Dinosaur Skin Feathers and Organs

Skin and its derivatives in modern vertebrates, such as nails, feathers, hooves, and hair, are composed of the structural protein keratin. Because most skin is soft tissue and has lower preservation potential than skeletal material (Chapter 7), the discovery of dinosaur body fossils that have any evidence of soft tissues are the cause of much celebration, often followed by much debate. Both older and recent finds of evidence of soft tissue clarify better what some dinosaurs looked like in life, and may indicate the placement of their internal organs, and validate the predicted presence of feathers or feather-like projections in a few species (Chapter 9 and 15). Not all dinosaur skin was soft, however, and dermal armor, formed originally as ossified plates set into the skin of a dinosaur, was a common accouterment to ankylosaurs (Chapter 12) and a group of sauropods called titanosaurs (Chapter 10). Other ossified dermal derivatives, osteoderms, include the dorsal plates or spines on stegosaurs (Chapter 12).

Skin impressions of dinosaurs typically indicate a similarity to modern reptilian skin in that they have patterns of scales (Fig. 5.10). In some cases the patterns are of equally-sized scales but others show definable patches of scales of different sizes. Stunning finds of feathered theropods from Lower Cretaceous deposits in China (Chapter 9) also demonstrate unequivocal evidence of some dinosaurs having feathers. These impressions of feathers are mostly associated with the dinosaurs' forelimbs and tails, but two theropods, Microraptor rui and Cryptovolans pauli, had feathers on both forelimbs and hind limbs (Chapter 9). Other Early Cretaceous theropods from China have, in close association with skeletal material, either carbonized fibers (probably downy feathers) or clearly-defined contour feathers (with central shafts). The presence of feathers and scales in modern birds thus lends support to hypotheses regarding the dinosaurs as ancestors of modern birds (Chapters 6 and 15). For a modern example of an animal that has both scales and different types of feathers, look at a chicken's foot for its scales and the rest of its body for down and contour feathers.

Evidence of dinosaur coloration is implied by patches of differing skin impression patterns, an interpretation that constitutes a weak hypothesis because of the lack of actually observed color differences. Banding in the aforementioned feather impressions, seen now as black and white stripes, however, is much more convincing evidence for dinosaur coloration. Because so little actual scientific data support interpretations of dinosaur colors, no multicolored or otherwise speculatively adorned dinosaurs are illustrated in this book. Evaluations of dinosaur vision, based on skeletal

FIGURE 5.9 Lateral view of right hind limbs in digitigrade mode. (A) Modern canine. (B) Modern human. (C) Early Cretaceous theropod Giganotosaurus of Argentina. Fernbank Museum of Natural History, Atlanta, Georgia.

Dinosaurs Organs

FIGURE 5.9 Lateral view of right hind limbs in digitigrade mode. (A) Modern canine. (B) Modern human. (C) Early Cretaceous theropod Giganotosaurus of Argentina. Fernbank Museum of Natural History, Atlanta, Georgia.

Theropods Skin

FIGURE 5.10 Hadrosaur skin impression, Late Cretaceous of North America. Mesa State Community College Museum, Tucumcari, New Mexico.

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