A Tooth Whorl of Edestus heinrichi (Chondrichthyes, Eugeneodontiformes) Displaying Progressive Macrowear

Abstract

Edestus is a Middle Pennsylvanian chondrichthyan possessing symphyseal tooth whorls in both the upper and lower jaws. The curvature of the tooth whorls prevents most of the crowns of the opposing whorls from occluding with each other. For that reason, it has recently been hypothesized that the tooth whorls were used to slash prey with a vertical motion of the anterior part of the body, not to cut prey caught between them. A tooth of Edestus minor having a truncated, smoothly worn apex has been reported previously. Here, a partial tooth whorl of a different species, Edestus heinrichi, is described. The apices of the crowns are worn, so that the crown heights are reduced by about one third. The more labial (older) of the two preserved crowns shows more wear than the more lingual (younger) one. In contrast to the previously reported E. minor tooth, wear is observed to the serrations as well as to the apices of the crowns. The observed wear on both the E. minor tooth and on the E. heinrichi tooth whorl supports the recent hypothesis on the function of the tooth whorls. In both cases, the apices might have been abraded by attempted predation on or scavenging of large fish having skin covered with denticles or scales.

Full text

A tooth whorl of Edestus heinrichi (Chondrichthyes,
Eugeneodontiformes) displaying progressive macrowear
Wayne M. Itano
Museum of Natural History, University of Colorado, Boulder, Colorado
wayne.itano@aya.yale.edu
Edestus is a Middle Pennsylvanian chondrichthyan possessing symphyseal tooth whorls
in both the upper and lower jaws. The curvature of the tooth whorls prevents most of the
crowns of the opposing whorls from occluding with each other. For that reason, it has
recently been hypothesized that the tooth whorls were used to slash prey with a vertical
motion of the anterior part of the body, not to cut prey caught between them. A tooth of
Edestus minor having a truncated, smoothly worn apex has been reported previously. Here,
a partial tooth whorl of a different species, Edestus heinrichi, is described. The apices of the
crowns are worn, so that the crown heights are reduced by about one third. The more labial
(older) of the two preserved crowns shows more wear than the more lingual (younger) one.
In contrast to the previously reported E. minor tooth, wear is observed to the serrations
as well as to the apices of the crowns. The observed wear on both the E. minor tooth and
on the E. heinrichi tooth whorl supports the recent hypothesis on the function of the tooth
whorls. In both cases, the apices might have been abraded by attempted predation on or
scavenging of large sh having skin covered with denticles or scales.
Keywords: Carboniferous, dental macrowear, Edestus, functional morphology
transactIons of the Kansas
acadeMy of scIence
Vol. 121, no. 1-2
p. 125-133 (2018)
IntroductIon
Edestus Leidy, 1856, is a Middle Pennsylvanian
chondrichthyan genus having an unusual,
possibly unique, dental morphology. It
possessed symphyseal tooth whorls of
approximately equal dimensions in both the
upper and lower jaws, in contrast to the better-
known Helicoprion Karpinsky, 1899, which
possessed a large, symphyseal tooth whorl
only in the lower jaw (Bendix-Almgreen 1966;
Lebedev 2009; Tapanila et al. 2013). The
curvature of Edestus tooth whorls prevents
most of the crowns of the opposing whorls from
occluding with each other. If the tooth whorls
were used to cut prey trapped between them, by
closing the jaws, the more labial (anterior) teeth
would be nonfunctional, and it is not obvious
why they would be retained. An alternative
hypothesis, that the tooth whorls were used to
slash prey with a vertical motion of the anterior
part of the body has been proposed recently
(Itano 2014). The tooth whorls would have
extended outside the oral cavity, as in Figure
1. It should be noted that the tooth whorls in
Figure 1 are based on those of Edestus newtoni,
which has tooth whorls that are more curved
than other species of Edestus. How much of
the tooth whorls were supported by cartilage
and how much simply covered by skin is
not known. Edestus might have possessed a
exible quadrato-mandibular joint, as suggested
by Zangerl and Jeremiah (2004), to enable
sideways motion of the tooth whorls and to
allow it to close its mouth. However, fossil
evidence for such anatomical details is lacking.
There being no obvious biological analogs,
the paired tooth whorls of Edestus have
been compared to man-made tools such as
scissors or tweezers (Peyer 1968, p. 73). A
different human-tool analog, the leiomano, was
proposed by Itano (2014). The leiomano is an
indigenous Hawaiian weapon, consisting of a
club lined with shark teeth (Buck 1957). The
reproduction of a leiomano shown in Figure
2 is based on one observed on Cook’s third
voyage (Cook and King 1784, pl. 67, g. 1).

