The Lumpers Or The Splitters

[Triceratops]

Hello!

What are your views on merging dinosaur species together? Do you think that Jack Horner is right and Stygimoloch, Dracorex and Pachycephalosaurus are one or do you think that they are different animals? Like wise do you think Nanotyrannus is just a baby T. rex?

I would love to hear your thoughts about this big debate

[Auspex]

I think it is a process, and ultimately each case will be decided when there is enough physical evidence to constitute proof.

We've come a long way, and still have a long way to go.

[Arion]

I used to have strong opinions about this on both sides. As far as genera go, it has been argued that the concept of a "genus" is somewhat arbitrary (I suppose some feel there's a bit of phylogenetic utility to it, but I know many don't agree), so my own personal views have resulted in splitting and clumping genera somewhat arbitrarily (and changing my mind quite a bit over the years). Pachycephalosaurid taxonomy has been all over the place over the last 15 years, reflective of our increasing (but still incomplete) understanding of these dinosaurs. One of the things that's become apparent is that many of the distinctive ornamental characters of pachycephalosaurs developed ontogenetically, and hence juveniles of different species looked more alike than the adults did. (As an example of this, see Goyocephale and Homalocephale, both known only from immature material). A similar observation could be made about some ceratopsians too (see Triceratops/Torosaurus).

Greg Paul has taken some unconventional stances on dinosaur taxonomy as far as splitting-clumping goes (see The Princeton Field Guide to Dinosaurs for a plethora of examples); I can't say I find his approach justifiable, especially since I'm not aware of any rationale for the majority of his clumpings. Personally, I feel that determining the validity of a species has as much to do with stratigraphy and paleoecology as it does the morphology of the species. In other words, i) is there concrete evidence of stratigraphic partitioning indicating that two morphotypes did not overlap temporally? and ii) could the environment support two species with similar ecological roles?

I tend to prefer clumping at the generic level personally, but that's only my inconsistent opinion. Without stratigraphic or ecological context any discussion about whether two species are the same is moot. (For example, the Dashanpu dinosaur fauna includes quite a number of sauropods that to my knowledge were not separated temporally. However, they all possess unique skull and jaw structures and evidently fed on different things, so their coexistence was ecologically viable).

As Auspex said, it's a process, and the big key to making it easier is to not name every thing that isn't an exact carbon copy of something else. That has more often than not created a whole lot of clutter (and unavailable names) when more specimens become available.

That's myy five cents

- Arion

[ashcraft]

I consider the triceratop group to be ecologically equivalent to deer in North America (still evolving), and the antelope in Africa (mature group of different species filling many niches). The skeletons of these groups are very similar, save the male head ornamentation.

Brent Ashcraft

[megabass22]

I prefer whatever our current evidence points towards. I don't think that Triceratops and Torosaurus should be in the same genus/species, as their differences are too many in my opinion.

Sadly we can't classify dinosaurs in the same way as we classify modern animals (through genetics), but we have to base it on how "different" they look from each other.

Example:

http://upload.wikimedia.org/wikipedia/commons/9/9d/Lambeosaurus_lambei_BW.jpg

[tmaier]

When there is such a small sample size, lumping and splitting loose their context. That's the nice thing about invertebrates, you normally find the whole critter and a lot of them, allowing a better study of what needs to be lumped and what should be split.

Yes, I believe vertebrates are pretty flawed creatures to begin with, and are doomed for failure. Why is the armour on the inside and the gooshy parts on the outside? Obviously a design flaw.

[Brewcuse]

A really interesting discussion of taxonomies can be found in David Weinberger's Everything Is Miscellaneous. He details taxonomic concepts from Linneaus to Mendeleev's Periodic Table to Dewey's Decimals, among others. He examines classification issues and how they've evolved over time (with the overriding theory that the networked Web is more powerful than any single, closed system).

It seems to me that classifying fossil species relies heavily on speculation, extrapolating from minute specimens, and is constantly revised with new evidence (and academic impetus to publish, no doubt)— which means that a continual lumping and splitting will obtain.

