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Cambrian Cannibals: Agnostid Trilobite Ethology and the Earliest Known Case of Arthropod Cannibalism. Mark A. S. McMenamin Department of Geology and Geography Mount Holyoke College 2010. The Puzzling Agnostids.

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cambrian cannibals agnostid trilobite ethology and the earliest known case of arthropod cannibalism

Cambrian Cannibals: Agnostid Trilobite Ethology and the Earliest Known Case of Arthropod Cannibalism

Mark A. S. McMenamin

Department of Geology and Geography

Mount Holyoke College

2010

the puzzling agnostids
The Puzzling Agnostids
  • Due to their small size, agnostid trilobites have defied attempts to properly interpret their:
  • Affinities
  • Environmental preferences
  • Ethology
  • Feeding strategies or “eat-ology”
peronopsis interstricta
Peronopsis interstricta
  • Middle Cambrian
  • Wheeler Formation
  • Millard County, Utah
bite marks to pygidial margin
Bite marks to pygidial margin

Source: L. E. Babcock, 2003, in Kelley et al., ed., Predator-Prey Interactions in the Fossil Record

agnostid damage shredded thorax
Agnostid damage: shredded thorax

N.B.: Trilobites are on the same bedding plane.

captured small agnostid
Captured small agnostid

Photo credit: Marian Rice

damaged remains of smaller agnostid
Damaged remains of smaller agnostid

Photo credit: Marian Rice

proportion of samples showing large and small agnostids juxtaposed
Proportion of samples showing large and small agnostids juxtaposed

16%

84%

N=44; blue=juxtaposition; red=no juxtaposition

proportion of multi agnostid samples showing evidence of cannibalism
Proportion of multi-agnostid samples showing evidence of cannibalism

42%

58%

red=no evidence; blue=evidence of cannibalism

how might a seek and destroy
How might a “seek and destroy” . . .
  • cannibal predator be blind?
  • Hypothesis: agnostids used an alternate sensory modality, such as chemotaxis (or, say, response to electrosensory stimuli), to locate their prey.
  • Is there any way to test this?
  • Let’s take a second look at the “snapshots.”
the origins of cannibalism
The origins of cannibalism

Modified from J. Keith Rigby, 1978, Jour. Paleo. 52:1327 with

data from: D. Collins et al., 1983, Science 222:166, fig. 2.

ottoia cannibalism
Ottoia cannibalism
  • Ottoia—Earliest known case of cannibalism, 505 my.
  • The case for cannibalism here is fairly certain (as opposed to the alternative of scavenging dead priapulids by swallowing them whole), as cannibalism is common in modern priapulids.
  • The Burgess Shale is slightly older than the Wheeler Shale; both are Middle Cambrian.
  • No direct evidence yet to my knowledge for cannibalism in the Early Cambrian.
early history of cannibalism
Early History of Cannibalism
  • Early cannibals are not necessarily associated with vision-directed predation.
  • Ottoia and Peronopsis were both presumably blind animals.
  • The earliest Cambrian ichnofossil Treptichnus pedum may have been formed by a stem-group priapulid.
  • The behavioral tools associated with macropredation may have been refined within a single species before being unleashed on the rest of the biosphere.
triops longicaudatus
Triops longicaudatus
  • Jessica McMenamin and our home school Triops experience.

You are what you eat!

Photo Credit: Steve Jurvetson

triops and agnostid compared
Triops and agnostid compared

Agnostus pisiformis: “possibly

raptorial antennae”—C.O.R.E.

Photo Credit: USGS

arthropod cannibalism
Arthropod Cannibalism
  • DiscoveryNews discussion of cannibal agnostids; A. Horning comment.
  • http://news.discovery.com/animals/early-animals-cannibals.html
flip over all burgess shale agnostid specimens in your teaching collection
Flip over all Burgess Shale agnostid specimens in your teaching collection

MHC Sample 3020

Labelled Pagetia bootes (Walcott)

Unlabelled, new specimens of Ottoia on the reverse side!

acknowledgments
Acknowledgments
  • Thanks to:
  • Lee Bouse, Douglas Fleury, Jerry Marchand, Jessica McMenamin, Steve Dunn, Marian Rice and Jacqueline Boisvert for assistance with various aspects of this research.