Aglaspida Fossils - Aglaspidida

Fossil Pictures


Phylum Arthropoda
Stem-group Chelicerata
Order Aglaspidida

Also see:
House Range
Utah Fossils of the Cambrian Explosion
Trilobite Relatives



The Aglaspida (Aglaspids) are an unranked (incertae sedis) clade of early arthropods that due to their resemblance to horseshoe crabs were once believed to ancestral horseshoe crabs, and were included with the chelicerata. Most recently, aglaspids are held to be distinct group, possibly closely related trilobites, and possibly linking the trilobites with the Chelicerata. Although aglaspid fossils are distributed worldwide, they are relatively uncommon in the fossil record. They are, in fact, one of the largest non-trilobite arthropod groups in the fossil record.

Aglaspids had 8 to 12 pairs of appendages and a prominent telson. These morphological characteristics have caused considerable support for Aglaspids being the maker of Protichnites ichnofossils. Protichnites of the Upper Cambrian Mount Simon Sandstone in Wisconsin have been suggested as the first footprints on land in the fossil record, possibly marking the transition to terrestrial life that took tens of millions years more to complete.

Aglaspid Arthropod
Beckwithia typa
Beckwithia typa
Weeks Formation
Millard County, Utah

Hesselbo S.P. (1989) The Aglaspidid Arthropod Beckwithia from the Cambrian of Utah and Wisconsin, Journal of Paleontology, 63(5) 636-642
Hesselbo S.P. (1992) Aglaspidida (Arthropoda) from the Upper Cambrian of Wisconsin. Journal of Paleontology, 66:885-923.