Catacoeloceras cf. jordani GUEX, 5 cm diameter (or Catacoeloceras cf. engeli forma jordani if you prefer the forma type )
In summer 2012 I had the good fortune to find the above pictured ammonite at Hawsker.
I have pictured the unprepped specimen before here and finished the preparation early this
year. The preservation was somewhat special since the ammonite´s outer whorl was covered
by softer matrix and could be prepped with the air abrader straight away, allowing the spines
to be preserved.Only the inner whorl was covered by a small knob of harder matrix that had
to be carefully removed with an airpen.
I did initially have some trouble identifying the species – the outer whorl is close to what SCHLEGELMILCH lists as Peronoceras andraei, which according to HOWARTH is a synonym of Peronoceras perarmatum, but I could not find any visible fibulation on the inner whorls, which are also quite finely ribbed.
Catacoeloceras cf. jordani, inner whorls without visible fibulation
Generally, the features of this ammonite (more on this see below) point more to
Catacoeloceras,HOWARTH lists a Catacoeloceras dumortieri but the measurements
do not agree – Catacoeloceras dumortieri seems to have more depressed (wider) whorls
and a lower rib density (and we´ll get to it later).
GUEX (1972) as the oldest Catacoeloceras and whose measurements, taken from pictures
in literature, are pretty close to this specimen, but I still left the naming at
Catacoeloceras cf. jordani, also due to the factthat the specimen was not found in situ,
but in cliff fall debris.
could have evolved into this species, and with the few specimen in my collection, I can see
intermediates between the two forms, but lacking the necessary amount of specimen to
prove it, this remains speculation.
Assignment of different species to Catacoeloceras or Nodicoeloceras varied wildly by author
until the late 1970s / early 1980s, HENGSBACH in 1985 defined the morphological
differences between Catacoeloceras and Nodicoeloceras as follows :
- Catacoeloceras never ever shows (real) fibulation
- Nodicoeloceras sometimes shows fibulation on the inner and/or outer whorls
- Intermediate ribs crossing the complete whorl without bifurcation are relatively common
with Nodicoeloceras, relatively rare with Catacoeloceras
(e.g. 2-4 per whorl, the above pictured Catacoeloceras has 6) - Nodicoeloceras usually has more dense ribbing
worked on Catacoeloceras, instead of creating different species names for every different
whorl section, he created forma types of C. raquinianum and C. engeli and applied some
other existing species.
The only issue with his work in relevance to Yorkshire is that most of his specimen were
quite small, mostly in the range below 30 mm, so with most Yorkshire specimen exceeding
this size, his work his difficult to apply (if you do not want to break apart you rare & prized
specimen…). Additionally most of his ammonites were not collected from specific known
horizons, which can also be difficult in the steep-hilled badlands of the french Causses,
where most of the ammonites he examined came from.
I lack the amount of material to do any meaningful statistics to distinguish forma types
anyway…
1978 as follows, so once you know which bed the ammonite is from, the distinction is clear :
Ranges of Catacoeloceras and Nodicoeloceras, compiled from HOWARTH, RIEGRAF
In April this year, when visiting Mike Marshall, he showed me this beautifully prepped,
7 cm, Catacoeloceras raquinianum (which I naturally could not leave without & bought
it off him…) :
Catacoeloceras raquinianum (D´ORBIGNY, 1844), 7 cm, complete specimen
how difficult it is to estimate the appearance of a complete adult ammonite form an inner
whorl (which this seems to be, and a bit pathological as well) :
Small inner whorl of Catacoeloceras raquinianum, 3 cm, purchased from Mike Marshall
they’re the same species. The fully grown adult specimen shows characteristics of
Catacoeloceras crassum on the outer whorl, though the whorl is probably not as wide.
