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Palaeontologia Electronica
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Itano, Wayne M. 2019. Oriented microwear on a tooth of Edestus minor (Chondrichthyes, Eugeneodontiformes): Implications for
dental function. Palaeontologia Electronica 22.2.39A 1-16. https://doi.org/10.26879/831
palaeo-electronica.org/content/2019/2603-edestus-minor-microwear
Copyright: July 2019 Society of Vertebrate Paleontology.
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Oriented microwear on a tooth of Edestus minor
(Chondrichthyes, Eugeneodontiformes):
Implications for dental function
Wayne M. Itano
ABSTRACT
The symphyseal tooth whorls of the Carboniferous chondrichthyan Edestus con-
sist of files of teeth having sharply-pointed, serrated crowns, joined at their bases. A
single tooth whorl was present in each jaw. How these tooth whorls functioned is
unclear, since their convex curvature allows only a few of the most lingual crowns of
opposing tooth whorls to occlude. Rather than working in opposition, like scissors, the
more labial teeth might have been used to cut and disable prey with a vertical motion of
the anterior part of the body. Provided the scratches observed on the surface of Edes-
tus teeth can be inferred to have been generated in the process of feeding, their orien-
tation might be used to distinguish whether the teeth were used mainly in occlusion, to
cut prey trapped between the jaws, or mainly to cut prey situated outside the oral cav-
ity. Edestus minor teeth having unusually good surface preservation were examined for
microwear. The teeth are from the Strawn Group (Desmoinesian, Middle Pennsylva-
nian) of San Saba County, Texas, USA. The best-preserved crown surfaces display
scratches 50 to 500 micrometers long. The scratches are oriented predominantly
transversely to the basal-apical axis. This observation appears to support the vertical
slashing hypothesis. However, the possibility that interaction with the substrate contrib-
uted to the observed wear cannot be discounted.
Wayne M. Itano. Museum of Natural History, University of Colorado, 1995 Dartmouth Ave., Boulder,
Colorado 80305, USA. wayne.itano@aya.yale.edu
Keywords: Pennsylvanian; Texas; Chondrichthyes; Edestidae; sharks; functional morphology; dental
microwear
Submission: 3 November 2018. Acceptance: 26 May 2019.
INTRODUCTION
Edestus sensu lato (including Lestrodus
Obruchev, 1953, and Edestodus Obruchev, 1953)
is a chondrichthyan in the order Eugeneodon-
tiformes Zangerl, 1981, that possessed symphy-
seal tooth whorls of similar sizes in both jaws. It is
known from Pennsylvanian deposits ranging in age
ITANO: EDESTUS MINOR MICROWEAR
2
from Bashkirian to early Kasimovian and geo-
graphically from North America, Britain, and Russia
(Itano et al., 2012).
Edestus sensu lato may be unique among
chondrichthyans in possessing two large, symphy-
seal tooth whorls of similar sizes, with blade-like,
sharply-pointed, serrated crowns. Teeth are shed
from the outer, labial end and replaced at the inner,
lingual end, as in a normal chondrichthyan tooth
file. This unusual dentition is best known from the
holotype of Edestus mirus Hay, 1912, which shows
both tooth whorls of a single individual (Figure 1).
The convex curvature of the tooth whorls prevents
all but the two or three lingualmost crowns of each
whorl from occluding with the corresponding
crowns of the opposing whorl. Itano (2014) pro-
posed that the tooth whorls were used in an uncon-
ventional way, not to cut prey caught between
opposing tooth whorls (scissors-mode), but to
slash prey situated outside the oral cavity, with a
vertical motion of the whole head (Figure 2).
Given that possession of a flexible neck, as in
the Devonian tetrapod-like fish Tiktaalik (Daeschler
et al., 2006), is unknown in any chondrichthyan,
the vertical motion might have been carried out by
(1) flexing of the whole body between a U and
inverted-U shape or (2) vertical motion of the front
part of the body by using the pectoral fins like
wings (Itano, 2014, p. 215-216). At present, there
is no postcranial fossil evidence of Edestus to
either support or refute either of these two possibil-
ities.
