fossils

A Cretaceous Haidomyrmex as the first trap-jaw ant?

Haidomyrmex zigrasi Barden & Grimaldi 2012

In case we needed a reminder we still don’t know much about the ancient ants that wandered about under dinosaur feet, Phillip Barden and David Grimaldi have described some bizarre extinct species in the genus Haidomyrmex:

The discovery of two distinct, near-complete specimens belonging to the Cretaceous ant genus  Haidomyrmex Dlussky prompts a detailed description and discussion of a remarkable mandibular morphology. The specimens, preserved in 98 million-year-old amber from northern Myanmar, are described here as  Haidomyrmex scimitarus, n. sp., and  Haidomyrmex zigrasi, n. sp., with diagnostic differences provided between them as well as with  H. cerberus Dlussky (also in Burmese amber). Relationships and comparisons of  H. scimitarus, H. zigrasi, H. cerberus, and the recently described  Haidomyrmodes mammuthus Perrichot from Cretaceous French amber are also discussed.  Haidomyrmex was probably arboreal, cursorial, and a specialized trap-jaw predator, utilizing its enormous mandibles and cranial morphology in concert to capture prey. Mandibles appear to have moved in a plane oblique to the dorsoventral and horizontal axes of the body, unlike the lateral-plane movement of modern ants. The additions of these new fossils provide insight into some of the earliest yet surprisingly specialized ants that roamed the Earth.

These fossils confront the thin stereotype of evolution as progressing from simple ancestors to complex, specialized modern descendants. In spite of some typically ancestral traits (short antennal scapes, waist with a single petiole), Haidomyrmex mandibles are every bit as unusual as the weirdest, most derived present day ant mouthparts. Barden & Grimaldi interpret these as yet another independent instance of a trap-jaw mechanism, a conjecture I view as likely considering the shape of the mandibles, the forward-pointing eyes, and the presence of what appear to be trigger hairs.

This ant’s vertical trap is distinctly different from modern lateral traps, however. Have a look at some present-day species.

One speculation of the paper I don’t buy is this:

The long, slender mesosoma with oblique sutures, short metasoma, and the very long legs and antennae suggest that Haidomyrmex was arboreal. This extreme body structure is found in unrelated extant ants that are arboreal, specifically Oecophylla (Formicinae) and Leptomyrmex (Dolichoderinae).

Leptomyrmex species are, in fact, mostly ground-nesting. And there are a great many other slender soil-nesting ants. The most we can justifiably say is that the eyes and long appendages indicate an above-ground forager. Still, this is a minor interpretive quibble with a significant new discovery.


source: Barden, P. Grimaldi, D. 2012. Rediscovery of the Bizarre Cretaceous Ant Haidomyrmex Dlussky (Hymenoptera: Formicidae), with Two New Species. American Museum Novitates Number 3755:1-16. 2012 doi: http://dx.doi.org/10.1206/3755.2

Rare amber ants on ebay

Paraneuretus (Formicidae:Aneuretinae), photo by ebay seller rmvveta

Here’s something unusual for the well-financed collector: Paraneuretus, an extinct genus from a nearly extinct subfamily of ants.  This pair of fossilized worker ants is selling on ebay today for over $400. Out of my budget for these sorts of things.

Most amber ants up for auction belong to common extinct species: Azteca, Tapinoma, Camponotus and so forth, usually from the Dominican or Baltic amber deposits and pertaining to extant genera. This is the first aneuretine I’ve seen.

What’s interesting about these ants? Well, they’re one of those neither-this-nor-that fossils that are intermediate between groups of modern ants. Aneuretines have a single petiolar node and a body structure much like the modern subfamilies Dolichoderinae and Formicinae. But unlike either of those, Paraneuretus retains a stinger. It’s like a proto-dolichoderine before the ancestral stinger was lost in favor of more derived chemical defenses.

A single aneuretine persists today: Aneuretus simoni, a small and probably endangered species from Sri Lanka.  Genetic analyses of that species show it to be sister to dolichoderines, as one would expect.  What is less clear is where fossils like Paraneuretus fit.  They might be relatives of Aneuretus, but their similarity might just be an artifact of retained ancestral traits, with Paraneuretus genealogically closer to the dolichoderines.  In any case, it is a fascinating fossil and a glimpse at an earlier ant body plan only rarely seen today.

By the way, if any of you end up buying these ants I urge you to consider donating the specimens to a museum where they will be available for scientific research.  Other specimens do exist, but these are in beautiful condition.