Long-leggedness in cataglyphoid Baltic amber ants

All truly thermophilic ants inhabiting the subtropical belts of our planet—Cataglyphis (Formicinae) in the southern Palearctic region, Ocymyrmex (Myrmicinae) in southern Africa and Melophorus (Formicinae) in Australia—are characterised by extremely long legs and remarkable locomotor agility including extremely high running speeds (relative to body size). In the classic surveys of the rich assemblages of Eocene Baltic amber ants, Gustav Mayr (1868) and William Morton Wheeler (1915) described a few specimens that exhibited some Cataglyphis-like traits. They assigned them to the genera Camponotus and Formica, respectively, but more recently Gennady Dlussky (2008) considered these traits sufficient enough to establish a new genus—Cataglyphoides—for them. Using micro-computed tomographic 3D reconstructions, we show that the relative lengths of the Cataglyphoides legs and the relative contributions of different leg segments (femur, tibia, basitarsus) to the lengths of the legs, fully fit the allometric functions determined for extant Cataglyphis species. Moreover, fossil Formica flori specimens taken from the same Baltic amber deposits have highly significantly shorter legs, and in this respect coincide with extant Formica species. It is also the cuneiform to nodiform petiole characterising the most agile extant Cataglyphis species and promoting their agility and the slit-like shape of the propodeal spiracle found in all truly thermophilic ants that we observe in Cataglyphoides. We discuss the occurrence of a cataglyphoid ant in Eocene northern Europe in the light of hypotheses about the phylogeography of extant Cataglyphis species and surmise that Cataglyphoides has evolved in parallel to, and in this context has acquired a set of traits characteristic for, the most highly advanced Cataglyphis species.