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An abraded tooth of Edestus (Chondrichthyes, Eugeneodontiformes):
Evidence for a unique mode of predation
Wayne M. Itano
Museum of Natural History, University of Colorado, Boulder, Colorado 80309
wayne.itano@aya.yale.edu
The paired symphyseal tooth whorls of the Carboniferous chondrichthyan Edestus
are perhaps the most enigmatic dental structures of any known vertebrate. The tooth
whorls have been compared to scissors or to saw blades. It is commonly held that the
tooth whorls were used in opposition, to cut prey caught between them. However, the
curvature of the whorls makes such a function inefcient and therefore implausible. A
symphyseal tooth of Edestus minor from the Pennsylvanian of Texas provides the rst
new information bearing on the function of Edestus tooth whorls in over a century. The
tooth is truncated apically, and the surface of the surviving portion is worn smooth. The
orientation of the abraded surface, perpendicular to the axis of the crown, suggests that
the tooth whorls were used to slash prey with a vertical motion of the anterior part of the
body. Such a mode of predation apparently has not been reported in any other organism,
extinct or extant. In contrast to Edestus, wear to the symphyseal teeth of Helicampodus
is to the sides of the crowns, probably resulting from contact with the opposing dentition.
Unpublished notes of W. Langston, Jr. (1921–2013) on the interpretation of the Edestus
tooth from Texas are discussed.
Keywords: Carboniferous, Chondrichthyes, dentition, Edestus, functional morphology,
Helicampodus, Smithwick Shale, Texas
TransacTions of The Kansas
academy of science
Vol. 118, no. 1-2
p. 1-9 (2015)
inTroducTion
Edestus Leidy, 1856, is a chondrichthyan
genus in which symphyseal tooth whorls of
similar size are present in both the upper and
lower jaws. A tooth whorl is a tooth family
in which the teeth are rigidly joined at their
bases (Maisey et al. 2014, p. 587). Edestus
tooth whorls are so unlike any other dental
structures that, in the nineteenth century,
they were thought by some to be defensive
spines or structures analogous to the rostrum
of the extant sawsh Pristis (Eastman 1903).
Edestus specimen USNM V7255 from the
Desmoinesian of Iowa (Fig. 1), which is the
holotype of E. mirus Hay, 1912, and which
consists of two tooth whorls and some poorly
preserved cartilage of the same individual,
established that the tooth whorls were located
in the oral region and that one was in the upper
jaw and one in the lower jaw (Hay 1912).
The function of Edestus tooth whorls has
remained enigmatic, but has not received much
recent attention. There has been a tendency to
consider the Edestus tooth whorl to be a less
extreme form of that of Helicoprion Karpinsky,
1899, and to give more consideration to the
latter genus, e.g., Eaton (1962). However,
Helicoprion differs from Edestus in having
only one large symphyseal tooth whorl, which
is located in the lower jaw (Bendix-Almgreen
1966; Lebedev 2009; Tapanila et al. 2013), so
there is no reason to assume similarities in the
function of the tooth whorls.
The most common interpretation of Edestus
tooth whorls has been that they were used
in opposition, like scissors or pincers, to cut
or grasp prey, e.g., Peyer (1968, p. 73): “In
Edestus the tooth bases reach enormous size
and combine to form tooth-bearing spines
that protruded medially from the snout and
the lower jaw and presumably functioned as
2 Itano
serrated tweezers or scissors.” However, the
curvature of the whorls makes them inefcient
for such a function, since only a few of the
most lingual crowns could have been brought
together, with the more labial teeth seeming to
have no function. An alternative hypothesis,
proposed recently (Itano 2014a), is that the two
tooth whorls extended far outside the mouth
and were used to slash and disable prey with a
vertical motion of the anterior part of the body.
See Fig. 2 for a hypothetical reconstruction of
Edestus consistent with this hypothesis.
