FIGURE 9.4 Feathers associated with four limbs of Microraptor, an Early Cretaceous feathered theropod species from China. Reprinted by permission from Macmillan Publishers Ltd: Nature, Xu et al. "Four-winged dinosaurs from China", Vol. X, 2001.

theropods, such as Troodon, even fall in the same range as modern ostriches. However, less than 5% of all dinosaur species have had their EQs calculated. This means that considerable data are needed to test the currently accepted generalization that theropods, gram for gram, had the largest brains of dinosaurs relative to their bodies. Of course, EQ also holds implications for IQ (intelligence quotient), a subject of considerable debate among not just paleontologists but also psychologists and neurophysiologists.

Finally, theropods were different from other dinosaurs as they are the only ones known so far whose skeletal remains have shown definite evidence of feathers similar to those seen in modern birds. Long conjectured by some paleontologists and artists, the concept of feathered dinosaurs was, until recently, a poorly supported hypothesis that had little to no body fossil evidence. Discoveries of the 1990s and first decade of the twenty-first century have changed all that. As of the writing of this book, feathers have been confirmed from at least nine species of theropods (Fig. 9.4). In traditional zoology, feathers constituted one of the unique distinguishing features of birds, but now at least a few non-avian theropods have joined this formerly exclusive club. The addition of feathers to other characteristics uniting probable theropod ancestors with avian descendants also further strengthens hypotheses of their evolutionary relationships (Chapter 15). However, the functions of the feathers in theropods are still a source of dispute in dinosaur research, especially in how they relate to dinosaur physiology (Chapter 8).

Overall, theropods were different from other dinosaurs in many ways, whether through their light bones, speedy movement on two legs, carnivory, larger brains, or feathers. Such special characteristics supply reasons why theropods remain enduring symbols of dinosaurs in the public eye, but they also provide incentives for further scientific study. Such research is especially focused on how theropods evolved, where they lived (and when), and how they behaved in their everyday lives.

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