Eophrynus – Late Carboniferous (318-299 Ma)

 Today, we’re going back to the Carboniferous period! If you’ve been following this blog for a while, you might remember Westlothiana, a little amphibian and/or reptile* that looked a little like a lizard. As I said back then, vertebrates were only just getting started on land. They were mostly small, skittering animals. Arthropods, though, were a different case. They first arrived on land in the Silurian period, almost 60 million years before fish took their first soggy, awkward steps onto land. Arthropods were the first animals in earth’s history to fly, and had set up shop pretty firmly by the Carboniferous period.

The earth was wetter and covered in rainforests back then. There was also a lot more oxygen in the air. Insects and other arthropods have very simple respiratory systems. Air flows into their bodies through openings in their exoskeletons called spiracles, then makes its way into the air sacs and distributed accordingly. This is all I know about arthropod breathing. But, this system is much less efficient than the one seen in vertebrates. It puts a size cap on terrestrial arthropods. If they get too big, the air can’t flow through their bodies, and they can’t breathe. But, in the Carboniferous, arthropods were able to get HUGE, thanks to the increased oxygen content of the air. And Eophrynus is… not one of them.

No, Eophrynus is around an inch long (2.5cm, for you non-yanks). It’s a little arachnid from the late Carboniferous. It’s is a Trigonotarbid, an order of arachnids that lived from the late Silurian until the early Permian. They were closely-related to spiders, but slightly more archaic. They were shaped similarly, but didn’t make silk, and their front pair of limbs—called pedipalps—weren’t modified into claws or pincers. Also, there’s no evidence they used them to deliver sperm into females, which is apparently something spiders have been doing for a while.

 It’s a little hard to say exactly how closely or distantly they were related. Arachnids are hard to sort phylogenetically, partially because they all share a very similar body plan. We can usually say if they’re closer to spiders or scorpions, but we haven’t quite figured out much beyond that. We have theories, sure, but it’s not quite set in stone. Well, it’s the fossil record, so, it’s… You know what I mean.

Anyway, like most arachnids, Eophrynus was a predator. It lived on the forest floor, and used its long legs to chase down other, smaller arthropods. But, of course, being a tiny arthropod, it was probably eaten by small amphibians and reptiles. Its abdomen was lined with protective spikes in an attempt to keep this from happening, but let’s be real, if something wants to eat you badly enough, it will. Look at Koalas and Eucalyptus, or Mongooses and venomous snakes. Animals are buckwild.

That’s our animal for today! I’ve talked about invertebrates a few times on this blog, but they’ve always been marine. Marine invertebrates are my favorite group of animals, and I think my bias has been a little clear here.

And, I’ll talk about giant Carboniferous insects soon, I promise. I like them, too. I just want to give the lesser-known, more mundane animals their time to shine, too.