[Auspex]

The taxonomy of fossil organisms is fundamentally different from that in contemporary biology. The taxonomy of even living species is somewhat fluid. I am a birder, with an "ABA Area Life List", documenting every species I have seen in North America, north of Mexico. The last four species I was able to add to my list were:

Pacific Winter Wren

Mexican Whippoorwill

Bell's Sparrow

Ridgeway's Rail

I saw and documented these birds between 15 and 20 years ago, before they were officially split-out recently as discrete species.

One of the criteria now in vogue for splitting a species is a breeding range that is completely isolated (in space and/or timing). This sort of information is not directly preserved in the fossil record, especially with terrestrial vertebrates, so paleontologists are looking through a rather cloudy lens.

[Triceratops]

Thanks for all yor interesting replys!:-)

[Triceratops]

When there is such a small sample size, lumping and splitting loose their context. That's the nice thing about invertebrates, you normally find the whole critter and a lot of them, allowing a better study of what needs to be lumped and what should be split.

Yes, I believe vertebrates are pretty flawed creatures to begin with, and are doomed for failure. Why is the armour on the inside and the gooshy parts on the outside? Obvioously a design flaw.

Good point;-)

[RichW9090]

George Simpson once tried to explain what differentiates splitters from lumpers amongst the paleontologists.

Given two specimens, if they couldn't be told apart, splitters made them different species. If they could be told apart, splitters made them different genera.

[siteseer]

I realize you're talking about dinosaurs but fossil sharks and rays present a very similar situation. The vast majority of known extinct shark species, like some dinosaur taxa, are based solely on isolated teeth. That's great if every tooth referred to a given species shows some character particular to that species. That is not always the case. Think about some of the small theropod teeth from the Cenomanian of Morocco. Collectors want a definite name for them but they may represent more than one taxon. Scientists have learned from past experience that teeth alone are not a strong basis for a name (consider Revueltosaurus or Azendohsaurus - both named as early dinosaurs but the latest evidence places them in other groups). They are willing to wait for some association of these teeth in jaw sections with at least a partial skeleton composed of a number of bones complete enough to compare to apparent relatives.

Consider this cautionary tale from the realm of rays:

Within an article reviewing Eocene shark and ray teeth from Antarctica (Welton and Zinmeister, 1980) the authors discuss a sample of over 300 modern dentitions of the California bat ray (Myliobatis californicus which was acquired as the result of a fishing competition. While all the dentitions certainly belonged to the same species (identified by its external soft anatomy), an unexpectedly wide range of variation in several characters of the tooth plates was observed - wide enough that had the individual teeth been found as isolated fossils, they would have been referred by at least some researchers to more than one species with perhaps a new one proposed as well.

To get back to your questions, I'm leaning toward Horner being right because the establishment of those three genera does not seem to leave any room for growth stages or other variation. I think it is reasonable to assume that the animal did develop in its early years in an outward way (and not identically across the population) beyond the size increase. In the same way I think Nanotyrannus is a young Tyrannosaurus. In the past 15-20 years, the Hell Creek Formation has become a vacation destination for fossil hunters. In the frenzy for T. rex material more of what would be the rarest forms in its ecosystem are being found more often. As time goes by and no T. rex juveniles are found but more Nanotyrannus specimens come to light, I think it becomes more likely that Nanotyrannus is a juvenile form.

Hello!

What are your views on merging dinosaur species together? Do you think that Jack Horner is right and Stygimoloch, Dracorex and Pachycephalosaurus are one or do you think that they are different animals? Like wise do you think Nanotyrannus is just a baby T. rex?

I would love to hear your thoughts about this big debate

Edited September 21, 2014 by siteseer

[Carcharodontosaurus]

I believe that Nanotyrannus is a juvenile T. rex. It definitely has a lot of juvenile features, and it is weird that no juvenile rexes have been found if the former genus is valid. I'm not so sure about Torosaurus/Triceratops, though.

