Greenwaltarachne pamelae was an orb-weaver spider that lived in what is now Montana, USA, during the mid-Eocene, around 46 million years ago.
Known from a single fossil of an adult female, it had a body length of about 2mm (~0.08″) and a legspan of around twice that. The specimen is even well-preserved enough to show banded markings on the legs resembling those of some modern orb-weaver species.
It would have lived in what was then a rift valley with a tropical climate, along the shoreline of the ancient 160km long (~100 miles) Lake Kishenehn. It was part of a highly diverse ecosystem full of numerous other invertebrates – including miniscule fairyflies, and even mosquitoes with evidence of blood preserved inside their bodies – and a wide variety of mammals ranging from tiny rodents to large brontotheres.
References:
- Dawson, Mary R., and Kurt N. Constenius. “Mammalian fauna of the middle Eocene Kishenehn Formation, middle fork of the Flathead River, Montana.” Annals of Carnegie Museum 85.1 (2018): 25-60. https://www.researchgate.net/publication/327631872_Mammalian_Fauna_of_the_Middle_Eocene_Kishenehn_Formation_Middle_Fork_of_the_Flathead_River_Montana
- Downen, Matthew R., and Paul A. Selden. “Fossil spiders (Araneae) from the Eocene kishenehn formation of Montana, USA.” Palaeontologia Electronica 23.3 (2020): a56. https://doi.org/10.26879/1135
- Greenwalt, Dale, and Conrad Labandeira. “The amazing fossil insects of the Eocene Kishenehn Formation in northwestern Montana.” Rocks & Minerals 88.5 (2013): 434-441. https://doi.org/10.1080/00357529.2013.809972
- Greenwalt, Dale E., et al. “Hemoglobin-derived porphyrins preserved in a Middle Eocene blood-engorged mosquito.” Proceedings of the National Academy of Sciences 110.46 (2013): 18496-18500. https://doi.org/10.1073/pnas.1310885110