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Unrestricted egg size and the evolution of obligatory parental care in birds
SVPCA Conference
Platform presentation (20 minutes)
*Gareth J Dyke
Gary W Kaiser
Parental care in birds ranges from nest-mound monitoring in megapodes to extended periods of chick provisioning in albatrosses. Avian neonates also vary from being able to run, even fly, within a few hours of hatching (‘precocial’) to those emerging blind, naked, and entirely dependant on their parents (‘altricial’). We document the evolution of avian developmental strategies using a recent morphology-based phylogeny (Livezey & Zusi, 2007), present correlations between strategies, egg weight and female body mass, and examine the developmental mode of the Early Cretaceous Confuciusornis. Sequencial loss of precocial features in hatchlings characterises the evolution of birds. Altriciality is derived within Neoaves, while a set of precocial strategies are seen in earlier lineages, including basal Neornithes and their Mesozoic counterparts (Zhou & Zhang, 2004). This evolutionary transition also encompasses an increase in relative egg size: fully altricial taxa produce significantly larger eggs compared to female body mass while those of precocial birds are smaller. Skeletal constraints on egg size, seen in Jurassic and Early Cretaceous birds (Archaeopteryx, Confuciusornis, Enantiornithes), are absent from later diverging lineages. The evolution of unrestricted egg size likely precipitated the subsequent diversification of wide-ranging reproductive strategies in living birds.
London 2020