Macrowear sustained during life has been
reported on a tooth of E. minor from the Smithwick
Shale (Pennsylvanian, late Atokan = Moscovian) of
San Saba County, Texas, USA (Itano, 2015). The
apex of the crown is truncated, and the surface of
the remaining part is smooth and convex, as if
worn by repeated contact with an abrasive surface,
such as the skin of a large fish covered with scales
or denticles. The fact that the abraded surface is
roughly perpendicular to the basal-apical axis of
the crown appears to support the slashing-mode
hypothesis over the scissors-mode hypothesis.
Similar apical wear has recently been reported on
two crowns of a partial tooth whorl of E. heinrichi
from a shale bed overlying the Herrin (No. 6) Coal
(Pennsylvanian, late Desmoinesian = late Mosco-
vian) of Randolph County, Illinois, USA (Itano,
2018).
Observations of dental microwear have long
been used to elucidate dental function and diet in
extant and extinct animals. The first application of
FIGURE 1. USNM V7255, holotype of Edestus mirus
(scale in cm). Copyright © Smithsonian Institution, all
rights reserved. Used with permission.
FIGURE 2. Reconstruction of the head of Edestus, illus-
trating the hypothesized, whole-head, vertical slashing
motion. The curvature of the tooth whorls is based on
the holotype of Lestrodus (originally Edestus) newtoni.
Modified with permission from copyrighted artwork by G.
Raham, www.biostration.com.
PALAEO-ELECTRONICA.ORG
3
dental microwear in paleontology seems to have
been by Simpson (1926), who used scratch direc-
tions to infer chewing movements in Mesozoic mul-
tituberculate mammals. More recently, 2D, feature-
based dental microwear observations have been
used to infer diet in mammals, as in distinguishing
browsers from grazers, using a scanning electron
microscope (SEM) (Walker et al., 1978) or a low-
magnification binocular light microscope
(Solounias and Semprebon, 2002). 2D microwear
analysis has been applied to fishes in a few cases
(Purnell et al., 2006; Purnell et al., 2007). A 2D
microwear analysis relies on human identification
of features such as scratches and pits and is sub-
ject to strong intra- and inter-observer errors (Mihl-
bachler and Beatty, 2012). A 3D dental microwear
texture analysis uses a confocal profilometer and
scale-sensitive fractal analysis to measure surface
textures without requiring the counting of individual
features (Ungar et al., 2003; Scott et al., 2006). A
3D dental microwear analysis is subject to smaller
intra- and inter-observer errors (DeSantis et al.,
2013; Arman et al., 2016) but requires specialized
equipment. The method has been applied to stud-
ies of dental microwear in mammals (e.g., DeSan-
tis, 2016) and fishes (Purnell et al., 2012; Purnell
and Darras, 2016), including, very recently, sharks
(McLennan, 2018).
In the present study, a form of 2D microwear
analysis was used. The orientation of microwear
features on the crown surfaces of an Edestus tooth
might help to distinguish between the two afore-
mentioned alternative hypotheses (scissors vs.
slashing). Scratches oriented mainly parallel to the
basal-apical axis would support the hypothesis that
the whorls were used in opposition, like scissors
(Figure 3.1), while scratches oriented mainly per-
pendicular to that axis would support the vertical-
slashing hypothesis (Figure 3.2). This presupposes
that the observed wear is indeed feeding-related,
which is not known a priori. There is also a possibil-
ity that scratches could have been generated
through interaction with the substrate. In addition,
wear acquired postmortem needs to be distin-
guished from wear acquired in vivo.
The two hypothesized functions of the teeth
need not be mutually exclusive. Possibly teeth at
an early stage of ontogeny might have been used
in occlusion, while they were still within the oral
cavity, and then used in a slashing, non-occlusal
manner at a later stage of ontogeny. However, the
possibility that the innermost teeth were used to cut
prey, while the outer two-thirds to three-quarters of
the teeth had no function runs into the objection
that those outer teeth carry a heavy cost in terms of
weight and water resistance, so it is not obvious
why they would be retained.
