[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Mesozoic Bird and Marine Reptile Stuff

From: Ben Creisler

A number of new papers about Mesozoic birds and marine reptiles:

Alyssa Bell and Michael J. Everhart (2011)
Remains of Small Ornithurine Birds from a Late Cretaceous (Cenomanian)
Microsite in Russell County, North-Central Kansas.
Transactions of the Kansas Academy of Science 114(1 & 2):115-123.
doi: 10.1660/062.114.0111 

Our analysis of vertebrate remains collected from a Cenomanian microsite in
the Lincoln Limestone, the basal-most member of the Greenhorn Formation in
Russell County, Kansas, identifies ornithurine (sensu Chiappe, 1996) avian
fossils. The specimens presented here are slightly younger than the oldest
avian remains known from North America (from the Woodbine Formation, Texas)
and of a similar age as the avians from the Asheville Formation in
Saskatchewan, Canada. This find thus connects the extensive geographic
range of the earliest North American birds from Saskatchewan south through
central Kansas and on to Texas. The specimens discussed here are
fragmentary, yet show features definitive of ornithurine birds. One
specimen is attributable to Ichthyornis, whereas another preserves teeth
characteristic of ornithurine birds. In addition to bird bones, the
microsite yielded numerous bony fish remains, shark teeth, coniasaur
vertebrae, and other lizard bones.

Michael J. Everhart (2011)
Rediscovery of the Hesperornis regalis Marsh 1871 Holotype Locality
Indicates an Earlier Stratigraphic Occurrence.
Transactions of the Kansas Academy of Science 114(1 & 2):59-68. 2011 
doi: 10.1660/062.114.0105 

The type specimen of a large, flightless marine bird, Hesperornis regalis,
was collected by O.C. Marsh in 1871. Due to the practices of the time, and
the lack of accurate maps, the type locality was initially recorded by
Marsh in a letter simply as the ?upper Cretaceous of Western Kansas,? and
then later reported as ?the gray shale near the Smoky Hill River in Western
Kansas.? Since the Smoky Hill Chalk Member of the Niobrara Formation is
exposed along the Smoky Hill River in present day Wallace, Logan and Gove
counties over a distance of more than 75 miles, this vague locality
information encompasses about 5 million years of depositional history. An
1880 account by Marsh narrows the locality down to the south bank of the
Smoky Hill River about 20 miles east of Fort Wallace in Logan County. The
results of a recent field investigation of the eastward route traveled by
Marsh's 1871 Yale College Scientific Expedition sheds light on the probable
locality of both the type specimen (YPM 1200) of Hesperornis regalis, and
also the first specimen with a skull and teeth (YPM 1206) collected in
1872. In turn, this provides important new data supporting an earlier
occurrence (Upper Santonian) of this species in the Western Interior Sea
over Kansas than previously assumed.

Marine Reptiles:

Bruce A. Schumacher (2011)
'Woollgari-Zone Mosasaur' (Squamata; Mosasauridae) from the Carlile Shale
(Lower Middle Turonian) of Central Kansas and the Stratigraphic Overlap of
Early Mosasaurs and Pliosaurid Plesiosaurs
Transactions of the Kansas Academy of Science 114(1 & 2):1-14. 
doi: 10.1660/062.114.0101 

A new specimen of russellosaurine mosasaur (FHSM VP-17564) from the middle
Fairport Chalk Member (Collignoniceras woollgari zone, early Middle
Turonian), Carlile Shale of central Kansas is among the earliest records of
a derived mosasaur known from the North American Western Interior Seaway.
Unequivocally the oldest recorded occurrence of a russellosaurine mosasaur
from Kansas, and one of only four Kansas occurrences consisting of more
than a single element, the specimen includes seven successive proximal
caudal vertebrae bearing articulating hemal facets. No demonstrable
characters ally the specimen to a more refined taxonomic subgroup, although
the relative dimensions of the vertebral centra are significantly longer
than equivalent caudal series in Platecarpus and Tylosaurus. This suggests
that the tails of early russellosaurines were composed of a lesser number
of longer caudal vertebrae than their successors, with less hydrodynamic
adaptation from the terrestrial condition. Size of the vertebrae in
relation to Platecarpus and Tylosaurus indicates a relatively large animal
roughly 3.2 m in total body length, although this may be an over-estimate
given the difference in vertebral dimensions as compared to more derived
russellosaurines of the Niobrara Formation. The middle of the Fairport
Chalk interval continues to produce a large number of vertebrate specimens
despite the rarity of exposures. A pliosaurid plesiosaur skull (FHSM
VP-321) is known from similar geographic and stratigraphic position as FHSM
VP-17564, and the record of pliosaurs (FHSM VP-17469) continues into
younger Blue Hill Shale (Prionocyclus hyatti zone, middle Middle Turonian)
demonstrating with certainty that pliosaurs and early mosasaurs inhabited
the same stretch of seaway for roughly one million years.

