Skepfeeds-The Best Skeptical blogs of the day

Pinniped Evolution

Posted in Neurologica by Skepdude on April 24, 2009

The joke is getting so overused now it is becoming a cliche in skeptical circles – what happens when a paleontologist fills in a gap in the fossil record? They create two gaps, one on each side. But it is often used because it pithily exposes the intellectual buffoonery of those evolution deniers (aka creationists) who deny common descent. What is a “gap;” how big does it have to be to call into question common decent; or rather how small do the gaps have to shrink before creationists will accept common descent?

Perhaps the biggest outright lie in the creationist camp, still frequently parroted, is that there is a lack of transitional fossils in the fossil record. That is why it is important to showcase to the public the steady stream of beautiful transitional fossils that are being added to our already copious fossil record.

In the most recent issue of Nature, scientist present yet another pesky gap filled in with a transitional fossil, this one an early pinniped – which includes seals, sealions, and walruses.

The fossil is between 20-24 million years old and is dubbed Puijila darwini. Here is the technical description from the Nature article.

The new taxon retains a long tail and the proportions of its fore- and hindlimbs are more similar to those of modern terrestrial carnivores than to modern pinnipeds. Morphological traits indicative of semi-aquatic adaptation include a forelimb with a prominent deltopectoral ridge on the humerus, a posterodorsally expanded scapula, a pelvis with relatively short ilium, a shortened femur and flattened phalanges, suggestive of webbing.

What this means is that the creature was able to walk on land, was likely a carnivore, but had some early adaptations to the water, such as webbed feat. Think of an otter (it was 110 cm long) with a long tale and the teeth of a dog.  The earliest pinniped fossils come from 20-28 million years ago, about the same time as this fossil, and already have fully developed flippers.

This fossil suggests answers to several unknowns – what evolutionary path did pinnipeds take, what are their closest relatives, and where greographically did their evolution take place? This fossil suggests they evolved in the fresh waters of the arctic, as opposed to the the northwestern US, where the earliest pinniped fossils were found. This one fossil does not settle this last question, but does suggest the arctic as a viable alternative.

I can anticipate the standard creationist denial. They will argue that this fossil cannot be a direct ancestor to pinnipeds because it is as old, and not older, than the earliest pinniped fossils with fully formed flippers.  This is true, as the authors of the Nature article readily state. Most fossils will not be direct ancestors to living descendants. This is because evolutionary relationships are bushy – they are not a ladder of linear progression. A randomly discovered fossil is therefore likely to be on a side branch, not one that lead directly to species that happen to be extant.

READ THE REST OF THIS ENTRY AT “NEUROLOGICA”

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