Do paleontologists ever assume that a fossil was a unique animal?

June 27, 2011 2:30 PM

Do paleontologists ever assume that a fossil was the only animal of its kind? Couldn't unique fossils have been mutants that never bred?
posted by vash to Science & Nature (22 answers total)

Fossils are pretty rare to begin with, and an animal with a sufficiently unique body that it was not distinguishable as a member of a species, is likely an animal that wouldn't have lived long. It's not inconceivable, but the odds of a fossil being doubly unique that way (i.e., fossilized and extremely mutated) are much longer than just assuming that the fossil is relatively typical of its kind.

Mutation doesn't typically take the form of something that looks like a brand new animal. It's much more commonly a particular trait that differs from the norm.
posted by fatbird at 2:38 PM on June 27, 2011 [5 favorites]

NYP, but it probably wouldn't make sense to decide that the fossil you just found is a unique mutant. It seems far more likely to me, as a lay person, that fossils are the preserved exception to the general case that dead animal bodies just disappear. In other words, since fossilization is relatively rare compared to destruction, the odds are that there were very many of these creatures, or we'd have never seen one at all.

I'd also consider that finding only one example of something would not be sufficient proof that you've ruled out the existence of others like it.
posted by Hylas at 2:42 PM on June 27, 2011 [1 favorite]

Response by poster: What about gene switches?
posted by vash at 2:42 PM on June 27, 2011

Response by poster: I admit that it's unlikely, but when a fossil is found that seems like it would be at a disadvantage, shouldn't it be considered?
posted by vash at 2:48 PM on June 27, 2011

Response by poster: "Mutation doesn't typically take the form of something that looks like a brand new animal. It's much more commonly a particular trait that differs from the norm."

I was talking about that.
posted by vash at 2:50 PM on June 27, 2011

A disadvantage compared to what? Every single creature is at a disadvantage for something, or hasn't adapted yet to some new part of their environment, and as people said above, the odds of that fossil being a mutant that a) the mutation was visible in the fossil record and b) lasted in the fossil record at all is just astronomically, vanishingly small, and very far from the most likely solution.
posted by brainmouse at 2:51 PM on June 27, 2011 [1 favorite]

It's obviously entirely possible that Fossil X is a one-off freakazoid, but the the likelihood is extremely low.

It's very unlikely that it'd be born all weird--let's say one in a million--and it's very unlikely that it'd be fossilized--let's say one in a million again. The likelihood of a mutant fossil would then be one in a trillion.

Pretty fair to assume Lucy is reg'lar people.
posted by Sys Rq at 2:51 PM on June 27, 2011 [2 favorites]

Response by poster: By disadvantage, I mean having a trait that would make it hard to live, let alone make it preferred.
posted by vash at 2:53 PM on June 27, 2011

Response by poster: It's not really specific; I have thought about it at times, but the most recent motivation was on television. The whorl shark seemed like a stupid animal(the version with the teeth on the outside). I'm not an expert, and it could have worked fine, but it made me think about it.
posted by vash at 3:01 PM on June 27, 2011

I think the more reasonable conclusion with the whorl shark is that the fossil may have originally been placed incorrectly on the animal -- I believe something like this was the first guess of how it worked, but newer reconstructions suppose that the whorl is farther back inside the mouth, like this (from here, which explains more about the thinking of the shape of this shark). Again, it's far, far more likely that we misunderstand a stand-alone fossil from a full species than it was a on-off mutated animal that made it to adulthood but didn't reproduce. Also, if I'm not mistaken we've found multiple fossils of the whorl shark, so it doesn't fit your only found one example anyway.
posted by brainmouse at 3:11 PM on June 27, 2011

Response by poster: That was why I said it wasn't a specific question...
posted by vash at 3:14 PM on June 27, 2011

Right, but that's an example of why your theory is functionally always the wrong one. There are (I think necessarily) more likely explanations for how that animal could have existed than to say "no it's just a one-off", a conclusion which would require an abundance of evidence.
posted by brainmouse at 3:17 PM on June 27, 2011 [4 favorites]

Best answer: Another thought: perhaps animals that are mutated in a way that makes it difficult to survive are much more likely to die stillborn or in infancy, rather than making it all the way to adulthood before getting kicked in the pants by natural selection? I believe baby dinosaur fossils are rare except for nesting horizons.
posted by skyl1n3 at 3:20 PM on June 27, 2011 [1 favorite]

Response by poster: That's a good point skyl1n3.
posted by vash at 3:23 PM on June 27, 2011

Occams Razor....
posted by yoyo_nyc at 3:52 PM on June 27, 2011 [2 favorites]

I think the problem you are talking about generalizes to rare examples of animals that are not known from fossils, but are extinct, or even non-extinct animals. Are you familiar with the idea of a holotype? Or a nomen dubium? The Wikipedia articles don't address your mutant case exactly, but they do address the possibility that a given specimen may not be a typical example of a species, or may lack some distinguishing feature that helps zoologists assign specimens to species, genera, etc., and the Great Librarians of Zoology have a mechanism to handle these situations.