I can see an interesting future scenario about this type of problem. Millions of years after we leave the Earth or die out, alien scientists visiting Earth, or a future sapient species, might discover the remains of different dog breeds like chihuahuas, bulldogs, great danes, pitbulls and German shephards, then classify them as different species or genera due to many differences between them.

[Arion]

George Simpson once tried to explain what differentiates splitters from lumpers amongst the paleontologists.

Given two specimens, if they couldn't be told apart, splitters made them different species. If they could be told apart, splitters made them different genera.

Haha that's good

I realize you're talking about dinosaurs but fossil sharks and rays present a very similar situation. The vast majority of known extinct shark species, like some dinosaur taxa, are based solely on isolated teeth. That's great if every tooth referred to a given species shows some character particular to that species. That is not always the case. Think about some of the small theropod teeth from the Cenomanian of Morocco. Collectors want a definite name for them but they may represent more than one taxon. Scientists have learned from past experience that teeth alone are not a strong basis for a name (consider Revueltosaurus or Azendohsaurus - both named as early dinosaurs but the latest evidence places them in other groups). They are willing to wait for some association of these teeth in jaw sections with at least a partial skeleton composed of a number of bones complete enough to compare to apparent relatives.

Consider this cautionary tale from the realm of rays:

Within an article reviewing Eocene shark and ray teeth from Antarctica (Welton and Zinmeister, 1980) the authors discuss a sample of over 300 modern dentitions of the California bat ray (Myliobatis californicus which was acquired as the result of a fishing competition. While all the dentitions certainly belonged to the same species (identified by its external soft anatomy), an unexpectedly wide range of variation in several characters of the tooth plates was observed - wide enough that had the individual teeth been found as isolated fossils, they would have been referred by at least some researchers to more than one species with perhaps a new one proposed as well.

To get back to your questions, I'm leaning toward Horner being right because the establishment of those three genera does not seem to leave any room for growth stages or other variation. I think it is reasonable to assume that the animal did develop in its early years in an outward way (and not identically across the population) beyond the size increase. In the same way I think Nanotyrannus is a young Tyrannosaurus. In the past 15-20 years, the Hell Creek Formation has become a vacation destination for fossil hunters. In the frenzy for T. rex material more of what would be the rarest forms in its ecosystem are being found more often. As time goes by and no T. rex juveniles are found but more Nanotyrannus specimens come to light, I think it becomes more likely that Nanotyrannus is a juvenile form.

Sounds like rays have the potential to be rather confusing. Going back to the Stygimoloch-Pachycephalosaurus issue, if recent restorations of Stygimoloch (in which the frontoparietal dome is rather small compared with the rest of the skull) are accurate, then I don't think there's any doubt that all three genera are the same. That would be interesting because it would demonstrate a different method of dome development in Pachycephalosaurus than in Stegoceras (i.e. the frontoparietal dome appears to expand outward from a central point, rather than the entire frontoparietal area inflating at an even rate).

[Axelorox]

This is a rather common question and always produces good discussion. Here's the answer I provided to a similar question asked on Quora:

"The question of whether certain dinosaur specimens are members of the same species (or genus) with some slight individual variation or are truly distinct species is a common one and can be difficult to answer in many cases due to relatively incomplete fossil remains to go off of. However, I tend to lean away from the side of the 'lumpers' (scientists who tend to lump multiple species/genera into one genus, such as in the whole Torosaurus/Triceratops debate). Here is an analogy that should put it into perspective:

Consider the lion (Panthera leo) and the tiger (P. tigris). If you were to look at one of each of these side by side, there would be no question that they are different animals. However, if you tried to spot the difference between their skulls (or even the whole skeleton), distinguishing them becomes a much harder exercise. Here are two unquestionably distinct species, with different appearances and social habits, yet on the skeletal level they are almost identical.

If a future paleontologist were to discover the fossils of these animals, it is very possible that they would consider them the same species, but as residents ofthe modern era we know this to be untrue. Unfortunately we do not have that advantage with non-avian dinosaurs, and never will (barring the invention of time travel)."

