Are Dinosaurs Getting Scarce?

[zopteryx]

It seems to me that dinosaurs are getting scarcer these days. I don't mean as fossils, new dinos are being named several times a month; I mean as a part of their environment. I know dinosaur numbers fluctuated over the ages, but I remember a time when scientists talked about a world "ruled" dinosaurs and that they were a dominant feature of the landscape. Today it seems as if the opposite is believed by many; the possibility that dinosaurs were actually rather uncommon. They support this by saying that the main reason we find so many is because most were large (by animal standards) and so their bones had a better chance of being discovered.

In short, I'm not sure what to believe. I grew up imagining a world with dinos (and other giant reptiles for that matter)everywhere (not literally, but you get the idea ), but now I hear some saying otherwise. If dinos didn't fill the major terrestrial niches on Earth, what did? What's everyone else think about this.

[Seijun]

Well, something had to have dominated the landscape. We find plenty of fossils of small dinosaurs and other small creatures though... Maybe HUGE dinosaurs were not as common as ants (after all, the landscape can only support so much) but I have always had the impression that smaller dinosaurs and primitive mammals were the most common land creatures around.

[sbell]

Much as all of the other sciences have (in some cases, finally) made their way into the realm of palaeontology--population statistics, genetics, ecology, environmental sciences, behavioural sciences--it means that we have really only viewed dinosaurs as 'animals' in recent years. By this, I mean that for a long time it seemed that paleo was far more interested in digging up the bones and looking at the big scary monsters.

More recently, and using more recent techniques (and ways of thinking), dinosaurs are treated as simply one part of their environment. An obvious part, I'm sure, but not the only one.

As an example, in just one quarry (the Scotty T.rex quarry) and very nearby, were found remains of sharks, rays, bony fish, lizards, salamanders, crocodiles, champsosaurs, turtles, maybe some other small reptiles, mammal teeth, bird bits, and at least one or two other dinosaurs (smaller pieces, but identifiable to group). Maybe even some molluscs. I can't remember the particulars, but I've seen the list, it's pretty long. This is just in the quarry itself, of course--there are other sites of similar age that expand the ecological diversity, to say nothing of the plants found.

So in a way--dinosaurs maybe dominated by size, but as in today, it was likely the little creatures that actually played the largest role (speaking only of vertebrates--the inconsiderate inverts with no shells don't leave much trace).

As for major niches--there is no end in variation of them, but very few are filled by large-sized bodies. So it wouldn't be surprising that, in terms of diversity, the faunas would skew heavily towards smaller. That would be just like today; no matter where you are, no matter how many large animals are around, their numbers are overwhelmed by the diversity and populations of the little stuff. It's just that, as fossils or as living animals, they are just so much harder to find or notice. The rewards can be huge though. I remember another site, in a National Park, doing a survey. We found a large bone; I think it tuned out to be a Triceratops radius or something. While the team leader assessed it, I was basically looking around--and in that same spot, the site turned out to contain gars, turtles, mammals, crocs, champsosaurs and...stuff. But you had to look more closely for the small bits and pieces, which I think is what drives a lot more researchers today--the pictures of the past are becoming more complete, and being treated more like real ecosystems, with multiple levels of complexity.

To summarize--I think what you are seeing is an increased and improved awareness of ecosystems from the past, and a willingness to explore and understand those systems, as opposed to simple dinosaur discovery.

No, I have never really thought about this before ;D... says the guy who is trying to come up with an improved gallery plan to represent just this sort of thing...

[Horridus]

What sbell said. Dinosaurs 'ruled' in the sense that mammals 'rule' today - just as when you look at the African savannah it's the 'charismatic megafauna' that'll catch your eye - ie. mammals - they are vastly outnumbered by the little guys.

Certainly, the standard narrative that mammals expanded into niches left vacant following the extinction of nonavian dinosaurs seems very true. Hell, mammals even filled niches left vacant by other reptile groups (I'm thinking of the oceans), although dinosaurs have at least held on to aerial dominance. Go archosaurs! ;D

[sid]

Plus, fossilization is a VERY rare event, so, for a dinosaur skeleton that became a fossil there are probably hundreds of that same species that didn't.

[sbell]

Feb 21, 2011 16:39:28 GMT sid said:

Plus, fossilization is a VERY rare event, so, for a dinosaur skeleton that became a fossil there are probably hundreds of that same species that didn't.

And just imagine how many hundreds of little animals didn't get preserved--never mind the ones in areas that were not conducive to fossilization at all!

[zopteryx]

I like this new way of thinking, seeing the environment as a whole. Mainly because I find the "little" things just as interesting as the big ones.

I still have a question though, does this mean that places like Dinosaur Nat. Monument were just the "Yellowstones" of the Jurassic? Meaning something specific in that area drew dinosaurs in (food, water,...) while the surrounding areas were relatively dino poor. Or is this line of thinking just a result of man's influences on our modern world?

[Griffin]

Well just because we don't find dinosaur fossils in an area doesn't mean they weren't living there at one time in the past. Fossilization is still a rare thing. Its likely dinosaurs were pretty well spread out all over just like different kinds of land animals are today.