Other chondrichthyans, both extant and
extinct, have had non-occlusal tooth-like struc-
tures, but attached to their rostra. These chon-
drichthyans comprise the extant Pristidae (sawfish)
and Pristiophoridae (sawsharks) and the extinct
Sclerorhynchidae. Analogies in function between
Edestus tooth whorls and the toothed rostrum of
the extant sawfish Pristis were proposed soon after
the discovery of Edestus (Hitchcock, 1856; Leidy,
1857). The rostrum of Pristis microdon is used both
to sense and to capture prey, by stunning or impal-
ing them or by pinning them to the substrate
(Wueringer et al., 2012). Observations of
microwear on rostral teeth of the sawshark Pristio-
phorus cirratus suggest that it also uses its rostrum
to capture prey, though not necessarily to impale
them (Nevatte et al., 2017). In that work, numbers
of scratches were counted, but the directional dis-
tributions of the scratches were assessed only
qualitatively. The extinct sclerorhynchid
Schizorhiza stroemeri has rostral teeth that are tri-
angular, with sharp cutting edges, so that its ros-
trum might have been used as a slashing weapon,
in a similar manner to the function that is hypothe-
FIGURE 3. Schematic diagram showing the orientation
of feeding-related scratches (red) on a tooth of Edestus
for tooth whorls used in opposition (1) or in vertical
slashing mode (2). Serrated crowns are blue, lingually
extended bases are brown.
ITANO: EDESTUS MINOR MICROWEAR
4
sized here for the Edestus tooth whorls (Kirkland
and Aguillón-Martinez, 2002; Smith et al., 2015).
The extant batoid Aetobatus narinari is an
example of a chondrichthyan in which teeth are
retained beyond the point at which they occlude
with the teeth of the other jaw. Photographs of the
upper and lower dentitions of a single individual
were published previously (Itano, 2018, fig. 7A-C).
It has been hypothesized that the projecting lower
dentition is used like a shovel, to uncover prey in
the substrate (Owen, 1840-1845, p. 47). Observa-
tions of this behavior are lacking. Also, the post-
occlusal extremity of the lower dentition of the
specimen examined does not show any increased
wear. While the absence of increased wear does
not rule out the “shovel” hypothesis, neither does it
provide any support for that hypothesis. Another
possibility is that the post-occlusal part of the lower
dentition (five teeth out of 19 visible on the speci-
men examined) has no function. In that case, it
might be that the lower symphyseal teeth are so
rigidly cemented together that it takes some time
for them to break off after they have ceased to be
functional.
The possibility that Edestus tooth whorls were
used to uncover or scrape prey, such as mussels,
from surfaces, has been suggested (Eaton, 1962).
While the tongue-like, projecting lower dentition of
Aetobatus forms a plausible shovel, the Edestus
tooth whorls (Figure 1) seem less well adapted to
either digging or scraping, but well adapted to cut-
ting through flesh. Zangerl and Jeremiah (2004)
suggested that Edestus might have rushed at prey,
with mouth wide open and teeth exposed, to cut
and disable prey. While this mode, which is roughly
analogous to extant billfish (Istiophoridae and
Xiphiidae), cannot be ruled out, it would seem that
narrow, spike-like teeth would better serve that
function than serrated, triangular teeth.
Cursory examination by the author of teeth of
E. heinrichi Newberry and Worthen, 1870, by opti-
cal microscopy and by SEM revealed a few
scratches, but these were not consistently present
and lacked any consistent orientation. Whether any
of the scratches were generated in vivo, rather
than postmortem, e.g., by abrasion or by damage
during preparation, was impossible to determine.
Teaford (1988) has discussed the problem of dis-
tinguishing wear acquired during life on mamma-
lian teeth from postmortem wear. In vivo wear is
“generally laid down in a regular fashion at specific
locations on the teeth” (Teaford, 1988). The
scratches observed on the teeth of E. heinrichi do
not appear to pass this test. Many, probably most,
Edestus teeth in museum collections originate from
carbonaceous shales associated with coal depos-
its. Crowns and bases of such teeth are commonly
stained black. The crown surfaces are diageneti-
cally altered and are sometimes coated with crys-
tals of marcasite. This form of preservation seems
to be detrimental to the preservation of in vivo
microwear.