126 Itano
The reproduction is lined with teeth of the
tiger shark, Galeocerdo cuvier. Presumably,
the leiomano was swung by hand in an arc so
that the shark teeth would penetrate the skin
and then slice through the esh of a human
opponent. According to the hypothesis of Itano
(2014), Edestus tooth whorls were used in a
similar manner to kill or disable large prey.
An isolated tooth of Edestus minor with a
truncated, smoothly worn apex was reported
recently (Itano 2015a). The wear was
hypothesized to be caused by contact with the
skin of large prey having skin covered with
hard denticles or scales. The large amount of
wear implies that penetration of the skin was
difcult and might have required repeated
strikes. Microwear, consisting of scratches
oriented mainly transverse to the basal-apical
axis, has been observed on other teeth of
Edestus minor (Itano 2015b).
Recently, a partial tooth whorl of a different
species, Edestus heinrichi, was found, which
shows macrowear to the two most preserved
teeth (Figure 3). Such wear does not appear to
have been observed previously on teeth of E.
heinrichi.
Institutional abbreviations: AMNH,
American Museum of Natural History, New
York, New York; ISM, Illinois State Museum,
Springeld, Illinois; NHMUK, Natural History
Museum, London, UK; TMM, Vertebrate
Paleontology Laboratory (formerly with the
Texas Memorial Museum), University of
Texas, Austin, Texas; UI, University of Illinois,
Urbana-Champaign, Illinois.
Systematic Paleontology:
Chondrichthyes Huxley, 1880
Euchondrocephali Lund and Grogan, 1997
Eugeneodontiformes Zangerl, 1981
Edestidae Jaekel, 1899
Edestus Leidy, 1856
Type species: Edestus vorax Leidy, 1856
Edestus heinrichi Newberry and Worthen, 1870
(Figures 3-5)
Holotype: UI X-442, a tooth whorl (Newberry
and Worthen 1870, pl. 1, g. 1). The holotype
is currently missing (D. Blake, personal
Figure 1. Hypothetical reconstruction of Edestus.
Tooth whorls are modeled on those of Edestus
newtoni. Other details of body are conjectural.
Drawing by Gary Raham, www.biostration.com,
used with permission. Figure 2. Reproduction of a leiomano, an
indigenous Hawaiian weapon lined with shark
teeth.

Transactions of the Kansas Academy of Science 121(1-2), 2018 127
communication, May 2013). Several casts are
extant, including AMNH FF 488, ISM 407040,
and NHMUK P.3151.
Material: AMNH FF 21226, a partial tooth
whorl, including two crowns, a small part of a
third crown, and parts of the bases.
Locality and age: Coal mine near Coulterville,
Randolph County, Illinois, USA. Shale bed
overlying the Herrin (No. 6) Coal, Pennsylvanian
Period, late Desmoinesian North American
Regional Stage (= late Moscovian Global Stage).
More precise geographic locality information is
on le at the AMNH.
Figure 3. Partial tooth whorl of Edestus heinrichi, AMNH FF 21226. A. Lateral view of whole
specimen. Labial end to left. Scale bar = 2 cm. B. Lateral view of most labial crown. Labial end to left.
Scale bar = 1 cm. Abbreviations: wa, worn apex; ws, worn serration; us, unworn serration.

