I think it would be quite difficult to say with assurance that modern species X has survived for significant periods of geological time. It is a commonplace of evolution that species replace other species within a genus over a matter of a few million years at most. There may well be a few ancient species around, but it would be a difficult thing to prove conclusively from fossils.
At the next level up taxonomically, the genus, the issue is quite different. Though many modern genera date only from the Pleistocene, and most of the rest from the Pliocene, there are clear evidences of long-lived genera. The Sumatran rhinoceros, Dicerorhinus, is a good first example; there are fossil members of this genus from the Miocene, about 15 million years old. Ceratodus, now extinct, had a remarkably long run, from the Devonian until the Cretaceous (nearly 350 million years) – and the living Queensland lungfish Neoceratodus is a very close relative. But the record holder, not only among animals but among all multicellular life, is the inarticulate brachiopod Lingula, present in the Early Cambrian Burgess shale and still happily filter feeding on sea floors.
Perhaps ralph124c is puzzled about how these slow-growing plants managed to feed the rapidly-growing dinosaurs? One factor that may have helped is the relative abundance of carbon dioxide in the Mesozoic atmosphere. Plants in those days didn’t have to gasp for CO[SUB]2[/SUB] in order to photosynthesise.
Seems like biological sea lawyering to me. It’s splitting hairs to the nth degree to go on about how today’s coelacanths aren’t the same creatures that were around 400 million years ago. For all practical purposes, coelacanths haven’t materially changed in 400 million years.
It’s not lawyering, it’s just distinguishing between levels of taxa. At higher levels, yes, coelacanths haven’t changed much over the past 400 million years. But Latimeria describes a different group of animals than does Macropoma, and together they represent a different group of coelacanths than does Coelacanthus. Members of the genus Latimeria itself were not around 400 million years ago (or, if they were, we certainly haven’t found any fossils of them).
How exactly are you identifying these as truly different species without the ability to see if they could mate and produce offspring? I always thought we were much less sure about the speciation of organisms only found in the fossil record.
Also, what importance does this have? In other words, what would be different if an animal only known in the fossil record were really the same species as a living one?
Forgive me if these questions are so involved that they need another thread.
All species concepts have disadvantages (such is the nature of trying to delineate lineages which are, in actuality, continua), and the Biological Species Concept (the species concept that involves producing viable offspring as a criterion) doesn’t work for fossil species. Often, fossil species are determined according to the Morphological (or Typological) Species Concept, which, while having pitfalls of its own, is no more problematic than any other species concept. Among other possible sources of error, one must be careful to account for sample sizes when describing variations between fossils (it has happened in the past that males and females were classified as separate species of a fossil group; such tends to happen when the disparity between sexes is large and the sample size is small).
There would, of course, be nothing wrong with a living species being exactly the same as a fossil species. However, we do know that all species undergo a “life cycle”, much as individuals do: they come into being, they persist for a time, then they die off. Finding a such a “Methuselah species” would be akin to finding a very, very old individual - noteworthy, certainly, and probably worthy of investigation in itself.
The life span of a species differs from group to group, however, so a long-lived species of mammal, for example, might be around for no longer than a short-lived reptilian species. And plant species, on average, may (or may not) persist longer than various animal species. Unfortunately, the fossil record does not provide enough detail to accurately determine the life span of most species.