http://www.ted.com/talks/jack_horner_shape_shifting_dinosaur...
It's also pretty entertaining to watch
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.
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.
And how was such massive size selected for? Is it just a matter of warmer climate and a feedback loop with larger and larger predators?
Air sacs not only allowed more efficient breathing but were also within skeletal structure, allowing for light weight strength. They also laid lots of small eggs so less reproductive investment per chick. Small heads on long necks with a sturdy body allowed long range eating without moving. With small heads and no chewing the disadvantages of long necks are well handled. For much more depth I encourage reading:
http://phenomena.nationalgeographic.com/2013/02/25/dinosaur-...
<speculative As a non-expert my own guess would be some kind of food-weight advantage feedback cycle. The larger ones were not just more protected from predation but with longer reach came wider access to edible plant material. However, the larger sauropod size, coupled with no chewing and low grade of food (and probably not stones users) required larger and larger (fermenting?) stomachs to get enough energy to support their size. (not directly related but, reasoning from whales they might have even been cancer resistant. And if you consider that their size strongly suggests a 'cold blooded' like metabolism, then given their size, sauropods could well have lived a couple hundred years) />
Scant evidence that a human was once very large certainly isn't evidence that "humans were bigger", and that in turn wouldn't be much evidence that a difference in the environment was causing it.
According to the Wikipedia page about Dinosaur size[1], the biggest (and longest) dinosaur is Amphicoelias fragillimus (at 122 tons), not Argentinosaurus. So, won't this new dinosaur be the second heaviest?
[1] http://en.wikipedia.org/wiki/Dinosaur_size#Heaviest_dinosaur...
Though I'm anything but expert on the topic, my understanding is that many dinosaurs were surprisingly light-weight for their size, and masses of many dinosaurs have been revised downward. As ancestors of birds, whose own bodies are generally of very low mass, and incorporate interesting features (hollow bones and internal air sacs) this isn't entirely surprising.
I hope we can develop things like clear underground imaging from aircraft, and start finding more and more of these incredible types of discoveries.
No sense of humor around here, looks like. The fact is, if we could revive dinosaurs, they would become game meat. What other purpose would they serve? To strip a forest in a day? To hunt and kill all the mammals?
As for the fundamental question of whether we should revive ancient species, the answer is "Of course!" To clone an animal using fully sequenced DNA would be an amazing achievement, and the programmed behavior in the DNA would be fascinating to study.
Of course, it's much more likely and scientifically feasible that we could clone more recent species such as Neanderthals which according to at least one scientist might be achievable today, or in the very near future. But dinosaurs are what capture people's imagination, and the bigger, the better.