There has been no new fossil evidence to
clarify the function of Edestus tooth whorls
in the century since the description of Edestus
mirus. Here, an Edestus tooth with an abraded
apex is reported, which provides some new
information. The tooth was found together
with undated, handwritten notes, apparently
for a never-published manuscript, in the ofce
of Dr. Wann Langston, Jr. (1921–2013) of the
Vertebrate Paleontology Laboratory of the
University of Texas, Austin, Texas, after his
death. A complete transcript of the notes is
included in the Appendix.
insTiTuTional abbreviaTions
ACM, Beneski Museum of Natural History,
Amherst College, Amherst, Massachusetts;
AMNH, American Museum of Natural History,
New York, New York; TMM, Vertebrate
Paleontology Laboratory (formerly with
the Texas Memorial Museum), University
of Texas, Austin, Texas; USNM, National
Museum of Natural History, Washington, D.C.;
YPM, Yale Peabody Museum, Yale University,
New Haven, Connecticut.
Figure 1. Holotype of Edestus mirus Hay, 1912,
USNM V7255, showing lower tooth whorl and
some teeth of the upper tooth whorl, after
Hay (1912, pl. 1, g. 1). Arrow points to the
labialmost tooth of the lower tooth whorl, which
is similar in shape to TMM 46034-1. The gure
is mirror-reversed for easier comparison with
Fig. 3A. Scale bar = 5 cm.
Figure 2. Reconstruction of Edestus newtoni,
after Itano (2014a, g. 17). Tooth whorls of
E. newtoni are more curved than those of
E. minor but are otherwise quite similar. It
is hypothesized that Edestus used its tooth
whorls to injure prey with a vertical motion of
the anterior part of the body. Modied with
permission from copyrighted artwork by G.
Raham, www.biostration.com.
Transactions of the Kansas Academy of Science 118(1-2), 2015 3
sysTemaTic PaleonTology
Class Chondrichthyes Huxley, 1880
Subclass Euchondrocephali Lund and
Grogan, 1997
Order Eugeneodontiformes Zangerl, 1981
Superfamily Edestoidea Hay, 1929
Family Edestidae Jaekel, 1899
Genus Edestus Leidy, 1856
Edestus minor Newberry, 1866
(Figs. 3A, 3B)
Edestus minor Newberry, 1866: pl. 4, g. 24
Edestus mirus Hay, 1912: pl. 1 and 2
Edestus minor Newberry: Itano, Houck and
Lockley, 2012: g. 12
Material. A single tooth, missing the apex and
part of the base, TMM 46034-1.
Locality and age. The tooth, TMM 46034-1
(Figs. 3A, 3B), was found in the vicinity of
Bend, San Saba County, Texas, in a shale bed
below the Cumminsia aplata (Cummins, 1891)
coral biozone. This places it within the lower
part of the Smithwick Shale (Plummer 1950).
Conodont faunas at the Bend section can be
used to date this bed (Grayson et al. 1991;
Lambert pers. com. 2014). The uppermost
Marble Falls Limestone, which conformably
underlies the Smithwick Shale, produced a
conodont fauna of Idiognathodus “klapperi,”
Idiognathoides ouachitensis, Neognathodus
atokaensis sensu lato, and Mesogondolella
clarki/donbassica. The term Idiognathodus
“klapperi” refers to some late Morrowan
to Atokan conodont elements that differ in
morphology from Idiognathodus klapperi
sensu stricto (s.s.), but like it incorporate
all dorsal ornamentation into the platform.
[These morphologies, like most others, had
previously been called Idiognathodus delicatus
(Barrick et al. 2013, p. 56).] The bed is
therefore in the Midcontinent N. atokaensis
zone (Barrick et al. 2013). The middle part
of the Smithwick produced Idiognathoides
ouachitensis, Declinognathodus marginodosus,
and Idiognathodus delicatus sensu lato, which
is latest Atokan (De. marginodosus zone).
Since the stratigraphic level at which the tooth
was found is bracketed by these two conodont
faunas, its age is late, but not latest Atokan
(Lambert pers. com. 2014).
Taxonomic notes. Nomenclatural problems
with Edestus minor have been discussed
elsewhere (Itano 2013, p. 189; Itano 2014b;
Itano, Houck and Lockley 2012, p. 403).
Figure 3. Symphyseal tooth of Edestus minor, TMM 46034-1. (A) Distal (side facing away from the
midline) view. Side of base with hollow groove is above. Lingual edge of crown is above; labial edge
is below. Note truncated apex. Scale bar = 5 cm. (B) Abraded surface of apex. Scale bar = 1 cm.
