Literature Review: Mesozoic Life Style

by Carl Strang

Today I close out my notes on last year’s published research pertaining to the Mesozoic Era. The following papers looked at the long-standing question of dinosaur metabolism, investigated the extent to which there were nocturnal dinosaurs, and made revelations regarding the reproduction and life history strategy of some non-dinosaur reptiles.

Were dinosaurs warm-blooded? Field Museum of Natural History exhibit.

Eagle, Robert A., et al. 2011. Dinosaur body temperatures determined from isotopic (13C-18O) ordering in fossil biominerals. Science 333:443-445. They looked at the isotopes of those elements in sauropod teeth, and found that these point to body temperatures of 36-38°C, similar to most modern mammals. Some models have indicated that their body mass would have resulted in even higher temperatures, and the authors suggest that the sauropods had heat-release mechanisms such as air-sac systems and circulatory networks that took advantage of the large surface-to-volume ratios in neck and tail (sauropods were the diverse herbivores that walked on 4 legs and had very long necks and tails).

Amiot, R., et al. Oxygen isotopes of East Asian dinosaurs reveal exceptionally cold Early Cretaceous climates. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1011369108     They looked at oxygen isotopes in bones and teeth of fossils in the Chinese Jehol fauna, and found that the climate there probably was temperate, with winters severe enough to force scaled reptiles (turtles, crocodiles) into hibernation and giving the advantage to dinosaurs that were feathered. Thus the famous high incidence of feathered dinosaurs in that area and time was not simply the result of better preservation of fossil detail, but a result of climatic conditions.

R. S. Seymour, S. L. Smith, C. R. White, D. M. Henderson, D. Schwarz-Wings. Blood flow to long bones indicates activity metabolism in mammals, reptiles and dinosaurs. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.0968     They looked at nutrient foramen diameters within bones of mammals, reptiles and dinosaurs of a wide range of body sizes. They found that diameter increases with metabolic rate in living species, and dinosaur foramen diameters are proportionately even larger than those of mammals, supporting high metabolic rate in dinosaurs.

Schmitz, Lars, and Ryosuke Motani. 2011. Nocturnality in dinosaurs inferred from scleral ring and orbit morphology. Science 332:705-708. They were able to connect archosaur species to nocturnal or diurnal habit based on eye-ring and skull structure. In general, like today’s amniotes, pterosaurs were mainly diurnal, terrestrial predators at least partly nocturnal, and large herbivores active day and night. Archosaurs are a large reptile group containing dinosaurs, pterosaurs and others.

Pterosaur skeleton, Field Museum of Natural History exhibit.

Junchang Lü, David M. Unwin, D. Charles Deeming, Xingsheng Jin, Yongqing Liu, Qiang Ji. 2011. An Egg-Adult Association, Gender, and Reproduction in Pterosaurs. Science 331: 321-324 DOI: 10.1126/science.1197323     A newly described fossil from China’s Liaoning Formation is a female Darwinopterus pterosaur with an egg still inside. There is enough detail in the fossil to show that the animal had wide hips and lacked a crest. This is being cautiously generalized as an indication that in other pterosaur species, hip width and crest presence or absence may allow identification of fossils to gender, and allow fossils of different genders that had been regarded as separate species to be combined under the same name. The egg had a parchment-like shell, and its size in comparison to the adult is like those of modern reptiles. The shell points to burial with water uptake after laying. “This evidence for low parental investment contradicts the widespread assumption that reproduction in pterosaurs was like that of birds and shows that it was essentially like that of reptiles.”

O’Keefe, F.R., and L.M. Chiappe. 2011. Viviparity and K-selected life history in a Mesozoic marine plesiosaur (Reptilia, Sauropterygia). Science 333:870-873. They describe a fossil that for the first time shows a fetus within an adult. The fetus is single and large, demonstrating birth rather than egg-laying, and single or small brood number, separating it from other marine reptiles but resembling marine mammals. The authors speculate that this may imply “sociality and maternal care.” Plesiosaurs were the large aquatic reptiles with long necks, and legs replaced by 4 large flippers.

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