Two New Insect Orders?

When a new species of insect is described as being distinct enough to represent a new order, it's kind of a big deal. So it certainly caught my attention over the past year when, not one, but two species from Cretaceous Burmese amber were considered worthy of the honour. Now, I'm going to be up front here and say that, while both are very interesting specimens, in both cases I think that the 'new order' label may be a trifle overblown. What's interesting to me is that my reasons for thinking so are different for both. Let's take a look, shall we?

Lateral and dorsal views of holotype of Alienopterus brachyelytrus, from Bai et al. (2016). Pink scale bar = 1 mm.

The first was published in March of last year by Bai et al. (2016) under the name of Alienopterus brachyelytrus. In overall appearance, Alienopterus resembled a long-legged cockroach, but with the head clearly visible instead of hidden by the pronotum in the cockroach manner. The head would have been mobile and capable of being turned in the manner of a modern cockroach or mantis. The forewings were hardened and reduced to small pads covering only the base of the hind wings, which retained their full length. The femora of the front legs bore a pair of dense rows of setae on their underside, and Bai et al. suggested that Alienopterus may have used these setae to help it grab prey.

A phylogenetic analysis of Alienopterus placed it together with the modern cockroaches and mantids, specifically as the sister group to the latter. Because Alienopterus lacked the primary distinguishing features of a mantis (such as the spined raptorial forelegs), and because of its distinctive wing morphology, Bai et al. made it the type and only species of a new order, the Alienoptera. But there are a number of reasons why I find this designation problematic. It is generally agreed these days that cockroaches and mantids (and termites) together form a clade known as the Dictyoptera. Many people have an idea that cockroaches are one of the oldest living groups of insects, having supposedly been around for hundreds of millions of years. But modern cockroaches and mantids only diverged sometime during the Jurassic and Cretaceous; earlier members of the Dictyoptera were cockroach-like, certainly, but they were just as close to mantids as to cockroaches, and also had features very distinct from either. If we are to recognise a distinct 'order' for Alienopterus purely on phylogenetic grounds, then we would also have accept several separate 'orders' for each of the various lineages of stem-dictyopterans. And as distinctive as Alienopterus is morphologically, it is not the only (or even the most) unusual member of the Dictyoptera. This is, after all, the lineage that has given the termites with their wood-chomping biology and baroque caste system, beetle-like taxa with full-on elytra, and active leapers like the Jurassic Skok svaba or the modern Saltoblattella montistabularis.

There is a definite paradox at play here. On the one hand, the question of which lineages get designated 'orders' is completely arbitrary because there is no formal definition for an 'order' except that it is a taxon that is somehow more significant than a 'family' (itself a completely arbitrary level). From that perspective, there is no inherent reason why the Dictyoptera should not get divided between any number of orders. But on the other hand, the concept of 'order' has a certain cultural cachet. 'Orders' are kind of the base units of entomology: the first thing that any student of entomology is likely to do is learn to distinguish between the various insect orders. Labelling a particular taxon an 'order' is a statement of value; it says that that taxon is somehow fundamentally important in a way that other taxa are not. And while, again, Alienopterus is a very interesting animal in terms of what it can potentially tell us about cockroach-mantis relationships, it is hard to see how it can be called 'fundamental'. There have been extinct 'orders' recognised from the fossil record, such as the Palaeodictyoptera, but such taxa represent notable radiations. With only a single known species, referring to Bai et al.'s taxon as 'Alienoptera' tells us little more than calling it an unplaced species within the Dictyoptera.

Various views of Aethiocarenus burmanicus from Poinar & Brown (2016).

The other new 'order' made its appearance in December, when Poinar & Brown (2017) published Aethiocarenus burmanicus (if you're confused about the date, it reflects the difference between the online and print publication). This was a very odd little insect: a flattened and wingless yet long-legged animal with long antennae. The most distinctive feature of Aethiocarenus is its head, which is globular with great bulging eyes and placed on a narrow neck. Poinar & Brown suggest that it may have made its living hunting in confined spaces, such as crevices in bark or among epiphytes. Because of its highly distinctive appearance from any other known insect, Poinar & Brown placed it in its own new order, the Aethiocarenodea.

In this case, my issue with the establishment of a new 'order' is that it is essentially a statement of ignorance. As distinctive as Aethiocarenus is, there are many equally unusual-looking insects that are not placed in their own 'order'—particularly among wingless forms that can get up to all sorts of freakiness. The overall 'jizz' of Aethiocarenus, particularly the distinct cerci, suggest that its affinities probably lie somewhere within the Polyneoptera, the group of insects including such forms as cockroaches, grasshoppers and stoneflies. Within other polyneopteran orders, a novice entomologist would be hard-pressed to recognise a sandgroper as a grasshopper, or the Javan cave-dweller Arixenia esau as an earwig. Similarly, without a formal analysis it is difficult to exclude the possibility that Aethiocarenus represents a kooky member of some already recognised order. And again, with only one known species, recognition of an 'order' Aethiocarenodea tells us little more than recognition of an unplaced Aethiocarenus.

REFERENCES

Bai, M., R. G. Beutel, K.-D. Klass, W. Zhang, X. Yang & B. Wipfler. 2016. Alienoptera—a new insect order in the roach-mantodean twilight zone. Gondwana Research 39: 317–326.

Poinar, G., Jr & A. E. Brown. 2017. An exotic insect Aethiocarenus burmanicus gen. et sp. nov. (Aethiocarenodea ord. nov., Aethiocarenidae fam. nov.) from mid-Cretaceous Myanmar amber. Cretaceous Research 72: 100–104.