Rules Of Speciation

[jkfoam]

In life the rules of speciation are different than for fossils. In life animals of a species must be capable of breeding with each other. For example two dogs of vastly different appearance can breed thus establishing beyond question that they are the same specie. With fossils this rule is obviously not available. We only have morphological differences in appearance to establish speciation. My question is, are there rules on what morphological differences are required to differentiate fossil species. I have collected in several US Eocene fossil localities that have an abundant gastropod assemblege. Several of the snail species are very similar to each other yet they are described in the literature as individual species even though they are found in several different but close geologic strata. For example, Buccitriton texanum and Buccitriton sagenum are two very similar sanails. Yet in another example we have a snail in two ajoining formations with, in my opinion, different appearance that are the same specie. Pseudoliva vetusta carinata is a snail found in the Eocene Stone City Formation and the Eocene Cook Mountain Formation that are similar in appearance but have significantly different apical angles yet they are not specie differentiated. This is also true but to a lesser extent for Distorsio (Personella) septemdentata. So my question, what are the rules for fossil speciation.

Thanks in advance for any and all responses

JKFoam

[Auspex]

It's a bit of a train wreck.

Since morphology is (largely) what we have to go on, fossil "species" are often "morphotypes". Peer review is there to keep an eye on how much splitting/lumping based on small differences gets into the mainstream, but heck, there are named species for which the order is unresolved!

Safest thing to do is to write your labels in pencil...

[ashcraft]

Species is a man-made group, there are many examples of groups of organisms that can interbreed and produce viable offspring, even though they are considered distinct speceis, an example would include coyotes and jackals. Even within the same species, some organisms can't necessarily interbreed, such as dogs. Think about chihuahuas and St. Bernard's. Physical impossibility without help from humans. We had a discussion once about the difference between polar bears and Kodiak grizzilies. Are they actually separate species, or color phases of the same species. A comment was made that you can take measurements from the skeleton and classify them into one or the other species, which is commonly done in living species. In the case of fossils, you don't normally have enough individuals to compile a normal parametric range to compare your fossils to, so in the case of the bears, I suspect they would end up in the same species.

As far as naming new species, it comes down to publication. If you are convinced you have found a new species, and can convince the people who are reviewing the publication that your data/conclusions are correct,then viola, you have a new species. Later authors may add to this, or have the organism renamed into another species if they can convince their reviewers they are correct.

I suspect that the number of species is highly under-rated in the fossil record, and highly-over rated in extant species.

Brent Ashcraft

[jkfoam]

It's a bit of a train wreck.

Since morphology is (largely) what we have to go on, fossil "species" are often "morphotypes". Peer review is there to keep an eye on how much splitting/lumping based on small differences gets into the mainstream, but heck, there are named species for which the order is unresolved!

Safest thing to do is to write your labels in pencil...

Auspex,

You are right, there are named specie for which the Order is unresolved. In fact there are named specie for which they are unsure of even the Phylum! That is where the expression "Incertae Sedis" is employed.

I don't mind writing the specie names in ink on my labels but I always try to write the literature reference I used in identification on the back of the label.

So, you are saying there are no rules just peer review, interesting, and I think I have to agree with you.

JKFoam

[Auspex]

The basic "rules" are to research all the literature, study all the holotypes/paratypes you can, and present your case for how your "new" specimen differs from the precedents.

[siteseer]

Species is a man-made group, there are many examples of groups of organisms that can interbreed and produce viable offspring, even though they are considered distinct speceis, an example would include coyotes and jackals. Even within the same species, some organisms can't necessarily interbreed, such as dogs. Think about chihuahuas and St. Bernard's. Physical impossibility without help from humans. We had a discussion once about the difference between polar bears and Kodiak grizzilies. Are they actually separate species, or color phases of the same species. A comment was made that you can take measurements from the skeleton and classify them into one or the other species, which is commonly done in living species. In the case of fossils, you don't normally have enough individuals to compile a normal parametric range to compare your fossils to, so in the case of the bears, I suspect they would end up in the same species.

