In Depth
The easiest way to describe Chimerarachne is as a spider with a tail, a tail similar to those seen in some whip scorpions. However, most researchers agree that while Chimerarachne looks similar to a spider it probably wasn’t a ‘true’ spider. Instead, Chimerarachne represents group of arachnids that might have had a shared ancestry with true spiders. In the earliest radiation of forms there would have been many spider-like forms, but only one evolutionary line leading to true spiders. How close Chimerarachne is placed to true spiders currently depends more upon interpretation of features between this specific genus and the true spiders as a group.
The body of Chimerarachne is composed into two segments, cephalothorax and abdomen. The abdomen of Chimerarachne is segmented, a trait seen in many primitive arachnids and spiders, including those of the Mesothelae group of spiders, some of which are still alive today. Chimerarachne had eight legs as well as a pair of pedipalps. At the time of writing four known species of Chimerarachne display palpal bulbs, organs that are used for transferring sperm during mating indicating that these individuals were males. The structure of these palpal bulbs is simpler than those seen in the previously mentioned Mesothelae spiders, with greater similarity to mygalomorph spiders (ground dwelling spiders such as tarantulas and trapdoor spiders. Chimerarachne also had fangs, and like those of true spiders, these were hairless. At the time of writing it is impossible to say if Chimerarachne was venomous, and if so how potent the venom, if present, was. Of course the standout feature of Chimerarachne is the thin whip-like tail. What this tail was for is unknown, it may simply have been a primitive feature that had been retained from arachnid ancestors hundreds of millions of years before. However, nature has a way of reducing useless unused body parts that serve no practical or display function, so the observation that the tail is still present after so long lends some weight as to the tail once serving some kind of function, even if it was only vestigial by the Cretaceous.
Chimerarachne also possessed spinnerets, though in a very different arrangement to those seen in true spiders. Two pairs of these are very well developed and similar to those seen in the Mesothelae spiders. There are two additional pairs of stubs that might represent two additional pairs of spinnerets, possibly in the process of being formed.
Chimerarachne would have certainly been a predator of other small invertebrates of similar or smaller size. The fact that all known specimens of Chimerarachne have been found trapped in amber suggests that Chimerarachne may have hunted upon the trunks and branches of trees, either actively searching for prey or maybe lurking within cracks and ambushing creatures as they passed by.
Further Reading
- Cretaceous arachnid Chimerarachne yingi gen. et sp. nov. illuminates spider origins. - Nature Ecology & Evolution. 2 (4): 614–622. - Bo Wang, Jason A. Dunlop, Paul A. Seldon, Russel J. Garwood, William A. Shear, Patrick M�ller & Xiaojie Lei - 2018. - Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils. - Nature Ecology & Evolution. 2 (4): 623–627. - Diying Huang, Gustavo Hormiga, Chenyang Cai, Yitong Su, Zongjun Yin, Fangyuan Xia & Gonzalo Gribert - 2018.
