What Were the First Animals to Walk on Land?

The question asked is "What were the first animals to walk on land" --- not "What were the first fully terrestrial animals to walk on land." Thus, an animal that walks on land only part of its time and whose ability to breathe air is undetermined still qualifies, and the first such animals to do this were euthycarcinoids and giant slug-like animals. Your statement "...no fossils have been found of the animals that made [Climactichnites and Diplichnites]" is not entirely correct.

While fossils of the slug-like animals that made Climactichnites still haven't turned up, several fossils of the euthycarcinoids that made Diplichnites (and Protichnites) have been found in Wisconsin and Quebec. Impressions of the Wisconsin euthycarcinoid have been found that essentially show that euthycarcinoid making Protichnites.

The fossil and experimental evidence for this Cambrian land-walker is just as strong as the evidence for air-breathing myriapods in the Silurian. See the 2010 and 2012 papers from the Journal of Paleontology written by Collette and Hagadorn, and Collette, Gass and Hagadorn, respectively, which I referred to earlier. To this date (10-FEB-2016) no one has refuted those studies, and they have been cited in several peer-reviewed publications.

@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.

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.

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.

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.

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?

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.