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Coprolites in the Ravens Throat River Lagerstätte of northwestern Canada: implications for the middle Cambrian food web
Kimmig, Julien Pratt, Brian R.
Kimmig, Julien
Pratt, Brian R.
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Abstract
The Rockslide Formation (middle Cambrian, Drumian,
Bolaspidella Zone) of the Mackenzie Mountains, northwestern Canada, hosts the
Ravens Throat River Lagerstätte, which consists of two, 1-m thick intervals of
greenish, thinly laminated, locally burrowed, slightly calcareous mudstone yielding a
low-diversity and low-abundance fauna of bivalved arthropods, ‘worms’, hyoliths,
and trilobites. Also present are flattened, circular, black carbonaceous objects
averaging 15 mm in diameter, interpreted as coprolites preserved in either dorsal or
ventral view. Many consist of aggregates of ovate carbonaceous flakes 0.5–2 mm
long, which are probably compacted fecal pellets. Two-thirds contain a variably
disarticulated pair of arthropod valves, and many also contain coiled to fragmented,
corrugated ‘worm’ cuticle, either alone or together with valves. A few contain an
enrolled agnostoid. In rare cases a ptychoparioid cranidium, agnostoid shield,
bradoriid valve, or hyolith conch or operculum is present; these are taken to be due to
capture and ingestion of bioclasts from the adjacent seafloor. Many of the coprolites
are associated with semi-circular spreiten produced by movement of the worm-like
predator while it occupied a vertical burrow. Its identity is unknown but it clearly
exhibited prey selectivity. Many coprolites contain one or more articulated hyoliths,
ptychoparioid trilobites, or outstretched agnostoid arthropods oriented dorsal side up.
These are interpreted as opportunistic coprovores drawn to the organic-rich fecal mass
while it was lodged near the entrance to the burrow. This argues that hyoliths were
mobile detritivores, and agnostoids were mainly nektobenthic or benthic, like the
ptychoparioid trilobites. Fecal matter was probably an important source of nutrition in
the Cambrian food web.
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2018-04-03
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Society for Sedimentary Geology
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Kimmig, Julien & Brian R. Pratt (2018) Coprolites in the Ravens Throat River Lagerstätte of northwestern Canada: implications for the middle Cambrian food web. Palaios 33: 125–140.