Lytoceras ceratophagum (16 cm) and half a Cleviceras exaratum (9 cm), both pyritized

In the Yorkshire lias another relatively rare family of ammonites is the Lytoceratidae – finding a Lytoceras always makes a day a great collection day, the evolute shell shape reminiscent of  a “horn of plenty” and the complex suture make the ammonites very appealing.

Lytoceras is a rather “conservative” genus that remained relatively unchanged from the lower lias up to the upper cretaceous, its rarity in Yorkshire having something to do with the water depth : Lytoceras is considered a deep water genus that only occasionally strayed into the relatively shallow waters of the Cleveland basin.

Lytoceras seems to get more common during toarcian times, this may have to do with a temporary high in water levels that also allowed tethyan species like Frechiella to migrate in.

All of the liassic species that occur in Yorkshire have a more or less round whorl section, and have more or less evolute shells where the whorls hardly touch each other. The ribs on the shell generally show a typical fimbriation – a fringing of the ribs that leads to a characteristic shell pattern. A feature of the shell that is rarely preserved due to its fragilty (both during times of embedding and during preparation…) are the so-called flares – ribs that have developed into thin collar-like extensions of the shell.

Finding a Lytoceras with preserved flares is a real highlight – prepping it a real challenge, for the thin calcite flares almost break if you look at them – preparation is only possible in softer matrices where low impact prep methods (e.g. air abrasion) can be utilized.

One thing I did not know before reading newer literature about the topic (HOFFMANN 2010) for this post was that a pronounced sexual dimorphism has been
recognized in the Lytoceratidae, with relevant macroconch / microconch pairs so far published being

Lytoceras cornucopia  /  Lytoceras (Trachylytoceras) annulosum

Lytoceras ceratophagum / Lytoceras (Trachylytoceras) nitidum

Section of septarian nodule with Dactylioceras sp (front) and Ovaticeras ovatum (back)

If you read the title of this blog and start to worry that I might stop working on the book and on the blog – well, don’t. This is just referring to the subject of this post, the ammonite genus Ovaticeras…
The title specimen by the way (you might have guessed by the quality of the prepwork) is a specimen purchased from Mike Marshall. Maximum size of the Ovaticeras on this piece is 8 cm.

Gagaticeras in my mind somehow is more of a coincidental find, casually picked up on the way somewhere else – which of course does not do this fine ammonite genus any justice.Around Robin Hoods Bay it has been reasonably common in the last couple of years (though I´ve noticed a drop in the last 2-3 years), I´ve mostly found them almost eroded free or in nodules that were thrown onto the beach during storms, the beds they occur in are very often sanded over – since most of the coast is a SSSI you´re not really supposed to do any large-scale digging in them anyway.

As you start collecting Gagaticeras ammonites, at first sight they mostly look the same (especially in the field), you put them in the drawer as “Gagaticeras gagateum”.
You collect some more, clean them up as good as you can (they´re not easy to prep well because of their delicate inner whorls), put them in the drawer.

After a while, when looking into the drawer at what you´ve accumulated over the years, you begin to wonder and see little differences, a more pronounced keel here, rursiradiate ribbing there, differences in rib density etc.  A while ago after I acquired an air abrader, a re-preparation helped to work out some more details in the inner whorls.

When starting to document the Gagaticeras species for the book, I was really surprised (and pleased of course 🙂 )to see that I do actually have the four species that HOWARTH mentions in his Robin Hoods Bay / Bairstow collection paper !  I must admit though that it did take me some time to find the most characteristic specimen
for each species, there seem to be many intermediates (like the one pictured above, which has a very high rib density but almost no keel and no rib angle at the venter), which all the authors that have recently written about them (HOWARTH 2002, SCHLEGELMILCH 1976, GETTY 1973,…) have taken as a sign that intra-species variation may make it appear that there are more species than there really are – but that´s always the problem when you do not have a large enough collection to do statistical tests.

Gagaticeras gagateum (YOUNG & BIRD, 1828)

Gagaticeras gagateum, 3.5 cm, with aperture & keel view

Gagaticeras neglectum (SIMPSON, 1855)

Gagaticeras neglectum, 4 cm

Gagaticeras neglectum, 4 cm, keel view

Gagaticeras finitimum (BLAKE, 1876)

Gagaticeras finitimum, 3.7 cm, with aperture & keel view

Gagaticeras exortum (SIMPSON, 1855)

Gagaticeras exortum, 3 cm, with keel with

G. exortum is the easiest to identify : Ribs are quite rursiradiate (leaning backwards), there is just a hint of a keel.
If my collection were considered representative, it would be the rarest species of the four. Rib density on the figured specimen is
23 ribs / whorl at 30 mm diameter, another specimen I´ve seen has 26 ribs/whorl at 50 mm diameter.

In case you´re wondering what this all has to do with jet beads ?
Well, “gagateus” is the greek name for jet and the citation in this post´s title is from YOUNG & BIRD´s original 1828 description of “Ammonites gagateus”
and simply refers to similarity of the black whorls with jet beads…