The skull has 2 anterior cervical vertebrae in place of it that are drastically modified to allow support for the big head. An odd specimen. See paper for details, it's short. Gavrilov, V.M. 1998. Rationale for the evolutionary increase in basal metabolic rate of Passeriformes.
Passerine birds have a BMR higher than other birds and mammals.
This paper describes the BMR of passerines relative to other birds and discusses the implications for the behavior and biology of the beasts. Figured GSP would get a kick out of this paper. Lee, Y.-N. 1997. Looks like one, though. Biochemical and geochemical analysis of bones of ichthyosaurs from this famous site.