|
|
Post by theropod on Jun 22, 2013 13:55:02 GMT 5
|
|
|
|
Post by creature386 on Jun 22, 2013 13:55:58 GMT 5
Reply to Grey: He only wanted to say that we don't know the true king, he has listed something known.
|
|
|
|
Post by Grey on Jun 22, 2013 14:31:25 GMT 5
Reply to Grey: He only wanted to say that we don't know the true king, he has listed something known. The knowledge is in the realm of the known...I understand what he means, but even if we are far to have found all what has existed, it is not necessary true that we don't have found record or close records in some cases. And this is itself speculation. He doesn't need to say that, we know that something new can come up...or not. |
|
|
|
Post by Grey on Jun 22, 2013 14:37:02 GMT 5
Spectacular for sure but I don't think this is a direct match for the skull of the largest pliosaurs in terms of robustness and teeth potency, even if exceeding them in size. McHenry points on that pliosaurs are perhaps the most dominant marine predators of all time as a group, and they directly replaced these very large macrophagous ichthyosaurs, despite that the rest of the ichthyosaurs survived until the Cretaceous. Until more information comes, I would not see these guys outclassing K. queenslandicus and P. macromerus. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Jun 22, 2013 14:37:18 GMT 5
Likely an undiscovered species, but among the known animals, Pliosaurus macromerus... We of course talk about animals known of all time or we enter into the realm of baseless speculation ! I was just stating which is most likely true. As for known animals I already gave my answer. |
|
|
|
Post by Grey on Jun 22, 2013 14:39:13 GMT 5
We of course talk about animals known of all time or we enter into the realm of baseless speculation ! I was just stating which is most likely true. As for known animals I already gave my answer. I know, but we know it is most likely true, that's why we don't count it. And I'm always uncomfortable with such claims. Yes this is most likely, this is not certain though. As often in paleo, we don't know. |
|
|
|
Post by Grey on Jun 22, 2013 15:40:24 GMT 5
Not always but often related !
White shark and megalodon did not rely on the same food sources and thus were not competitors. Squalicorax wasn't a competitor for the large tylosaurines, which in turn outclassed the largest sharks as Ginsu and perhaps Ptychodus.
More often, the most efficient at reproducing, having access to food and/or most powerful survives.
I don't say that plesiosaurs contemporaries of these ichthyosaurs destroyed them, I say that pliosaurs occupying the same niche ruled the oceans a far longer time and developped a killing apparatus more spectacular from a macrophagous viewpoint than ichthyosaurs at parity. Hence, pliosaurs appear to me the most spectacular and dominant predators.
Individually, the most dominant predator in the sea has often been the largest. Even today, orcas are the largest and most powerful mammal-eating carnivores on Earth !
I don't think McHenry suggestions in his ten years in the making thesis are unlikely at all as I've seen nothing contradicting him. He simply compared the sizes of all apex carnivores in history and came rationally to the observation that most were in the 10 tons range, and few in the 10-20 tons range.
Megalodon and leviathan are exceptions because of the time in which they evolved, they were related to the huge diversification and increase in size of baleen whale, during one of the richest period in terms of marine life ever.
Kent :
So how did meg get so big? It just happened to evolve during the Neogene polytaxic maximum when marine ecosystems were some of the richest and most complex in the Earth's history. In the North Atlantic in the Middle Miocene there were 12 large macrophagous shark species, compared to only 5 today. There were also more whale and porpoise species than today. So their was simply enough large prey around to support a huge superpredator. And iy just happened to be meg.
But McHenry is right. It does not mean that no pliosaur (and thus one of these ichthyosaurs) couldn't have exceeded 20 tons, but the pattern of apex carnivores in history at any time simply indicates this.
Anyway, I have to agree these ichthyosaurs are intriguing and that it is no surprising finally, as we lacked of big macropredators in that group.
Only, I doubt they rival pliosaurs in terms of sheer power.
|
|
|
|
Post by coherentsheaf on Jun 22, 2013 16:07:09 GMT 5
Hm if the giant icthyosaurs are proportioned like Ophtalmosaurus or Stenopterygius I get a weight between 40 and 60 tonnes for the 16m individual, considerably in excess of the numbers I consider typical for giant pliosaurs, megatooth sharks and raptorial whales. I take this as rather safe indication that something is not right about these numbers... we will see.