Roger B. J. Benson; Karl T. Bates; Mark R. Johnson; Philip J. Withers
Cranial anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from
the Early Jurassic of Somerset, United Kingdom 
Journal of Vertebrate Paleontology 31(3): 562 - 574 
DOI: 10.1080/02724634.2011.572937 
The taxonomy and systematics of the earliest plesiosaurians is poorly
resolved. This limits our understanding of the diversification of one of
the most successful clades of secondarily aquatic tetrapods. Here we
provide a robust diagnosis of Thalassiodracon hawkinsii from the
Pre-planorbis Beds (Triassic-Jurassic boundary interval) of the United
Kingdom, and suggest that at least two other, previously unrecognized
plesiosaurians are present in the same deposits. Computed tomography of an
exceptionally preserved skull, and examination of previously undescribed
(or briefly described) specimens yields new anatomical data.
Thalassiodracon has a dorsomedian ridge on the premaxilla, a squamosal
bulb, four premaxillary teeth, and a heterodont maxillary dentition.
Several features of Thalassiodracon, including the squmosal bulb, broad
anterior termination of the pterygoids, heterodont dentition, and single
foramen in the lateral surface of the exoccipital, are plesiomorphic or
represent pliosauroid synapomorphies. Among pliosauroids, Thalassiodracon
shares a parietal that extends far anteriorly, a broad, interdigitating
posterior termination of the premaxilla, and a short posteroventral process
of the postorbital with Hauffiosaurus and pliosaurids. Thus, we suggest
pliosaurid affinities for Thalassiodracon, in contrast to most recent
phylogenetic studies. The early stratigraphic position of Thalassiodracon
coincides with the earliest occurrence of Rhomaleosauridae (the sister
taxon of Pliosauridae). The relatively long neck and small skull of
Thalassiodracon indicate that the robust skeleton and macropredaceous
habits of rhomaleosaurids and pliosaurids were derived independently. 

New information on Hauffiosaurus (Reptilia, Plesiosauria) based on a new
species from the Alum Shale Member (Lower Toarcian: Lower Jurassic) of
Yorkshire, UK
Palaeontology 54 (3): 547?571, May 2011
DOI: 10.1111/j.1475-4983.2011.01044.x

An almost complete, three-dimensionally preserved plesiosaurian from the
Hildoceras bifrons Zone of the Alum Shale Member (Whitby Limestone
Formation; Lower Toarcian) of Yorkshire, UK, is described in detail. This
represents a new species of Hauffiosaurus, H. tomistomimus, distinguished
from H. zanoni (Harpoceras serpentinum Zone, Lower Toarcian, Germany) by
the proportionally shorter neck and strongly concave preaxial margin of the
tibia. It differs from H. longirostris (previously
?Macroplata?longirostris; Har. serpentinum Zone, Yorkshire) by the absence
of prominent midline ridges on the dorsal surface of the premaxillae and
ventral surface of the mandibular symphysis, and the absence of midline
pterygoid contact ventral to the basioccipital. Several synapomorphies
support a monophyletic Hauffiosaurus: broad longitudinal troughs occupy the
dorsolateral surface of the maxilla and the posterior half of the lateral
surface of the dentary; basicranial fontanelle bounded laterally by
posterolaterally elongate projections of an undetermined ossification; and
the neural arch contacts the rib facet in all postaxial cervical vertebrae.
However, the systematic position of Hauffiosaurus, as a pliosauroid or
basal plesiosauroid, remains uncertain. There is little evidence for
geographic differentiation of Lower Toarcian plesiosaurian faunas in the
United Kingdom and Germany as minor differences between abundant taxa may
arise from temporal offset of fossils from these regions, and marked
taxonomic differences are confined to rare taxa whose absence in one or
other area may be attributable to incomplete sampling. Lack of consensus on
the relationships of Lower Jurassic plesiosaurians requires further
detailed description of Lower Jurassic taxa.