128 Itano
Recent chronostratigraphic work, based on
conodont biostratigraphy and on interregional
correlation by use of major glacial-eustatic
cyclothems, allows rather precise dating of
the Herrin Coal (Falcon-Lang et al. 2011;
Falcon-Lang et al. 2018; Heckel 2008; Heckel
et al. 2005; Heckel et al. 2007). The Herrin
Coal lies within the Pawnee major cyclothem,
which is close to and below the Moscovian –
Kasimovian boundary. The Altamont and Lost
Branch major cyclothems lie above the Pawnee
major cyclothem and below the Desmoinesian
– Missourian boundary. The youngest known
Edestus remains are from the Altamont major
cyclothem in both North America (Lake Neosho
Shale Member of the Altamont Limestone)
(Hamm and Cicimurri 2005) and in Russia
(early Krevyakinian regional substage) (Lebedev
2001). The Altamont major cyclothem is the next
one above the Pawnee major cyclothem. Major
cyclothems are spaced by approximately 400 kyr.
results
AMNH FF 21226 is a partial tooth whorl.
Whether it represents part of an upper or lower
tooth whorl is not known. It contains the two
most labial crowns and parts of their bases (Fig.
3A). The apices are truncated, and the apical
surfaces are smooth and convex (Figs. 3A-B,
4A-B). The serrations on both the labial and
lingual edges of the crowns show wear (Figs.
3A-B, 5). The degree of wear to the serrations
is greater near the apices than near the bases
(Figs. 3A-B). The apex of the most labial crown
shows more wear than that of the second most
labial crown. Figure 6 shows an image of the
most labial crown rotated 12º counterclockwise
and overlaid on top of an image of the second
most labial crown. The outlined area represents
the amount of increased abrasion of the most
labial crown compared to that of the second
most labial crown.
Figure 4. AMNH FF 21226. A. Apical view of most labial crown. Labial end to left. Scale bar = 5
mm. B. Apical view of second most labial crown. Labial end to left. Scale bar = 5 mm.

Transactions of the Kansas Academy of Science 1211(1-2), 2018 129
dIscussIon
Analogies of Edestus tooth whorls with
toothed rostra of sawsh and other
chondrichthyans: Functional analogies of
the tooth whorls of Edestus with the toothed
rostrum of the extant chondrichthyan, Pristis
(commonly called the sawsh), were proposed
soon after the discovery of Edestus (Hitchcock
1856; Leidy 1857) and have continued up to
the present (Long 2011, p. 107). On examining
a tooth whorl of Edestus, Louis Agassiz was of
the opinion that it had projected from the front
of the head of a sh, with the teeth pointing
outward and to the side and with another such
tooth whorl placed symmetrically on the other
side of the head (Hitchcock 1856). Placed
in this way, the pair of tooth whorls would
bear some resemblance to a Pristis rostrum,
which has teeth pointing outward on each side.
Agassiz’s reconstruction of Edestus differs in
two respects from more recent reconstructions.
First, the teeth are oriented in a horizontal,
rather than vertical, plane. Second, the apices
of the crowns of the opposite tooth whorls are
directed away from each other, rather than
toward each other.
The toothed rostrum of Pristis microdon is
known to be used both to sense prey and to
capture prey (by stunning or impaling prey,
or by pinning and manipulating them on the
substrate) (Wueringer et al. 2012). Of course,
only the latter function (capturing prey) is
thought to be analogous to Edestus. In the
absence of direct observational data, studies
of microwear of rostral teeth of the extant
sawshark Pristiophorus cirratus suggest that
it also uses its rostrum to capture prey, though
not necessarily to impale them (Nevatte et
al. 2017). Among both extant and extinct
chondrichthyans possessing sawsh-like rostra,
Schizorhiza, from the Upper Cretaceous, is
the one most closely analogous to Edestus.
Pristidae, Pristiophoridae, and Sclerorhyncidae
(other than Schizorhiza) have elongated,
narrow teeth arranged along the lateral margins
of the rostrum, forming comb-like structures.
In contrast, the rostral teeth of Schizorhiza
stroemeri are densely-packed, triangular, and
attened and have sharp cutting edges, so as
to form a double-edged, continuous, serrated,
cutting blade that could have been used as
a slashing weapon (Kirkland and Aguillón-
Martinez 2002; Smith et al. 2015).
The Aetobatus dentition: another example of
post-occlusal retention of teeth: The dentition
of the extant batoid Aetobatus provides an
example of a chondrichthyan in which teeth
are retained after the time when they occlude
Figure 5. AMNH FF 21226. Lateral view of part
of most labial crown, showing abraded apex
and abraded serrations. Labial end to right.
Scale bar = 5 mm. Abbreviations: ws, worn
serration; wa, worn apex.
Figure 6. AMNH FF 21226. Image of most
labial crown overlaid on top of that of the second
most labial crown. Outlined area represents the
amount of increased abrasion of the most labial
crown relative to that of the second most labial
crown. Labial end to right. Scale bar = 1 cm.