[ashcraft]

Species is a man-made definition, the organisms don't care. We perceive different species, but are they different genetically? Dogs/woves/coyotes are all considered different species, but are their genomes different? They have some alleles that are more or less common within their group, leading to different physical appearances, but alleles that are only found in one group are extremly rare to non-existant at that level of relatedness.

I am no fan of the biologic species concept.

Brent Ashcraft

[FossilDAWG]

George Simpson once tried to explain what differentiates splitters from lumpers amongst the paleontologists.

Given two specimens, if they couldn't be told apart, splitters made them different species...

Well, of course, because one was found on a Tuesday, and the other on a Friday.

Almost as bad: one was found in Kansas, the other in Colorado, so they must be different, even if you can't see it.

Don

[Auspex]

...Almost as bad: one was found in Kansas, the other in Colorado, so they must be different, even if you can't see it.

If one could deduce their habitats and ranges, and show that the populations were long isolated from one another, a case could be made by today's definition of "species". Cf: the erstwhile Solitary Vireo, long regarded as races and now split into three species based on isolation-induced evolution of behavioral and cosmetic differences.

It is nigh unto impossible to do this from fossil remains, though!

[FossilDAWG]

If one could deduce their habitats and ranges, and show that the populations were long isolated from one another, a case could be made by today's definition of "species". Cf: the erstwhile Solitary Vireo, long regarded as races and now split into three species based on isolation-induced evolution of behavioral and cosmetic differences.

It is nigh unto impossible to do this from fossil remains, though!

Unfortunately, in the case of fossils we are stuck with morphospecies. Even worse, morphology tends to change over time (punctuated equilibrium notwithstanding) so we are sometimes forced to draw arbitrary lines dividing ancestor/descendant species. Further, some body parts might change while others remained static, so distinguishing descendants from ancestors may well also require finding just the right bone. Fortunately in the case of mammals teeth seem to serve well in this regard.

Geographic isolation can be a tricky issue when it comes to describing species, in my opinion. For example, some freshwater fish, such as arctic char, were able to live in the large lakes that formed behind retreating glaciers at the end of the last glaciation. Eventually water levels receded, leaving behind a myriad of lakes, each with their own population of char. These populations have been largely isolated for ~12,000 years now, and in some cases minor differences in vertebral counts, number of lateral line scales, or gill rakers have developed. However all the populations are fully interfertile in the lab, no reproductive barriers have evolved. One ichthyologist I knew, an ancient fellow at the time, described hundreds of species of char, finding tiny differences from lake to lake. No-body else has accepted any of these species, and recognize only a single widespread and somewhat variable species. It turned out the ichthyologist was a creationist who firmly believed that those differences, however tiny, had always been present and reflected divine intent. The fellow believed in extinction but not evolution, and was insistent that humans were around in the Cambrian alongside trilobites, but in such a small population that they never happened to preserved as fossils (the same applied to all other vertebrates as well).

Behavior, though, can also serve a critical role in reproductive isolation and speciation. For example, flies in the genus Rhagoletes feed on hawthorn, a relative of apples and native to North America. When apples began to be cultivated in North America, apple-feeding specialists evolved from the hawthorn-feeding ancestors. It's clear that there are two distinct gene pools now, as there is essentially no interbreeding between the two populations as females "call" (produce pheromones to attract males) at different and non-overlapping times. Because there is virtually no measurable gene flow between the populations, they are recognized as distinct species. You would never see that in fossils, so you would not recognize the split until enough time had passed for morphological differences to accumulate.

Don

[Auspex]

Some of the Galapagos finches' bills have changed, measurably, in the short time since Darwin collected his specimens. This time span would be invisible in the fossil record, and is yet another example of the handicaps to developing an understanding of ancient speciation. The Paleobiological revolution brought new tools to the task, with a new way of 'seeing', but the view from the wayback machine is pretty murky. We just have to accept that the term "species" has a slightly different meaning when applied to long extinct organisms.