A name may also be considered a nomen dubium if its name-bearing type is fragmentary or lacking important diagnostic features (this is often the case for species known only as fossils). To preserve stability of names, the International Code of Zoological Nomenclature allows a new type specimen, or neotype, to be chosen for a nomen dubium in this case.

75.5. Replacement of unidentifiable name-bearing type by a neotype. When an author considers that the taxonomic identity of a nominal species-group taxon cannot be determined from its existing name-bearing type (i.e. its name is a nomen dubium), and stability or universality are threatened thereby, the author may request the Commission to set aside under its plenary power [Art. 81] the existing name-bearing type and designate a neotype.

For example, the crocodile-like archosaurian reptile Parasuchus hislopi Lydekker, 1885 was described based on a premaxillary rostrum (part of the snout), but this is no longer sufficient to distinguish Parasuchus from its close relatives. This made the name Parasuchus hislopi a nomen dubium. Texan paleontologist Sankar Chatterjee proposed that a new type specimen, a complete skeleton, be designated. The International Commission on Zoological Nomenclature considered the case and agreed in 2003 to replace the original type specimen with the proposed neotype.

The whole thing is very Borgesian, but it is left as an exercise to the reader if its more of an Analytical Language of John Wilkins thing or an On Exactitude In Science thing. Actually maybe a Library of Babel thing? BRB gotta go read some Borges...
posted by jeb at 3:57 PM on June 27, 2011 [1 favorite]

As far as I am aware the assumptions are either a) independent species or b) hoax/error, given the relative rarity of fossils. More subtle relationships like adult/juvenile seem to cause a bit of a stir when proposed.

layperson speaking, hopefully useful
posted by furiousthought at 4:06 PM on June 27, 2011

...assume that a fossil was the only animal of its kind?

Ego (I discovered a new species, wo0t!) and career advantage (I discovered a new species and got a big publication and my grant was renewed) both militate against it.
posted by jfuller at 4:41 PM on June 27, 2011

Best answer: I did some anthropology dabbling in college, and have family members with anthropology degrees. Consequentially I have talked to several actual anthropologists who have tried to classify fossils / non-fossilized human skeletons. People absolutely do consider the idea that the remains they have found might contain anomalies and might not be representative of a species.

A former professor of mine (who, as it happens, is sort of a big, as-seen-on-TV name in anthropology) once found a fossil he considered to be a possible example of a homo sapiens x homo neanderthalensis hybrid. He did indeed strongly consider the possibility that the fossil may have been a diseased individual instead. And he made a point of explaining his thought process on that particular find in detail to his students, so that we would understand how difficult it can be to figure out the true significance of a fossil find.

Are there a few attention-seeking fossil hunting cowboys out there claiming new species on flimsy evidence? Of course there are. But there also plenty of serious scientists ready and eager to challenge those people.
posted by BlueJae at 7:17 PM on June 27, 2011

You're basically asking, "Why should we assume that X is what it appears to be (a surviving fossil record of a typical animal), instead of a freakishly unlikely, massively mutated, really really rare specimen with no others like it ever?"

And the answer is: Occam's Razor, a solid, well-known premise that guides scientific inquiry. There is no reason to assume the simplest answer isn't right, until a specific flaw in that assumption is found.
posted by IAmBroom at 7:18 PM on June 27, 2011 [2 favorites]

It's worth noting that pathological specimens would be far more common than actual genetic aberrants. One of the earliest Neanderthal specimens was actually an old and infirm man, which contributed to a lot to the idea of Neanderthals as primitive and brutish ape-men.
posted by Panjandrum at 8:57 PM on June 27, 2011

Best answer: In actuality, even before a unique specimen got to the stage of classification conundrum posted by jeb, it might well have lain in a dusty specimen drawer in some museum or university field collection office, waiting for something like it to turn up, to help facilitate classification. Few fossil specimens collected in the field are of such quality and completeness that they can serve to define their species, entirely. Mostly, fossils are records of individual animals, who died drinking, eat or walking over soft mud, at various points in their individual development/life cycle.

For most very unique specimens, the usual response of senior scientists to "wait awhile" until additional specimens are discovered is usually correct. Unique specimens cause people to look closer and harder for the evidence that proves they are not, actually, unique. Some times, that is provided by new specimens dug out of the ground, but some times, the fellows for a new fellow are actually found in those dusty old specimen drawers, where they've lain waiting for classification and more, similar specimens to themselves.
posted by paulsc at 5:52 AM on June 28, 2011 [1 favorite]