Anomalocaris
canadensis
Some of the most celebrated problematic fossil
organisms are the Cambrian-aged anomalocarids (Arthropoda, Dinocarida,
Radiodonta, Anomalocaridae), the namesake of which is Anomalocaris
canadensis Whiteaves, 1892. The genus name “Anomalocaris”
means “strange shrimp”, which is ironically appropriate, because
the name was given to fossil remains identified as shrimp bodies. But,
anomalocarids are anything but shrimp. These creatures had medium-sized
to large bodies (extrapolated up to ~3 meters long) with a head having a pair
of grasping claws & short-stalked eyes & a pineapple ring-shaped mouth,
plus a body with two lateral rows of swimming flaps (see animated reconstructions of
entire animal).
The first anomalocarid fossils (isolated grasping
claws) were discovered in the 1880s from British Columbia’s Burgess Shale
Formation (see
summary of Burgess Shale). They were identified as shrimp bodies
lacking heads (see photo below).
Anomalocaris canadensis Whiteaves, 1892 grasping claw (~8.5 cm long).
(YPM 35138, Yale University’s Peabody Museum,
New Haven, Connecticut, USA).
In general, paleontologists didn’t recognize
that these Anomalocaris fossils represented parts of a much larger
organism. The true nature of the complete Anomalocaris organism
wasn’t realized until very rare complete specimens (see photos) were excavated
from Burgess Shale quarries by the Royal Ontario Museum.
The mouthpiece of Anomalocaris canadensis
turned out to be an already-known fossil previously identified as a jellyfish -
Peytoia nathorsti (see below). Anomalocaris mouthpieces
resemble pineapple rings, consisting of a radially arranged series of plates
with inward-directed spines. Some bitemarks found on trilobites &
other fossil arthropods are consistent with anomalocarid mouthpiece morphology.
Anomalocaris canadensis Whiteaves, 1892 mouthpiece (~5.25 x ~4.25 cm). This fossil was formerly identified as
“Peytoia nathorsti”.
(YPM 5825, Yale University’s Peabody Museum, New
Haven, Connecticut, USA)