New articles

[bh480@scn.org]

From: Ben Creisler bh480@scn.org

Here are a few recent articles that may not have been 
mentioned in list correspondence.

LEHMAN, THOMAS M. and ALAN B. COULSON
A JUVENILE SPECIMEN OF THE SAUROPOD DINOSAUR ALAMOSAURUS 
SANJUANENSIS FROM THE UPPER CRETACEOUS OF BIG BEND 
NATIONAL PARK, TEXAS
Journal of Paleontology: Vol. 76, No. 1, pp. 156-172.
ABSTRACT
 A juvenile specimen of the titanosaurid sauropod 
Alamosaurus sanjuanensis, recovered from just below the 
Cretaceous/Tertiary boundary horizon in Big Bend National 
Park, Texas, is from an individual less than half the size 
of adult specimens referred to this species. The 
disarticulated skeleton was preserved in deposits of a 
shallow flood-plain pond and includes elements not 
previously described, allowing for an improved diagnosis 
for this species. The elongate opisthocoelous cervical 
vertebrae have non-bifid posteriorly deflected neural 
spines with deep postspinal fossae. The dorsal vertebrae 
have wide spatulate neural spines with strong prespinal 
laminae, and lack hyposphene-hypantrum articulations. 
Alamosaurus sanjuanensis exhibits a unique morphology of 
the ischium, evident even in this juvenile specimen. 
Comparison with other titanosaurid species suggests that 
A. sanjuanensis is most closely related to an unnamed 
titanosaur from Peiropolis, Brazil and 
Neuquensaurus australis from Argentina.

(Note: The article provides a new skeletal reconstruction 
of Alamosaurus)

Caldwell, Michael W.& Michael S. Y. Lee 
Live birth in Cretaceous marine lizards (mosasauroids). 
Proceedings: Biological Sciences Volume: 268 Number: 1484 
Page: 2397 -- 2401 

Abstract: Although live-bearing (viviparity) has evolved 
around 100 times within reptiles, evidence of it is almost 
never preserved in the fossil record. Here, we report 
viviparity in mosasauroids, a group of Cretaceous marine 
lizards. This is the only known fossil record of live-
bearing in squamates (lizards and snakes), and might 
represent the oldest occurrence of the trait in this 
diverse group; it is also the only known fossil record of 
viviparity in reptiles other than ichthyosaurs. An 
exceptionally preserved gravid female of the aigialosaur 
Carsosaurus (a primitive mosasauroid) contains at least 
four advanced embryos distributed along the posterior two-
thirds of the long trunk region (dorsal vertebrae 9-21). 
Their orientation suggests that they were born tail-first 
(the nostrils emerging last) to reduce the possibility of 
drowning, an adaptation shared with other highly aquatic 
amniotes such as cetaceans, sirenians and ichthyosaurs; 
the orientation of the embryos also suggests that they 
were not gut contents because swallowed prey are usually 
consumed head-first. One embryo is located within the 
pelvis, raising the possibility that the adult died during 
parturition. Viviparity in early medium-sized amphibious 
aigialosaurs may have freed them from the need to return 
to land to deposit eggs, and permitted the subsequent 
evolution of gigantic totally marine mosasaurs. 

>
Lingham-Soliar, Theagarten.
The ichthyosaur integument: skin fibers, a means for a 
strong, flexible and smooth skin.       
Source: Lethaia 
Volume: 34 Number: 4 Page: 287 -- 302   

Abstract: The ichthyosaur skin is examined in order to 
further our understanding of the adaptation of these 
animals to the aquatic medium and their locomotory 
efficiency. Softtissue structures in two excellently 
preserved specimens of the ichthyosaur Stenopterygius 
quadricissus and in a partial skull of Ichthyosaurus 
provide unique data on the integument of advanced or 
tunniform ichthyosaurs. A system of fibers of three 
classes based on thickness and in different levels of the 
integument covered almost the entire surface of the body. 
The thickest fibers are located deepest in the skin and 
the thinnest outermost. The latter consist of at least two 
superimposed layers of fine fibers that extend in opposing 
directions to form a lattice or orthogonal meshwork. The 
angles of these fibers vary between 25 ° and 75 ° to the 
long axis of the animals, depending on their location in 
the body. The fibers of the two other size classes, lying 
deeper in the tissue, were observed in single layers. The 
thickest fibers extend in near parallel rows approximately 
60 °-80 ° to the long axis of the animal in the area near 
the midpoint of the body and 90 ° in the post-dorsal fin 
region. The intermediate-sized fibers were apparently 
oriented at ca. 50 °-75 ° to the animal's long axis and 
were regularly spaced. Of considerable interest is their 
attachment dorsally to longitudinal fibers. This contrasts 
with the general condition of helically arranged fibers in 
fast-swimming marine vertebrates such as tuna and sharks, 
but compares with the condition in sirenians. Fibers were 
observed in the dorsal and caudal fins but not in the 
limbs. The fibers in ichthyosaurs are the thickest so far 
noted in marine vertebrates. The presence of a complex 
system of fibers, which includes an orthogonal meshwork of 
the finest of these, suggests that creasing of the skin 
would have been minimized, a condition highly important in 
reducing drag during the locomotion of marine animals.