It is now generally assumed that the pterosaurs were hairy (Sect. 6.3). They were almost certainly tachymetabolic also, according to Fleming and Lips (1991) (Sect. 6.7.1). In recent years, several fossils of non-avian therapod dinosaurs with well-preserved integumentary coverings have been discovered. Apart from numerous specimens of Caudipteryx, which possessed true feathers (Ji et al. 1998), however, fossils of only one or two other genera of feathered dinosaurs have so far been discovered. One of these, belonging to the family Dromaeo-sauridae, has been recently discovered in Liaoning Province, China (Ji et al. 2001). Dating back ca.130 my, it was covered from head to tail in a downy fluff of feather-like fronds. This makes it indisputable that a body covering similar to feathers was present in some non-avian dinosaurs. The dromaeosaurs were advanced therapods (Chap. 11) and were probably more like birds in appearance than giant lizards. The patterns of feathers on the arms and tail were similar to those of Caudipteryx zoui. Much of the controversy over the origin and early evolution of birds (Sect. 11.5) centres on whether or not they were derived from caelurosaurian therapod dinosaurs. These animals from the Upper Jurassic and Lower Cretaceous probably could not fly. Phylogenetic analysis showed them to be even more primitive than Archaeopteryx, the earliest known bird. They represent stages in the evolution of birds from feathered, ground-living bipedal dinosaurs and show that the origin of feathers was unrelated to the origin of flight.
Although most authors accept that crocodiles and birds are sister-groups (Benton 2004), Brian Gardiner (1982,1993) produced a radical alternative hypothesis based on a character analysis of living tetrapods. He concluded that mammals and birds are sister-groups (Supercohort Haematothermia), sharing numerous specialisations with crocodiles and, before them, Chelonia (Sect. 11.5). This interesting speculation lies somewhat beyond the scope of the present volume, but it does support the hypothesis that the primary function of both feathers and hair was initially thermoregulatory.
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