Centennial Honors College
Western Illinois University
Undergraduate Research Day 2014
Poster Presentation
Sheltering Behavior of Silurian-aged Trilobites
Matthew Kenneth Juron
Faculty Mentor: Thomas Hegna
Geology
Fossils typically preserve only the shape of an animal and remain silent on how the
organism lived. On rare occasions, fossils are preserved in such a way as to record
evidence of the animals’ behavior. These rare occasions give us important glimpses into
the past.
This study focuses on two sets of trilobite specimens that seem to exhibit hiding or
sheltering behaviors as their last living acts (‘cryptic behavior’ sensu Chatterton et al.,
2003). Both sets of specimens involve two orders of trilobites: Lichida and Phacopida,
and were collected in ‘float’ material (i.e. loose rock) from the Silurian Gun River
Formation of Anticosti Island, Canada. In the first specimen, a small, complete phacopid
trilobite of the genus Acernaspis is preserved enrolled inside of a much larger tail
between the doublure and outer shell belonging to Lichid trilobite genus Arctinurus.
Acernaspis was essentially within a cave made out of the shell of a much larger relative.
Getting an enrolled, dead Acernaspis specimen inside of the larger tail purely with
physical force is highly unlikely and would amount to a Silurian hole-in-one.
The second specimen consists of three more Acernaspis inside another Arctinurus.
Although the Acernaspis positions are consistent with sheltering behavior, the
Arctinurus is more fragmented and gives it a higher degree of uncertainty, and thus will
be the focal point of further study.