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What were the First Animals to Walk on Land?

Fossilized footprints can reveal information about an extinct animal's behavior.
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The first animals to walk on land are unknown. There is evidence that soft-bodied arthropods and slug-like animals visited the land as far back as 510 million years ago, in the Cambrian era, leaving behind mysterious tracks called Climactichnites and Diplichnites. These tracks are mysterious because no fossils have been found of the animals that made them. Some of these trace fossils are as wide as four inches. Perhaps these animals did not actually breathe air, and only slimed along on land for short periods as a way of moving from pond to pond.

According to scientific consensus, the first verified land animal was a one-centimeter myriapod. Present-day examples of myriapods include millipedes and centipedes. This myriapod, discovered in 2003 in Scotland and named Pneumodesmus newmani, is dated to 428 million years ago. Paleontologists can tell it lived on land because its fossil shows it possessed spiracles; holes that insects, spiders, rays, and sharks use for breathing air. Prior to the discovery of newmani, the oldest known air-breathing creature was a spider-like organism from 410 million years ago.

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The first land-walking animals are often incorrectly cited as Devonian transitional forms called “fishapods” because they are intermediate between fish and true tetrapods. An example is the fish Tikaalik, which lived approximately 375 million years ago, during the Devonian period. It is remarkable that such organisms are so frequently cited as the first land animals when land animals from more than 50 million years before, such as Pneumodesmus newmani, are now widely known. The effect may have something to do with a bias in favor of the more familiar vertebrates over invertebrates.

The earliest land animals probably lived in oxygen-poor shallow pools near land. As the first vascular plants developed, they would have choked the areas around these pools with weeds, making it evolutionarily advantageous to climb over and around them via quick forays onto land areas. The land at that time would have been much more nutrient-rich than the water, as plants colonized the land before animals and left their decaying plant matter everywhere. Bacteria and fungi broke down much of the plant matter but it still would have been appealing to a hungry fish. Around 365 million years ago, some fish (so-called “fishapods”) developed limbs and climbed onto the land. The appearance of the first true trees about 370 million years ago would have helped this along, by depositing more nutrients into the soil and making the environment more habitable.

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anon291230
Post 6

@lightning88: I'm not an expert, but from what I've read, mudskippers actually independently discovered life on land much later than our own ancestors. They are "ray finned fish" similar to most familiar bony fish whereas we arose from the separate group "lobe finned fish". There are still lobe finned fish around however. The coelocanth is the best known example but it lives entirely in the water. Lungfish are an example of lobe finned fish that can survive droughts out of water but they don't make a habit of living out of water like the mudskipper.

I learned some of this from "The Ancestors Tale" by Richard Dawkins.

kennethgass
Post 5

The confirming study I mentioned earlier was published in the May, 2012 issue of the Journal of Paleontology. The first land-walkers were euthycarcinoids. As far as we know, there are no surviving species.

kennethgass
Post 4

Update: Body fossils of arthropods known as euthycarcinoids have now been found in the same Cambrian beds that preserve Protichnites and Diplichnites trackways. J. Collette and J. Hagadorn published those fossils in the Journal of Paleontology in 2010.

Other material has now been found that further links those trackways with the body fossils and the study is currently being wrapped up for publication.

naturesgurl3
Post 3

Thanks for this article -- the detailed and clear writing really made it great.

I also liked how you didn't get stuck into the "First Encyclopedia of Animals" mentality and only stick with vertebrates -- very well researched and written.

lightning88
Post 2

Are all the animals that first walked on land extinct now, or are there still remaining "living fossils"?

I know that a lot of the animals considered endangered or extinct have later showed up as living fossils, like coelacanths and the like.

And I know that there are still some "fishapod" like animals today, like mudskippers. So are all the animals mentioned above extinct, or do any of them still exist?

rallenwriter
Post 1

Hah, can you imagine a Baby's First Animals book that included tetrapods -- now that would be a book worth investing in.

It would be even better if those first 100 animals books were written according to the real first 100 animals, as far as we know. I think that would be a much better "My First Book of Animals" than those ones that only focus on farm animals.

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