[3] However, the group is not monophyletic and more recent phylogenetic studies have found Megapodiidae and Cracidae to be successive early branching lineages of Galliformes.

[4] The numbers of species are from the list maintained by Frank Gill, Pamela Rasmussen and David Donsker on behalf of the International Ornithologists' Union.

This does not provide any assistance in evaluating the hypothesis (Pereira et al., 2002) that the split between the 4 main lineages of our time occurred quite rapidly, approximately in the Oligocene or slightly earlier, somewhere between 40 and 20 mya.

Thus, the assumption that the modern diversity started to evolve in the late Paleogene, continuing throughout the Miocene and onwards, must also be considered hypothetical given the lack of robust evidence.

The ichnotaxon Tristraguloolithus cracioides is based on fossil eggshell fragments from the Late Cretaceous Oldman Formation of southern Alberta, Canada which are similar to chachalaca eggs (Zelenitsky et al., 1996), but in the absence of bone material their relationships cannot be determined except that they are apparently not from a dinosaur.

It was usually caused by changes in topography which divided populations (vicariant speciation), mainly due to the uplift of the Andes which led to the establishment of the modern river basins.

The distribution of curassow and piping-guan species for the most part follows the layout of these river systems, and in the latter case, apparently many extinctions of populations in lowland areas (Grau et al., 2005).

[9] Cracids range in size from the little chachalaca (Ortalis motmot), at as little as 38 cm (15 in) and 350 g (12 oz), to the great curassow (Crax rubra), at nearly 1 m (39 in) and 4.3 kg (9.5 lb).