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Raiders of the New Papers

A few new tidbits; though readers of some of the paleo-oriented blogs will have already seen a couple of these, I don't think they've been mentioned here yet...

Humphries, S., Bonser, R.H.C., Witton, M.P., and Martill, D.M. 2007. Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biology 5(8):e204. doi: 10.7371/journal.pbio.0050204.

ABSTRACT: Just because a component of an extinct animal resembles that of a living one does not necessarily imply that both were used for the same task. The lifestyles of pterosaurs, long-extinct flying reptiles that soared ancient skies above the dinosaurs, have long been the subject of debate among palaeontologists. Similarities between the skulls of living birds (black skimmers) that feed by skimming the water surface with their lower bill to catch small fish, and those of some pterosaurs have been used to argue that these ancient reptiles also fed in this way. We have addressed this question by measuring the drag experienced by model bird bills and pterosaur jaws and estimating how the energetic cost of feeding in this way would affect their ability to fly. Interestingly, we found that the costs of flight while feeding are considerably higher for black skimmers than previously thought, and that feeding in this way would be excessively costly for the majority of pterosaurs. We also examined pterosaur skulls for specialised skimming adaptations like those seen in modern skimmers, but found that pterosaurs have few suitable adaptations for this lifestyle. Our results counter the idea that some pterosaurs commonly used skimming as a foraging method and illustrate the pitfalls involved in extrapolating from living to extinct forms using only their morphology.

Erickson, G.M., Rogers, K.C., Varricchio, D.J., Norell, M.A., and Xu, X. 2007. Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition. Biology Letters. doi: 10.1098/rsbl.2007.0254.

ABSTRACT: The timing of sexual maturation in non-avian dinosaurs is not known. In extant squamates and crocodilians it occurs in conjunction with the initial slowing of growth rates as adult size is approached. In birds (living dinosaurs) on the other hand, reproductive activity begins well after somatic maturity. Here we used growth line counts and spacing in all of the known brooding non-avian dinosaurs to determine the stages of development when they perished. It was revealed that sexual maturation occurred well before full adult size was reached-the primitive reptilian condition. In this sense, the life history and physiology of non-avian dinosaurs was not like that of modern birds. Palaeobiological ramifications of these findings include the potential to deduce reproductive lifespan, fecundity and reproductive population sizes in non-avian dinosaurs, as well as aid in the identification of secondary sexual characteristics.

Roopnarine, P.D., Angielczyk, K.D., Wang, S.C., and Hertog, R. 2007. Trophic network models explain instability of Early Triassic terrestrial communities. Proceedings of the Royal Society of London B 274:2077-2086. doi: 10.1098/rspb.2007.0515.

ABSTRACT: Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction.

Mustoe, G.E. 2007. Coevolution of cycads and dinosaurs. The Cycad Newsletter 30(1):6-9.

INTRODUCTION: Cycads were a major component of forests during the Mesozoic Era, their shade of their fronds falling upon the scaly backs of multitudes of dinosaurs that roamed the land. Paleontologists have long postulated that cycad foliage provided an important food source for reptilian herbivores, but the extinction of dinosaurs and the contemporaneous precipitous decline in cycad populations at the close of the Cretaceous have generally been assumed to have resulted from different causes. Ecologic effects triggered by a cosmic impact are a widely-accepted explanation for dinosaur extinction; cycads are presumed to have suffered because of their inability to compete with fast-growing flowering plants that appeared during the mid-Cretaceous "angiosperm explosion." This paper explores a different hypothesis, i.e., that the evolutionary fates of cycads and dinosaurs were inextricably intertwined, and the Late Cretaceous extinction of theese reptiles was the triggering event that cuased cycads to diminish to their present status as "living fossils." The main tenet of this hypothesis is cycads depdended on herbivorous dinosaurs to disperse their seeds, and the disappearance of these herbivores led to a precipitous decline in the geographic range and numerical abundance of cycads. Evidence comes from the toxicology of extant cycads, their seed dispersal strategies, anatomical characteristics of herbivorous dinosaurs, and the geographic distribution and taxonomic diversity of modern and fossil cycads.

Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT  84770   USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and     dinogami@gmail.com


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