|
|
|
|
Post by Grey on Jun 22, 2013 16:15:46 GMT 5
Hm if the giant icthyosaurs are proportioned like Ophtalmosaurus or Stenopterygius I get a weight between 40 and 60 tonnes for the 16m individual, considerably in excess of the numbers I consider typical for giant pliosaurs, megatooth sharks and raptorial whales. I take this as rather safe indication that something is not right about these numbers... we will see. These numbers are rather in the range of the largest sperm whales and megatooth. However, I would more likely use Temnodontosaurus with a streamlined built as a structure, which would bring something above the 20 tons range. Shastasaurus and Shonisaurus despite not being macrophagous have been quite slimmed as well. Another quote of my discussions with Kent : People working on ichthyosaurs tend to have lower weight estimates for two reasons. First, they have body outlines for some species, and so can get better estimates. Second, they use cetacean data for their estimates. Cetacean body mass increases more slowly at very large than expected (i.e., a blue whale weighs less than what would be from extrapolations of lengths and weights of smaller whales). This appears to be for biomechanical reasons and is believed to apply to all really large marine animals.
|
|
|
|
Post by theropod on Jun 22, 2013 16:19:48 GMT 5
Usually, the most adaptable and opportunistic (which reminds me, Spinosaurus is not a good example or an opportunist, it is a very specialized creature that likely attacked various kinds of small to medium-sized prey, but not an opportunist by means of attacking a truly wide range, even of large prey) survives. Rodents will certainly survive longer than cetaceans or carnivorans. The great white survived because C. megalodon was specialized in whales that were no longer easily accessible.
In the rare event of two apex predators competing for the exact same food source, it will be the most efficient and specialized that survives (given the food source continues to exist), not necessarily the most powerfull all around.
My point about the apex predators was simply that we only have a small sample, and from that alone cannot conclude much, not can we exclude the possibility that comparable gigantic food sources existed also during other times (eg. in terrestrial ecosystems during the mesozoic there were baleen-whale sized sauropods leading to a diversification in carnosaurs), or that a predator might evolve to be gigantic based on smaller prey (eg. T. rex also approached the size of many large carnosaurs while preying on smaller, but armoured prey), or, as already stated by MCHenry, based on strong specialization (but I would still like to see the pliosaur with clear adaptions for suction feeding, deep diving or a cephalopod diet). We can for example see huge (15-23m) Ichthyosaurs that were squid suckers, analogous to sperm whales.
I would rather consider it a piece of luck the Livyatan holotype is obviously large, and a matter of large sample size in C. megalodon, even tough these two are undoubtedly the largest known macropredators.
Other predators were not necessarily constrained to sizes below 20t. Depending on their built, 14-16m macrophagous Ichthyosaurs (Liassic temnodontosauridae sp., triassic Himalayasaurus) may have exceeded it, and in the case of Pliosaurs there are also at least indications of larger size (listed above, especially the giant undescribed teeth and the large vertebra). In fossil taxa, it is typically unwise to consider what you have clear evidence for the absolute limit (eg. even despite 31 known individuals being smaller, a 14-15m T. rex is fully possible and likely existed at some time).
|
|
|
|
Post by theropod on Jun 22, 2013 16:25:23 GMT 5
|
|
|
|
Post by theropod on Jun 22, 2013 16:27:57 GMT 5
I had no opportunity to do anything but skim this yet, but what I see suggests a tunniform, not serpentine, body shape for a liassic ichthyosaur. |
|
|
|
Post by Grey on Jun 22, 2013 16:29:00 GMT 5
Theropod, my point still stands.
Very often the apex predator outcompeting the other has been known to be the largest and most powerful even if there are others factors that I've quoted above.
For the rest, honesty I don't even know what you mean.
Yes we don't have all the record fossil but we have a good record fossil which indicates a size pattern through the evolution time. This does not exclude the possibility of larger, rare predators that we are unaware of, but we can still see that the trophic systems have at any time limited a specific range due to various reasons (ecological ressources, biomechanical limits).
All the rest is speculation which does not interest me.
|
|
|
|
Post by Grey on Jun 22, 2013 16:30:42 GMT 5
They are already as they approach the sperm whale size and are matches for pliosaurs. |
|
|
|
Post by theropod on Jun 22, 2013 16:39:07 GMT 5
Can you give me a good example were this was the case? I suppose you haven't read Darwin, 1859  And that there are no apparent biomechanical limits indicating a restriction of marine macropredators to 20t or less (both Livyatan and C. megalodon are clearly in excess of 30t) is also apparent. We cannot derive any clear limitations from the fossil record. This is not speculation on some potential size. It is somewhat speculative, yes, but is is not supported either that all but one marine apex predators were below 20t. It was different before Livyatan was described, and I think McHenry wasn't aware of Himalayasaurus or the Liassic giant ichthyosaurs either. |
|