4 Itano
The holotype of E. minor is a single, isolated
tooth, AMNH FF477, since it is the sole
specimen upon which the original description
by Newberry (1866) was based. A tooth whorl
containing seven teeth, ACM 85, was described
and gured by Hitchcock (1856), but not named
by him. That specimen was later referred to
E. minor by Newberry (1889, pl. 39, g. 1),
and has been treated by some as if it were the
holotype (Itano 2014b). For a recent depiction
of ACM 85, see (Itano 2014a, g. 3B). While
the crowns of ACM 85 resemble those of E.
minor, there are also some differences. The
serrated edges of the crown of E. minor taper
continuously to the apex. The edges of the
crowns of ACM 85 taper slowly near the base
and more rapidly near the apex. Specimen
USNM V7255 (Fig. 1) was designated as the
holotype of a new species, Edestus mirus Hay,
1912, because the crowns differed from those
of ACM 85 (Hay 1912), ignoring the fact that
they are not distinguishable from the crown
of AMNH FF477. Thus, E. mirus should be
considered to be a junior synonym of E. minor,
since USNM V7255 displays no characters
to distinguish it from AMNH FF477. It might
prove necessary to refer ACM 85 to a species
other than E. minor, but the range of variation
within E. minor should be investigated before
making such a redesignation.
Tooth TMM 46034-1 is here referred to
Edestus minor sensu stricto (s.s.) because
the edges of the crown taper rapidly and
continuously toward the apex, as in the
holotype of E. minor, AMNH FF477 (see, e.g.,
Itano 2014b, g. 10), and in USNM V7255
(see, e.g., Itano 2014b, g. 13), and unlike in
ACM 85. Also, the strongly-curved “hook”
in the crown-base margin of TMM 46034-1,
toward the labial end, resembles that in AMNH
FF477 and in USNM V7255. In ACM 85,
the “hook” is not so pronounced. Langston
identied TMM 46034-1 as Edestus vorax
Leidy, 1856 (see Appendix). This is likely due
to an error in Newberry and Worthen (1870,
pl. 1, g. 2), where a gure of ACM 85 was
mistakenly labeled as Edestus vorax.
TMM 46034-1 is the largest reported tooth of
Edestus minor s.s. The crown, when complete,
would have measured about 5 cm from the
apex to the midpoint of the margin between the
crown and base and 4.5 cm across that margin.
This is more than twice the size of the holotype
of E. minor and also larger than any of the
crowns on USNM V7255.
Zangerl and Jeremiah (2004) pointed out that
the bases of Edestus teeth continue to grow
after the crowns are formed. Thus the base of
a fully mature tooth, about to be shed, can be
much larger than that of a newly-formed tooth
(Zangerl and Jeremiah 2004, g. 6). TMM
46034-1 has a quite massive base and may be a
shed tooth. As in all Edestus teeth, the base has
a hollow v-shaped groove on one side, within
which the next tooth formed. Another tooth,
from the Desmoinesian Strawn Group of Texas
(Itano, Houck and Lockley 2012, g. 12), and
here referred to E. minor s.s,, has a smaller
base and may be a newly-formed tooth that was
separated from the tooth whorl by post-mortem
decomposition of the whorl. The curved shape
of the base of TMM 46034-1 differs from that
of many other Edestus teeth, but it is similar to
that of the most labial (most anterior) tooth of
the lower tooth whorl of USNM V7255 (Fig. 1).
inTerPreTaTion by W. langsTon, Jr.
Langston noted that the way in which Edestus
used its teeth was not understood and that the
worn Edestus tooth might provide some new
information on this matter (see Appendix).
He seems to have assumed that Edestus
resembled some edestoids from the Permian
of Greenland described by Nielsen (1952),
such as Sarcoprion edax Nielsen, 1952, which
has a symphyseal tooth whorl in the lower
jaw as well as some smaller teeth in the upper
jaw. Langston apparently was unaware of the
evidence, from USNM V7255, that Edestus
has two symphyseal tooth whorls of similar
size, or, more likely, discounted that evidence.
He appears to be referring to Sarcoprion when
he refers to wear on the sides and near the
Transactions of the Kansas Academy of Science 118(1-2), 2015 5
bases of the symphyseal teeth and to the lack
of wear to the apices. Nielsen speculated that
the wear observed on the sides of the lower
and upper symphyseal tooth crowns was due to
scraping of the crowns against each other, with
a scissors-like action. The sides of the lower
symphyseal teeth of Sarcoprion appear to have
been worn by contact with a pavement of small
lateral teeth (the “dentigerous plates” referred
to by Langston) in the upper jaw.
