A Fine Fossil Flipper
Seymour Island is located near the northern end of the Antarctic Peninsula. This prolific fossil site has yielded up a massive haul of fossil penguin bones starting over the past century. Thousands of specimens have been collected and there is evidence for about a dozen different species of penguins living side by side in the area roughly 40 million years ago. One of the biggest species is named Anthropornis nordenskjoeldii. Anthropornis means “man bird”, referring to its massive size and “nordenskjoeldii” honors polar explorer Adolf Erik Nordenskiöld. Somewhat ironically for the honoree of a penguin species name, his explorations were primarily in the high North. Among other exploits, he collected fossils on the island of Spitsbergen.
One of the difficulties of studying the Seymour Island penguins is that despite the abundance of bones, almost all of them are isolated. The area seems to have been an estuary, and the frenetic meeting of river and ocean waters may have worked to scatter penguin bones all around. I’ve looked at hundreds of specimens of Seymour Island penguins, and the only two specimens I have ever seen that include more than one bone are a “fossil knee” including the patella, piece of the femur and a piece of the tibiotarsus and a hip socket with a chunk of the femur stuck in it. Isolated bones can be frustrating when there are multiple species that are the same size living in an area. How can we tell whether this sharp beak belongs to that wing? How can can we tell whether the wide foot bone belongs to the penguin with the long neck bones? It poses a particularly difficult challenge to efforts to understand fossil penguin locomotion, because we really want whole flippers or hindlimbs from a single bird if we are going to predict diving or walking style accurately.
As it turns out, a nearly complete flipper from Seymour Island has been known from nearly 60 years. The great New Zealand penguin paleontologist Dr. Brian J. Marples studied the bones in 1953. Marples was a very cautious paleontologist, and avoided naming new species or assigning bones to the same individual unless there was overwhelming evidence. He noted the bones all fit together, but gave them separate numbers and they ended up with their own little tags in the collection. Flash forward to 2012. Dr. Piotr Jadwiszczak at Uniwersytet w Białymstoku revisited the bones in a recent paper. He found evidence from the preservation, siding, and proportions of the bones that they most likely belong to a single individual. This lets us finally get a good idea how the flipper of Anthropornis was built. Leg bones were recovered nearby too, and they probably also belong to this particular penguin.
The flipper is robust – very bulky compared to modern species. One of the strangest things about the flipper is that the tip of the flipper shows a “modern” plan, with the third metacarpal extending past the second (in essence, the bone that would make up the base of the middle finger in a person is longer than the bone that would make up the pointer finger). This advanced feature suggests that Anthropornis may have been more closely related to living penguins than previously thought, although other features of the skeleton would argue that it was very primitive. A primitive feature of the flipper is the great angling between the bones, which results in a somewhat more auk-like wing as opposed to the very straight wings of modern penguins. In the past, this angling has been connected to poorer diving capacities, but as Dr. Jadwiszczak and our own papers have noted this is not necessarily true. Auks can reach tremendous depths, and they are at a disadvantage compared to penguins because of their higher buoyancy and less dense bones. Anthropornis appears to have been a strong diver based on the flipper.
Reference: Jadwiszczak, P. 2012. Partial limb skeleton of a “giant penguin” Anthropornis from the Eocene of Antarctic Peninsula. Polish Polar Research 23: 259-274.