130 Itano
with the teeth of the opposite jaw, similarly
to Edestus. While its diet varies regionally,
Aetobatus narinari appears to be a hard-prey
specialist, feeding mainly on shelled gastropods
and bivalves and on hermit crabs (Schluessel,
Bennett and Collin 2010). A preserved jaw of
the white-spotted eagle ray, Aetobatus narinari,
was examined for this study (Fig. 7). Wear on
both the upper dentition (darker region in Fig.
7B) and the lower dentition (depressed region in
Fig. 7C) is clearly visible on this specimen. The
longitudinal (postero-anterior) extents of the
worn parts of the dentitions are 23 mm (upper)
and 55 mm (lower). This implies that about
3.2 cm (about 5 teeth) of the anterior part of
the lower dentition are retained after the point
where they occlude with the upper dentition.
Thus, the lower dentition projected signicantly
beyond the upper dentition. These observations
are consistent with those of Gudger (1914). At
least since Owen (1840-1845, p. 47), it has been
surmised that the projecting lower dentition
was used like a shovel, to dig prey from the
sandy sea oor. Direct observational evidence
for this behavior appears to be lacking. If the
post-occlusal lower dentition is used in this
way, such use does not seem to cause visibly
increased wear to the anteriormost part of the
dentition (Fig. 7C).
Macrowear on AMNH FF 21226, antemortem
or postmortem?: The wear observed on
the crowns of AMNH FF 21226 certainly
occurred prior to the death of the individual that
possessed them. If the wear had been due to
some postmortem process, such as tumbling in
sediment, one would expect to see wear also to
the lateral faces of the crowns and to the bases. In
an Edestus tooth whorl, teeth are shed at the labial
end and added at the lingual end, so the more
labial teeth are older. The fact that the more labial
tooth shows a greater degree of wear than the
other one implies that the tooth wear took place
over an extended period of time. The difference
in wear observed between the two crowns (Fig.
6) probably represents the amount of wear that
occurred during one tooth replacement interval.
Why is Edestus heinrichi macrowear
so rare?: The fact that wear is denitely
observed on AMNH FF 21226 and yet is so
rarely observed on other specimens of Edestus
heinrichi is puzzling. The author has directly
observed many crowns of E. heinrichi and
has not observed any other case in which
macrowear was apparent. Zangerl and Jeremiah
(2004, p. 10), in discussing a collection of many
E. heinrichi tooth whorls and isolated teeth,
stated that “True wear on any of the blades of
the Jeremiah collection has not been observed.”
The wear observed on AMNH FF 21226 is
unusual and must reect atypical circumstances.
The lack of wear on most crowns of Edestus
heinrichi may reect a normal diet of small or
soft prey that would not cause much damage to
the apices or serrations of the crowns, such as
small sh or soft-bodied cephalopods. A diet of
soft-bodied cephalopods has been hypothesized
for Helicoprion (Lebedev 2009; Ramsay et
al. 2015; Tapanila et al. 2013). Zangerl and
Jeremiah (2004, p. 17) suggested that Edestus
fed on jellysh.
Figure 7. Preserved jaws of white-spotted eagle
ray, Aetobatus narinari, from the Phillipines. W.
Itano personal collection, specimen number
2020. A. Both jaws. Upper dentition above,
lower dentition below. B. Occlusal view of
upper dentition. C. Oblique lateral view of lower
dentition. All scale bars = 2 cm.