However, the wear to TMM 46034-1 differs
from that observed in the symphyseal teeth of
Sarcoprion. There is little or no wear to the
sides of the tooth, and the apex is truncated and
worn smooth. It is difcult to reconcile the wear
present on TMM 46034-1 with a Sarcoprion-
like dental function. Apparently Langston was
unable or unwilling to draw any conclusions.
The draft manuscript ends in mid-sentence.
neW inTerPreTaTion
Tooth TMM 46034-1 has a truncated apex (Fig.
3A). The exposed surface on the remaining
part of the tooth is smooth and convex (Fig.
3B). The smooth surface is presumably a result
of abrasion during life. Given what is known
of the morphology of the tooth whorls (e.g.,
from Fig. 1), it is difcult to imagine how the
wear could have resulted from contact with
an opposing dentition. More likely, part of the
apical tip was broken off, perhaps as a result
of striking a hard object, leaving the internal
dentine of the crown exposed. Subsequent,
repeated contact with prey having an abrasive
outer covering, such as skin covered with
thick scales (e.g., palaeoniscoid sh) or
dermal denticles (e.g., chondrichthyans)
might have resulted in the observed smooth
surface. It seems unlikely that the wear
could have occurred postmortem, given the
good preservation of the rest of the tooth,
particularly the surface of the crown. The
large extent of the wear seems to indicate slow
tooth replacement compared to that in extant
sharks. The orientation of the abraded surface
indicates motion of the tooth perpendicular to
its basal-apical axis, most likely in the vertical
plane (since the serrated edges would be most
effective in that case), in order to disable
prey by cutting them. This action might have
been carried out by moving the anterior part
of the body up and down, probably with jaws
xed relative to each other. Such a mode of
predation does not seem to have been reported
in any other organism, either extinct or extant.
This form of damage does not appear to have
been reported previously in Edestus teeth.
The breaking of an Edestus tooth might have
been a rare event, which might account for it
apparently not having been observed before.
The fth and sixth crowns from the labial
end of the tooth whorl that is the holotype of
Edestus newtoni Woodward, 1917, display
damage to their lingual edges, in the form
of gouges, as noted by Woodward (1917, p.
2). Photographs of the damage have been
published recently (Itano 2014a, gs. 14,
15). The gouges might have resulted from
predation-related damage that was not
sufcient to break off the tips of the teeth,
although other causes, including postmortem
breakage, cannot be eliminated. The broader
shapes of the crowns of other species of
Edestus, such as E. heinrichi Newberry and
Worthen, 1870, might have made them less
susceptible to breakage.
conTrasT WiTh TooTh Wear in Helicampodus
Figure 4 shows a symphyseal tooth whorl
of another edestoid, Helicampodus kokeni
Branson, 1935, from the Permian of
Pakistan. Due to the limited fossil record
of Helicampodus, there is no way to know
whether this represents an upper or lower
tooth whorl and whether one or two such tooth
whorls were present. What can be observed are
planar wear facets on several of the crowns.
The facets were noted by Branson (1935). In
Fig. 4 the facets are enhanced by observation in
reected light. The facet on the second crown
from the left in Fig. 4 is the best preserved. The
facet on the third crown from the left might
6 Itano
have extended further to the top and right, but
damage to the surface of the crown makes this
difcult to determine. The rightmost crown
has no wear facet. As in the Edestus tooth
TMM 46034-1, the extent of the wear probably
indicates slow tooth replacement. The facets
presumably resulted from contact with teeth of
the opposing dentition. This indicates that the
teeth were used to cut prey between the jaws,
as in Sarcoprion, possibly with a scissors-like
action.
The orientation of the tooth whorl is not
immediately obvious. However, it seems likely
that the largest crown (rightmost in Fig. 4)
is the most recently formed (youngest and
most lingual). If this is the correct orientation,
then the amount of wear increases from the
youngest to the oldest tooth (from right to left),
as would be expected. Such an orientation
would imply that the basal parts of the crowns
project lingually rather than labially, the
opposite of the situation in Helicoprion and
Sarcoprion.
conclusion
Damage to a tooth of Edestus minor,
apparently due to contact with prey rather than
with an opposing dentition, indicates the use
of the symphyseal tooth whorls to slash prey
with a vertical motion of the anterior part of the
body. Wear to the sides of the symphyseal teeth
of some other edestoids, such as Sarcoprion
and Helicampodus, is likely due to contact with
the opposing dentition and indicates the use of
the teeth to cut prey trapped between the jaws.
