IPC Roundup 4: Think on your toes
In another of the IPC fossil talks, Dr. Piotr Jadwiszczak described new fossil foot bones from Antarctic penguins. Even though Dr. Jadwiszczak showed details of the bones at his IPC talk, I thought it was best to wait for the paper describing these fossils to be released before writing about it, to avoid spilling the results too soon.
The fossils in question are new examples of the tarsometatasus that preserve strange features in the first toe region. Modern penguins have four toes. The second, third, and fourth toes are large and weight-supporting. The first toe, also known as the hallux, is very small. It consists of three bones – a metatarsal which connects to the tarsometatarsus (the main bone of the foot) and two phalanges, or toe segments, the second of which bears a tiny claw. These bones are almost never found in fossil penguins because they are small and thus easily swept away by currents or overlooked in the rocks. We have thus assumed that penguins have always had a tiny first toe, which is also consistent with the small size of this toe in their close living relatives, the petrels and albatrosses.
The new fossils complicate this picture. Several of them preserve a very well-developed scar for the ligament that attaches the first toe to the foot. This suggests the first toe may have been much larger in some early penguins. Interestingly enough, another specimen suggests even more variation. This bone (pictured below) suggests that the metatarsal may have been coalesced (basically absorbed) into the tarsometatarsus, perhaps leaving no external trace of a first toe at all. Fully understanding what was going on with these early penguins is going to require fossils that preserve the whole foot – another reason to keep excavating in Antarctica.
Reference: P. Jadwiszczak and A. Gaździcki. In press (published online 2013). Short Note: First report on hind-toe development in Eocene Antarctic penguins. Antarctic Science.