First Land Animals Shuffled Like Seals

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The world’s first 3D reconstruction of a 4-legged animal backbone reveals that the first animals on land moved like seals.


One of the studied animals was a fierce-looking, toothy beast known as Ichthyostega. It lived 374 – 359 million years ago and was a transitional species between fish and terrestrial animals.

Ichthyostega is thought to have navigated through shallow water in swamps, probably lured by food.

Now we know that it probably moved by dragging itself across flat ground, using its front legs to crutch itself forward, much like that of a mudskipper or seal.

The findings are published in the journal Nature.

Lead author Stephanie Pierce, of the University of Cambridge’s Department of Zoology, was quoted as saying in a press release, “The results of this study force us to re-write the textbook on backbone evolution in the earliest limbed animals.”

Written By: Jennifer Viegas
continue to source article at news.discovery.com

9 COMMENTS

  1. Having recently watched a talk given by Jerry Coyne, he shows how whales evolved to lose their legs over time. Here it shows that fish came first and, over time developed legs. Can someone please clarify? So, with the whales, they started as fish – then over millions of years developed legs – then over millions of years evolved again to lose these legs? Is this right? x

  2. In reply to #1 by SarahH:

    Here it shows that fish came first and, over time developed legs. Can someone please clarify? So, with the whales, they started as fish – then over millions of years developed legs – then over millions of years evolved again to lose these legs? Is this right? x

    We – humans, mammals, birds, reptiles, amphibians – all share a common ancestor with fish. There’s a bit of a taxonomy joke that says either “fish” don’t exist as a group, or we’re all fish. =)

    Here is a chart of fin to limb evolution

    There’s a long path from fish to mammals. Whales are indeed descended from some four-legged terrestrial mammal, losing their hind limbs entirely and having their forelimbs evolve into flippers. If you look at the bones in the flipper of a whale, you’ll see the same bones in your arms and hands.

  3. Thank you for the response Kim. So, looking at the drawing in your link, and in the case of whales it went: fin to limb to fin. Through the stages shown in the diagram and then back again. Crazy. x

  4. In reply to #3 by SarahH:

    Thank you for the response Kim. So, looking at the drawing in your link, and in the case of whales it went: fin to limb to fin. Through the stages shown in the diagram and then back again. Crazy. x

    Well, just slightly different – a fin doesn’t have bones in it, while the whale flipper does. They’re considered analogous structures. They’re built differently, but serve similar functions. Another example of an analogous structure would be the wing of a fly and the wing of a bird. It is neat that whales are animals that have ancestors originating from the sea and then later returned to it, though. =)

    We can kind of see that in just about every group of animal, too, though most are obligated to be on land for at least some portion of their life. Ancient reptiles did it, looking similar to modern whales, and we still have turtles and sea snakes, though they must lay eggs on shore. Penguins and alcids (like puffins) spend a lot of time swimming under water, too.

  5. In reply to #1 by SarahH:

    Having recently watched a talk given by Jerry Coyne, he shows how whales evolved to lose their legs over time. Here it shows that fish came first and, over time developed legs. Can someone please clarify? So, with the whales, they started as fish – then over millions of years developed legs – then over millions of years evolved again to lose these legs? Is this right? x

    Whales are mammals. The fish-like ancestors @OP .. …. .. . . . .. . .. .

    {like the modern amphibious fish – Mudskippers – video.nationalgeographic.co.uk/video/animals/fish-animals/spiny-rayed-fish/mudskippers/ }

    made their way on to land and evolved into amphibians like newts and frogs. Then over millions of years they developed waterproof skins to become reptiles, and later some of the reptiles evolved into mammals. In the case of whales, some of these mammals became swimmers, but still breathed thorough lungs, not gills.

    The closest living modern relative of whales, is the 4 legged Hippopotamus, which is semi aquatic, living in lakes and rivers.

    Here is an animated sequence illustrating the evolution of whales from sample species of fossils – showing the progressive reduction in legs from Pakicetus to the more modern form of whale body.
    nationalgeographic.com/2010/08/egyptian-whale/whale-animation

    At the top of the page there are links to a related “feature article” and “photo gallery” about whale fossils in the Egyptian desert.

  6. In reply to #3 by SarahH:

    Thank you for the response Kim. So, looking at the drawing in your link, and in the case of whales it went: fin to limb to fin. Through the stages shown in the diagram and then back again. Crazy. x

    It would seem crazy, but it makes a lot more sense when you consider the conditions that drove the changes. When some fish like species were evolving to become land animals the seas were very dangerous with savages looking hunters, but when they had gone, the sea would have seemed a much more inviting place with an abundance of food.

  7. In reply to #1 by SarahH:

    You also might be interested in the evolutionary path of tortoises (or land turtles), which starts with an aquatic species evolving into a land based animal. It’s descendants later evolved into a new aquatic species and finally descendants of them evolved into the land based turtles we see today.

    Whales, dolphins, seals and sea lions are all descendants of land based mammals who have slowly adapted towards a more aquatic lifestyle. Their heritage shows in the fact they still have lungs and a skeleton that is homologous* to every other mammal known to man. They also swim by moving their tails up and down, instead of side to side like a fish because their spines were initially (meaning by their ancestors) used for walking and galloping.

    *homologous means that while the sizes and shapes of their bones may vary from other mammals, all mammals have the same amount of bones arranged in the same way. Where our pinky is relatively frail, it is very strong and large in bats and used to support it’s wings. Our hind legs are thick and strong to support our weight, while whales don’t need it because they are supported by the ocean. But we all have them.

  8. Question…..I think I am on safe ground saying that humans who exercise a portion of their anatomy, like their extremities – show increased bone growth in those areas, not just muscles, due to increased blood supply, and the stresses imposed. (Steps cautiously out onto thin ice). Could it not be that the first fish-like creatures who ventured out onto the land, grew stronger/longer bones in their fins/flippers ? Could evolution be partly driven by their adaptation to their environment ? Is there any proof at all that things like bone structure can be inherited ? (Even asking this I think I am displaying my ignorance.)

  9. In reply to #8 by rod-the-farmer:

    Question…..I think I am on safe ground saying that humans who exercise a portion of their anatomy, like their extremities – show increased bone growth in those areas, not just muscles, due to increased blood supply, and the stresses imposed. (Steps cautiously out onto thin ice). Could it not be that the first fish-like creatures who ventured out onto the land, grew stronger/longer bones in their fins/flippers ?

    There would certainly be survival potential for those individuals which had the flexible capability to develop stronger limbs in response to loading.

    Could evolution be partly driven by their adaptation to their environment ? Is there any proof at all that things like bone structure can be inherited ? (Even asking this I think I am displaying my ignorance.)

    Bone structures are certainly inherited, but capability for flexible individual adaptations to environmental conditions, like the examples you give, can also be inherited.

    Bigger effects over the longer term, can come from changes in genetic switches, which dictate when growth should start and stop, during (embryonic or early) development. – Hence different sizes of animals, limbs and their proportions.

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