Tracking Mesozoic birds across the world

Early Cretaceous bird tracks have been found in North America, China, South Korea and Japan. The identification of many of the tracemakers as ornithurine birds rather than enantiornithines is supported by the overall morphological and behavioural similarity to tracks left by modern shorebirds, as well as indicators of ground-to-air takeoff. Various morphologies found in Asia, including web-footed, anisodactyl and zygodactyl tracks, indicate a very high diversity of birds. The most common are anisodactyl shorebird-like tracks represented by Aquatilavipes, Koreanaornis, Ignotornis and others. Such ichnogenera as Aquatilavipes and, more recently, Koreanaornis, have been discovered on both sides of the Pacific Ocean. Koreanaornis is more specific in its distinguishing criteria, unlike Aquatilavipes, which may be a taxonomic wastebasket. The appearance of the same ichnogenera across great distances implies that either ornithurine birds evolved long-distance migration in or before the Early Cretaceous, or that ornithurine birds arose before the Cretaceous. Molecular data support an Early Cretaceous origin for modern bird families, and shorebird-like tracks have been reported from very near the Jurassic-Cretaceous boundary. Shorebird-like trackways have been reported from the Early Jurassic of Africa and North America (e.g. Trisaurpodiscus), suggesting an even earlier origin for ornithurine birds.