Thursday, October 17, 2013

Cusplet ~ Sound and Sight

This is a small post making a small point or two.

To my ear, there is something melodious and even soothing about the sound of the word cusplet.   Though the word does not appear in the Oxford English Dictionary or, for that matter, in most other dictionaries, it’s not uncommon in the biological and paleontological literature on teeth, particularly shark teeth.  Google’s Ngram Viewer shows that cusplet first appeared in books in English in the middle to late 1800s and really only took hold in the middle of the 1900s.

(The Ngram Viewer is a fascinating tool which gauges the frequency (Y axis) with which specific words or phrases appear by publication year (X axis) among all the words in millions of Google’s digitized books.)

Bretton W. Kent (Fossil Sharks of the Chesapeake Bay Region (1994)), defines a shark tooth cusplet as follows:
a small, enameloid-covered projection lateral to the basal margin of the crown.  (p. 92)
In other words, it’s a little cusp that appears at the base of a tooth’s main cusp.  The sound of the word (at least to me) belies the purpose of this dental feature – grasping a shark’s intended victim.

Visually, for that matter, the cusplets on fossil shark teeth also contradict their predatory purpose, seeming singularly fragile.  Perhaps my reaction to cusplets is a function of how often they have worn away or broken off in the course of the long journey undertaken by fossil shark teeth to reach my hands.  That some cusplets make it through this threat-filled time travel is really quite remarkable.

Take, for example, the cusplets on this sand tiger tooth I recently found at the Calvert Cliffs  The tooth is roughly 16 million years old (mid Miocene Epoch).

I’ve identified this as a tooth from Carcharias reticulata (Probst, 1879), relying on Kent’s Fossil Sharks.  Much of the doubt associated with this identification isn’t a function of my usual waffling.  Rather it stems from debate among the experts because both the genus and species names of this Miocene shark are up for grabs.

Kent’s description notes that teeth from this species are graced with “long, slender cusplets.”  The German priest Dr. J. Probst (1823 – 1905), the first to name this species, identified it as Lamna reticulata and noted that its teeth were distinguished from those of another similar species by “their smaller size and especially by their cusplets.”  (Beiträge zur Kenntniss der Fossilen Fische aus der Mollase von Baltringer, Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg, Volume 35, 1879, p. 145-146.)  To be totally candid, when Probst used the word Nebenspitzen in his description, I departed from Google Translate which rendered that as “secondary peaks.”  “Cusplets” seemed right.

I was momentarily sidetracked when I tried to find out who Probst was.  His birth and death dates come from an article that appeared in the journal Stuttgarter Beiträge Zur Naturkunde in 2002 (Gunter Bechly and Volker J. Sach, An Interesting New Fossil Dragonfly (Anisoptera:  Libellulidae: “Brachydiplacini”) from the Miocene of Germany, With a Discussion on the Phylogeny of Tetrathemistinae and a Fossil List for the Locality Heggbach).  Other than those dates and his two titles – priest and Dr. – I have nothing for him except several papers he wrote, all in German and largely beyond my ken.  Perhaps buried in them is the answer to another question I considered worth pursuing, where did this paleontologically inclined priest come down on evolution?

Both Kent and Probst drew attention to the cusplets on this species, so, it seems appropriate to conclude this “postlet” with a closeup of one of the specimen’s cusplets.

The cusplet has a cusplet.  Actually, Kent notes that this is a possibility with the teeth of this species.  It's quite an accomplishment that these two cusplets survived the vicissitudes of the fossilization process virtually intact.  Admittedly, the secondary cusplet on the other side did not fare as well, but I guess that’s life . . . .

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