Ichthyosaurs: the dolphin reptiles

When you think about the large creatures you might see in the ocean, perhaps whales and sharks come to mind. The fossil record suggests that the diversity of large, ocean-dwelling animals in earth’s past included many other groups, such as marine reptiles known as ichthyosaurs.

Ichthyosaurus_sp_2
Ichthyosaurus

Ichthyosaurs lived during the Mesozoic era of earth’s history, appearing in the fossil record during the earliest Triassic (~251 million years ago) and disappearing during the late Cretaceous (~94 million years ago). Fossils have been found on every continent except Africa and Antarctica.

OLYMPUS DIGITAL CAMERA
Ophthalmosaurus icenicus

Ichthyosaur means “fish-lizard”, though they look even more similar to dolphins due to their overall body shape and elongated snout. However, these were most certainly not dolphins. Some of the diagnostic features include the possession of several bones in their skulls that dolphins lack, different vertebrae, retained hindlimbs and a tail fin that extended in a vertical plane rather than a horizontal plane as in dolphins, not to mention various skeletal features found in reptiles but not mammals.

temnodontosaurus
Temnodontosaurus trigonodon

They also got much larger than the largest of dolphins, as displayed by the massive Shonisaurus and Shastasaurus.

shonisaurus
Shonisaurus popularis

shonisaurus-size

shastasaurus-size

It’s unclear what drove ichthyosaurs to extinction, as they appear to have died out before many of their other Mesozoic contemporaries, such as the dinosaurs. One common hypothesis is that other successful marine reptiles outcompeted ichthyosaurs.

Questions for Creationists

Ichthyosaurs lived in oceans around the world, so shouldn’t they have survived Noah’s flood the way whales and sharks did? If they went extinct after the flood, what would have caused it? Why is there no evidence of ichthyosaurs being caught and eaten by humans? Wouldn’t massive beasts like Shonisaurus or Shastasaurus have been reported by now if they were still alive?

12 thoughts on “Ichthyosaurs: the dolphin reptiles

  1. http://www.sci-news.com/paleontology/extinction-ichthyosaurs-03692.html

    New Research Sheds Light on Extinction of Ichthyosaurs

    Ichthyosaurs were predatory marine reptiles that ranged in size from 1 to 69 feet (0.3 – 21 m) long. They swam the world’s oceans while dinosaurs walked the land.

    Despite their profound adaptations to the aquatic realm and their apparent success throughout Triassic and Jurassic periods, these marine reptiles disappeared roughly 30 million years before the end-Cretaceous mass extinction (65 million years ago) that marked the end for dinosaurs and the beginning of the age of mammals.

    Current hypotheses for this early demise involve relatively minor biotic events (increased competition with other marine reptiles, or a diversity drop in their assumed principal food resource), but are at odds with recent understanding of the ichthyosaur fossil record.

    “Recent data challenge this view of ichthyosaur history, indicating that Early Cretaceous ichthyosaurs were taxonomically, phylogenetically and – possibly – ecologically diverse, even a few million years before their extinction,” said study lead author Dr. Valentin Fischer, of the University of Liège, Belgium, and the University of Oxford, and his colleagues.

    The researchers analyzed the extinction of this marine group thoroughly for the first time.

    Using a battery of cutting-edge techniques to quantify ancient biodiversity and its fluctuations, they were able to reconstruct the evolution of the ichthyosaurs during the last 120 million years of their lifetime and assess the causes of their extinction.

    “We compared the diversity of ichthyosaurs with the geological record of global change, emphasizing the dynamics of these datasets,” Dr. Fischer said.

    According to the team, a two-phase event suppressed their ecological diversity and wiped out the group at the beginning of the Late Cretaceous, about 100 million years ago.

    At that time, the Earth’s poles were essentially ice-free, and sea levels were much higher than today.

