Arachnomorphs

"a close up of a rock with a eclipse of a mark and a red mark in the bottom left of the eclipse "Some of the strangest looking Cambrian arthropods are grouped with the arachnomorphs, a group that includes extinct forms such as trilobites and eurypterids and modern groups such as spiders, ticks, and horseshoe crabs.

Understanding the evolutionary relationships of Cambrian arachomorphs to one another, as well as resolving paleobiogeographic patterns within the group, has been a major focus of research by paleontologists at the University of Kansas in recent years. For more details on this research, please click here to go to the Evolution and Paleobiogeography webpage.

Below we provide a gallery of some of the non-trilobite arachnomorph fossils that have been discovered in Utah. These include fossils of the following species:

  • Dicranocaris guntherorum Briggs and Lieberman et al., 2008
  • Nettapezoura basilika Briggs and Lieberman et al., 2008
  • Emeraldella sp. Walcott, 1912
  • Leanchoilia superlata Walcott, 1912
  • Leanchoilia? cf. protogonia Simonetta, 1970
  • Mollisonia symmetrica Walcott, 1912
  • Sidneyia sp. Walcott, 1911a
  • Utahcaris orion Conway Morris & Robison, 1988
  • Beckwithia typa Resser, 1931

In addition to these non-trilobite arthropods, we also present the first known specimen of the common trilobite species Elrathia kingii (Meek, 1870) that shows traces of the thoracic appendages.

 

Gallery of Arachnomorphs

Note: Marks on all scale bars are centimeters (cm) unless indicated otherwise.

Dicranocaris guntherorum Briggs & Lieberman et al., 2008

a gray rock with a darker gray mark that has a long body and a half circle as a head

University of Utah (UU) 06011.03 (Holotype). Wheeler Formation, Drum Mountains, Millard County, Utah. Figure 5.1 in Briggs and Lieberman et al. (2008).

a gray rock with a darker shade of a eclipse of a body and fades off into a line

KUMIP 135148 (Paratype). Wheeler Formation, House Range, Millard County, Utah. Figure 5.4 in Briggs and Lieberman et al. (2008).

a close up of a dark tan gray with a faded eclipse and black marks in the middle

KUMIP 314079 (Paratype; Part, counterpart). Wheeler Formation, House Range, Millard County, Utah. Figure 5.6 in Briggs and Lieberman et al. (2008).

Nettapezoura basilika Briggs and Lieberman et al., 2008

a close up of a gray rock with a outline of a fish body with a tail at the end
University of Utah (UU) 04083.02 (Holotype). Marjum Formation, House Range, Millard County, Utah. Figure 4.1 in Briggs and Lieberman et al. (2008).

Emeraldella sp. Walcott, 1912

a tan rock with a close up of a pink circle with a darker shade in the middle
KUMIP 204791. Marjum Formation, House Range, Millard County, Utah. Figure 10 in Briggs and Robison (1984).

Leanchoilia superlata Walcott, 1912

a close up of a yellow thick line molded into a rock

KUMIP 204783 (Part, counterpart). Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figured as "Unknown Arthopod 1" by Conway Morris & Robison (1988; fig. 23.1a, 23.1b).

a close up of a dark gray stripe in a rock with a red mark on the bottom left

KUMIP 314028 (Part, counterpart). Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 7.1 in Briggs and Lieberman et al. (2008).

a close up of a long dark mark that is shaped like a drop at the top on a gray rock

KUMIP 314029. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 7.2 in Briggs and Lieberman et al. (2008).

a close up of a oval with a darker body than the gray rock it is on

KUMIP 314030. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah.

a red long body with a half circle as a head

KUMIP 314031. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 7.3 in Briggs and Lieberman et al. (2008).

Leanchoilia? cf. protogonia Simonetta, 1970

a close up of a gray rock with a half a circle as a head on the left side and a long body made up of ovals
University of Utah (UU) 06011.01. Marjum Formation, House Range, Millard County, Utah. Figure 8.2 in Briggs and Lieberman et al. (2008).

Mollisonia symmetrica Walcott, 1912

a close up of a gray rock with a dark brown oval body with a head at the right end of the body

KUMIP 314041. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 9.3 in Briggs and Lieberman et al. (2008).

a close up of a gray rock with a faint outline of a fish like body

University of Utah (UU) 06011.04. Wheeler Formation, Drum Mountains, Millard County, Utah. Figure 9.1 in Briggs and Lieberman et al. (2008).

Sidneyia sp. Walcott, 1911a

a gray rock with some dark brown marks in the middle of the rock

KUMIP 204798. Wheeler Formation, House Range, Millard County, Utah. Figure 14.4 in Briggs and Robison (1984).

a close up of a gray rock with a smudge of brown and lines coming out of the body going down

KUMIP 204799. Wheeler Formation, House Range, Millard County, Utah. Figure 14.1 in Briggs and Robison (1984).

a gray rock with a blue mark in the middle and curved lines molded into the rock

KUMIP 314033. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 6 in Briggs and Lieberman et al. (2008).

Utahcaris orion Conway Morris & Robison, 1984

a close up of a gray and yellow rock with a large long body with a circle of a head at the bottom

KUMIP 204784. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 21.1a, 21.1b in Conway Morris & Robison (1988)

a close up of a yellow rock with a dark smudge in the middle

KUMIP 204785. Spence Shale Member of the Langston Formation, Wellsville Mountains, Box Elder County, Utah. Figure 21.2 in Conway Morris & Robison (1988).

Beckwithia typa Resser, 1931

a close up of a yellow rock with a gray half circle smudge in the middle
KUMIP 314099. Weeks Formation, House Range, Millard County, Utah. Note: see Hesselbo (1989) for details on the occurrence of Beckwithia in the Cambrian of Utah.

Elrathia kingii (Meek, 1870)

a close up of a gray rock with a ellipse body and a outlines of a shell
University of Utah (UU) 06011.05. Wheeler Formation, Drum Mountains, Millard County, Utah. Figure 10.1 in Briggs and Lieberman et al. (2008). Note: scale bar equals 5 mm.