The origin of hummingbirds

Hummingbirds are the tiniest of living birds.
They are famous for hovering with wings beating so rapidly they essentially blur from view. Today hummingbirds live only in the New World.

Prum et al. 2015
based on DNA, nested hummingbirds with swifts and these nested with the nocturnal nightjars. That is the traditional nesting.

In the LRT 2015
based on morphology, hummingbirds nest with the extinct Eocypselus (Fig. 4, 50 mya) and the sea gull, Chroicocephalus (Figs. 1, 3; extant). Mayr 2004 reported on an Old World hummingbird, Eurotrochilus inexpectatus (Fig. 4; 30 mya), from the early Oligocene.

Elsewhere on the cladogram,
swifts nest with owls in the large reptile tree (LRT, 1129 taxa).

Figure 1. A sea gull hovering. Many birds can do this for short periods, but sea gulls are phylogenetic sisters to hummingbirds, so this is where it all began for hummers.

Figure 1. A sea gull hovering. Many birds can do this for short periods, but sea gulls are phylogenetic sisters to hummingbirds, so this is where it all began for hummers.

To be fair,
swifts also hover. And here is a sample of that on YouTube. https://www.youtube.com/watch?v=9u8YuBGQWb0
It should be noted that swifts do not feed while hovering. They speed through the air snatching insects in flight. On the other hand, gulls do hover, and here is another image of that (Fig. 2). Gulls appear to hover only in a breeze, which is often present at shorelines. Thus gulls represent the awkward origin of hummingbird hovering, which improved with faster wingbeats. a deeper sternum and a smaller size.

Figure 2. The smallest gull, Hydrocoloeus_minutus, hovering while feeding.

Figure 2. The smallest gull, Hydrocoloeus_minutus, hovering while feeding.

Fossils tell us
that hummingbird-sized specimens, like Eocypselus (Figs. 3, 4), lived 50 mya and probably originated much earlier. One-sixth the size of the small gull, Hydrocoloeus (Figs. 2, 3), Eocypselus had a relatively short, small beak and shorter legs, though still longer than the wings.

Figure 2. Chroicocephalus, the smaller Hydrocoloeus, the much smaller Eocypselus and the ruby-throated hummingbird, Archilochus to scale.

Figure 3. Chroicocephalus, the smaller Hydrocoloeus (the smallest living gull), the much smaller Eocypselus and the ruby-throated hummingbird, Archilochus to scale.

Of course, small size is key to hummingbird evolution.
At this point, I’m not aware of any gulls smaller than Hydrocoloeus, whether extant or in the fossil record. I would like to see a skeleton of Hydrocoloeus to see if it had a larger sternum relative to the 1.25x larger Chroicocephalus. I also wonder if it has a faster wingbeat when hovering based on its smaller size.

Figure 3. Eocypselus from 50 mya, Eurotrochilus, from 30 mya and Archilochus, the extant ruby-throated hummingbird to scale.

Figure 4. Eocypselus from 50 mya, Eurotrochilus, from 30 mya and Archilochus, the extant ruby-throated hummingbird to scale.

The fossil Eutrochilus
(Fig. 4, Mayr 2004) bridges the time gap between Eocypselus and extant hummingbirds and would appear to be a complete and fully realized hummingbird itself, living some 30 mya, while originating much earlier. Eocypselus (Fig. was not much different in size or morphology.

Old World vs. New World
So, based on Eutrochilus, hummingbirds used to be in Europe. Now they are restricted to the New World. Why? There is a long list of hummingbird eaters online here. Something killed European hummingbirds in the Old World… maybe microbes?

Vultures had a similar split.
Today we have New World vultures (like Coragyps, derived from petrels) and Old World vultures (like Torgos, derived from falcons) in the LRT. The odd exception to this hemispherical split is the dodo, Raphus, and its kin, all New World flightless vultures isolated on islands in the Old World. Then there’s a report of an Old World vulture in Miocene Nebraska (Zhang et al. 2012). Really, what’s to stop them? And what killed Old World vultures in the New World? So again, there’s another mystery in need of a good explanation.

References
Mayr G 2004. Old World fossil record of modern-type hummingbirds. Science 304:861–864,
Ksepka DT, Clarke JA, Nesbitt SJ, Kulp FB and Grande L. 2013. Fossil evidence of wing shape in a stem relative of swifts and hummingbirds (Aves, Pan-Apodiformes). Proceedings of the Royal Society B: Biological Sciences 280 (1761): 20130580. doi:10.1098/rspb.2013.0580. Supplementary materials here.
McGuire JA et al. (7 coauthors) 2014. Molecular Phylogenetics and the Diversification of Hummingbirds. Current Biology, 2014; DOI: 10.1016/j.cub.2014.03.016
Zhang Z, Feduccia A and James HF 2012. A Late Miocene Accipitrid (Aves: Accipitriformes) from Nebraska and Its Implications for the Divergence of Old World Vultures. PLoS ONE7(11): e48842. https://doi.org/10.1371/journal.pone.0048842

https://wordpress.com/post/pterosaurheresies.wordpress.com/10805
https://www.livescience.com/44593-first-hummingbird-evolutionary-tree.html

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.