A Missing Link
The fossil mammal Puijila darwini is a "missing link" in the evolution of a prehistoric land mammal into modern, marine ones—specifically seals and their relatives.
Anatomical analysis of the specimen shows that this animal is an early, intermediate form along a multi-branched evolutionary journey from land to sea: Puijila has both terrestrial and semi-aquatic characteristics.
At first glance, Puijila's feet, legs and tail seem to belie the flippers and streamlined bodies that we see today. But closer inspection of the fossil reveals aquatic tendencies. The shape of the Puijila's forelimbs and shoulders provided power, as if the animal were a swimmer or a digger. However, it would not have been much of a digger because it had relatively small claws. It could have been a swimmer, though, because its long, flattened toe-bones are similar to those seen in some web-footed animals. These and other physical characteristics indicate the semi-aquatic nature of Puijila.
From Feet to Flippers
Moreover, and despite several otter-like characteristics, Puijila has been identified as a relative of modern pinnipeds (true seals, sea lions and the walrus). Virtual 3D reconstructions of the skull revealed additional seal characteristics.
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The land-to-sea transition has been poorly understood for pinnipeds. Scientists have long understood that marine mammals evolved from terrestrial ancestors. Observing that true seals and the sea-lion lineage (sea lions and the walrus) are so different from one another, scientists thought it likely that they evolved from different ancestors. In other words, the land-to-sea transition would have occurred twice for pinnipeds.
Recent anatomical and molecular evidence now suggests a single origin for pinnipeds instead. As Puijila lived at the same time as many fossil flippered pinnipeds, it does not appear in a direct line to modern pinnipeds. Rather, it seems that a Puijila-like ancestor may have given rise to both Puijila and to flippered pinnipeds.
The Scientific Publication
The journal Nature published the original scientific account of the species Puijila darwini and its implications for theories of pinniped evolution. Co-authors: Natalia Rybczynski, Mary Dawson, Richard H. Tedford.
- Purchase a copy of the scientific paper from the journal.