main article image
The fossil Kampecaris obanensis. (British Geological Survey)

This May Have Been Earth's First-Ever Land Animal

CARLY CASSELLA
6 JUNE 2020

The first creepy crawlies to climb out of Earth's ancient lakes and make their way on land may very well have done so with hundreds of tiny feet.

After carefully dating the earliest bug fossils ever discovered, scientists now think an extinct genus of myriapod, a relative of modern millipedes, represents the earliest direct evidence of an animal living and breathing on land.

 

Life on Earth started in a primordial soup, and bugs - or more specifically arthropods, including insects, spiders and centipedes - are thought to be some of the first animals to leave this comforting bath for good.

In fact, other types of insects are suspected to have beat myriapods to land. But we only have indirect evidence of their soil-based forays through tracks and trails, and these may only represent fleeting excursions to the world above, rather than making it their permanent home, like myriapods did.

Discovered for the first time in 1899 on a Scottish isle, the fossil of the myriapod Kampecaris obanensis has now been radiometrically dated to roughly 425 million years ago.

If the new date is correct, these ancient many-legged ones would be the oldest land animals to have lived out of water. And their journey was pioneering.

Just 20 million years after Kampecaris, the fossil record reveals bountiful bug deposits, and 20 million years after that, spiders and insects appear to be thriving in forest communities.

"It's a big jump from these tiny guys to very complex forest communities, and in the scheme of things, it didn't take that long," says geoscientist Michael Brookfield from the University of Texas, and the University of Massachusetts in Boston. 

 

"It seems to be a rapid radiation of evolution from these mountain valleys, down to the lowlands, and then worldwide after that."

This is, of course, only based on the fossils we have found so far, but researchers say the fact that there are no other discoveries out there, despite looking at some of the best preserved sediments from this era, could indicate the end of the road.

kerrera south coastKerrera's south coast. (Michael Brookfield)

If the team is right, and this ancient species was indeed the first of all water-to-land pioneers that we know of, then it looks like we've been seriously underestimating how quickly this transition occurred.

According to a technique called molecular clock dating, which is based on the mutation rate of DNA, fossils of stemmed plants in Scotland have also turned out to be roughly 75 million years younger than we once thought, coinciding with the Kampecaris timeline.

Not only were bugs in Scotland adapting to life on land at a rapid pace; this finding implies forests were doing so at much the same rate, and it's very likely the two are somehow connected.

 

Given how important these bugs are thought to be in our planet's history, Brookfield was surprised to find this fossil hadn't been dated before, although he admits it is time-consuming and delicate work.

When analysing these ancient rocks, scientists must extract microscopic inclusions of zircon, which can be used to accurately date sediment. 

This practice requires an eagle eye and a careful hand, and given how quickly these zircons can be accidentally flushed away, there's not a lot of room for error.

Geoscientist and co-author Stephanie Suarez has been mastering this technique since her undergraduate years, and she's used it in the past to prove a different millipede specimen (Pneumodesmus newmani) was not the oldest bug on land, but was actually 14 million years younger than we thought.

After years of careful work, she now gets to crown a new victor. Who knows if we'll get to dethrone it one day, too.

The study was published in Historical Biology.