Cambrian Fossils in the Bright Angel Shale

of Northern Arizona

Hyolithid Fossils Section

(Site SW)

  The Burgess Shales Hyolithid shows the living appearance of this mollusc like animal. The Operculum is the fan shaped protrusion on its lower left, here connected by its wing shaped hinges.
Updated 7/12/17
Along with many well preserved Zacanthoides trilobites from this locality, we have also found in the same layers large numbers of well preserved Hyolithes sp. many with fan shaped operculums still attached. Sizes varied from around 1 cm to over 4 cm for the larger specimens. Also, many loose operculums were in the mix. No trace of the two external appendages - "Helens" were found. Here we will photo document the conchs and operculums in numerous close up and microscope images.
This image from the book "The Fossils of the Burgess Shale" by Briggs, Erwin and Collier is a similar genus as our finds, and shows the still attached fan or pectin shaped operculum still attached on the left. The Hyalithid was able to pull this shut on a hinge to seal off the conch and protect the soft parts from predators. The fracture line seen running longitudinally down the conch was visible as well in many of our specimens, and may be caused by cracking from compression during diagenesis. The helens are very delicate and may have been made of a material such as a scleroprotien which normally will not preserve. Notice the "retraction" slots for the helens in the conch.
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This specimen from our collections shows the triangular cone shaped conch pointing upward, and the attachment for the operculum on the bottom. The red dot is 1/4" in all images. Preservation is in a green shale that is very fine grained.
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A loose operculum is seen here. Hordes of this component were found in direct association with the conchs on many slabs. In most cases, they stayed within a few centimeters from the originating conchs. Note the "wings" on the bottom where the hinge was attached to the conchs wing flanges. Size ~ 1cm.
About these images: Most here were taken with a logitech web cam which can focus less than 1cm from the fossils. Those taken with the stereo microscope are at 10x, and taken with a Sony digicam held to the eyepiece and set for autofocus and exposure. Web cam image set - Conchs and Conchs with Operculums or thier attachment bases
(click to enlarge to full size) The fracture line can be seen in this specimen
(click to enlarge to full size) The fracture line can be seen in this specimen
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Free Operculums
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Conchs without operculums:
(click to enlarge to full size) The fracture line can be seen in this specimen
(click to enlarge to full size) The fracture line can be seen in this specimen
(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
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(click to enlarge to full size) The fracture line can be seen in this specimen
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Microscope cam - 10x image set:
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