[HillOBeans]

Does anyone else here ever wonder if some of these "new" dinosaurs are really just re-discoveries of known dinosaurs? The article even mentions that the skeletal remains are incomplete. What if a number of these sauropods are really all the same species, albeit at different stages of their life? Is size alone enough to create a new classification? Perhaps growth continued throughout the life of a sauropod, and the largest ones were just the oldest?

[mediocregopher]

I think you'll find this ted talk interesting, as it explores that exact idea:

http://www.ted.com/talks/jack_horner_shape_shifting_dinosaur...

It's also pretty entertaining to watch

[HillOBeans]

Yes. This. This is exactly the sort of thing I was thinking...

[mapt]

So the problem is - the very concept of a species is not particularly well defined, and loses a large degree of meaning in paleontology amidst lack of fossil-record data (both extreme scarcity and geographical patchiness) and the additional dimension of time.

A species is a particular genetic type which does not routinely interbreed with other related types it encounters, and retains some physiological differences from them, as a forked, internally consistent genetic branch.

We're a hundred million years late to demonstrate that the sauropods were or weren't interbreeding. We don't have that behavior to observe. We don't have any DNA, a fairly accurate way of demonstrating breeding pools, to work with. We only have the occasional left third rib, and equations derived from the most similar complete skeletons we know of. Even when we do find a complete skeleton, we can only date it to a certain degree of precision, and while understanding that there is an evolutionary tree that is constantly sprouting and changing branches, we have nothing to really demarcate when one species "becomes" another - we are speculating about two specimens' reproductive compatibility with millions of years between them.

Could you breed with a proto-human? Would you? How far back? Would the kids come out alright? Would you call them a new subspecies or pick one of the parents' taxonomy? On top of that, to represent the last several millions of years of subtle changes, new branches, & trimmed branches in hominid genetics, what if you only have 6 specimens closer than chimpanzees, mostly age/sex-indeterminate, only one of which is a complete skeleton? How do you draw an org chart of the hominids then?

There are size variations corresponding to age and gender, heritable variations within a breeding pool, variations corresponding to differential nutrition & the good times vs the bad times for a population, variations corresponding to individual sickness and injury, variations corresponding to the entire population getting steadily larger or smaller for a thousand or thirty thousand or a million years, variations corresponding to sudden changes in habit associated with adaptations to rapid changes in environment, variations corresponding to drift from a parent population associated with permanent reproductive incompatibility as well as reversible reproductive isolation.

The historical paleontological record is thousands of times richer in micro-scale detail than we have the data to describe, even if we did have good words to describe it with that the popular media could understand. But they want to talk in terms of species, because that's what people are familiar with.

[privong]

I don't think species are classified solely on size. I'm pretty sure juvenile specimens have been discovered and identified as being the same species as the adult specimens. Yes, mistakes have been made, but my impression is that the bone shapes play a substantial and important role, perhaps moreso than just the size.

[theoh]

The idea that you can determine the size of an animal from a single bone comes from Cuvier and was an early development in paleontology. I don't know how much progress there has been on the task of putting it on a firm scientific footing. http://en.wikipedia.org/wiki/Georges_Cuvier#Principle_of_the...

[Retric]

Lower leg bones are likely to directly relate to body weight where say teeth on the other extreme have little to so with it. Overall, it's note quite BS because it can be somewhat true.

Ex: Sabertooth cat and http://en.wikipedia.org/wiki/Narwhal

[dm2]

Sure it's possible.

The scientists that study this kind of thing try to check for similarities and classify them as the same or different when appropriate.

They probably classify them as different if the time they lived (based on the surrounding rock they were found in) or their bone structures is sufficiently different from anything previously discovered.

It's also a lot easier to merge two classifications rather than split a group into two.

http://en.wikipedia.org/wiki/Titanosauriformes

http://en.wikipedia.org/wiki/Sauropoda