Third of Dino Species Never Existed

[crypto1]

A Third of Dinosaur Species Never Existed?
Brian Handwerk

Many dinosaurs may be facing a new kind of extinction—a controversial theory suggests as many as a third of all known dinosaur species never existed in the first place.

That's because young dinosaurs didn't look like Mini-Me versions of their parents, according to new analyses by paleontologists Mark Goodwin, University of California, Berkeley, and Jack Horner, of Montana State University.

Instead, like birds and some other living animals, the juveniles went through dramatic physical changes during adulthood.

This means many fossils of young dinosaurs, including T. rex relatives, have been misidentified as unique species, the researchers argue.

How T. Rex Became a Terror

The lean and graceful Nanotyrannus is one strong example. Thought to be a smaller relative of T. rex, the supposed species is now considered by many experts to be based on a misidentified fossil of a juvenile T. rex.

The purported Nanotyrannus fossils have the look of a teenage T. rex, Horner said in the new documentary. That's because T. rex's skull changed dramatically as it grew, he said.

The skull morphed from an elongated shape to the more familiar, short snout and jaw, which could take in large quantities of food.

But the smoking gun, Horner said, was the discovery of a dinosaur between the size of an adult T. rex and Nanotyrannus.

Nanotyrannus—actually a young T. rex in Horner's view—had 17 lower-jaw teeth, and an adult T. rex had 12.

The midsize dinosaur had 14 lower-jaw teeth—suggesting that it was also a young T. rex, and that tyrannosaurs gradually traded their smaller, blade-like teeth for fewer bone-crushing grinders in adulthood.

Triceratops Transformation

The paleontologists also amassed a large collection of Triceratops fossils, which had died in various stages of life, from eastern Montana's Hell Creek formation from the late Cretaceous epoch (145.5 to 65.5 million years ago).

The dinosaur skulls, which ranged from dinner plate-size to human-size, came from a range of animals.

When the paleontologists studied the skulls, they found that the youngest animals' tiny, straight horns changed as they got older: Juveniles' horns actually curved backward, whereas adult horns pointed forward.

The animal's distinctive neck frill also changed—the triangular spiked bones surrounding the frill in juveniles became flattened and lengthened into a bony fan-like shield.

"In this ten-year project we were able to collect a very good growth series that no one had ever seen before, and see this transformation that occurs," Goodwin said.

"We could document the extreme changes that occur with growth, [like] the direction that the horns are pointing."

Birds of a Feather

Clues to why dinosaurs underwent such dramatic physical changes may be found in their closest living relatives—birds experts say.

Hornbills, for example, don't sport their distinctive helmet-like head casque (see hornbill picture - at top) until they are about three-quarters grown.

Like deer antlers, the casque helps other animals discern between mature adults and juveniles.

In the same way, dinosaurs' changing appearances might have also promoted visual communication.

For example head knobs or horns, likely paired with color variations, may have created unmistakable visual displays that made sure members of a species recognized one another.

They may also have identified dinosaurs as male or female and marked them as mate-seeking breeders or juveniles in need of protection.

Exaggerated Conclusion?

Hans-Dieter Sues, a paleontologist at the National Museum of Natural History in Washington, D.C, said that scientists discovered in the 1970s that some duck-billed dinosaur species were in fact animals in different stages of maturity—representing a smaller number of species.

Sues, who was not involved in the new research, agrees that some dinosaur species from the late Cretaceous may prove to be juveniles of other species.

"Many dinosaurs—just like many present-day vertebrates—changed a lot in their appearance as they grew up," he said.

But "some of [these] conclusions are controversial," Sues cautioned, adding that the idea that up to a third of all species may be reclassified is an exaggeration.

In fact, Sues suspects that a second wave of dinosaur extinction is unlikely—unless, that is, fossil hunters hit the jackpot.

"Testing such hypotheses is difficult," he said, because "it requires more fossil material than is currently available."

for National Geographic News
October 9, 2009

news.nationalgeographic.com/news/2009/10/091009-dinosaur-species-never-existed.html

[Griffin]

Weren't Nano's and Rex's teeth designs totally different? Unless the animal lost its teeth and regrew them.

[sid]

Well, it's make sense to some degree... Look for example at all the species identified by a single bone and nothing else


And regarding Nano-T, i always assumed it was a juvenile Rex.