    Analyses revealed that this two-phase extinction can be associated both with reduced evolutionary rates (a failure to evolve novel body plans for a prolonged period) and intense climate change (strong variations in sea surface temperatures and sea levels).

    “Although the rising temperatures and sea levels evidenced in rock records throughout the world may not directly have affected ichthyosaurs, related factors such as changes in food availability, migratory routes, competitors and birthing places are all potential drivers, probably occurring in conjunction to drive ichthyosaurs to extinction,” Dr. Fischer said.

    This study supports a growing body of evidence suggesting that a major, global, change-driven turnover profoundly reorganized marine ecosystems at the beginning of the Late Cretaceous, giving rise to the highly peculiar and geologically brief Late Cretaceous marine world.“Ichthyosaurs disappeared in the course of this turnover, while numerous lineages of bony fishes and sharks evolved,” the scientists said.

    So, what does this sound like? Perhaps a Global Flood so severe that the Ichthyosaurs could not survive? While other hardy species did survive. Perhaps…

    1. Hi! Thanks for your comment!

      Without reading the article in detail, it indeed appears that the authors are associating the decline and ultimate extinction of ichthyosaurs with a period of high sea levels. This is, as you might assume, relatively common in invoking the extinction of different lineages of organisms. Not only rising sea levels, but also lowered sea levels, global temperature changes, volcanism, meteor impacts and an assortment of other massive climatic fluctuations that, understandably, would affect the survival of certain groups of organisms.

      But let’s go with the hypothesis that you’re obviously invoking, that of Noah’s Flood being responsible for the extinction of ichthyosaurs. As a legitimate hypothesis, it has to be testable and be able to account for other aspects relating to the biology of these organisms and the geology associated with them. Here are a couple thoughts:

      1. You suggest that ichthyosaurs were less “hardy” than other organisms that survived this flood. In what way? These species were obviously highly adapted to living in the oceans, so what about them kept them from surviving this flood? How are goldfish hardier than ichthyosaurs? Sea turtles? Manatees? Jellyfish? The minuscule pocket shark?

      2. Why are ichthyosaurs only found in rocks that are not associated with any modern species of animals? Why don’t we find dolphins with them? Or sea lions? Or humpback whales? Or manatees? Or green sea turtles? Or great white sharks?

      1. RM

        “1.You suggest that ichthyosaurs were less “hardy” than other organisms that survived this flood. In what way?”
        Aren’t they already ‘less hardy’ in the standard evolutionary view,considering they are regarded as becoming extinct even before the dinosaurs?

        “2. Why are ichthyosaurs only found in rocks that are not associated with any modern species of animals?”
        The same can be asked of coelacanths. To the best of my knowledge, to date fossil coelacanths have not been found in association with ‘modern’ species, even though they definitely are still alive today and contemporary with modern marine species.

        1. Hi RM, thank you for your comment!

          Aren’t they already ‘less hardy’ in the standard evolutionary view,considering they are regarded as becoming extinct even before the dinosaurs?

          As described in the post, my understanding of the current consensus is that there isn’t an obvious sort of signal regarding the timing of their extinction, much like the end-Cretaceous extinction event that appears to have wiped out the dinosaurs (minus birds), marine reptiles, some early mammals, etc. Some scientists hypothesize that it was through competition with other marine reptiles that led to their demise, but, of course, this is a difficult idea to test. We don’t know if they were eating the same foods, if they interacted with each other much, etc.

          So in one sense, you’re right: this hypothesis is suggestive of them being potentially “less hardy”, but this is specifically in contrast to other marine reptiles that no longer exist. The point I was trying to make in that comment, however, is if the creationist view is right, why did ichthyosaurs all go extinct after the Creator made them some 10,000-6,000 years ago? Why would It create anything just to have them be outcompeted by, say, dolphins and seals and sea turtles? And furthermore, why don’t we find any evidence of ichthyosaurs living side-by-side with dolphins, seals, sea turtles or any modern species, which would potentially give evidence of such competition?