[FossilDAWG]

I can't recall the names off the top of my head, but there was a husband/wife team who lived on the Galapagos for years and tracked what was happening with the bird beaks, and related that to climate and seed availability. Climate and rainfall vary a lot, sometimes with years of well above- or below-average rainfall, and this affects the size of the seeds the birds are feeding on, and that influences bill size and shape. I recall some birds underwent changes that were comparable to the between-species differences. From a biological point of view things would change one way for a few years, then change back for several years, so over the long haul there was little net change. From a paleontological perspective, where we rarely can put specimens into a temporal sequence unless millenia are involved, we would probably see a number of distinct species.

Don

[tmaier]

I can't recall the names off the top of my head, but there was a husband/wife team who lived on the Galapagos for years and tracked what was happening with the bird beaks, and related that to climate and seed availability.

That was C. Darwin. The babe you saw him with was his mistress. Don't mention it to his wife.

http://en.wikipedia.org/wiki/Darwin%27s_finches

[LanceH]

The whole lump/split thing has made it difficult for me to study Texas ammonites.

Trying to match fossils to old photos and then trying to harmonize names with the old and new literature and changes is a nightmare. I have learned to curse the name Keith Young.

[siteseer]

Don,

You're thinking of the Grants. Jonathan Weiner wrote a great book, "The Beak of the Finch," about them:

http://www.amazon.com/dp/067973337X/?tag=googhydr-20&hvadid=40094670127&hvpos=1t2&hvexid=&hvnetw=s&hvrand=5953716377006634010&hvpone=11.73&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_1he1k6b0ht_b

Jess

I can't recall the names off the top of my head, but there was a husband/wife team who lived on the Galapagos for years and tracked what was happening with the bird beaks, and related that to climate and seed availability. Climate and rainfall vary a lot, sometimes with years of well above- or below-average rainfall, and this affects the size of the seeds the birds are feeding on, and that influences bill size and shape. I recall some birds underwent changes that were comparable to the between-species differences. From a biological point of view things would change one way for a few years, then change back for several years, so over the long haul there was little net change. From a paleontological perspective, where we rarely can put specimens into a temporal sequence unless millenia are involved, we would probably see a number of distinct species.

Don

[Boesse]

I went to Montana State for my undergrad and master's, and am good friends with John Scannella and took several classes from Jack - so on one hand you could say I'm biased, but on the other hand, I had the distinct fortune of seeing all of the specimens they deduced their hypothesis from, and with regards to Torosaurus synonymy, I think it's pretty watertight. There is a fair amount of individual and ontogenetic variation in Triceratops, and also a bit curious that the proponents of Torosaurus-as-a-separate-genus have relied upon smaller sample sizes and not made use of paleohistology - which John and Jack of course used as an independent source of age data aside from just overall size. Furthermore, the point that always drove home hardest for me was that no juveniles of Torosaurus have yet been identified (a single smallish Torosaurus specimen exists, but appears to exhibit adult bone texture on the skull - unfortunately, the specimen is not available for histological sampling, so using it as evidence of Torosaurus looking differently as a juvenile is a moot point anyway).

With regards to Pachy/Stygi/Draco, the evidence is absolutely strong. Read Mark Goodwin's paper in PLOS One about it. As for Nanotyrannus... again, the same argument holds: it's known from the Lance Fm., and is the same age as Tyrannosaurus, but somehow magically no juvenile T. rex specimens exist and all smallish tyrannosaurid specimens are considered Nanotyrannus by some, in the vacuum of genuine histologically-determined ontogenetic age. Jane, a T. rex at the Burpee Museum, has a Nanotyrannus skull but with the bone histology of a juvenile: again, histology takes care of the taxonomic mess and clearly indicates that the Nanotyrannus morph is just a juvenile. People have cited the higher tooth count, but one MOR specimen formerly known as "B-rex" (the one that produced Mary Schweitzer's soft tissue discoveries) is a subadult female and has an intermediate number of teeth between adult T. rex and Nanotyrannus - demolishing one of the only strong arguments in favor of Nanotyrannus "validity".

Otherwise, one point that Jack always hammers into his students is "We're scientists - we're in the hypothesis testing business - not in the verification business."