Gilboa - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 101

Mountain may signal the presence of
insects. A bristletail called Gaspea was
macerated from Middle Devonian beds of
the Gaspé Peninsula, Canada (Labandeira
et al ., 1988). This would be the oldest
insect in North America, except that
Jeram et al . (1990) considered it was more
likely to be a modern animal or molt
which was in a crack in the piece of rock.
The only unequivocal evidence for true
insects in the Devonian is a pair of jaws
called Rhyniognatha hirsti from the
Rhynie Chert. These were first reported by
Hirst and Maulik (1926); Tillyard (1928)
described them and suggested that they
were 'insect-like'. The specimen was
studied by many experts over the years,
until Engel and Grimaldi (2004)
confirmed that they belong to a true
insect.

labyrinthodont folds extended, without
destroying it by sectioning (MacEwan,
2002, 2004). In tetrapods, the folds run
much further into the teeth than they do
in fishes. If it were tetrapod, the new
record would pre-date the previous
earliest known form by approximately
10 million years. The results were not
conclusive, but suggested that the tooth
was a little more likely to be tetrapod than
fish; more material from South Mountain
would be decisive in solving this tantalizing
puzzle.

P ALEOECOLOGY OF G ILBOA
The Gilboa Lagerstätte consists of a
number of separate localities, each of
which represent slightly different
habitats (Banks et al ., 1985). The stump
localities represent swamp forest with
large trees and a considerable variety of
undergrowth, judging from the number
of different plants recorded: in addition
to Eospermatopteris trunks there is the
Aneurophyton foliage, lycopods,
horsetails, and cladoxylopsids. The
undergrowth most likely consisted of
bushes and ground cover (creepers), all
of which are extinct forms, did not have
veined leaves, and reproduced by means
of spores rather than seeds. So, we can
envisage a forest not unlike many seen on
Earth today in habitat structure but
composed of very different types of plant.
We have no evidence for the animal life
which lived in these localities. One aspect
of the plant evidence which must be
borne in mind, however, is that since the
forest was inundated and, eventually
killed, by fast-flowing water carrying sand,
some of the vegetation preserved in the
sandstone might well have been
transported from elsewhere by the water,
and not be indicative of plants actually
growing in the forest. The tree stumps are
clear indicators of in situ preservation
(i.e. they are autochthonous); the foliage
debris in the sandstone might have
drifted in (i.e. could be allochthonous).
At Brown Mountain, Leclercqia is the
dominant plant: a creeping lycopod like the

Vertebrates
At South Mountain a bed, approximately
40 cm (16 in) thick, includes bones
concentrated in a chaotic mass of pebbles
and plant debris, including large branches
up to 50 cm (20 in) long. The vertebrate
material consists largely of fragmented
plates of placoderms (primitive armored
fish) and acanthodian (spiny shark)
denticles. The discovery of a single tooth
at South Mountain was exciting because,
though partly pyritized, vertical striations
on the lower third of the tooth
represent infolding of the tooth wall -
a characteristic feature of a type of tooth
known as labyrinthodont. This type of
tooth occurs in the earliest tetrapods - the
first vertebrates on land - but also occurs
in coelacanth fish. Placoderms had no
true teeth, but possessed sharp-edged
plates in their upper and lower jaws, which
could be used for puncturing, cutting, and
crushing. Acanthodians similarly lacked
teeth but possessed long gill-rakers for
suspension feeding. Vicky MacEwan, of
the University of Manchester, UK, took the
tooth to a high-resolution X-ray computed
tomography unit at the University of Texas
to see inside the tooth in order to
determine how far into the tooth the