[sbell]

Feb 21, 2011 22:29:33 GMT zopteryx said:

I like this new way of thinking, seeing the environment as a whole. Mainly because I find the "little" things just as interesting as the big ones.

I still have a question though, does this mean that places like Dinosaur Nat. Monument were just the "Yellowstones" of the Jurassic? Meaning something specific in that area drew dinosaurs in (food, water,...) while the surrounding areas were relatively dino poor. Or is this line of thinking just a result of man's influences on our modern world?

I think Yellowstone stands out, but overall that would be the norm--concentrations of (large) animals are unusual enough to be remarkable for a reason, and it probably has to do with available food. It is only in unusual circumstances that enough food is present to have a lot of large animals together (think of Ngorongoro crater--anywhere else, that many large mammals could not exist). And it just so happens that wetter areas with good drainage have lots of plants and cover--so they support lots of herbivores, which in turn support lots of predators. Those also happen to be good environments for fossilization.

[dinoguy2]

Feb 21, 2011 22:29:33 GMT zopteryx said:

I like this new way of thinking, seeing the environment as a whole. Mainly because I find the "little" things just as interesting as the big ones.

I still have a question though, does this mean that places like Dinosaur Nat. Monument were just the "Yellowstones" of the Jurassic? Meaning something specific in that area drew dinosaurs in (food, water,...) while the surrounding areas were relatively dino poor. Or is this line of thinking just a result of man's influences on our modern world?

Dino Monument is a slice of the Morrison formation. So it's only a tiny part of a much larger whole preserved ecosystem. The Morrison spans from Colorado, to Utah, Wyoming, Montana, etc. So it's a pretty huge area you're dealing with. The range of say, Camarasaurus was probably similar to the range of modern North American megafauna like Buffalo (well, before humans wiped them all out). So while you would be unlikely to find a camarasaur in New York (or a buffalo for that matter, outside the zoo...), it doesn't mean they were isolated.

With that said, there is evidence that some dinosaur preferred certain environments (no big surprise). For example in the late Cretaceous, things like hadrosaurs, tyrannosaurs and nodosaurs are usually found by the coast, in lowland, wetland environments, while many ceratopsians, ankylosaurs, pachycephalosaurs etc. are more upland in the hilly portions of the terrain.

So individual species were likely isolated from each other to some degree or another, but they usually had 'equivalents' in all environments we find preserved. Another good example is mid-Cretaceous Mongolia. We're starting to learn that while "Velociraptor" and "Protoceratops" are present in most of those formations, each individual locality has a different species. So while you may find Velociraptor mongoliensis in the high-desert dune fields (Djadochta formation) with Protoceratops andrewsi and Oviraptor philoceratops, in the slightly lusher areas (Bayan Mandahu formation) just over the Chinese border has the same 'types' but different species: V. osmolskae, P. hellenikorhinus, and Linheraptor.

[Blade-of-the-Moon]

I would love to know what species occupied the areas that fossils wouldn't form in..like mountainous regions. Who knows what we're missing.

[zopteryx]

Feb 22, 2011 4:21:26 GMT Blade-of-the-Moon said:

I would love to know what species occupied the areas that fossils wouldn't form in..like mountainous regions. Who knows what we're missing.

I imagine some specialized raptors and small ornithopods. Mountainous peaks certainly would have been no place for large dinos, they were probably even avoided by most of them.

[dinoguy2]

Feb 25, 2011 2:01:58 GMT zopteryx said:

Feb 22, 2011 4:21:26 GMT Blade-of-the-Moon said:

I would love to know what species occupied the areas that fossils wouldn't form in..like mountainous regions. Who knows what we're missing.

I imagine some specialized raptors and small ornithopods. Mountainous peaks certainly would have been no place for large dinos, they were probably even avoided by most of them.

Interestingly, one of the most common, if not THE most common dinosaur in the Hell Creek and Lance formations is the dromaeosaur Richardoestesia. Despite this, it's only known from teeth. Nary a scrap of skeleton to be found.

I've always suspected, and this might have been floated in print at some point, that Richardoestesia was a mountain species and it's teeth were frequently washed to the lowlands by streams and floods, where they then fossilized. Any bones would have been eroded beyond recognition by this process.

Also interestingly, Micky Mortimer has found richardoestesia to be a microraptorine. The only other late-surviving microraptorine is Hesperonychus, also known mainly from numerous teeth and claws, with only one fragmentary skeleton. Could be the mountains of the Cretaceous were indeed dominated by small ornithischians plus microraptors.

[Libraraptor]

I´m with Horridus and sbell and think our look at dinosaurs simply has widened. While early paintings and reconstructions focussed on the bizarre animals themselves and their impression on man, we nowadays seem to be able to put them into a much wider context.
It´s a phenomenon not only in dinosaur palaeontology, but also in, hm, let´s say extraterrestrial biology. While early imaginations of aliens focussed on bizarre imaginations, nowadays we embed alien research into the broader context of real biology.
To transfer W.J.D. Mitchells thesis to this topic: It´s the change from dinosaurs / aliens as cultural icons and transitional objects to their reconstruction as beings that really existed / most probably do exist.