Mistaken Point - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 20

Ivesia
These larger discoidal impressions
(5-60 cm [2-24 in] diameter) are also
highly variable, including 'lobate discs'
with inwardly pointing V-shaped ridges,
'bubble discs' with rounded craters near
the margin, and the peculiar 'pizza discs'
with closely-spaced pustules covering the
surface ( 20 ). The presence of a stalk on
the latter suggests that it may also be a
holdfast or even a floating body tethered
to the seabed (Narbonne et al ., 2001).

diameter), but shows immense variation in
size (up to 100 mm [4 in] diameter) and
preservational styles (Gehling et al ., 2000).
Most commonly in negative hyporelief, it
exhibits a raised rim and ridges radiating
from a slit ( 19 ), while in positive hyporelief
it has concentric ornamentation, or it may
be a flat disc with a central boss. A few
specimens possess a stalk and appear to be
the holdfasts of fronds of Charnia . It may
be that Aspidella includes the holdfasts of
more than one genus of frond.

19

19 The disc-like fossil Aspidella
from the Fermeuse Formation
at Ferryland, Avalon Peninsula.
Coin 22 mm 0.9 in in
diameter.

20

20 The disc-like fossil Ivesia,
known as pizza discs, from
the Drook Formation at Pigeon
Cove, Avalon Peninsula. Scale
bar is in cm and inches.