Careful. Most people don’t know that the Amazon was dotted with populous, agricultural communities in pre-Columbian times, but “The Brazilian Rainforest” encompasses a lot of area that isn’t part of that same Amazonian ecosystem.
Yeah, we’ve covered this before. Those infectious diseases spread faster than the Conquistadors and other European explorers, so by the time the Europeans entered all of the Americas, it looked very sparsely settled. But some estimates put the deaths of Native populations at 90%. And, as most of us are aware, there are still some “uncontacted” people in the Amazon basin.
The problem with writing this in the context of this thread is that there’s not nearly as much certainty about this hypothesis as would be implied by its use in this context.
Yes. Aquilops is a genus containing one know species: A. americanus. The typical lifespan of a species is not generally more than 10 million years; thus, one can say that it is literally impossible for there to be any surviving members of A. americanus; no species sticks around for 100 million years.
No population remains static for an extended time (in geological terms). By necessity, even if Aquilops lineage continued, its descendants would differ enough from A. americanus that they would be placed in a different species; very likely, in a different genus, as well, since the population would have had to adapt to numerous environmental changes over the course of 100 million years +.
So, I can confidently claim that, even if a small population of ceratopsian dinosaurs were found to be extant, they would absolutely not belong to Aquilops.
I’m not trying to be difficult, here; this is not my field. I have questions.
When we talk about crocodiles being unchanged for 100 million years or more, I’m not sure I understand how that squares with your declaration that after 10 million, no dice. I asked about the genus, not the species[sup]*[/sup], so I’m not sure when we switched to A. americanus as opposed to more generically some heretofore unknown species of Aquilops.
But I’m sure it’s because I’m missing some distinction that’s obvious. Help me?
A distinction I remember from high school. King Phillip Couldn’t Order Fresh Ground Steak.
We don’t know that crocodiles haven’t changed in 100 millions years. We see superficial characteristics that are similar for much longer time periods but we assume they’ve changed a great deal in that time. If Aquilops survived the extinction event we would expect them to be different by now (or if they finally died out after a million or so years).
We talk about the phenotype of crocs showing little change over a long period of time. We don’t have any croc DNA from 100M years ago, so we wouldn’t know definitively, but we do know that genotypes change over time, so we expect that to have happened regardless of the phenotype.
Plus, it’s very dodgy talking about extinct species since we define species as populations that generally do not interbreed even when they occupy the same territory. When populations are separated temporally, we use our best estimate to determine if they were separate species or not, and by that we usually have to rely on morphological analysis instead of DNA analysis. But as DF already said, we don’t expect a species to remain the same species for 100M years.
The reason a species would have to change over the millions of years is because the original version wasn’t adapted to the changing environment, and needed to change to survive. But if there was some exception to this - if there was some rare instance of a species which could survive in a unusually broad variety of environments - then it could survive without changes for far longer than the 10 million.
The entire question in the OP was whether there might be some such rare exception. You can’t answer that question by pointing to the general rules that are based on the vast majority of species.
The OP accepted the obvious premise that there are very few if any species of dinosaur in the world. The question was whether we can definitively say that there are zero. I don’t see what you’re bringing to bear on that question other than to say, effectively, that “there can’t be an exception because the vast majority are otherwise”, which makes no logical sense.
It’s because people are looking at different taxonomic levels. “Crocodiles” is a broad group, encompassing many genera and species, over a very long period of time. The basic crocodile shape has not been altered much by evolution - the environmental demands of a fresh-water ambush-predator reptile remain largely the same today as they were 100 million years ago. But, the small morphological changes build up over time, such that existing species of crocodile are not the same as extinct species. The overall body plan remains the same, but the details do not. In terms of Linnaean taxonomy, “crocodiles” represents an entire Order, composed of different Families, Genera and species.
As for the switch from genus to species, many dinosaur names are coined with both a new genus and species (oftentimes, a re-evaluation will place several previously-distinct genera and species into one genus). What we know as “Aquilops” is one single species, Aquilops americanus. That species would have lasted no longer than 10 million years; probably fewer. Aquilops as a genus might have persisted for a while longer, but after 100 million years and at least one catastrophic extinction event, any survivors would have faced a different enough world, with its concomitant changes in adaptive pressures, that they would be unlikely to be classified as the same genus, though they would still be ceratopsian descendants of Aquilops.
Even the “newly discovered to be extant” coelocanths were placed in a genus distinct from the fossil versions, after all.
Correct me if I’m wrong about this, but for animals, there is an official body of scientist that determine species designation for populations, but all the higher levels of classification are not supervised in the same way, so we have to rely on consensus to determine which is which.
And my understanding is for extant species. Is that also true for extinct populations?
OK, thanks - this raises more questions, though, and I hope I’m not taxing your patience.
Obviously there is seldom a bright dividing line, such that we could point to a female croc and say, “She’s species 1,” and her eggs will hatch into species 2 members.
But at some point we theoretically reach the divide such that if I had a TARDIS and a croc wrangler, and I brought back a croc from 30 million years ago, it would not interbreed with current specimens. Is that accurate?
Is the issue purely biological? I seem to remember reading about finches in a valley that were separated and became two species, unable to interbreed, but the issue was (I thought) social mating behavior more than biology. Or am I just conflating concepts?
But you are correct. Sometimes it’s behavior that prevents mating, and if that is the case, the populations will still be considered separate species. This will be true even if fertile offspring can be produced artificially. If it’s a physical barrier separating them, and they would interbreed if that barrier were removed, then they are considered to be subspecies.
Strictly speaking, it’s all scientific consensus. The ICZN (International Code for Zoological Nomenclature) dictates rules for naming various taxonomic levels, but has nothing to say about what gets included in those levels. But, for example, if I coin a new Family name, then that Family is considered valid so long as I meet all the assorted requirements (dissemination method, not already in use, correct format, etc.). I can include 1 or 1000 species in that Family (of course, since most modern taxonomists deal with clades, who gets included will be defined by the clade itself, but it’s usually fairly arbitrarily defined as to which node gets what Linnaean category).
