Dimetrodons don't count.

July 22, 2014 6:52 AM

How many kinds of dinosaurs were alive at the same time?

I understand that there are fewer than 1,000 distinct kinds or species of dinosaurs (maybe many fewer), but that dinosaurs lived on earth for about 150 million years. This would mean that even if a single species lived for 10 million years, there could be no more than 50 or so species alive at any one time. Yet I had assumed that dinosaurs were a bit like mammals in the sense that hundreds or thousands of distinct kinds lived all at once.

So if you went back to the time when dinosaurs lived, how many species would be alive on any given day?

(I'm not asking how many individuals could have been alive at one time, as that is a different ask altogether.)

posted by Thing to Science & Nature (4 answers total)

Your 1,000 number may only be the species we have definitively identified. I was just at Field Station Dinosaurs this weekend (granted, it's a kids park), and one source there referenced a million/millions of unidentified species we are still learning about - basically, people have found lots of dinosaur pieces that we still have no idea how to put together - and those are just the ones that we have found and that were able to be fossilized.
posted by Mchelly at 7:06 AM on July 22, 2014

This table (from this paper) shows estimates of the number of actual dinosaur genera (groups of species) existing in various periods of the Mesozoic. For comparison, there are today about 1300 living mammal genera (6000 species) and 2100 living bird genera (9700 species).
posted by gubo at 7:19 AM on July 22, 2014 [4 favorites]

I love this question, and have been curious about it myself.

Some perspective:

Total Number of Dinosaur Species* > Number of Dinosaur Species Extant at one Time > Number of Species with Members that were Fossilized After Death** > Number of Dinosaur Fossils which are Discoverable*** > Number of Dinosaur Fossils which Have Been Discovered > Number of Discovered Dinosaur Fossils which have been Described as Species

* Definition of "species" is debatable, even with extant creatures.
** It is entirely possible--perhaps probable--that some species of dinosaur simply never left any fossils, anywhere.
*** Some fossils are inaccessible due to geology, and the human reluctance to excavate the entire surface of the Earth.
posted by General Tonic at 7:40 AM on July 22, 2014 [2 favorites]

I imagine the dinosaurs filled the same sort of environmental niches as mammals and birds, from shrew/jay size to creatures a dozen times as large as an elephant or more, so I'd bet a good rule of thumb is to add the number of those presently existing (or known to have existed before the current mass extinction), and you'd be pretty close. We have no idea of the biodiversity that once existed. You have to remember that for every fossil discovered, there must be a million that fossilized and eroded before they were discovered, and that for every one of THOSE, there must have been ten million animals that died, decomposed, and decayed in circumstances that didn't permit fossilization.
posted by Captain l'escalier at 7:20 PM on July 22, 2014 [1 favorite]