          The same can be asked of coelacanths. To the best of my knowledge, to date fossil coelacanths have not been found in association with ‘modern’ species, even though they definitely are still alive today and contemporary with modern marine species.

          Yes, coelacanths are a great exception to that general rule! A few others exist, such as the Laotian rock rat. Evolutionary biologists think such Lazarus species, those that were thought extinct but were then ‘resurrected’ via discovery, have continued to persist just barely, often by living in refugia habitats. So coelacanths used to be much, much more abundant, and then they disappear from the fossil record entirely, so we thought they were extinct. But then we’ve discovered two species in the past century (though perhaps more are out there) that live in ocean caves and only come out at night, perhaps persisting by living in these very specific habitats with minimal competition and minimal exposure to environmental stress. I should point out though, the species that persist today are not anatomically identical to those that existed before, but they are undeniably coelacanths.

          To be clear, evolutionary theory suggests that (1) some lineages of organisms, like coelacanths, can arise and persist over long periods of history (e.g.,tens of millions of years), whereas (2) other lineages may be contemporaneous with lineages like coelacanths, but then go extinct.

          So to your point, extremely rarely, we find these Lazarus species, but if all organisms were contemporaneous with those still alive today, we should find far, far more examples of their fossils existing side-by-side with the remains of today’s species and/or we should find more examples of supposedly extinct organisms living today. If we found that ichthyosaurs, thalattosuchians, plesiosaurs, mosasaurs, along with all of the many many groups of extinct organisms (1) existed side by side with today’s organisms based on fossils and/or (2) still exist today, then giant chunks of evolutionary theory would be in big, big trouble.

          Frankly, I would absolutely love it if #2 was true. Evolutionary theory being largely overturned for the sake of finding ichthyosaurs and other extinct groups would be wonderful!!

          1. RM

            “Why would It create anything just to have them be outcompeted by, say, dolphins and seals and sea turtles? And furthermore, why don’t we find any evidence of ichthyosaurs living side-by-side with dolphins, seals, sea turtles or any modern species, which would potentially give evidence of such competition?”
            That presupposes it was competition that did them in.

            “If we found that ichthyosaurs, thalattosuchians, plesiosaurs, mosasaurs, along with all of the many many groups of extinct organisms (1) existed side by side with today’s organisms based on fossils and/or (2) still exist today, then giant chunks of evolutionary theory would be in big, big trouble. Frankly, I would absolutely love it if #2 was true. Evolutionary theory being largely overturned for the sake of finding ichthyosaurs and other extinct groups would be wonderful!!”
            And why aren’t coelacanths, jellyfish, crinoids, nautiluses, horsehoe crabs, stromatolites, hexanchid sharks, lungfish, sturgeon etc considered evidence enough.

            1. Hi RM:

              “That presupposes it was competition that did them in.”

              Sorry, I didn’t mean to imply that was the only possible explanation.

              “And why aren’t coelacanths, jellyfish, crinoids, nautiluses, horsehoe crabs, stromatolites, hexanchid sharks, lungfish, sturgeon etc considered evidence enough.”

              Well, they’re clearly evidence enough for you! 🙂 But not for me and roughly 95-99% of the active biologists around the world.

              I’ll be presumptuous and speak on behalf of the other biologists: the problem for us is that while the examples you list do indeed exist, it still represents a tiny sliver of all of the known diversity of life out there. For instance, if you go to the rocks representing the Cambrian period, we’ve never found a single amphibian (8,000 exist today, plus extinct species), lizard (10,000 today, plus extinct), bird (10,000 today, plus extinct), jawed fish (>30,000 today, plus extinct), arachnid (100,000 today, plus extinct), plant (320,000 today, plus extinct) or insect (>1,000,000 today, plus extinct), just to mention some of the groups. And similarly, when you looked at the fauna that existed in the Cambrian, close to none have any representatives today.

