By looking for maxilloturbinal bones in dinosaur skulls, paleontologists may eventually determine whether these creatures had a fast metabolism, he thinks.
Called the maxilloturbinals, the bones form thin, folded sheets inside the nasal passages of birds and mammals.
Through experiments with live rats, squirrels, ferrets, rabbits, and opossums, Hillenius showed that the maxilloturbinals function as a water conservation mechanism, recovering moisture from the breath of mammals.
The maxilloturbinals work as a humidifier-dehumidifier system.
Looking back in the fossil record, Hillenius traced the evolution of endothermy in mammals by searching for maxilloturbinals or the internal ridges to which they attached.
In a previous paper (Hillenius 1992), I presented experimental evidence that supports a strong association between endothermy and the respiratory turbinates of mammals, the maxilloturbinal bones.
The maxilloturbinal is the most extensive and complex mammalian turbinal element.
The mammalian maxilloturbinal is usually considered homologous to the main reptilian concha (e.g., Kingsley 1926; Allison 1953; Parsons 1970; Moore 1981).
In some small rodents and insectivores, which have relatively small maxilloturbinals, the nasoturbinal may be as important as the maxilloturbinal in modifying respired air and reducing respiratory water loss (Adams 1972; Wohrmann-Repenning 1975; Popp and Martin 1984).
In summary, of the mammalian nasal turbinates, only the maxilloturbinal shows a clear functional relationship to endothermy.
Finally, the maxilloturbinal is supported by a separate ridge, which is situated in the anterolateral portion of the nasal cavity, apart from the others.
In contrast, the ridge of the maxilloturbinal is located in the respiratory passage, anterior to the transverse lamina.