Protoconch

Hajar, where is that photo of the protocones from? I ask only because they look rather similar to the hyolithids I'm working on, which are ALSO from the middle Devonian of Ontario, though they're from the Arkona Shale rather than the Hatch Formation...
 
Hi Hallucigenia. It's from Ontario County, New York (Ontario County, New York - Wikipedia).

Here's a zoomed-out view of the specimen showing a 6 cm orthocone embedded in the mass of "protocones" (nice word - is that term widely used?).
 

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See the discussion at the end of the article below, some thoughts on the size of the protoconch (ammonitellas and nautiltellas (sic?)) as they pertain to taxonomy.

KRÖGER, B & MAPES, R. (2004) Embryonic orthoceratid nautiloids of the Imo Formation (Lower Carboniferous-Upper Chesterian) of Arkansas (USA). Journal of Paleontology 78: 560-573

Download a copy on this page.
 
Scared to weigh in here, given the experience of you all.

A quick (and ignorant) question.

Do you think that we are talking eggs that are individually released into the water column, eggs (many) enclosed within some other structure (e.g. gelatinous egg mass) released into the water column that floats freely, or eggs that are individually (or collectively) attached to the substratum.

I'm looking at Recent ceph (and molluscan) repro strategies, and how protoconch size (or embryo size), shape and sculpture might be influenced (temperature has a significant effect on size). There is a lot of literature on this for Gastropoda, and some for cephalopods.
 
Steve O'Shea;145313 said:
Do you think that we are talking eggs that are individually released into the water column, eggs (many) enclosed within some other structure (e.g. gelatinous egg mass) released into the water column that floats freely, or eggs that are individually (or collectively) attached to the substratum.

That question needs a lot more study Steve. This old thread mentions a lot of very young (? Embryonic) ammonoids mixed in with microgastropods and adult ammonoids. Several questions need to be answered; were these gathered together by hydrodynamic transport or were they in some kind of buried “gelatinous mass”, did all the ammonoids (and gastropods) lay their eggs at the same time and in the same place?

This thread mentions a small “clump” of small (? embryonic) ammonoids, an egg mass or coprolite?

And this thread mentions questionable cephalopod eggs attached to graptolites. (a link to the Kozlowski paper here)

Still, more questions than answers.

Sorry about the broken link Hajar :oops:
 
OK, excellent -- further fuel for my consistent irritation with people using size to make species-level taxonomic distinctions! Grr.

Kevin, that is a truly amazing pile of protoconchs in that first thread. I'm inclined to think that whatever burial mechanism led to that kind of assemblage is also involved in Hajar's specimen in this thread -- I mean, I'd expect tiny ammonites to be eaten by other animals rather than being able to fall to the seafloor mostly-intact and in a consistent location! Clearly it's some kind of seafloor lag deposit, but intuitively it isn't obvious that you'd get all that many (tiny, presumably tasty) planktonic ceph larvae actually making it to the seafloor in the first place. Interesting! What is the matrix? -- it looks like sandstone in the photo?
 
The matrix of the fossil bearing bed is calcarenite (shell fragments mostly, little or no quartz). Another bed, a few meters higher in the section, has the same fossils (without the small gastropods and ammonitellas) is a shell lag made up of broken bivalve shells in a siltstone matrix. both of these beds are in a soft fissile shale. The lower bed occurs sporadically over a very large area (a few hundred square kilometers) so there were probably a great number of small ammonoids in the area.
 
Kevin, what do you know about the record of palaeo-oxygenation in your succession? Any evidence for mass kills associated with algal blooms (as discussed for the Oxford Clay by Wilby et al. 2008. Preserving the unpreservable: a lost world rediscovered at Christian Malford, UK. Geology Today, 24, 95-98)? Have you published on that ammonite bed?

This looks relevant: Taphonomy and Paleobiological Implications of Middle Devonian (Eifelian) Nautiloid Concentrates, Alaska on JSTOR It talks about a combination of biological (group spawning and mass mortality) and physical phenomena.

I enjoyed watching these baby cuttlefish:

I don’t see these accumulations of tiny protoconchs as lags (i.e. accumulations of larger/denser clasts with the smaller/less dense clasts winnowed out). (Here's a paper I should read: http://www3.interscience.wiley.com/journal/118648511/abstract?CRETRY=1&SRETRY=0). Given their low densities and small grainsizes I would expect them to suspend easily under even weakly turbulent conditions, so they would better represent fallout from suspension. There is no preferred orientation of the tiny orthocones seen in the Hatch Formation specimen.
 
A few papers on (very) similar fossils, mostly pertaining to the ontogeny of ammonoid shells.

Landman, Neil H., 1994, Exceptionally well-preserved ammonites from the Upper Cretaceous (Turonian-Santonian) of North America : implications for ammonite early ontogeny. American Museum novitates ; no. 3086

Landman, Neil H., 1987, Ontogeny of Upper Cretaceous (Turonian-Santonian) scaphitid ammonites from the Western Interior of North America : systematics, developmental patterns, and life history. Bulletin of the AMNH ; v. 185, article 2

Landman, Neil H., 1985, Preserved ammonitellas of Scaphites (Ammonoidea, Ancyloceratina). American Museum novitates ; no. 2815

Get a copy here (the 1987 paper is 25M)
 
Another one of these Early Devonian (Emsian) goniatites from Morocco; Sellanarcestes, 14 mm from Bou Tchafine.
 

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