Figure 4. Holotype of Helicampodus kokeni Branson, 1935. Distal (side) view of symphyseal tooth
whorl. Labial direction is to the left. Edges of wear facets are marked. Scale bar = 2 cm. Division
of Vertebrate Paleontology, YPM 2181. Courtesy of the Peabody Museum of Natural History, Yale
University, New Haven, CT.
Transactions of the Kansas Academy of Science 118(1-2), 2015 7
acKnoWledgmenTs
I thank J. C. Sagebiel (TMM) for bringing
tooth TMM 46034-1 to my attention, for
facilitating its loan, and for supplying
information on its provenance, including
unpublished notes of W. Langston, Jr. I
thank L. Lambert (University of Texas at
San Antonio) and J. Barrick (Texas Tech
University) for information on the conodont
dating of the Smithwick Shale. I thank D.
Briggs and D. Brinkman (YPM) for access to
collections. I thank H. Blom (University of
Uppsala) for suggesting to me that Edestus
teeth be examined for wear that might indicate
the method of use of the tooth whorls. I thank
David Ward and two anonymous reviewers for
their comments, which led to improvements in
the manuscript.
liTeraTure ciTed
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Transactions of the Kansas Academy of Science 118(1-2), 2015 9
Appendix: Transcript of Langston notes
[Transcript made by W.M.I from copies of handwritten notes of W. Langston, Jr. Blanks to be
lled in later are represented by em-dashes.]
Among the extinct cartilaginous shes whose skeletons are but rarely found fossil, none is more
enigmatic than the group termed edestids. Known since —, & of cosmopolitan distribution in
Pennsylvanian to Triassic rocks, edestid teeth have been discussed in dozens of technical reports.
But like some related taxa (Helicoprion, Sarcoprion, etc.) nothing is known of the endoskeleton in
edestids. Edestid teeth were larger, evidently fewer in number & thus did not form the spectacular
whorls seen in the related Helicoprion. It is reasonably inferred that these teeth were situated in
the symphysis of the lower jaw, that replacement occurred from within the mouth & successive
teeth roled [sic] upward, forward, & outward, to be shed from the anteroventral edge of the jaw.
How the animals used the teeth is still not clear though the literature contains many & varied
suggestions, ranging from the clearly impossible to the ludicrous.
An edestid tooth referable to Edestus vorax Leidy has come to hand, which may shed a little light
on the natural history of the group. The specimen (TMM —) was found in the Smithwick shale,
about — feet below a conspicuous — exposed in a — on — highway — of the town of Bend, —
County, Texas. The age is —. The nder, Mr. — of — has generously donated the specimen to the
Texas Memorial Museum of the University of Texas at Austin.
The specimen is well preserved & shows no traces of post-mortem abrasion. As a single specimen
it seems likely that it is a shed tooth (edestid teeth are often preserved in articulated systems of
three to — teeth.) Its distinctive edestid character is clearly shown in g. —; its gross morphology
agrees with teeth of E. vorax described by — & hence will not be discussed further here. What is
of interest is the tip which is worn away by rubbing against something during life. Since tip wear
has not been reported in edestids before, the question is, how was this tooth worn & what may this
reveal about its relationships to other structures or about habits of the edestids.
Accepting the current view that these teeth were situated in the mandibular symphysis, the
following functions & relationships to other structures have been postulated:
1) —
2) —
3) —
4) —
5) —
The suggestion that the tooth whorl in Edestus tted into a median groove in the cranial rostrum is
derived from evidence available in —. These teeth somewhat resembling edestids “bit” into such a
groove which was apparently bordered on each side by dentigerous plates. Rubbing against these
plates produced wear on the sides & near the base of the symphyseal teeth; apparently, however,
the tips did not occlude with any hard structure as they are apparently unworn. This in fact is about
the only evidence available concerning the relationships of symphyseal teeth to adjacent structures
in the whole group of edestid-like shes and of his interpretation Nielsen states (—), “—
