Figure 1.

Evolution of foot‐based swimming in birds and general avian skeletal anatomy. (A) Foot‐based swimming has evolved at least six times within birds as denoted by black radiations within major gray bird lineages. The phylogeny is based on Prum et al. (2015). Branch lengths are not to scale. Dashed lines represent completely extinct groups. Common names of representative swimming birds from each lineage are listed to the right of the phylogeny. (B) General skeletal anatomy of birds annotated using the helmeted Guineafowl (MCZ 341648). tr., trochanter; i.c., iliac crest; i.f., iliac fossa; o.f., obturator foramen; il.f., ilioischiatic fenestra; is.f., ischiopubic fenestra; c.c., cnemial crest; MTP, metatarsophalangeal joint.