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Fwd: Edestus, The Strangest Shark?



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---------- Forwarded message ----------
From: Ben Creisler <bcreisler@gmail.com>
Date: Fri, Aug 15, 2014 at 4:42 PM
Subject: Edestus, The Strangest Shark?
To: dinosaur@usc.edu, VRTPALEO@usc.edu



Ben Creisler
bcreisler@gmail.com

Since the once notable/now notorious Discovery Channel Shark Week is
about over--with a fresh batch of "dreckumentaries" rife with
speculative malevolent giant and/or ultra-intelligent modern sharks,
as well as relict monster sharks, all supported by fake witnesses,
fake experts, or duped real scientists and interviewees--I thought I
would point out a recent paper about the genuine (and still
mysterious) Paleozoic shark Edestus.

Wayne M. Itano (2014)
Edestus, The Strangest Shark? First Report from New Mexico, North
American Paleobiogeography, and a New Hypothesis on Its Method of
Predation.
The Mountain Geologist 51(3): 201-222

The pdf can be read and downloaded at:

https://www.academia.edu/7781162/Edestus_the_Strangest_Shark_First_Report_from_New_Mexico_North_American_Paleobiogeography_and_a_New_Hypothesis_on_its_Method_of_Predation



Two incomplete teeth of the chondrichthyan genus Edestus are reported.
They were collected from the Gray Mesa Formation (Pennsylvanian, late
Desmoinesian), Socorro County, New Mexico, in 1996. The
better-preserved tooth belongs to Edestus sp. cf. E. heinrichi. The
other cannot be identified beyond the generic level. These are the
first specimens of the genus known to be reported from New Mexico. The
only other specimens known from the Rocky Mountain region are from
Colorado. Both the New Mexico and Colorado collections are from marine
limestones. In North America, Edestus is most common in marine black
shales of the Illinois Basin, but to date has not been found in marine
gray shales or limestones in the Appalachian Basin. The failure to
find Edestus remains in the Appalachian Basin is probably the result
of the precise timing and limited extent of marine incursions into
that region. Edestus might have been less tolerant of restricted
marine environments than other chondrichthyans collected from
Pennsylvanian deposits in the Appalachian Basin. The function of the
symphyseal tooth whorls of Edestus is obscure, inasmuch as their
convex curvature makes them poorly-adapted to the “scissors” function
proposed in some previous studies. Alternatively, it is proposed here
that Edestus teeth were used to disable prey with a slicing action
carried out with a vertical motion of the head, with jaws fixed
relative to each other, and not with a scissors-like action of the
jaws moving relative to each other. This hypothesis is supported by
the author’s observations of wear and damage on the teeth of the
holotype of Edestus newtoni. Helicoprion tooth whorls are similar to
those of Edestus in that they contain sharp, serrated tooth crowns
along the convex margin of the whorls and extend outside the oral
cavity. The whorls might have functioned similarly to the manner that
is hypothesized for Edestus, that is, to slash prey with a downward
motion of the head, with jaws fixed. This proposed similarity in form
and function would likely represent convergence.