[Griffin]

I really don't know if its a safe idea to cut dinosaur diversity down by a third. There are so many different species of animals alive today that if you had only ever seen the skeletons of them, would assume they were the same. Look at the skeletons of a blue and gold macaw and a scarlet macaw. They are totally different species living in the same general area of the world, yet if one were left with nothing but their bones, they would appear identical. Dinosaurs occupied almost every niche on land during the mesezoic. There had to be many many different species.

[sid]

Oct 12, 2009 17:36:43 GMT Griffin said:

I really don't know if its a safe idea to cut dinosaur diversity down by a third. There are so many different species of animals alive today that if you had only ever seen the skeletons of them, would assume they were the same. Look at the skeletons of a blue and gold macaw and a scarlet macaw. They are totally different species living in the same general area of the world, yet if one were left with nothing but their bones, they would appear identical. Dinosaurs occupied almost every niche on land during the mesezoic. There had to be many many different species.

Mmh... You've got a point. Maybe we are both right!

[Horridus]

Nanontyrannus looks awfully like Jane, but then Bakker and others have always claimed that the bones are fused together, making it an adult. I think a truly conclusive study is in the works.

Otherwise I am inclined to agree with Griffin. Seems like a good argument.

[crypto1]

It could spell the end of all those collectors of tiny dinosaur replicas. They'd have to relabel everything, young of "this" or "that" species. :-)

It is logical that if there were a great diversity of large adults that some of their juveniles would be misidentified as distinctive species by certain individuals wishing to name something after themselves or a benefactor or an old lover.

[Megaraptor]

Nanotyrannus is the only one at the moment that is almost certain is a juvenile of another species.

[kuni]

What about Deltadromeous/Bahariasaurus?

[[][][]cordylus[][][]]

^ That's the same thing though, isn't it? Isn't just that the name issue hasn't been sorted out?

[Megaraptor]

But deltadromeus and Bahariasaurus were from wo different families, say some paleontologists(A.K.A. those scientists who need to shut their traps for a bit).

[crazycrowman]

"Look at the skeletons of a blue and gold macaw and a scarlet macaw. They are totally different species living in the same general area of the world, yet if one were left with nothing but their bones, they would appear identical"

Though griff, I agree for the most part with what you are saying, those 2 birds are actually different on a skeletal level, and can be distinguished as such just on the basis of bones - Thats part of what defines them as a distinct species from one another, and not "morph", or "locality based color form" or "subspecies" of one another - as are Greenwings, Millitarys, Buffons, Blue Throats, and so on. I am sure dinosaurs varried from one another just like modern animals do. Some species have a great deal of varation due to normal variants as well - Iguanas are a good example of this - the Common Green Iguana in one part of its range produces a male covered in long ornate spikes, with an enormous dewlap, that is splashed with blues, orange and sometimes even red during its reproductive season, while in another, it produces a larger, bulkier male with less elaborate spikes, a fairly small dewlap, that is a gray green in color with a rosy tint to the head and jowls - and these are both (*currently*) considered the same species.

All of this made me think of things like the Western Flicker and the Eastern Flicker - those birds would be nearly identical on a skeletal basis, and where the 2 come together, they produce an intergrade - a bird known as the Gilded Flicker. Now, in part because of that, taxonomists are lumping the 2, and the intergrade bird into a species known as the "Northern Flicker", so, we "lost" them as 2 defined species - The same goes for North American Ratsnakes - they used to be defined as species, then subspecies, and now they are being lumped into "regional morphs" of a superspecies - Pantherophis alleghaniensis - The Eastern Ratsnake. Even though the Black Ratsnakes from Maine look like very different animals, with different behaviors, and somewhat different body shapes then the Everglades Ratsnakes from Florida.

The taxonomy of modern animals isn't that "firm" either, and things are always flip-flopping around with the more we learn (sometimes frustratingly so!)

I did watch the "Decoding dinosaurs" program on NG last night, about this (Along with the Ardi special that was on Discovery) and both were Interesting programs. I was so ready to scream foul at Horner/Goodwin on the Pachycephalosaurus = Mature Adult, Stygimoloch = Subadult, Dracorex = Juvenile - grouping, but you have to admit, when they show those skulls side by side, and you really look at the location of the horns on all 3 "species", along with the general morphology, it'd be pretty strange if they were indeed different defined species, and not at least subspecies or something of one another.