The cranial anatomy and taxonomy of Peloneustes philarchus (Sauropterygia,
Pliosauridae) from the Peterborough Member (Callovian, Middle Jurassic) of
the United Kingdom
Palaeontology 54(3): 639?665, May 2011
DOI: 10.1111/j.1475-4983.2011.01050.x

Peloneustes philarchus is the most abundant pliosaurid from the
Peterborough Member of the Oxford Clay Formation (Callovian) of the UK. It
is a valid taxon possessing a unique character combination, including a
single autapomorphy: the interdentary symphysis is raised dorsally on a
narrow platform. Twenty-one specimens can be positively referred to P.
philarchus. However, other specimens previously referred to Peloneustes,
from the Peterborough Member near Peterborough, and the lower Oxfordian
strata of Marquise, northern France, represent distinct, unnamed taxa. The
skull of P. philarchus is described in detail, including new information
from an uncrushed, three-dimensionally preserved specimen and a specimen
with a well-preserved palate. Well-preserved material clearly indicates
that P. philarchus lacked nasals, but possessed a lacrimal. A previously
unrecognised ?palpebral? forms part of the dorsal orbit margin adjacent to
the prefrontal. The number of maxillary (30?31) and dentary (36?44)
alveoli, the number of dentary alveoli adjacent to the mandibular symphysis
(13?15), the number of foramina on the frontal and jugal, the breadth of
the parasphenoid, breadth of the anterior (narial) process of the palatine
and the presence of a lappet of the angular that extends onto the
posterodorsal surface of the retroarticular process vary among individuals
but are not considered sufficient to justify the recognition of new taxa.
The presence of an open palpebral?prefrontal suture, the size of the
ventral midline tubercle of the basioccipital and the presence of an
anterior interpterygoid vacuity seem to vary with body size.

Charlie J. Underwood; Anjali Goswami; G. V. R. Prasad; Omkar Verma; John J.
Flynn (2011)
Marine vertebrates from the 'middle' Cretaceous (early Cenomanian) of South
Journal of Vertebrate Paleontology 31(3): 539 - 552 
DOI: 10.1080/02724634.2011.574518 
Vertebrate fossils have been known from South India's Cauvery Basin since
the 1840s, but records of marine vertebrates from the late Albian to
Turonian Karai Formation have been limited to a single set of ichthyosaur
remains. Recent surface collecting and sieving of lower Cenomanian
glauconitic mudstones has yielded the first ichthyosaur material reported
in India over the last 140 years, as well as a diverse and previously
unrecorded shark assemblage. The ichthyosaur material, including several
teeth and vertebrae, is assigned to the sole described Cretaceous genus
Platypterygius and to the species P. indicus (Lydekker, 1879). Eight
species of shark (one squaliformes, two hexanchiformes, and five
lamniformes) are recorded. A new hexanchiform genus Gladioserratus is
erected, and two new species (Gladioserratus magnus, gen. et sp. nov., and
Dwardius sudindicus, sp. nov.) are named. Many of the shark genera within
this largely species-level endemic fauna are known from high paleolatitudes
elsewhere, with many showing an antitropical distribution, but are absent
in Tethyan areas. This first description of the Karai Formation marine
fauna documents the previously unappreciated diversity and unique character
of India's Cretaceous marine vertebrates, and indicates a cool-water
paleoenvironment for the marine vertebrate assemblage. 

Mark T. Young, Mark A. Bell and Stephen L. Brusatte (2011) 
Craniofacial form and function in Metriorhynchidae (Crocodylomorpha:
Thalattosuchia): modelling phenotypic evolution with maximum-likelihood
Biology Letters (advance online publication)
doi: 10.1098/rsbl.2011.0357 

Metriorhynchid crocodylomorphs were the only group of archosaurs to fully
adapt to a pelagic lifestyle. During the Jurassic and Early Cretaceous,
this group diversified into a variety of ecological and morphological
types, from large super-predators with a broad short snout and serrated
teeth to specialized piscivores/teuthophages with an elongate tubular snout
and uncarinated teeth. Here, we use an integrated repertoire of geometric
morphometric (form), biomechanical finite-element analysis (FEA; function)
and phylogenetic data to examine the nature of craniofacial evolution in
this clade. FEA stress values significantly correlate with morphometric
values representing skull length and breadth, indicating that form and
function are associated. Maximum-likelihood methods, which assess which of
several models of evolution best explain the distribution of form and
function data on a phylogenetic tree, show that the two major
metriorhynchid subclades underwent different evolutionary modes. In
geosaurines, both form and function are best explained as evolving under
?random? Brownian motion, whereas in metriorhynchines, the form metrics are
best explained as evolving under stasis and the function metric as
undergoing a directional change (towards most efficient low-stress
piscivory). This suggests that the two subclades were under different
selection pressures, and that metriorhynchines with similar skull shape
were driven to become functionally divergent. 

mail2web - Check your email from the web at