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Hadrosaurs as ungulate parallels: lost life styles and deficient data

100%
Carrano M. T., Janis C. M.
Acta Palaeontologica Polonica
|
1999
|
tom 44
|
nr 3
237-261
Hadrosaur dinosaurs (Ornithischia: Hadrosauridae) were abundant in Late Cretaceous terrestrial environments of North America and Asia. Their derived dental and postcranial specializations for herbivory have led to the suggestion that these dinosaurs were analogous to modern ungulates in lifestyle. Ungulates display a suite of morphological features that are correlated with diet, habitat preference, and sexual dimorphism. In this paper we examine several of these same features in hadrosaurs in order to determine whether they display similar patterns under multivariate analysis. Initial results confirm the resemblances between hadrosaurs and ungulates but suggest that missing data may considerably affect the outcomes of statistical analyses. Using the hadrosaur dataset as a template, we artificially degrade the (previously complete) ungulate datasets and perform the same analyses. Results are consistent with earlier results and provide an opportunity to assess the impact of missing data on the original multivariate structure. Our results support the hypothesis that hadrosaurs were similar to ungulates in patterns of ecomorphology.
2
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Modes of ventilation in early tetrapods: costal aspiration as a key feature of amniotes

100%
Janis C. M., Keller J. C.
Acta Palaeontologica Polonica
|
2001
|
tom 46
|
nr 2
The key difference between amniotes (reptiles, birds and mammals) and anamniotes (amphibians in the broadest sense of the word) is usually considered to be the amniotic egg, or a skin impermeable to water. We propose that the change in the mode of lung ventilation from buccal pumping to costal (rib-based) ventilation was equally, if not more important, in the evolution of tetrapod independence from the water. Costal ventilation would enable superior loss of carbon dioxide via the lungs: only then could cutaneous respiration be abandoned and the skin made impermeable to water. Additionally efficient carbon dioxide loss might be essential for the greater level of activity of amniotes. We examine aspects of the morphology of the heads, necks and ribs that correlate with the mode of ventilation. Anamniotes, living and fossil, have relatively broad heads and short necks, correlating with buccal pumping, and have immobile ribs. In contrast, amniotes have narrower, deeper heads, may have longer necks, and have mobile ribs, in correlation with costal ventilation. The stem amniote Diadectes is more like true amniotes in most respects, and we propose that the changes in the mode of ventilation occurred in a stepwise fashion among the stem amniotes. We also argue that the change in ventilatory mode in amniotes related to changes in the postural role of the epaxial muscles, and can be correlated with the evolution of herbivory.
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