Evolution and systematics

Five species comprise one of the most uniform families in the ornithological world. Early taxonomists, analyzing museum skins tagged with exceedingly sparse field notes and puzzling over their relationships, allied them in a mixed bag: nightjars, trogons, jacamars, puffbirds, barbets, motmots, kingfishers, broadbills, cotingas, manakins, flowerpeckers, and tyrant-flycatchers. Until about 1900, all were regarded as variations of the Jamaican tody (Todus todus), then Todus viridis. Ultimately, these endearing Caribbean birds entered the order Coraciiformes, reflecting close kinships with motmots and kingfishers.

Fossils are unfortunately extremely scant: ancestral fossils (Palaeotodus emryi), are known from the Oligocene of Wyoming (37-24 million years ago), France, and Switzerland. Palaeotodus, although fragmentary, suggests close affinities with today's tody motmot (Hylomanes momotula) and the Swiss fossil Protornis glarniensis, a missing link between contemporary todies and motmots.

Geographical, paleontological, behavioral, morphological, and genetic data aid in the construction of a hypothetical evolutionary scenario for tody evolution. Approximately 30 million years ago, a primitive motmot/tody-like ancestor inhabited Northern Hemisphere forests. Twenty million years ago, climates began cooling, and by seven million years ago, only relict (from an earlier geological period) tody-motmot populations survived. Eventually, Central American birds similar to today's todies flew eastward, colonizing large Caribbean islands and evolving into five species. This was possible because of Ice Age glaciations (one million years ago), when polar icecaps froze gigantic volumes of sea water, lowering sea levels worldwide by about 300 ft (90 m), thus reducing distances between continents and islands.

Was this article helpful?

0 0

Post a comment