A group of Edestus teeth was located in the
course of a review of North American occurrences
of Edestus (Itano et al., 2012). These teeth are all
from the same locality and display various states of
preservation. The bases and crowns are light-col-
ored and clearly have a different taphonomic his-
tory compared to the ones originating from
carbonaceous shales. The crowns were examined
for the presence of scratches by optical micros-
copy.
Institutional Abbreviations
TMM, Vertebrate Paleontology Laboratory (for-
merly with the Texas Memorial Museum), Univer-
sity of Texas, Austin, Texas, USA; USNM, National
Museum of Natural History, Washington, District of
Columbia, USA.
MATERIAL AND METHODS
Material
One fragmentary crown of Edestus sp., TMM
40234-19; 13 complete or partial crowns of Edes-
tus minor, TMM 40234-8, TMM 40234-13, TMM
40234-14, TMM 40234-15, TMM 40234-16, TMM
40235-17, TMM 40234-18, TMM 40234-20, TMM
40234-21, TMM 40234-22, TMM 40234-23, TMM
40234-24, and TMM 40234-25, all from the same
locality. Previously, some were given the common
number TMM 40234-1. All now have individual
specimen numbers. Some are shown in Figure 4.1-
7.
Locality and Age
Upper Strawn Group, Pennsylvanian, middle
Desmoinesian (Moscovian global stage), approxi-
mately 310 Ma, 5 km west of Richland Springs,
San Saba County, Texas, USA.
Remarks on Material
Although they have been in the collections of
the TMM for a long time, these Edestus teeth
appear not to have been reported in the published
literature until noted by Itano et al. (2012). The col-
lector and date of collection are unknown. They
were transferred from the Texas Bureau of Eco-
PALAEO-ELECTRONICA.ORG
5
nomic Geology some time ago, with no prove-
nance information other than what is stated here in
the “Locality and age” section. They might have
been collected during the surveys of E. Cope and
W.F. Cummins in the late nineteenth century (J.C.
Sagebiel, pers. comm., 2011).
Methods
Measurement of scratches. All of the teeth listed
in the Material section were examined under a bin-
ocular microscope for the presence of scratches
that could be attributed to in vivo wear. Attempts
were made to distinguish such scratches from
cracks, preparation marks, and other types of post-
mortem damage. Figure 5.1-3 shows various linear
features on the surface of TMM 40234-17 that are
and that are not attributed to in vivo wear. Figure
5.1 shows gouges and deep scratches in a crossed
pattern that are interpreted as the result of a pre-
parator removing matrix with a sharp implement.
Figure 5.2 shows a region where most of the linear
features form an angular network of cracks. These
are interpreted as the result of differential expan-
sion of the inner dentine and the outer, hyperminer-
alized layer. (In the absence of histological studies
of the hypermineralized outer layer, it is not here
referred to as enameloid. Duffin (2016) has shown
that the outer, hypermineralized layer teeth of E.
heinrichi and of several other eugeneodontiform
chondrichthyans are composed not of enameloid,
but rather of a compact form of dentine made up of
very small crystallites, 0.5 µm in length.) Figure 5.3
FIGURE 4. Teeth of Edestus sp. (1) and Edestus minor (2-7). TMM 40234-19 (1), TMM 40234-8 (2), TMM 40234-17
(3), TMM 40234-18 (4), TMM 40234-24 (5), TMM 40234-25 (6), TMM 40234-23 (7). Scale bars equal 1 cm.
ITANO: EDESTUS MINOR MICROWEAR
6
shows a small region where some shallowly
incised scratches, which are interpreted as in vivo
wear, can be seen among the more prominent
cracks. The longer scratch is isolated, but the other
one consists of a pair of parallel scratches sepa-
rated by 35 µm.
It is common in dental microwear studies to
examine small areas of tooth surfaces, typically a
few hundred micrometers across (Walker et al.,
1978; Ungar, 1996; Williams et al., 2009).
