Diving Birds in the Seas of ... Kansas?

Spent the day at the Dinosaur Discovery Museum in Kenosha, Wisconsin today, and found this guy among the dinos:

Hesperornis sp., Dinosaur Discovery Museum, Kenosha Co, WI 3/1/2014

This is Hesperornis, a diving bird from the late Cretaceous. This particular one lived, or at least died, in Kansas. The genus was first described in 1872 by Othniel Marsh. (1)

It looks an awful lot like this bird:

Red-throated Loon (Gavia stellata), Nome, AK, 8/10/2012

This is a Red-throated Loon (Gavia stellata), from Nome, Alaska. Even still living, you can see some similarities with Hesperornis, in the shape of the body and the jaw. You can't see it from this shot, but the feet are set well back on the body, also like Hesperornis. The loon is known to eat primarily fish, and with that build, Hesperornis is believed to have done so as well. So, we have a fossil bird from 70 million years ago, that was similar to modern loons both ecologically and morphologically. Must be a direct ancestor of loons, right?

Wrong.

In fact, Hesperornis split off from the line that ended up as modern birds quite some time back, around 130 million years ago. (2) In that first photo, there are a couple of traits that hint at that fact. First, Hesperornis was flightless -- in fact, the only remnant of the wings is a couple of vestigial humeri (upper arm bones).

Red-throated Loon (Gavia stellata), Nome, AK, 8/8/2012

As you can see from this shot, loons still have wings, and although they don't fly as much as many birds, they are perfectly capable of not only flying but covering long distances during migration. And here's the other hint:

Hesperornis sp, Dinosaur Discovery Museum, Kenosha Co, WI  3/1/2014

This closeup of the head of Hesperornis clearly shows a most un-birdlike trait (at least to our eyes): it had teeth! This really shouldn't be a surprise, since birds are descended from maniraptoran theropod dinosaurs, most of which were well supplied with teeth. But the common ancestor of modern birds lost their teeth sometime in the Cretaceous period, perhaps about the time that Hesperornis was using it's teeth to catch Mesozoic fish.

This sort of evolution, where unrelated species develop similar traits, is known as convergent evolution, and it happens a lot. Convergence almost always leaves plenty of signs, though, where each species' separate evolutionary history is still clearly visible to a close look.

Interestingly, loons aren't the only species convergent with Hesperornis. Mosasaurs, a group contemporary to Hesperornis, developed some unique jaw architecture, otherwise only found in Hesperornis and its close relatives. (3) What makes this case particularly interesting is that mosasaurs were closely related to (and possibly nested within) the Varanidae, commonly known as monitor lizards -- the two lineages would have split 200 million years earlier!

Geology and biology are very different disciplines, but thanks to the wonders of fossilization, evolution ties them together into a fascinating way of thinking about the world.

(1) Marsh, O. C. (1872). Preliminary description of Hesperornis regalis, with notice of four other new species of Cretaceous birds. American Journal of Science, (17), 360-365.

(2) http://www.tolweb.org/Aves/15721

(3) Gregory, J. T. (1951). Convergent evolution: the jaws of Hesperornis and the mosasaurs. Evolution, 5(4), 345-354.