              Furthermore, the groups of organisms that seem to have persisted over long periods of time, such as the horseshoe crabs, hexanchid sharks, lungfish, etc. do not look exactly like the species we have today. We can tell that they’re, say, a horseshoe crab, but they’re different from our time’s.

              If we’re to posit that all life formerly co-existed, such as in an Eden-like world or immediately post-Noah’s ark (which some Creationists believe), the assumption is that we would see an incredible degree of mixing of species. We should find ichthyosaurs swimming alongside whales, and mesozoic mammals walking alongside squirrels, but as of yet, the overlap has proved to be extremely minimal.

              1. RM

                “..rocks representing the Cambrian..”
                Aren’t Cambrian remains regarded to be marine creatures and therefore wouldn’t be expected to include most of your examples.

                “… the assumption is that we would see an incredible degree of mixing of species. We should find ichthyosaurs swimming alongside whales, and mesozoic mammals walking alongside squirrels..”
                Maybe that’s a wrong assumption. Seals and turtles are definitely around at present, but I seem to recall they don’t regularly meet each other, with both mostly inhabiting different climate areas.
                Dolphins and tiger sharks definitely co-exist but in another sense they don’t; as I understand it, dolphins actually do their best to avoid tiger sharks as they are a lethal threat to the dolphins.
                And if I recall correctly, tiger sharks don’t regularly meet with great white sharks as they are both apex predators that probably compete with each other at some level, so they avoid each other (mostly).
                And a reminder from the coelacanth and their absent interaction with ‘modern fossils’; what you think you can deduce from the absence of mixed fossil assemblages may not tell the whole story.

                1. Hi RM! Replies below:\

                  “Aren’t Cambrian remains regarded to be marine creatures and therefore wouldn’t be expected to include most of your examples.”

                  All of the animals we have found in the Cambrian are indeed marine, yes, but there are terrestrial deposits that COULD yield fossils if any indeed existed at that time. The reality is that nearly all preservation of remains appears to happen in aquatic environments, due to the possibility of rapid burial and the lack of oxygen post-burial. Even terrestrial organisms are typically found in what we believe are rivers and lakes. Despite this, none of these modern terrestrial organisms are found in the Cambrian; indeed, no terrestrial animals or plants exist from this time (so far)!

                  But even if we stuck with marine organisms, the pattern persists. I cannot comment as well on non-vertebrates, but no modern fishes exist in the Cambrian (coelacanths, sharks, seahorses, tuna, eels, etc.), and there are absolutely no whales / dolphins, sea turtles, seals, penguins, other sea birds, marine iguanas, manatees, or sea otters.

                  “Maybe that’s a wrong assumption. Seals and turtles are definitely around at present, but I seem to recall they don’t regularly meet each other, with both mostly inhabiting different climate areas.”

                  Yes, you’re right, absolutely, this can happen (though in this case, seals and turtles definitely do overlap in distribution, but depends on the area and species). But the point is that we have entire assemblages of extinct organisms that completely fail to overlap with modern species. In my Cambrian example, for instance, you’ll find trilobites, anamalocaridids, conodonts, and others that don’t exist today, but no modern species will be mixed in with them.

                  Similarly, go look at terrestrial deposits in which dinosaurs are found (Mesozoic). Geologists think these rocks amount to 140 million years. Over all of these rocks, which have been examined to death (because people love dinos!), nobody has found a single modern mammal or bird mixed in with them. When you find this pattern repeatedly, consistently, and all over the world, it suggests that these organisms never overlapped, and if they never overlapped, how can that be reconciled with a pre- and post-Ark world that most Creationists posit?.

                  To return to the subject of this post, if you find a single indisputable example of an ichthyosaur swimming in the same seas as whales, seals, manatees, penguins, etc. this would be EXTREMELY interesting, and I’m sure paleontologists will be scratching their heads. If you find many such cases, then, wow, I’d love to watch the evolutionary biology community scramble to figure out what’s going on. It’s theoretically possible without outright overturning evolutionary theory, but if such discoveries kept happening across different rocks (corresponding to what we think are different eras) and different organisms (ichthyosaurs in the Cambrian with whales and mosasaurs and modern sharks), our field would have a serious reckoning!