[crypto1]

Crazycrowman wrote: "I was so ready to scream foul at Horner/Goodwin on the Pachycephalosaurus = Mature Adult, Stygimoloch = Subadult, Dracorex = Juvenile - grouping, but you have to admit, when they show those skulls side by side, and you really look at the location of the horns on all 3 'species', along with the general morphology, it'd be pretty strange if they were indeed different defined species, and not at least subspecies or something of one another."

Exactly.

Thanks for sharing that insight.

[kevin]

Jane is a nanotyrannus/juvie rex. She is displayed at Burpe, in Rockford Il, which happens to be my home town. The debate over what exactly she is continues. Apparently, aside from the teeth, there are small but definitive skull structure differences. It seems odd that all these changes happened, but ya. The trikes are just wierd growth wise. That study on the horn growth has been around a while, and the horns go straight, then peel back, then staighten and go forward again. Just wierd, but I expect no less from these animals these days. There could also be major male/female differences we are not aware of for many of the rarer animals. The only way to nail it down is to have mass graves. Often we are lucky to get bits of a single specimen, so I would think our ideas on their appearance would have to remain fairly open and flexible.

Also, although the tranformation from Jane to Sue seems radical, the growth rate of tyrannosaurs is said to be quite rapid, and these changes were occurring at phenomenal rates. So, if you get three specimens, young, juvie and adult, they are in transition, and would look like three different animals. Especially as Jane has fused bones, and appears as an adult. If we can't rely on that to age the animal, well then all is up in the air.Just think, from a very bird like hatchling to an adult tyrannosaur in only a few years. THe changes would have to be visible almost daily. Quite astonishing I think.

[fleshanthos]

I saw daily visible changes in ducklings that were bought for my uncle as an easter joke present. It was unbelievable how much they changed every 24 hours alone!

While my Cockatiel hardly changed much (aside from getting somewhat larger) from 7-week hatchling onward.

[Griffin]

Oct 18, 2009 18:41:20 GMT fleshanthos said:

I saw daily visible changes in ducklings that were bought for my uncle as an easter joke present. It was unbelievable how much they changed every 24 hours alone!

While my Cockatiel hardly changed much (aside from getting somewhat larger) from 7-week hatchling onward.

I know exactly what you mean. Here at Rutgers we are working with broiler chicks and every time I go in there to take care of them they look more and more like adult chickens.

[stoneage]

Oct 18, 2009 18:43:43 GMT Griffin said:

Oct 18, 2009 18:41:20 GMT fleshanthos said:

I saw daily visible changes in ducklings that were bought for my uncle as an easter joke present. It was unbelievable how much they changed every 24 hours alone!

While my Cockatiel hardly changed much (aside from getting somewhat larger) from 7-week hatchling onward.

I know exactly what you mean. Here at Rutgers we are working with broiler chicks and every time I go in there to take care of them they look more and more like adult chickens.

So your doing research to support Horners theory?

[kuni]

I don't think this is a big deal, though it certainly has some emotional impact, and I gather Horner enjoys tweaking the public consciousness re: paleontology.

The phenotypic diversity of dinosaurs isn't going anywhere. That's totally real. It's just that it's not always divided up into neat little "species" boxes.

[Griffin]

Oct 19, 2009 23:20:37 GMT stoneage said:

Oct 18, 2009 18:43:43 GMT Griffin said:

I know exactly what you mean. Here at Rutgers we are working with broiler chicks and every time I go in there to take care of them they look more and more like adult chickens.

So your doing research to support Horners theory?

I know you are kidding but just so other people don't think I'm supporting horner's theory, especially after the paragraphs I wrote earlier on this thread.......No I am not. More like research about rapidness of growth from different kinds of feed. Even so, baby chicks look different mostly because of the change in feathers and other soft tissue bits, something we couldn't see from dino bones.

[brontozaurus]

While there are most certainly dinosaur species that are really the misidentified younger forms of others, I don't think it's safe to say that a third of known dinosaur species didn't exist.

I take issue with the Dracorex/Stygimoloch/Pachycephalosaurus theory. Why would a creature have smaller spikes as it grew older? Wouldn't it grow larger ones?