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Wise as an owl - 147 million years of avian brain evolution
SVPCA Conference
Platform presentation (20 minutes)
*Angela C Milner
Stig. A Walsh
Although the term ‘birdbrain’ is commonly used as an insult indicating lack of intelligence, many living bird species display cognitive abilities equalling and even exceeding those of many mammals (Lefebvre et al., 2004). The avian brain has evolved along a course parallel to that of the mammalian brain and, for most avian species, the ability to fly has apparently resulted in constraints on brain volume relative to body size (encephalisation quotient: EQ) and overall brain shape (Jerison, 1973). The endocranial cast associated with the holotype specimen of Archaeopteryx (147 ma) and recent micro-CT investigations of its skull, demonstrate the earliest-known bird already possessed a brain similar in EQ to living species (Domínguez et al., 2004). However, recent micro-CT analysis of non-avian theropod skulls (e.g., Kundrát, 2007) has also shown that some also possessed EQs within the range of living avian species. Our recent analysis (Milner & Walsh, in press) of the brains of two Lower Eocene (55 ma) fossil birds demonstrates that avian brain shape and EQ of these taxa were almost entirely like those of living bird species.

Here we discuss the significance of brain enlargement in avian and non-avian theropods in the context of the evolution of powered flight and overall cognitive ability. We suggest that the most important neurological evolutionary trends in Jurassic to Cenozoic birds are probably mostly related to sensory integration and cognition than to flight adaptation. However, although some skeletal specialisations for flight may have affected overall brain enlargement, others, such as the development of the telencephalic wulst region (involved in integration of visual stimuli) may be related to those specialisations.

London 2020