Written by Joe Ballenger
We try to keep track of new developments with the posts we write, so that people can keep up with what’s going on in science. So if there’s a really significant update to something we’ve written in the past, we try to write about it.
We’ve talked about mantis and cockroach evolution in the past. Nancy wrote a post about how mantids are related to cockroaches, and I wrote about why mantids only have one ear. It’s likely they only have one ear because of their relation to cockroaches, and Nancy’s post does a great job explaining why scientists believe cockroaches and mantids are closely related to one another.
This week, a paper came out which added a new chapter to Nancy’s post on mantis evolution. Specifically, an extinct order of insects-appropriately called Alienoptera-was discovered which seems to have features of both cockroaches and mantids. It’s an evolutionary intermediate between the two, and it’s the sort of fossil that’s really important in figuring out how these insects are all related.
Meet Alienopterus brachyelytrus.
Insect fossils are always really cool, because it’s a glimpse of life from the past. A lot of insect groups are completely unrecognizeable to entomologists today, and some are similar enough to be closely related.
At first glance, it might be pretty easy to see how Alienoptera would have features of mantids and cockroaches. The head and body are pretty mantis-like, except for the wings. However, if you look closer, you’ll notice some weird things about the body. The legs actually resemble another insect order, the Mantophasmatodea. The thorax, where those legs come out, are more like a grasshopper. The front wings are shortened, like those of an earwig.
So there’s a lot going on in the picture, and exploring the relationship between cockroaches and mantids is going to require us to look at some really obscure features.
One of the unique features of mantids is a brush on their femur. It’s not something you’ll see unless you know where to look. Once you know where to look, and what this brush looks like, it jumps right out.
However, at the same time, the legs aren’t entirely mantislike. They’re shaped differently, and lack spines which the mantids use to grab prey. Instead of spines, they have hairlike bristles they may have used the same way the mantis uses their spines.
Another couple of features of the legs link these animals to cockroaches. There’s a special segment on the legs-a specific piece of armor-which is unique to cockroaches, mantids and the like. Unfortunately, neither the article or the internet gives us a great picture of this plate, but it’s another one of those unique features which places it closer to mantids and cockroaches than other groups (namely the Mantophasmatodeans).
There’s another neat feature that’s really informative, these big pads at the end of the legs. These pads, called arolia, help bugs stick to slippery surfaces. Mantids don’t have these pads, but cockroaches do. The arolia on the left is from a hissing cockroach, and you can see the arolia in the Alienopterus on the right…they’re the big things at the end of the legs.
By themselves, they’re not that informative. Lots of bugs have them. One group, the Mantophasmatodeans, have pads which look very similar to this. However, Mantophasmatodeans lack many of the mantis/cockroach-like features Alienopterus has. It’s likely that these similar features are the result of living in a similar habitat, and having similar hunting styles.
Another unique feature of the mantis is the shape of the head. They have a head that’s triangular, whereas a cockroach has a head that’s the shape of a watermelon seed. On the head, the mantis has a trio of light-sensitive patches called ocelli. Cockroaches sometimes have two (or none), whereas mantids always have three. I’ve highlighted them with white arrows, so you can see them more easily.
Alienopterus has three ocelli, and a head shape like that of a mantis. The head just isn’t very cockroach-like, even if the legs are more cockroach like than mantis like.
The Bottom Line
Alienopterus is a really important fossil, and it’s good for teaching about paleontology. It’s got a lot of features which look very roach-like and very mantis-like, but it also has a lot of body parts that are completely unique.
When you look at an evolutionary tree made from modern organisms, you always have to remember that you’re not seeing the trunk. Any animal you see is more like a branch off the tree, than a trunk.
Regardless, Alienopterus sheds light on what happened during the mantis/cockroach split…and I think it’s really cool.
Works Cited/Image Credit:
Ming Bai, Rolf Georg Beutel, Klaus-Dieter Klass, Weiwei Zhang, Xingke Yang and Benjamin Wipfler (2016). “†Alienoptera – a new insect order in the roach – mantodean twilight zone”. Gondwana Research.
A special thanks to the following people for sending us the paper via Twitter:
Edit 3/10/2016, 10: 15 PM: The original post was edited for clarity, to more clearly communicate which groups we were drawing distinctions between.