                  1. RM

                    Hello again!

                    “But the point is that we have entire assemblages of extinct organisms that completely fail to overlap with modern species.”
                    Maybe what this means is that there were entire assemblages of flora and fauna that were contemporary but also separate and distinct, and maybe even actively avoiding each other. Consider the concept of endemic species amplified.

                    “…nobody has found a single modern mammal or bird mixed in with them.”
                    I understand they’ve found parrot remains in a dinosaur layer, although it is also contentious:
                    https://www.nature.com/articles/23841

                    “…if you find a single indisputable example of an ichthyosaur swimming in the same seas as whales, seals, manatees, penguins, etc. this would be EXTREMELY interesting, and I’m sure paleontologists will be scratching their heads.”
                    Will they or will they come up with explanations or excuses to explain it away by ‘reworking’ or something.
                    Not about ichthyosaurs, but in this fossil hunter’s account, he evinced some surprise at discovering a buffalo skull in a Cretaceous marine deposit. He thinks it was a case of the skull washing down into a gully and getting reburied hundreds or thousands of years ago. Maybe it is, but the thing is, how come he or other evolutionists did not consider that maybe, just maybe, some buffaloes were contemporary with Cretaceous type marine life. And to be clear, I don’t mean the buffalo were living in the oceans, but imagine buffalo on land while the sea next to them had Cretaceous marine life…
                    http://oceansofkansas.com/aug98mos.html
                    And apart from all that, never forget coelacanths…

                    1. Hi RM! Sorry for the especially slow reply. Been swamped given the COVID-19 crisis.

                      “Maybe what this means is that there were entire assemblages of flora and fauna that were contemporary but also separate and distinct, and maybe even actively avoiding each other. Consider the concept of endemic species amplified.”

                      I suppose that’s theoretically possible, and certainly an interesting possibility. But extreme endemism seems to poorly explain things when you have widespread extinct species that aren’t intermixed with modern species. As one salient example, take ammonoids. The paleobiology database (https://paleobiodb.org/navigator/) records almost 77,000 occurrences of these shelled squid-like creatures, being found from Middle Paleozoic rocks all the way through Cretaceous rocks, on every single continent plus islands. So this seems to argue against the extreme endemism example, given that they were apparently extremely widespread yet never seemed to coexist with whales, manatees, seals, sea lions, etc.

                      “I understand they’ve found parrot remains in a dinosaur layer, although it is also contentious”

                      Yes, it is my impression that it’s contentious. But hey, who knows? A little bit of overlap is consistent with evolutionary theory, Note that the (putative) parrot is found in the very lowest layers of the dinosaur-bearing rocks, corresponding to the last 3 million or so years of dinosaur existence (https://en.wikipedia.org/wiki/Lance_Formation). If the parrot was found in the early Cretaceous, that would be more wild, Jurassic would be shocking, and Triassic… well, scientists would think the whole thing was a hoax! It would be like finding a radio in King Louis XIV’s tomb! Or a television in George Washington’s house. But, again, if we do find such evidence, and we find it consistently, evolutionary theory would have to be reworked extensively, just like history would have to be reworked in the radio and television examples.

                      “Will they or will they come up with explanations or excuses to explain it away by ‘reworking’ or something.”

                      Let’s say you find a radio in King Louis XIV’s tomb. Based on all of the data we have up to this point regarding the evolution of technology, and specifically radios, and our records for when Louis lived and how they communicated back then…. how would you assume the radio got there? I would think it was a hoax or a mistake before ever considering the possibility that King Louis had a radio in his possession. But let’s say that we find that the monarchs of Belgium, Germany, Italy, China, Japan, Russia, etc. all turned up with radios in their tombs, and then we uncovered contemporary written records describing radios, and these written records could be confidently carbon-dated to the late 1600s, early 1700s, etc. Then we’re going to have a serious reckoning with our understanding of history!

