 
Moscow. The latter was based on far less well-preserved 
specimens, including a holotype (a posterior skull roof) 
that can no longer be found in the collections of the PIN 
and which, along with other materials, was reportedly 
returned to the Institute of Vertebrate Palaeontology and 
Palaeoanthropology, Beijing. Some remnants of the original 
material attributed to P.alashanicus have been located in 
the PIN collections. Both taxa, established by A. K. 
Rozhdestvensky, are re-described using all of the 
available material collected during the early Sino-Soviet 
expeditions. Probactrosaurusalashanicus is considered to 
be a junior subjective synonym of P.gobiensis. Further 
comparisons are made with the recently described species 
Probactrosaurus mazongshanensis Lu, 1997. The latter does 
not appear to be referable to the genus Probactrosaurus. 
Probactrosaurus is a gracile ornithopod (ranging between 4 
and 6 m in length). The skull is unadorned by any form of 
cranial crest; however, the premaxillary beak is deflected 
ventrally and the dentition is similar to that seen in 
more derived hadrosaurid ornithopods. The postcranial 
skeleton is notable for its gracility, in particular the 
elongate forearm and manus, and the retention of a small, 
conical pollex spine. Systematic analysis suggests that 
P.gobiensis is a derived non-hadrosaurid iguanodontian 
ornithopod and the basal sister-taxon to the clade 
Hadrosauridae. The phylogeny of currently known 
iguanodontians is reviewed.© 2002 The Linnean Society of 
London, 
Chatterjee, Sankar, and Zhong Zheng 2002.Cranial anatomy 
of Shunosaurus, a basal sauropod dinosaur from the Middle 
Jurassic of China. Zoological Journal of the Linnean 
Society, 2002, 136: 145-169.
Shunosaurus, from the Middle Jurassic of China, is 
probably the best-known basal sauropod and is represented 
by several complete skeletons. It is unique among 
sauropods in having a small, bony club at the end of its 
tail. New skull material provides critical information 
about its anatomy, brain morphology, tooth replacement 
pattern, feeding habits and phylogenetic relationships. 
The skull is akinetic and monimostylic. The brain is 
relatively small, narrow and primitively designed. The 
tooth replacement pattern exhibits back to front 
replacement waves in alternating tooth position. The teeth 
are spatulate, stout and show well-developed wear facets 
indicative of coarser plant food. Upper and lower tooth 
rows interdigitate and shear past each other. Tooth 
morphology, skull architecture, and neck posture indicate 
that Shunosaurus was adapted to ground feeding or low 
browsing. Shunosaurus exhibits the following cranial 
autapomorphies: emargination of the ventral margin of the 
jugal/quadratojugal bar behind the tooth row; postorbital 
contains a lateral pit; vomers do not participate in the 
formation of the choanae; pterygoid is extremely slender 
and small with a dorsal fossa; quadrate ramus of the 
pterygoid is forked; quadratojugal participates in the jaw 
articulation; tooth morphology is a combination of 
cylindrical and spatulate form; basipterygoid process is 
not wrapped by the caudal process of the pterygoid; 
trochlear nerve has two exits; occlusal level of the 
maxillary tooth row is convex downward, whereas that of 
the dentary is concave upward, acting like a pair of 
garden shears; dentary tooth count is 25 or more; and the 
replacing teeth invade the labial side of the functional 
teeth. Cranial characters among the basal sauropods are 
reviewed. As Shunosaurus is the earliest sauropod for 
which cranial remains are known, it occupies an important 
position phylogenetically, showing the modification of 
skull morphology from the prosauropod condition. Although 
the skull synapomorphies of Sauropoda are unknown at 
present, 27 cranial synapomorphies are known for the clade 
Eusauropoda.© 2002 The Linnean Society of London.