Euthycarcinoids, arthropods that lived 500 million years ago, were the first animals to transition from sea to land, according to research. The discovery of fossils that preserve both euthycarcinoids and walking footprints allowed scientists to make the connection. The first land animals likely lived in shallow, oxygen-poor pools near land and bypassed weeds through rapid forays into land areas. About 365 million years ago, some fish developed limbs and climbed onto dry land.
According to research published in 2012, the first footprints on earth were the footprints of euthycarcinoids. Eutycarcinoids are arthropods that lived about 500 million years ago. Scientists were uncertain about the first animal to set foot on land and had long suspected amphibians or centipedes. However, recent research shows that it was actually the euthycarcinoids of the Cambrian period that first made the transition from sea to land. It was the discovery of fossils that preserve both euthycarcinoids and proticnites, i.e., walking footprints, that allowed scientists to make the connection.
In fact, the idea that arthropods may have been the first to walk on land had emerged way back in 1852 by Sir Richard Owen. He based the idea on fossil footprints in Quebec. However, the idea could not be proven until fossils of the animal responsible for the footprints were found. Then, the theory was only recently proven when the segmented tail of a euthycarcinoid was identified in one of the footprint fossils.
Aside from euthycarcinoids, one of the earliest verified land animals was a centimeter-long myriapod. Today’s examples of myriapods include millipedes and centipedes. This myriapod, discovered in 2003 in Scotland and called 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 to breathe the air. Before the discovery of newmani, the oldest air-breathing creature was a spider-like organism from 410 million years ago.
The first animals to walk the land are often erroneously cited as transitional Devonian forms called “fishapods” because they are intermediate between fish and true tetrapods. An example is the fish Tikaalik, which lived about 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 of more than 50 million years earlier, such as Pneumodesmus newmani, are now widely known. The effect may have something to do with a bias in favor of more familiar vertebrates over invertebrates.
The first land animals likely lived in shallow, oxygen-poor pools near land. When the first vascular plants developed, they would have choked the areas around these pools with weeds, making it evolutionarily advantageous to override and bypass them through rapid forays into land areas. The earth at that time would have been much richer in nutrients than water, as plants colonized the land before animals and left their decaying plant matter everywhere. Bacteria and fungi destroyed much of the plant matter, but it still would have been interesting to a hungry fish. About 365 million years ago, some fish (so-called “fishapods”) developed limbs and climbed onto dry land. The appearance of the first true trees about 370 million years ago would have aided this by depositing more nutrients in the soil and making the environment more habitable.
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