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

New refs

From: Ben Creisler bh480@scn.org
Browsing databases at the University library prrovides a 
distraction on this sad day. Here are a couple of new refs.

Seebacher, F. 2003. Dinosaur body temperatures: the 
occurrence of endothermy and ectothermy. Paleobiology  29 
(1): 105-122.
 Despite numerous studies, the thermal physiology of 
dinosaurs remains unresolved. Thus, perhaps the commonly 
asked question whether dinosaurs were ectotherms or 
endotherms is inappropriate, and it is more constructive 
to ask which dinosaurs were likely to have been 
endothermic and which ones ectothermic. Field data from 
crocodiles over a large size range show that body 
temperature fluctuations decrease with increasing body 
mass, and that average daily body temperatures increase 
with increasing mass. A biophysical model, the biological 
relevance of which was tested against field data, was used 
to predict body temperatures of dinosaurs. However, rather 
than predicting thermal relations of a hypothetical 
dinosaur, the model considered correct paleogeographical 
distribution and climate to predict the thermal relations 
of a large number of dinosaurs known from the fossil 
record (>700). Many dinosaurs could have had ?high? (30°C) 
and stable (daily amplitude 2°C) body temperatures without 
metabolic heat production even in winter, so it is 
unlikely that selection pressure would have favored the 
evolution of elevated resting metabolic rates in those 
species. Recent evidence of ontogenetic growth rates 
indicates that even the juveniles of large species (3000-
4000 kg) could have had biologically functional body 
temperature ranges during early development. Smaller 
dinosaurs (<100 kg) at mid to high latitudes (>45°) could 
not have had high and stable body temperatures without 
metabolic heat production. However, elevated metabolic 
rates were unlikely to have provided selective advantage 
in the absence of some form of insulation, so probably 
insulation was present before endothermy evolved, or else 
it coevolved with elevated metabolic rates. Superimposing 
these findings onto a phylogeny of the Dinosauria suggests 
that endothermy most likely evolved among the 
Coelurosauria and, to a lesser extent, among the 
Hypsilophodontidae, but not among the Stegosauridae, 
Nodosauridae, Ankylosauridae, Hadrosauridae, Ceratopsidae, 
Prosauropoda, and Sauropoda.

SHULTZ, M.R.,  A. FILDANI, and M. SUAREZ, 2003. Occurrence 
of the Southernmost South American Ichthyosaur (Middle 
Jurassic-Lower Cretaceous), Parque Nacional Torres del 
Paine, Patagonia, Southernmost Chile. PALAIOS: Vol. 18, 
No. 1, pp. 69-73.

An ichthyosaur discovered in the Ultima Esperanza 
Province, southern Chile, is the southernmost specimen of 
this group yet discovered in South America. The incomplete 
fossil consists of 17 vertebrae and associated neural 
arches and ribs. Occurring within a large block in glacio-
fluvial sediments adjacent to the Campo de Hielo 
Patagónico Sur, the remains cannot be given a species 
designation nor be dated with precision or tied to one 
specific formation at this time. However, the rock type, 
geologic occurrence of the block, and glaciology of the 
sector enable the material to be placed within the upper 
part of the Middle to Upper Jurassic Tobifera Formation or 
the Lower Cretaceous Zapata Formation. Although the fairly 
broad stratigraphic range and limited fossil material 
hamper careful stage-level paleobiogeographic analysis, 
this occurrence documents the existence of ichthyosaurs in 
the now closed Rocas Verdes back-arc basin. This 
occurrence extends the distribution of ichthyosaurs in 
South America some 1500 km south of previously reported 
fossil material. The fossil provides support for the 
existence of a possible migration seaway between southern 
South America and western Africa during the Late Jurassic 
associated with the breakup of the southern sector of 
Gondwana. This seaway would be the southern counterpart to 
the Hispanic Corridor that connected the Pacific to the 
west Tethys around the northern end of South America.