Friday Headlines, April 12, 2013
THE LATEST IN THE GEOSCIENCES
I grew up in Salt Lake City. (I know what you’re thinking. The answer is no.) Kennecott Copper was this massive open-pit mine up in the mountains that sometimes we’d get field trips to. Over the years, of course, it’s gotten deeper and deeper.
The walls of the pit are very steep, and it was bound to happen. Gravity always wins in the end. There was a land slide.
I think this title is a bit deceptive. This fish does lend some insight into why it is that humans have two arms and two legs, but it’s rather ego-centric to assume that this find applies only to humans.
This is actually more fundamental than this. Humans, as well as nearly all jawed vertebrates (that is animals that have backbones and jaws) have paired appendages. Two front legs, two back legs. Two wings, two sets of talons. And two front (pectoral) fins and two back (pelvic) fins. What we’re still trying to learn is when did these paired limbs evolve?
We’ve rather selfishly thought (and it’s been borne out a bit by the fossil record) that paired limbs are an exclusive trait within the jawed vertebrates. In other words, if it has paired limbs, it has a jaw. This new species of fish clearly has paired limbs. But it lacks a jaw.
Euphanerops is a new species of ostracoderm (‘bony skin’) fish that lived about 370 million years ago. This is about the time when fishes were starting to develop jaws (which is an interesting story). Ostracoderms lack jaws.
There are some jawless fishes still alive today, particularly hagfish and lampreys. They’re ugly critters, not nearly as stylish as the ancient, armored ostracoderms.
Euphanerops, unlike any known jawless fish including other ostracoderms, clearly has paired limbs. The argument here is not necessarily that paired limbs appeared in fishes before jaws, but that paired limbs may have evolved multiple times in several unrelated groups as an evolutionary experiment.