Transactions of the Kansas Academy of Science 121(1-2), 2018 131
The observed wear both to the apices and
to the serrations of AMNH FF 21226 (Figs.
3A-B) gives some indication of the nature of
the surface that caused the abrasion. Abrasion
of the apices of both crowns could have been
caused by contact with a large, rigid, abrasive
surface. However, such a surface would not
have been able to contact the serrations along
the edges of the crowns. The wear observed
to the serrations could have resulted from
feeding-related attempts to cut through large
prey having an abrasive skin covered with
hard scales or denticles. In such a case, the
skin could have exed under pressure from the
crowns, so that there could have been contact
between the serrations and the skin.
The pronounced macrowear to the apices of
AMNH FF 21226 might have resulted from
repeated strikes to the skin of massive dead
or sessile prey. Live and mobile prey would
not likely have stayed stationary long enough
for such activity to have sawed through their
skin. Two possible scenarios come to mind:
1) The usual prey was depleted, leaving the
individual to feed on something other than its
ordinary diet. 2) The individual was injured
so that it was unable to feed on mobile prey
and was forced to feed on prey, dead or alive,
that was immobile or poorly mobile. The wear
observed on a tooth of Edestus minor (Itano
2015a) might have resulted from a similar set
of circumstances.
Possible multiple functions of the Edestus
dentition: The sharply-pointed and serrated
nature of the crowns of Edestus teeth suggests
a primary function of slicing through esh of
prey. Since the curvature of the tooth whorls
prevents all but the innermost two or three
crowns from occluding with those of the
opposing tooth whorl, this seems to imply a
vertical, whole-head (leiomano) motion to
utilize most of the teeth in slicing esh. This
does not preclude other, secondary functions
for the teeth. The innermost teeth could
have been used to grasp or cut prey caught
between them. Secondary functions of the
outer teeth are possible, but less likely, since
they do not seem to be optimally-adapted
to such functions. The extended Aetobatus
lower dentition can plausibly be used as a
shovel for digging up prey; the Edestus tooth
whorl, probably not. The horizontally attened
rostrum of Pristis appears better-adapted to
pinning and manipulating small prey against
the substrate than the Edestus tooth whorls.
The outer teeth of Edestus could have been
used to snag prey like jellysh (Zangerl and
Jeremiah 2004), but spike-like teeth would
probably function better for that purpose.
conclusIons
The macrowear observed to the apices and
serrations of the two preserved crowns on
AMNH FF 21226 appears to be antemortem
and to be a result of repeated contact with
relatively massive prey having an abrasive outer
covering. The fact that the worn surfaces of the
apices are roughly perpendicular to the basal-
apical axes of the crowns suggests that the teeth
were used to cut prey with a motion transverse
to the basal-apical axes, consistent with the
recent leiomano hypothesis of Itano (2014).
acKnoWledgMents
I thank C. Bollman for nding the tooth
whorl AMNH FF 21226. I thank D. Blake
(UI) and C. Widga (ISM) for information on
the whereabouts of the holotype of Edestus
heinrichi. I thank H. Blom (University of
Uppsala) for suggesting that Edestus teeth
be examined for wear that might indicate
the method of use of the tooth whorls and O.
Lebedev (Paleontological Institute, Moscow)
for discussions on reasons for the scarcity of
Edestus teeth displaying wear. I thank two
anonymous reviewers for raising issues that
lead to improvements in the manuscript.

132 Itano
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