Dinosaurs overshadow everything. Looking at depictions of Mesozoic ecosystems, sometimes it's easy to believe that the food web in the heyday of the terrible lizards only included carnivorous dinosaurs, herbivorous dinosaurs, and plants. But it's worth zooming in a little - looking past the famous saurians - at the other, less-famous organisms of the time. Consider, for example, protospiders.
About 100 million years ago, in what's now Myanmar, four little arachnids independently became trapped in amber. These are the invertebrates now described as Chimerarachne yingi by paleontologist Bo Wang and colleagues, and they present mix-and-match features that place them close to the origin of the various eight-legged friends who've taken up residence in our homes and gardens.
At first glance, Chimerarachne doesn't look very much like house spiders you're familiar with. For one thing, it has a tail-like appendage called a flagellum. (This wasn't a weapon, but a sensory organ.) With an arachnologist's eye, however, you might spot features like fangs and silk-producing spinnerets that make Chimerarachne a closer relative of modern fossils than similar, previously-discovered fossils. They're not spiders, proper, but they're the next closest thing.
But this doesn't mean that true spiders evolved after Chimerarachne. The oldest representatives of true spiders are far older, dating back to about 300 million years ago. This means that Chimerarachne is a late-surviving member of the group from which true spiders likely emerged, so more-or-less "modern" spiders co-existed with members of their ancestral lineage for millions upon millions of years. The tale of Chimerarachne thus becomes a success story, just one of many ways of arachnid evolutionary expression persisting through time.
Name: Chimerarachne yingi
Meaning: Chimerarachne means "chimera spider" - in reference to the arachnid's mix of traits - while yingi honors the fossil's collector, Yanling Ying.
Age: Cretaceous, about 100 million years ago.
Where in the world?: Northern Myanmar.
What sort of organism?: An arachnid belonging to a group called the Uraraneida.
How much of the organism’s is known?: Four specimens in amber.
References:
Wang, B., Dunlop, J., Selden, P., Garwood, R., Shear, W., Müller, P., Lei, X. 2018. Cretaceous arachnid Chimerarachne yingi gen. et. sp. nov. illuminates spider origins. Nature Ecology & Evolution. doi: 10.1038/s41559-017-0449-3
Huang, D., Hormiga, G., Cai, C., Su. Y., Yin, Z., Xia. F., Giribet, G. 2018. Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils. Nature Ecology & Evolution. doi: 10.1038/s41559-018-0475-9
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