An inordinate fondness for systematics
Graptolite fossil of some sort.
Thought graptolite too but looks like graptolites tend to have thicker 'teeth'... though Rastrites sp. seems to be the closest fit. Ooooh – longispinus! http://www.redes-cepalcala.org/ciencias1/Images5/fosiles/rastrites_sp.jpg =D
Psi Wavefunction nailed it. So I'm forced to try and steal some points. Rastrites is indeed a graptolite, of the family Monograptidae. Graptolites are pelagic colonial members of the phylum Hemichordata. Diagnostic features of Rastrites are the elongate and isolate nature of each theca along the stipe and their simple apertures. It lived during the Llandovery epoch of the Silurian Period.
i was going to ask if this was an archaeocyathid in cross section - but then I found the same pic using the graptolite namehttp://www.redes-cepalcala.org/ciencias1/Images5/fosiles/rastrites_sp.jpg
I was going to guess, "A child's chalk drawing of the Sun," but....
Three points to Psi, two to Adam, and one to Dave. The uniserial rhabdosome with long and widely-spaced thecae indicates Rastrites.
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