RE: Transitional Forms/Fossils
November 12, 2022 at 1:05 pm
(This post was last modified: November 12, 2022 at 1:29 pm by Anomalocaris.)
A better conceptual definition of transitional fossil is the fossil of an organism from some population within which speciation is believed to have subsequently occurred.
In practice, the incompleteness of the fossil record and challenges in correlating of fossil morphology to speciation, which is ultimately a biomelocular and not strictly a morphological thing, makes rigorous application of the conceptual definition I offered above difficult. So in practice, the term transitional fossil is often applied to the fossil of an organism whose morphology seems to be intermediate between those of a known later species, and the group of earlier species from amongst which its more distant evolutionary ancestors are believed to be found.
So strictly speaking, we usually can not be certain that what we think are transitional fossils actually lies on the direct line between beginning and ending points of the transition in question. It could just represent one of several related species that all developed some part of the characteristics which would later define a definitive daughter specie.
A beautiful example is an archaeopteryx, a fossil of a feathered flying creature so dinosaur like in bone morphology that were it not for the bird like feathers it would be instantly be classified as a small dinosaur. Yet it had feathers so bird like in both morphology and layout that they are essentially indistinguishable from those of birds. Archaeopteryx has been held up for over a century as the archetypical transitional fossil, in its case between birds and dinosaurs. But close study of archaeopteryx suggest it is in fact not a direct ancester of later birds. In fact it doesn’t even count amongst its own direct ancesters or descendants the last common ancester between birds and land dwelling dinosaurs. So strictly speaking the actual line of archaeopteryx ended and did not transition from dinosaur to birds.
But it nonetheless has value as transitional fossil. Why? Because it first showed dinosaurs can and did evolve necessary bird like features, even if it itself did not represent the actual instance when birds arose from amongst dinosaurs.
In practice, the incompleteness of the fossil record and challenges in correlating of fossil morphology to speciation, which is ultimately a biomelocular and not strictly a morphological thing, makes rigorous application of the conceptual definition I offered above difficult. So in practice, the term transitional fossil is often applied to the fossil of an organism whose morphology seems to be intermediate between those of a known later species, and the group of earlier species from amongst which its more distant evolutionary ancestors are believed to be found.
So strictly speaking, we usually can not be certain that what we think are transitional fossils actually lies on the direct line between beginning and ending points of the transition in question. It could just represent one of several related species that all developed some part of the characteristics which would later define a definitive daughter specie.
A beautiful example is an archaeopteryx, a fossil of a feathered flying creature so dinosaur like in bone morphology that were it not for the bird like feathers it would be instantly be classified as a small dinosaur. Yet it had feathers so bird like in both morphology and layout that they are essentially indistinguishable from those of birds. Archaeopteryx has been held up for over a century as the archetypical transitional fossil, in its case between birds and dinosaurs. But close study of archaeopteryx suggest it is in fact not a direct ancester of later birds. In fact it doesn’t even count amongst its own direct ancesters or descendants the last common ancester between birds and land dwelling dinosaurs. So strictly speaking the actual line of archaeopteryx ended and did not transition from dinosaur to birds.
But it nonetheless has value as transitional fossil. Why? Because it first showed dinosaurs can and did evolve necessary bird like features, even if it itself did not represent the actual instance when birds arose from amongst dinosaurs.
