Where did the ichthyosaurs go?

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, the animal for which ichthyosaurs are named.

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?

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2 thoughts on “Where did the ichthyosaurs go?

  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?

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