BITTEN TRILOBITES
Trilobites are important and common fossils in
Paleozoic rocks, especially in the Cambrian. Much is known about their
paleobiology, ontogeny, evolutionary patterns, etc. One of the less well
known aspects of trilobitology is the significance of malformations, or
deformities in the preserved exoskeleton. One category of trilobite
malformation is healed bite marks. Below are photos of three
different bitten trilobite specimens.
Elrathia
kingii (Meek, 1870) trilobite
with healed bite mark (2.8 cm long) from the Wheeler Formation (Middle
Cambrian) of western Utah’s House Range.
This is one of the most
abundantly preserved trilobites species on Earth. It is affectionately called “Joe Trilobite”
by some trilobite workers. Elrathia
kingii is abundantly preserved in the Wheeler Formation of the House Range
in northern Millard County, western Utah, USA. Many specimens are
commercially prepared and sold throughout America. Occasionally,
specimens can be found with healed bite marks. This Elrathia
trilobite has a healed bite mark on the left pleural lobe of the posterior
thorax. Three pleurae are strongly malformed. Most bites on
trilobites are blamed on unsuccessful anomalocaridid predation, but other
Cambrian organisms are also known to have preyed on trilobites.
Classification: Arthropoda, Trilobita, Polymerida, Alokistocaridae
Stratigraphy & age: upper Ptychagnostus atavus Interval-zone (=
lower Bolaspidella Assemblage-zone), Wheeler Formation, upper Middle
Cambrian
Isotelus
maximus Locke, 1838 trilobite
with healed bite mark (above & below) from the Arnheim Formation (Upper
Ordovician) of southwestern Ohio’s Flat Run Trilobite Lagerstätte. This large outstretched specimen has a healed
injury on the right side of the cephalon (head). The exoskeleton has
partially regenerated and a small, anomalous genal spine has started
growing. The regenerated exoskeleton indicates that the injury was not
lethal - the bite mark is evidence of unsuccessful predation.
This trilobite specimen, plus the large enrolled
specimen shown below, have healed bite marks on their right sides. Published census information of bitten
trilobites has shown that a statistically significant percentage of specimens
have bite marks on their right sides.
This is a great example of “handedness” (behavioral lateralization) in
the fossil record.
Classification: Arthropoda, Trilobita, Polymerida, Asaphidae
Stratigraphy & age: Flat Run Trilobite Lagerstätte, near-top Sunset
Member, mid-Arnheim Formation, lower Richmondian Stage, upper Cincinnatian Series,
upper Upper Ordovician
Locality:
Flat Run Trilobite Quarry, far-southern Clay Township, far-southwestern
Highland County, just E of Sicily, E of Mt. Orab, southwestern Ohio, USA.
Collected & prepared by Dan Cooper.
Public display at Ohio State University’s Orton
Geology Museum (Columbus, Ohio, USA).
Isotelus
maximus Locke, 1838 trilobite
with healed bite mark (above & below) from the Arnheim Formation (Upper
Ordovician) of southwestern Ohio’s Flat Run Trilobite Lagerstätte. This large enrolled specimen has a bite mark
on the right side of the pygidium (tail).
Notice the scalloped edges of the bite mark - this reflects the
morphology of the attacker’s mouth parts.
Classification: Arthropoda, Trilobita, Polymerida, Asaphidae
Stratigraphy & age: Flat Run Trilobite Lagerstätte, near-top Sunset
Member, mid-Arnheim Formation, lower Richmondian Stage, upper Cincinnatian
Series, upper Upper Ordovician
Locality:
Flat Run Trilobite Quarry, far-southern Clay Township, far-southwestern
Highland County, just E of Sicily, E of Mt. Orab, southwestern Ohio, USA.
Collected & prepared by Dan Cooper.
Public display at Ohio State University’s Orton
Geology Museum (Columbus, Ohio, USA).
For more info. on bitten and malformed trilobites and
behavioral asymmetry, see the following papers (& the papers cited in
them):
Babcock & Robison (1989) - Nature 337:
695-696.
Babcock (1993) - Journal of Paleontology 67:
217-229.
Babcock (2007) - Role of malformations in elucidating
trilobite paleobiology: a historical synthesis. in Fabulous
fossils - 300 years of worldwide research on trilobites. New York
State Museum Bulletin 507: 3-19.