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

anatomy and brain endocasts, nevertheless may provide indirect information suggesting that some dinosaurs were brightly colored, possibly for species identification and attracting mates (Chapter 8). Some researchers also propose that some dinosaurs were brightly colored because this trait is exhibited by some of their modern relatives (some reptiles and birds). On the other hand, dull colorations is just as likely for herbivores, allowing them to blend more easily into Mesozoic landscapes and avoid the attention of hungry predators. This could also have been the case for predators, with a dull coloration camouflaging them from their prey.

As mentioned previously, muscle attachment sites on bones are another way to tell where some soft tissues were located, but any remnants of the muscle tissue itself are yet to be discovered in association with dinosaur bones. Pseudomorphs (false forms) of dinosaur muscles for the theropod Pelecanimimus polyodon, however, were found in Lower Cretaceous rocks of Spain. In this instance, a special, rapid postburial mineralization process (Chapter 7) mimicked the three-dimensional structure of the musculature. Musculature and other soft tissues also can be inferred for dinosaur digits through toe-pad impressions in some dinosaur tracks, giving a sense of the actual size of a dinosaur foot with all of its original skin and muscles (Chapter 14). Toe-pad impressions help to identify phalangeal formulas of dinosaur feet, which can help to narrow down the potential tracemakers of some dinosaur footprints.

Other soft parts of dinosaurs include their internal organs, of which we have much better information based on actual evidence, rather than the speculation of only about 15 years ago. For example, one of the most spectacular discoveries of preserved dinosaur soft parts was that of a small Early Cretaceous theropod found in Italy, Scipionyx samniticus. The specimen has a clear outline of its intestine, some muscles, and possibly a trachea (windpipe) and liver. Besides this direct evidence, gastroliths in a small, localized area within the rib-cage region of a dinosaur constitute indirect evidence of a former crop and gizzard, which are muscular digestive organs located anterior and posterior to the stomach, respectively, in modern birds. Gastroliths were most likely an aid to grinding up difficult-to-digest plant material in some herbivorous dinosaurs, such as sauropods (Chapters 10 and 14). At least one Early Cretaceous theropod (Caudipteryx zoui), presumably a meat eater, also had a concentration of small gastroliths in its abdominal region (Chapter 9). Remains of small animals within the body cavity of a dinosaur also can point toward

FIGURE 5.11 Restoration of skin and musculature for: (A) Late Triassic theropod Coelophysis bauri of North America: Denver Museum of Science and Nature; (B) Late Jurassic sauropod Apatosaurus louisae of North America: Dinosaur National Monument, Utah.

the former location of either its stomach or intestine (Chapter 9). For evidence of reproductive organs, one feathered theropod from China contains two egg-like structures within the posterior part of its abdominal region, which is evidence for an oviduct (birth canal).

Well-preserved skulls can provide three-dimensional approximations of dinosaur brain exteriors. This helps in determining whether room existed in parts of the skull for other tissues, such as in the nasal region, related to physiological functions (Chapter 8). Brain endocasts, which are casts of the braincase in a skull, reveal a minimum value of brain volume, which is measured in cubic centimeters. Endocasts also indicate the relative sizes of the different parts of the brain used for sensory perception, such as the olfactory bulb (related to smell), and they show the locations of nerves and blood vessels that related to a dinosaur's physiology (Chapter 8). When a skull has been crushed from compaction or damaged by further preparation, computed tomography (CT) scans render digital images that represent accurately the skull interiors that also can be rotated in three dimensions for easier study (Chapters 9 and 15).

Although still relatively sparse in comparison to skeletal anatomy, the fossil record of dinosaur soft-part anatomy is actually better than the popular perception that only bones tell the story of dinosaur bodies. The preceding examples also provide important supplemental information to help dinosaur paleontologists better "flesh out" these animals, rendering their restorations more accurate than if they only used skeletal material. Thus, using all of the information available from dinosaur fossils and comparative anatomy with extant vertebrates, restorations of dinosaur musculature result in what are probably better estimates of the overall forms of dinosaurs. Dramatic models derived from this information can show us what some dinosaur limbs and bodies may have looked like if we had the opportunity to dissect a recently dead specimen (Fig. 5.11).

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