Coronate inner whorl of Catacoeloceras raquinianum
TREATISE, the resemblance of at least a few specimen with what I used to lump into
Catacoeloceras puteolum struck me, especially when looking at a specimen found in April
at Ravenscar (unfortunately I cannot show a comparison picture from the Treatise due to
copyright) :
Catacoeloecras dumortieri (DE BRUN), 6 cm, complete specimen with hood at mouth border, unfortunately inner whorl not preserved
Catacoeloceras dumortieri, in fact they were both mentioned as early as in HOWARTH´s
1962 paper “The Jet Rock Series and the Alum Shale Series of the Yorkshire Coast”,
with C. dumortieri from the Peak Shales at Ravenscar, and C. puteolum as “not found”.
“Yorkshire fossil hunters” Facebook group revealed the potential existence of two groups
which differ in their maximum whorl width, one group with a maximum whorl width of up
to 20-25 mm, the other one with a maximum whorl width of up to 30 mm :
Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border, associated with severall Pseudolioceras boulbiense, purchased from Mike Marshall
Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with mouth border
Venter view of Catacoeloceras dumortieri (DE BRUN), 6 cm, complete specimen with wonderfully carved out mouth border, a work of prep art by Mike Marshall
Catacoeloceras puteolum (SIMPSON, 1855), 7 cm, only a few mm missing of the mouth border, purchased from Byron Blessed
Venter view of Catacoeloceras puteolum (SIMPSON, 1855), 7 cm
Until about 2-3 cm, the inner whorls look the same for both groups with a rib density of
about 32/whorl, then the specimen of the group reaching a larger whorl width continue
the growth in whorl width beyond about 20-25 mm up to 30 mm and reach a higher rib
density on the outermost whorl of > 36 ribs/whorl (i.e. retaining an almost constant
distance between ribs), while he group with a smaller max. whorl width do not increase
their whorl width and have a constant rib density of about 32 ribs/whorl on the outermost
adult whorl (i.e. increasing absolute distance between ribs on the outer whorl).
I´m almost sure the group with the bigger maximum whorl width can be associated with
Cataceloceras puteolum, while the group with the smaller max. whorl width is
Catacoeloceras dumortieri – if proven to be found within the same bed (which seems
possible, given the same association with Pseudolioceras boulbiense), they could –
given their similarity in the inner whorls – as well be variants of the same species or
sexual dimorphs.
When writing this blog post, I had the most difficulty finding a representative example
for Catacoeloceras crassum. I have a few candidates, some are inner whorls, one is slightly
pathological, none are complete adults, with the associated uncertainties this poses
(as seen above…). Catacoeloceras crassum is characterized by not having significant
tubercles at the bifurcation points of the ribs, being much like an inflated
Dactylioceras commune.
2 inner whorls Catacoeloceras crassum, 4 & 5 cm
Catacoeloceras crassum (YOUNG & BIRD, 1828), 6 cm, slightly pathological
Catacoeloceras crassum, 5 cm diameter
many of the finds from Yorkshire as well – what we amateurs find most often comes from
cliff falls, most of the time touched by the sea – more work is needed to clarify exact horizons
in which these ammonites occur. Catacoeloceras is a very interesting but also intensely
variable genus – only collections from specific horizons can quantify that variability.
Literature
R.HENGSBACH, 1985 : Die Ammoniten-Gattung Catacoeloceras im S-französichen und
S-deutschen Ober-Toarcien, Senckenbergiana-lethaea 65
W.RIEGRAF, 1986 : Stratigraphische Verbreitung der Ammonitengattung Catacoeloceras
im Toarcium Europas, Senckenbergiana-thethaea 67
M.K. HOWARTH, 2013 : TREATISE ONLINE 57, Part L revised, Volume 3B,
Chapter 4 : Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea, The University of Kansas
M.K.HOWARTH, 1962 : The Jet Rock Series and the Alum Shale Series of the Yorkshire Coast,
Proc. Yorkshire Geological Society 33
L. RULLEAU, P. LACROIX, M. BÉCAUD, J.P. LE PICHON, 2013 : Les Dactylioceratidae du
Toarcien Inférieur et Moyen, und famille cosmoplite, Dédale Editions
sud des Causses (France) et révision des ammonites décrites et figurées par Monestier (1931),
Eclogae geol. Helv 65/3
Yorkshire Ammonites (and other fossils ) revisited 