Brent Ashcraft

Yes, it is artificial. It's an attempt to sharply characterize a living reproducing group or a dead one from just parts of its most durable anatomy, accounting for all variations. If you held a biologist down, and demanded a definition of a species and then did the same to others, you would get varying answers but all would include something about the ability to interbreed while also providing exceptions.

Jkfoam, that polar bear/grizzly thread was interesting. You should check that out.

I might have noted this in that or another thread but you can find a definition of species in "Evolution of Insects" (Grimaldi and Engel, 2005):

"A discrete group of individual organisms that can be diagnosed, or defined on the basis of certain specialized features, and that had a common ancestor and unique evolutionary history."

Some might say that is too general to be useful. Others might say it's hard to be specific (pun intended) and add that it's pretty good.

[Auspex]

A comforting perspective from Calvin, of Calvin and Hobbes:

"That's the problem with science; a bunch of empiricists trying to describe things of unimaginable wonder."

[ashcraft]

"A discrete group of individual organisms that can be diagnosed, or defined on the basis of certain specialized features, and that had a common ancestor and unique evolutionary history."

I like that, I think I'll use it in class as another way to attempt to define a species

Brent Ashcraft

[jkfoam]

I have always heard that a Grizzly Bear a Brown Bear and a Kodiak Bear were all the same species and that diet accounted for the variation in size. Now a Polar Bear and a Grizzly Bear being the same specie is something I will read up about. Interesting.

With regard to speciation it appears that there are no set rules for the differentiation between similar fossil forms. It is up to the investigator and peer review or published argument by other investigators. I think I will continue to keep my faith in T.A. Conrad and Calvin and Hobbes.( No one has argued with Conrad about B. sagenum since 1865.)

JKFoam

[Nicholas]

This reminds me of a chapter I did in a class about the scientific cultural battle between the splitters and lumpers. Speciation is still something which is very much a war zone when trying to nail down precise rules. Many scientists (at least represented in my classes) take on very different variations based on either splitting and lumping.

I can't wait to see the replies here, it may answer a question which has baffled me for some time.

[MikeR]

In life the rules of speciation are different than for fossils. In life animals of a species must be capable of breeding with each other. For example two dogs of vastly different appearance can breed thus establishing beyond question that they are the same specie. With fossils this rule is obviously not available. We only have morphological differences in appearance to establish speciation. My question is, are there rules on what morphological differences are required to differentiate fossil species. I have collected in several US Eocene fossil localities that have an abundant gastropod assemblege. Several of the snail species are very similar to each other yet they are described in the literature as individual species even though they are found in several different but close geologic strata. For example, Buccitriton texanum and Buccitriton sagenum are two very similar sanails. Yet in another example we have a snail in two ajoining formations with, in my opinion, different appearance that are the same specie. Pseudoliva vetusta carinata is a snail found in the Eocene Stone City Formation and the Eocene Cook Mountain Formation that are similar in appearance but have significantly different apical angles yet they are not specie differentiated. This is also true but to a lesser extent for Distorsio (Personella) septemdentata. So my question, what are the rules for fossil speciation.

Thanks in advance for any and all responses

JKFoam

Hi JK

I had this same type of discussion with a fellow fossil shell collector this week about lumpers and splitters and species variation. A good example of this is the Genus Ecphora. Ed Petuch has identified over 40 different species of Ecphora in the Virginia and Maryland Miocene whereas Lauck Ward recognizes only 9 species and subspecies together. If looked at separately each Ecphora is obviously different however Ward will argue that if you look at say one hundred collected from one locality and lay them side by side you will encompass an entire selection of all morphotypes grading into each other that indicate species variation. You see much of the same type of variation in Melongenidae with shoulder spines which help anchor the shell in high energy environments, but which Petuch also has split into a myriad species (i.e.fossil Busycon adversarius). I am told Cossman did the same type of splitting with French Eocene mollusks. I try to be as scientific as possible and like you I always include the reference (in my database). To a certain extent I can be wrong since this is my hobby and my reputation does not depend accuracy, but one day some institution might inherit my collection so I would like my data to be correct as possible. That is why I sometimes think that the location information is more important than the actual id.