                      I’d argue the same is true for evolutionary theory. The simplest explanation, based on all of our data, is that the buffalo skull was simply reworked into Cretaceous rocks. We know this can happen; glaciers move, rocks shift, etc. You could bury your parents in rocks surrounded by dinosaur fossils, but it doesn’t mean that your parents lived among the dinosaurs. But if those buffalos kept appearing in those Cretaceous rocks, and so did lions, and cheetahs, and gazelles, and zebras, and elephants, and pangolins, and not just in that formation but all over the world, and there was no reliable evidence of reworking… heck yeah evolutionary biologists are going to have a reckoning!

                      And based on the history of science, I feel confident that they would eventually accept it. Look at the big bang theory for instance or plate tectonic theory; their originators were mocked roundly, before these concepts were embraced. My PhD advisor had the same thing happen to him in a much more specific field regarding the evolution of mammals.

                      Will some people resist? Absolutely. I see this in my own field with people’s pet hypotheses, where it seems like they’re unable to consider any outside evidence. But sometimes the old guard has to die out for the new ideas to come in. A true scientist follows where the evidence leads, not where their favorite ideologies lead.

                      “And apart from all that, never forget coelacanths…”

                      Lol! Please make a flag or banner that says “Never forget the coelacanths!” I would buy one 🙂

  2. RM

    “… that they were apparently extremely widespread yet never seemed to coexist with whales, manatees, seals, sea lions, etc.”
    But again from coelacanths, their fossils so far have no co-existence with whales, manatees etc yet they are definitely co-existent.

    Your King Louis-radio suggestion is interesting but in and of itself, you overlooked one possibility. King Louis could have successfully developed a radio (perhaps with trusted staff) but kept its development secret from everybody else. Now in real-life something analogous apparently happened with Cornelis Drebbel. Drebbel was said to have invented an early submarine, and with it, some chemical formula that allowed the air inside to be breathable for crewmen for some hours underwater. However, he kept details on the formula a closely-guarded secret, never revealed it and till today, no one knows what it was exactly (some guesses but nothing definite). But I digress.

    What would be the amount needed of out-of-place fossils to change their mind.

    1. Hi RM!

      “But again from coelacanths, their fossils so far have no co-existence with whales, manatees etc yet they are definitely co-existent.”

      Yup, that is true. It gets complicated though. Previously, they were certainly much more common: paleobiodb.org shows them on every continent except for Antarctica, whereas now we’ve only found them near South and East Africa and Indonesia. Also, there were formerly at least dozens of species with a multitude of forms, but we now only know of two highly similar species. Today they live in deep-ish waters and hang out in caves, but maybe they were in different habitats before. Perhaps the absence of fossils is due to a change in habitats, change in distribution, a change in abundance and diversity (i.e., extinction), etc. Ultimately, it’s difficult to ascertain what happened with these guys, and the same can certainly be said for other organisms.

      Interesting about Drebbel! Never heard of that before. Adds an interesting wrinkle to the analogy.

      “What would be the amount needed of out-of-place fossils to change their mind.”

      Good question. Speculating here, as it’s difficult to imagine, but I think perhaps 5% “out-of-place” fossils would cause shockwaves. 10% would maybe bring our understanding of the fossil record into question. 25–50% would probably lead to a complete upheaval to the point of reworking evolutionary theory, some possibly abandoning it, etc.

      But the placements of fossils are not the only evidence for evolution so there would still be robust support for it. I imagine it would be like discovering that the archaeological record of Rome was completely misinterpreted, but it wouldn’t negate the manuscript evidence, genetic evidence, etc. But it would be a monumental shift in thinking, no doubt!

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