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Coelacanth, Lamprey And Hagfish


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The coelacanth, lamprey and hagfish all share the status of being relicts having survived nearly unchanged for 400 million years.

why are these organisms still present on earth when many of their relatives when extinct?

What aspects of their biology or ecology allowed for this? Do these fish add support of controversy to the theory of evolution by natural selection?

EDIT: The author is going to reword this inquiry; as there have been responses, we will wait and merge/delete as necessary.

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The coelacanth hasn't been around 400 million years, nor any of its close relatives. They are members of the lobbed finned fish, which are part of the bony fish group. Their ability to aestavate in fresh water has probably kept them around, although in a much more limited capacity (number of species) then the lobbed finned fish have filled in the past.

Lampreys and hagfish are the lone survivors of the agnathans, the jawless fish. They were once the most common type (only) fish in the water, and filled all the niches they could. There is a limit to what an agnathan can look like, and I suspect they look the same because that is the only way they can look.

If you were to take any of the three mentioned above from their beginning, and put them with modern examples, they would not be able to procreate, no matter how much they look similar. Genes mutate at a certain frequency, which builds up in a species genome over time. I don't remember the exact figure calculated, but over time the differences build up to the point that even though they are the same species, they can no longer interbreed.

Species is a tricky thing to define, and change is in the eye of the beholder. But it does make for some interesting intellectual exercises.

Brent Ashcraft

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paleozoicfish

What Brent means is that Latimeria (the extant coelacanth genus) has not been around for 400 million years, however, the group commonly referred to as coelacanths (family coelacanthidae) have been around for that long (slightly longer actually). This group is defined on a specific set of characteristics (as defined by paleontologists). Some fossil coelacanths look superficially similar to the modern species, but some look very distinct (example Allenypterus from bear gulch limestone in Montana - google it!).

Some arguments have been that these lineages 'evolve' slower (slower rate of evolution = rate of acquisition of new features) or as generalists have not been 'pushed' to change much (i.e. if it's working, no need to change it). The reasons from some groups surviving longer than others is something that is still being debated today and there are likely quite a range of processes and events driving this.

In the end - Brent is right that if you put them side by side (even if they looked similar and are ancestors), they would be genetically distinct. Commonly creationists use the LIVING FOSSIL coelacanth as the 'poster child' to prove that Darwin was wrong and that Evolution does not occur. I mean how could a fish from 250 million years ago (Coelacanth granulatus) look nearly identical to Latimeria chalumnae (modern coelacanth)! With a careful eye, one can discern a great number of differences between these species, but many people do not want to look below the surface and declare them the same.

On a side note - the term Living fossil is truly a subjective term to refer to an organism that superficially looks similar to an ancestor in the fossil record. Some common examples of this would be the coelacanth, ginko and the horseshoe crab. Of course, the ancestors only superficially look similar otherwise they would be the same organism. Even though almost all organisms around today have ancestors in the fossil record, you may notice that most are not referred to as living fossils - once again, this is purely because the modern examples are not as 'similar looking' to their fossil ancestors.

Well, that's enough for today.

-PzF

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The three tend to live in deepwater environments. They are members of once much more diverse groups. Across time those groups dwindled in diversity and seemed to disappear. There were coelacanth relatives during the time of the dinosaurs but then no fossils were found in rocks more recent than about 80 million years ago. From that scientists concluded that they died out at some point in the Late Cretaceous or perhaps even at the end of the period.

When live specimens were caught in the last century, scientists realized that they simply became less common and/or lived where their remains were not preserved (or where their remains remain undiscovered). The odds against an organism becoming a fossil are astronomical so it's even worse if it was an uncommon organism in its time. For whatever reasons the coelacanth's relatives could not overcome the revolving door of life's hazards elsewhere within ocean environments but the lineage that led to the modern coelacanth found a refuge off the Comoro Islands.

Lampreys and hagfish are the last of the jawless fishes. Once diverse themselves during the Silurian Period, jawless fishes were outcompeted by fishes that could consume larger amounts of food in a shorter time (and possibly consume jawless fishes). Jaws also allowed the animal to fight back against predators or discourage competitors for mates as well. By the end of the Devonian jawless fishes were nearly extinct and their fossil record appears to end in the Pennsylvanian. Only the miraculous Mazon Creek Fauna, which preserved numerous other soft-bodied animals, provides evidence that they lived that long after the end of the Devonian. Lampreys and hagfishes survived because some of them made the most of a niche largely uncontested by other fishes: the deepwater scavenger.

No, these fishes don't pose a problem for evolution. It's unknown when they became established where we can find them now but it's clear their relatives lived in more populated parts of the world in the distant past. Some members of their groups were pre-equipped to live in oxygen-poor environments - areas otherwise toxic to their competitors - so they stayed and continued to have babies long after their relatives died out elsewhere. If the environment doesn't change, the organisms tend not to change either, or should I say, individuals better-matched for their environment tend to survive and reproduce. However, environments tend to change over time: often gradually enough for the associated organisms to change with it; sometimes they suffer sudden and harsh interruptions. The deepwater zone rarely experiences an abrupt and fundamental change such as a sharp rise or fall in temperature or invasion of new predators, competitors, or parasites. These are factors which might lead to the extinction of the coelacanth, the lamprey, and the hagfish.

Part of the problem is that scientific observations and theories are often inaccurately restated in mainstream media. You can say that sharks, for another example, have been nearly unchanged since the Devonian and it would be true to the extent that cartilaginous fishes existed then and continue to live today, but in between, sharks have enjoyed distinct intervals of great success and suffered minor to major setbacks across time as well. Only a few Paleozoic genera survived into the Mesozoic and maybe half of the ones living in the Late Cretaceous, continued into the Cenozoic Era. Many of the those Early Cenozoic sharks died out across the last fifty million years. "Nearly unchanged" is a relative term when used to describe any long-lived lineage especially when the fossils are largely limited to teeth and/or faint body impressions.

The coelacanth, lamprey and hagfish all share the status of being relicts having survived nearly unchanged for 400 million years.

why are these organisms still present on earth when many of their relatives when extinct?

What aspects of their biology or ecology allowed for this? Do these fish add support of controversy to the theory of evolution by natural selection?

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Perhaps not, but, new member makes only two posts, both the same, in different boards. The last sentence says a lot, to me anyway, perhaps I'm wrong though.

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Some informative responses have sprung from the inquiry, in any case.

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Perhaps not, but, new member makes only two posts, both the same, in different boards. The last sentence says a lot, to me anyway, perhaps I'm wrong though.

I don't see anything wrong, but then again, maybe I am wrong too. From what I have read "The author is going to reword this inquiry; as there have been responses, we will wait and merge/delete as necessary", this is meaning that from what we say, they will edit it, and with the "necessary" shows that they will use what we say to prove a point that we have not come to conclusion to.

Having said that, I agree with siteseer and paleozoicfish, the fish has had no need to evolve. And no, fossils like this do not oppose evolution, it is just a slower process of it.

Edited by Kosmos
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