How many dinosaurs were there? | PLOS Paleo Community
There are more than 10,000 species of bird living on Earth today. If you recognise that birds are living dinosaurs, which overwhelming evidence indicates that they are, then this makes them more diverse than their living mammalian counterparts. So if you take the number of species to mean anything, this means we’re still in the reign of the dinosaurs! These days they’re just mostly a bit smaller and fluffier than their Mesozoic ancestors. But one massive question still remains for Palaeontologists and Neontologists: Why are there so many bird species around today, when we have relatively so few dinosaurs in the fossil record? This disparity is even more extreme when you consider that while non-avian dinosaurs were around for about 170 million years, there were only ever about 800 or so species of dinosaur, based on current records. The actual number fluctuates through time, as new species are discovered, and others are shown to be invalid through research broadly known as ‘taxonomy’.
Source: How many dinosaurs were there? | PLOS Paleo Community
Modern species are defined on mating ability (I believe, maybe I am out of date). Fossils are defined on morphology. What chance this introduces a systematic error between the two calculation methods
This is a great point! The mating ability theory is known as the biological species concept. It’s a bit difficult to measure in fossil species for obvious reasons – you can’t measure reproductive isolation in the fossil record. In the fossil record there is a quite subjective method applied called the morphospecies concept. How the two relate is still open for research!
Further complicating issue is that except for mass mortalities, even if you have two very similar specimens of a (morpho-)species, they’re almost certainly separated in time by many generations. So the question of interbreeding ability is really quite fraught. The complication of (possible) sexual dimorphism in the adults, and correctly assigning juvenile skeletons to adult (morpho-)species is just another issue.
My guess would be that we’re missing a lot of variability in species because we don’t have (much) of the feathers and other surface features, which were probably important for mating cues. But it’s still a guess.
(Problems logging in – 3rd attempt to post now!)
Brusatte of Edinburgh suggests an ocean of salt be taken with the detail of this work. The ideas are an approach to reducing the problems described, but the basic problem is that the fossil record is not very good, and significantly biased.