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Why did giant turtles survvie
Topic Started: Sep 20 2017, 06:39 AM (549 Views)
lerzid
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My question is how the leatherback family of turtles along with a few other sea turtle familys such as the loggerheads survived the K-pg mass extinction with well over a 1,000 lb while no other animals other than a few crocodilians did with more than 55.1156 lb.
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Yiqi15
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I'd say they were living in deep bethnic areas, which most likely weren't affected as other areas.
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lerzid
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Remember there where 2 species at the time of the K-pg. Mesodermochelys which was about as large as modern day leatherbacks which live in the Pelagic hunting jellyfish, and as far as we know it had a similar lifestyle to it's modern cousins. And there was the abberant and massive Ocepechelon which more adapted towards suction hunting fish converagent with seahorse and beaked whale. They hunted small schooling fish which tend to go closer to the surface. Mesodermochelys is probably the ancestor of post K-pg leatherbacks. My point is that these animals dont live in deep benthic areas. And also if that was the reason, why didnt deep sea ammonites survive?
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Fazaner
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2 species that were discovered from that time, for all we know there were many species of sea turtle around at the time. There could be small generalist species, they are just not discovered yet. And deep sea is not a "time capsule" of sorts, amonites prove that.
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lerzid
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Sea turtles fossilize with ease do to their hard carapace and marine enviroment. No Dermochelyid was smaller than 7 feet in length. The Dermochelyoids had quite a few more K-pg surviving turtles. Alienochelys whose fossils have been found both sides of the K-pg and where 8-9 ft in length. Corsochelys was a bit smaller at 7ft. Loggerhead sea turtle fossils can found in the Cretaceous and are still alive and they have consistently weighing 300 lb at maturity and growing to a massive 1,100 lb.
Edited by lerzid, Sep 20 2017, 05:25 PM.
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Tartarus
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A mass extinction isn't as black-and-white as "everything above X mass dies". Larger animals are more vulnerable to going extinct, but that doesn't mean their extinction is guaranteed. Some big animals survived the K-Pg extinction and it seems the large sea turtles you refer to were examples of this.
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lerzid
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I'm simply asking why giant turtles survived while small generalistic ammonites didnt
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Rodlox
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lerzid
Sep 20 2017, 08:30 PM
I'm simply asking why giant turtles survived while small generalistic ammonites didnt
either because they did, and we don't fully understand the Why yet,

or because they died out alongside the ammonites, and their niche was filled soon enough by other turtles that grew into giants.
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Talenkauen
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lerzid
Sep 20 2017, 08:30 PM
I'm simply asking why giant turtles survived while small generalistic ammonites didnt
Sea turtles don't function the same as ammonites. Ammonites had different biological limitations. Different diet, respiratory system, circulatory system, reproduction method, etc.

It's kind of a false equivalency, Lerzid.


That being said, the most agreed upon reasons for the ammonites' extinction are two factors:


1: They were mostly filter feeders, or at least fed upon other filter feeders. So, they directly or indirectly relied on healthy levels of plankton to survive.

2: They most likely spawned only once at the end of their lives, and the eggs and larvae most likely drifted on the surface as plankton (a similar strategy to related coleoids). Contrast this to nautiloids, who spawn multiple times in their lives, and do so close to the sea floor (away from worst effects of an asteroid strike).

The K/T extinction not only killed off their food supply, but drastically affected their already limited ability to breed. Thus, they died off.


.... At least, that's how the theory goes.
Edited by Talenkauen, Sep 20 2017, 10:50 PM.
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Flisch
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One theory why ammonites went extinct while other cephalopods survived is that ammonites produced planktonic larvae. The plankton ecosystem broke down during the aftermath of the K-T, so the entire reproduction system of the ammonites went down the drain as well. Add this to the fact that ammonites likely mated once and then died, and it's not unthinkable to imagine ammonites going extinct in such a case. Contrast this to the reproductive systems of modern nautiloids and squids and octopodes.

Also, just like belemnids it could be that some ammonite species actually survived the initial K-T but died out later as the ecologies of the seas changed.

I'm also suspicious of all these enigmatic "large animals surviving the K-T". I think it's likely that closely related species that are much smaller survived the extinction event and grew larger only a few million years later, which would be near impossible to track in the fossil record.
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IIGSY
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How do we know that ammonites mated only once? And don't modern cephalopods have planktonic larvae.
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Quote:
 
How do we know that ammonites mated only once? And don't modern cephalopods have planktonic larvae.


Extracted from wikipedia article about Ammonites extinction
 
One reason given for their demise is the Cretaceous ammonites, being closely related to coleoids, had a similar reproductive strategy in which huge numbers of eggs were laid in a single batch at the end of the lifespan. These, along with juvenile ammonites, are thought to have been part of the plankton at the surface of the ocean, where they were killed off by the effects of an impact. Nautiloids, exemplified by modern nautiluses, are conversely thought to have had a reproductive strategy in which eggs were laid in smaller batches many times during the lifespan, and on the sea floor well away from any direct effects of such a bolide strike, and thus survived.


And about the planktonic larva thing, yes, they have it, the thing is that the name of it is "Paralarvae" by the fact of not going through a metamorphosis but still counts as planktonic stage.
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