Cranial Anatomy Related to Respiration

Endothermic vertebrates have large spaces within their nasal cavities to accommodate folded bony or cartilaginous structures, which were often lined with mucous membranes called respiratory turbinates. These structures are essential to endotherms because they help to conserve the water and heat associated with the near-constant breathing that endotherms use for their more active metabolism. Turbinates ensure that as much as 60% of the water moisture that is inhaled is absorbed ("reclaimed") before being exhaled, otherwise its absence would quickly result in dehydration. Body-heat losses and energy demands would also accumulate if turbinates were not in place, the equivalent of leaving a window open on a cold winter day. Because of the essential function of turbinates in conserving water and heat, nearly all mammals and birds possess them and they can be used as undoubted indicators of endothermy in modern taxa. Searches for these structures (or at least enough room for them) in a few dinosaur skulls have so far not shown

FIGURE 8.8 Evidence of brooding and association of embryo with the theropod Oviraptor. (A) Skeleton of adult Oviraptor (missing its skull) on egg clutch. (B) Oviraptor embryo recovered from an egg that was previously interpreted as belonging to the ceratopsian Protoceratops. Both specimens recovered from Late Cretaceous strata in Mongolia. Transparencies 5789 (5) and K17685 (Photo. Mick Ellison). Courtesy of the Library, American Museum of Natural History.

FIGURE 8.8 Evidence of brooding and association of embryo with the theropod Oviraptor. (A) Skeleton of adult Oviraptor (missing its skull) on egg clutch. (B) Oviraptor embryo recovered from an egg that was previously interpreted as belonging to the ceratopsian Protoceratops. Both specimens recovered from Late Cretaceous strata in Mongolia. Transparencies 5789 (5) and K17685 (Photo. Mick Ellison). Courtesy of the Library, American Museum of Natural History.

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