Current Biology has a new paper describing a quadrupedal whale fossil.
Abstract
Cetaceans originated in south Asia more than 50 million years ago (mya), from a small quadrupedal artiodactyl ancestor [1, 2, 3]. Amphibious whales gradually dispersed westward along North Africa and arrived in North America before 41.2 mya [4]. However, fossil evidence on when, through which pathway, and under which locomotion abilities these early whales reached the New World is fragmentary and contentious [5, 6, 7]. Peregocetus pacificus gen. et sp. nov. is a new protocetid cetacean discovered in middle Eocene (42.6 mya) marine deposits of coastal Peru, which constitutes the first indisputable quadrupedal whale record from the Pacific Ocean and the Southern Hemisphere. Preserving the mandibles and most of the postcranial skeleton, this unique four-limbed whale bore caudal vertebrae with bifurcated and anteroposteriorly expanded transverse processes, like those of beavers and otters, suggesting a significant contribution of the tail during swimming. The fore- and hind-limb proportions roughly similar to geologically older quadrupedal whales from India and Pakistan, the pelvis being firmly attached to the sacrum, an insertion fossa for the round ligament on the femur, and the retention of small hooves with a flat anteroventral tip at fingers and toes indicate that Peregocetus was still capable of standing and even walking on land. This new record from the southeastern Pacific demonstrates that early quadrupedal whales crossed the South Atlantic and nearly attained a circum-equatorial distribution with a combination of terrestrial and aquatic locomotion abilities less than 10 million years after their origin and probably before a northward dispersal toward higher North American latitudes.
Figure 2. Preserved Parts of the Skeleton of Peregocetus pacificus gen. et sp. nov. MUSM 3580 (Holotype)
Can anybody with better paleontological knowledge provide some context for how this fossil fits in with the (alread rich) existing set of fossils that demonstrate the transition from land to water?
The phylogeny in the paper is a good place to start, it gives you an idea where in the transition this fossil fits if you imagine that the top = land, and the bottom = water (crude but roughly true).
When somebody explains the significance of the progression, they would have to deal with timelines. The crucial details being -
Above mentioned fossil is dated at 41 MYA. and the oldest fully aquatic whale fossil is dated at 49mya.
@davecarlson: Perhaps this distribution of 4 legged amphibious “whales” do not have much to do with the actual transition from land to water because of the timelines involved?
It looks more possible that the global dispersal of fully aquatic whales happened post their emergence.
Even if you disagree with the paper that came to the conclusion that that specimen is 40-46 mya, you can atleast be honest and say there is some uncertainty (there is very little) about that specimen instead of saying it’s 49 like it’s established fact.
As far as this specimen goes I’m not sure how much it tells us. No one is arguing that it’s a direct ancestor of modern whales. This could be a descendant of that ancestor. Descendants hold onto the traits of their ancestors so this could tells us about that transition.
I remember us discussing this same thing before… there is an alternative proposal for the date isn’t there?
Let’s assume it’s 40-46 Mya.(even the paper proposes 49mya as likely and supports 40-46 Mya because of it being in line with other fossil discovery if I remember correctly). Does it change the likelyhood that the dispersion of the 4 legged amphibians accounts for the dispersion of whales?
Or it might not… A lot of assumptions are involved.
If I understood right, this fossil of the 4 legged amphibians is 42 million years old. One assumption would be that it existed a few million years before it left a fossil. Or atleast it had very similar ancestors which lived say 45 Mya.
Sort of. The assumption is that the known fossil record is not perfect. Do you think that assumption is invalid? We see humans, chimps, gorillas, orangutans, and gibbons today. Can we use them to form a valid phylogenetic tree? Would we be able to make valid inferences about the path of evolution? Assuming your answer is “yes”, these whales make the same case, regardless of the ages of the fossils. (If your answer is “no”, we have a different argument.)
Still an assumption.
How do you define a “valid” inference about the “path of evolution”? Is it an inference of what has happened… Or one way it could have happened from the evidence available?
It’s an assumption that can be tested, and has been. Come out from the squid ink: do you accept that this assumption — that the fossil record is incomplete — is true, or not?
Of course it is. All science is such an inference. Do you think, at this late date, that there is a practical possibility of any other resolution of the phylogenetic tree than the standard one? Do you think that tree implies anything about evolution? Enough with the vague questioning. Tell me whether you accept mainstream science on these points or not. Are we starting that different argument or aren’t we?
I am not sure that evolutionary processes alone can achieve the change from a 4 legged amphibian to a basilosaurid.
That itself looks like a huge assumption. There are some inferences that support it… however too few for such a fantastic change.
Edit: And I am not going to convince myself to fall in line saying God helped Evolution.
Dodging the questions. The immediate context was primates, not whales. And we also weren’t talking about “evolutionary processes”, whatever you mean by that, but about common descent. That is, about what happened rather than why it happened.
I don’t believe it happened by purely natural means.
I have said this about common descent. If you believe in only natural causes and that spontaneous generation does not happen (i.e living organisms give birth to living organisms). Then common descent is the only possibility.
I see common descent also as a kind of derivative assumption.
Special creation at different stages + guided evolution.
Just guided evolution, where God directly crafts one type of organism from another over time.
In both the cases common descent becomes trivial as the change is not natural or stochastic…
You could call it designed descent.
Before you mention. I know there are Scientific difficulties in proving this. However I find the claim of organisms assembling by largely accidental processes over time irrational(as selection doesn’t play much if a role and it’s mainly drift, there is very little directionality involved in the changes).
Neither of those alternatives is clearly expressed. I don’t think even you are sure what you mean. And the second is common descent.
The first difficulty is that your hypothesis is so vague as to make no clear claim. Before there can be any discussion of scientific testing we have to know what you mean.
Once again, this is not a claim about common descent vs. creation but about the causes of mutation. That’s an entirely separate discussion. I will just add that you don’t seem to understand the claims of evolutionary biology well enough to engage in that discussion.
