Produced by the Population Genetics and Evolution class, Furman University

The Silurian: Trigonotarbids
Trigonotarbids were the first completely terrestrial animals (Wagoner 1995). These organisms most closely resembled and are most closely related to modern day spiders (Wikipedia 2010). These organisms lived in a variety of terrestrial habitats but were common in coal swamp ecosystems (University of Aberdeen 2010).The oldest fossils of Trigonotarbids were found in the Silurian Ludlow Bone Bed, and were formally described by Jason Dunlop (Trewin et al. 2010). Currently there are over seventy different Trigonotarbid species known, the oldest being Palaeotarbus jerami (Wikipedia 2010). Fossils have been found in Europe and North America, the best preserved specimens being found in Rhynie Chert of Scotland (Trewin et al. 2010). While these arthropods were not true spiders, they are placed with true spiders in the class Arachnida (Wagoner 1995). Trigonotarbids ranged in size from 4-20 mm (Trewin et al. 2010). They possessed eight legs with two tarsal claws at the end of each appendage, fangs, a head and abdomen region, and separate lateral and median eye tubercles (Trewin et al. 2010). Their obligate terrestriality is shown by their book lungs; respiratory structures found in terrestrial chelicerates today. Trigonotarbids lacked specialized silk-spinning organs ("spinnerets") and therefore had to stalk and ambush their prey-which were likely amphibious arthropods and worms venturing forth from the water on brief forays (Wikipedia 2010).

Page by Chapin Hardy
Fossil of Aphantomartus pustulatus, a trigonotarbid. Photo Credit: Ohio State University.

Trewin NH, Fayers SR, Anderson LI. 2010. Trigonotarbid arachnids. The Rhynie Chert. University of Aberdeen. Accessed February 16, 2010.

Waggoner B. 1995. Trigonotarbida and their Allies. University of California Museum of Paleontology. Accessed February 16, 2010.

Wikipedia. 2010a. Spider. Accessed February 16, 2010.

Wikipedia. 2010b. Trigonotarbida. Accessed February 16, 2010.