Fishy Mammalian Spines
|June 12, 2012||Posted by PaV under Intelligent Design|
Here it is: a mammalian/reptile vertebrate spine a hundred million years before it was to be fully used on land.
A spine with multiple segments is a feature of land-dwelling animals but the discovery of the same anatomical feature in a 345-million-year-old eel suggests that this complex anatomy arose separately from, and perhaps before, the first species to walk on land.
Tetrapods, which include the first species to walk on land as well as all modern mammals, reptiles, birds and humans, possess vertebrae organized into five distinct segments. From head to tail, the spinal vertebrae can be categorized into cervical, thoracic, lumbar, sacral and caudal sections, each with its own characteristic anatomy.
By contrast, fish vertebrae are typically categorized anatomically into two segments: caudal and pre-caudal. But the spinal column of Tarrasius shows a complexity more like that seen in tetrapods, with five segments separated by abrupt transitions.
Obviously, this creates problems for the Darwinian narrative:
“It’s the last trait to fall,” said Lauren Sallan, a graduate student in the Program in Integrative Biology at the University of Chicago Biological Sciences. “First, limbs were thought to show that a species was on land and walking, and now the vertebral morphology doesn’t mean that they’re on land either. So a lot of the things we associate with tetrapods actually arose first in fishes, and this is another example of that.
In fact, maybe it’s a really big problem:
“The morphology is just completely different in each series of vertebrae. Like a tetrapod, you can tell which segment you’re looking at from the basic morphology.”The appearance of tetrapod-like spinal organization in a ray-finned fish shatters the presumed relationship between complex vertebral anatomy and both walking and terrestriality. The eel-like Tarrasius possessed no hind fins and a long dorsal fin, indicating it used its surprisingly intricate spinal column for swimming, not walking. And while Tarrasius lived several million years after the first tetrapods with hands and feet, the discovery of these spinal features in a fish species confirms that this anatomy can evolve separate from the evolution of walking behavior.
In case Darwinists want to say, as they usually say, “Oh, this is no problem,” here’s the name of this eel: Tarrasius problematicus! (Of course, this name comes from the 1930’s, when science was science, and when truth mattered.)
And this was the author’s reaction:
But when Sallan, a graduate student in the Program in Integrative Biology at the University of Chicago Biological Sciences, looked at the NMS Tarrasius fossil, she found an anatomical feature that, according to conventional wisdom, should have only been present in the land-dwelling tetrapods.
“I shouted out ‘why does a fish need a sacrum?’ . . .”
(From the Univ. of Chicago website.)
But, not to worry, there’s always a “just-so” story ready at hand:
Instead, the commonalities suggest that similar environments or other selective pressures may produce convergent evolution of this complex spinal organization.
And, of course, there’s no need to try and think through how any of this is possible—for, after all, we know it happened; and, ‘outside of the light of evolution, nothing in biology makes sense.’ With these two axioms, any kind of “just-so” story is possible—and, acceptable. It’s so ennervating, really.
And, BTW, this find also spells “problems” for the “evo-devo” crowd:
Axial regionalization in Tarrasius could indicate tetrapod-like Hox expression patterns, possibly representing the primitive state for jawed vertebrates. Alternately, it could signal a weaker relationship, or even a complete disconnect, between Hox expression domains and vertebrate axial plans.
(From theabstract of Lauren Sallen’s paper)