[jkfoam]

MikeR,

You make some interesting points. I especially liked your discussion about the Melongenidae with sholder spines to help in a high energy environment led to specie differentiation by Petuch. I think that I under appreciate the adaptations some life forms develope in response to their environment.

Lumpers and splitters! I love this stuff.

And I agree with you about the locality information being the most important information on the fossil label.

JKFoam

[Frank Menser]

Species is a man-made group, there are many examples of groups of organisms that can interbreed and produce viable offspring, even though they are considered distinct speceis, an example would include coyotes and jackals. Even within the same species, some organisms can't necessarily interbreed, such as dogs. Think about chihuahuas and St. Bernard's. Physical impossibility without help from humans. We had a discussion once about the difference between polar bears and Kodiak grizzilies. Are they actually separate species, or color phases of the same species. A comment was made that you can take measurements from the skeleton and classify them into one or the other species, which is commonly done in living species. In the case of fossils, you don't normally have enough individuals to compile a normal parametric range to compare your fossils to, so in the case of the bears, I suspect they would end up in the same species.

Try breeding English bulldogs...

As far as naming new species, it comes down to publication. If you are convinced you have found a new species, and can convince the people who are reviewing the publication that your data/conclusions are correct,then viola, you have a new species. Later authors may add to this, or have the organism renamed into another species if they can convince their reviewers they are correct.

I suspect that the number of species is highly under-rated in the fossil record, and highly-over rated in extant species.

Brent Ashcraft

[ashcraft]

Part of the problem is that different species can be morphologically identical, but because of some other separatory reason, can't interbreed. There is a type of salamander whose name and location escapes me. This salamander gets into a large group for courtship/breeding called a rasenkris (sp?). Individuals on the periphery of two rasenkris will go to one or the other, and individuals from neighboring rasenkris can interbreed succesfully, but as the groups get further and further apart, eventually they can't interbreed anymore. I believe it has something to do with variations in their mateing dance. They are morphologically identical, but can't interbreed, are they a new species? There is also a rat in California whose home range was divided by and aquaduct/freeway. They can no longer interbreed either because of changes to the baculum in the males.

Try breeding English bulldogs...

No thanks, there not my type.

Comedian-at-large

Brent Ashcraft

[MikeR]

Like JK I also love this lumper and splitter stuff--probably because of my background in molecular biology i.e. DNA sequencing and genotyping.

I just today came across a recent reference published by the PRI describing all of the fossil cones from the SE Plio-Pleistocene. Again as a fossil shell collector who has collected from a number of shell pits in Florida, few references are available. One of the more recent is Petuch's Atlas of Florida Fossil Shells. Anyone who has used this can attest to it's poor dinstinction in photos between different species as well as its multitude of new species. The same shell collector that I mentioned in a previous post frustatratingly uses this reference without regard to the geology from where the shells are collected which compounds the inaccuracy. The mentality is "it does not matter where it comes from but what it looks like". The PRI pub states that 84 different species of Cones have been discribed from Plio-Pleistocene sediments from Virginia to Florida. Specifically from the abstract

"Forty of these taxa were described in the last 17 years and were published outside of the peer-reviewed literature,making their status as distinct species suspect, particularly because most are poorly illustrated, perfunctorily described, and based on few specimens." [A direct comment of Petuch's publications?]

By using a conservative morphological species concept (lumping?) that accepts large amounts of intraspecific morphological variation, they reduced the amount of species from 84 to 19 with one new species.

I do not know if speciation will ever be settled because without DNA or the ability to test interspecific breeding, speciation will always be in the eye of the beholder.

[Auspex]

The whole question of "what is a species?" is in flux, so the methods used to define them is only part of the muddle.

[FossilFreak]

speciation will always be in the eye of the beholder.

And the beholder typically has an incentive to claim a new species exist, especially if the beholder was the "first" to "discover" it.