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