In the collage below
are shown several views of a potentially new species of Ceratonurus excavated from the Bois d'Arc in
2009. I think it will be placed in the Back to the Past Museum in Cancun. This unusual specimen is the first from the genus
to be found so high in the Devonian rock column at BlackCatMountain.
All previous specimens were found in Haragan rocks. Photo numbers 1 and 7 show overall views of
the dorsal and anterior aspects. Photo number 2 shows the pygidium; 3 and
4 show close views of the thoracic margin near anterior and posterior
positions; and photo 6 shows details of the genal structure.
Like
its Haragan relative, this species has similar broadly sweeping lateral
thoracic spines, but these appear to be laid out more smoothly with respect to
each other, rather than undulating as is typical of Ceratonurus. Also, like its earlier relative, a series of
thoracic spines remain encrypted in the matrix between each of the prominent
thoracic spines. Three of these, labeled "a, b and c" are
exemplified in photo number 3. These remain covered in most specimens
because they are too difficult to excavate without damaging neighboring spines.
These cryptic spines turn ventrally into the matrix, and details of their
structure have not been described.
A
second distinction with the Haragan species can be seen in the more robust
structure of the ridge, which follows the facial suture. One view of this
ridge can be seen in photo 6, where the ridge passes behind the eye and merges
with the genal spine.
One
of the two occipital spines (photo number 5, indicated by "a") was
truncated by un-identified natural causes, representing an unusual pathological
deformity or predatory scarring. In photo number 2, I attempt to
highlight the diminutive, almost microscopic, lateral spines which adorn the
principal pygidial spines. These are indicated by "a" and
"b" in this photo.
At least three rows of tubercles and spines
adorn the free and fixed cheeks shown in photo number 6. The more
prominent of these are indicated by "a, b and c." Many of these
and other spines on the fossil have been severely truncated by the air abrasive
used to remove carbonate matrix from the cuticle surface. Only part of
their original height remains, and they originally terminated in an almost
microscopic, transparent tip. Based on observations from Bob Carroll,
many of the tubercles on the surfaces of these odontopleurids should actually
be counted as spines, and would be so had their tips not been removed by
weathering or artificial process such as excavation.