Scratches apparently generated in vivo were only
sparsely observed on the Edestus tooth studied
here. For that reason, and also to avoid possible
bias due to the choice of an area of the tooth sur-
face that did not represent the tooth surface as a
whole, an area as large as was practicable was
surveyed (several millimeters across). Compare
the studied area (Figure 6) to the entire side of the
tooth (Figure 4.3).
In order to count all of the scratches within the
studied area and to avoid double-counting, it is
best to obtain a single image having sufficient reso-
lution to view the scratches. In order to do this with
the photographic equipment that was available, it
was necessary to obtain many overlapping images
and to merge them into a single image. The proce-
dure for doing this is described in Appendix 1.
Once a blended single image is obtained, it
can be imported into a computer program and
viewed on the computer monitor at any desired
magnification. Viewing of small sections of the
blended single image was sometimes supple-
mented by viewing other images containing that
same area. The ImageJ program (version 1.50b,
Fiji distribution) (Schneider et al., 2012) was used
for this purpose. In ImageJ, the operator can mark
a line segment, as in Figure 7.1 (red mark). The
program automatically collects the numerical
parameters defining the line segment, including the
position, length, and angle with respect to horizon-
tal (Figure 7.2). For the present study, only the
angle is of importance.
Statistical methods. The angular data of the
scratches are analyzed according to circular statis-
tics (Mardia and Jupp, 2000). Rao’s equal spacing
test for uniformity (Mardia and Jupp, 2000, p. 108)
is used to test the null hypothesis that the
scratches are drawn from a uniform distribution.
The test measures the deviation of the differences
between angles and the uniform case, in which the
spacings would be 360º/n, where n is sample size.
To apply the test, it is necessary to make a simple
adjustment to the data, which was made also by
Varriale (2016) in his study of dinosaur dental
FIGURE 5. Surface features of TMM 40234-17 that are
either scratches acquired in vivo or which might be mis-
taken for them. 1, Region near the apex of the lingual
edge showing gouges and deep scratches probably
made by a preparator. Scale bar equals 1 mm. 2,
Region near the basal part of the lingual edge, showing
a network of angular cracks. Scale bar equals 500 µm.
3, Region on the opposite side of the crown from Figure
4.3, near the serrations on the lingual edge. Shallowly
incised scratches interpreted as in vivo wear are out-
lined in red. More deeply incised linear features are
cracks. Scale bar equals 500 µm.
PALAEO-ELECTRONICA.ORG
7
microwear. There is no distinction between a
scratch with angle θ and θ + 180º. Angles in the
data set are mapped into the range from -90º to
+90º. If each angle is multiplied by 2, the data set is
mapped into the range from -180º to +180º. If 180º
is added to each angle, which does not affect the
angular spacing, the data set is mapped into the
range from 0º to 360º, and the formula (Mardia and
Jupp, 2000, eq. [6.3.45]) for the quantity L that
characterizes the deviation from angular uniformity
can be applied directly:
where Ti is the ith angular interval in the data set.
The mean direction of the scratches is calculated
according to Eqs. 2.21-2.24 of Mardia and Jupp
(2000). The sample circular standard deviation is
calculated according to Eq. 2.3.11 of Mardia and
Jupp (2000). Since the calculations of the mean
direction and the circular standard deviation are
carried out on doubled angles, the values obtained
in this manner must be divided by two in order to
obtain the final results.
RESULTS
Initial Survey of All Teeth
All of the teeth listed in the Material section
were examined for the presence of scratches that
could be attributed to in vivo wear. The tooth from
the sample that at first appeared to be the best-
preserved, TMM 40234-8 (Figure 4.2; Itano et al.,
2012, figure 12), was unsuitable for this study
because of the presence of a transparent coating,
possibly shellac. The coating caused reflections
that partially obscured small surface features,
including scratches. Removal of the coating (Wil-
liams and Doyle, 2010) was not attempted, since
exploratory microscopic examination indicated
that, while some scratches were present, the den-
sity of such scratches was less than on other teeth,
in particular, TMM 40234-17. Also, the teeth were
on loan from another institution, and such cleaning
would have had the potential to cause damage.
Many of the teeth in the sample were considered
not useful for this study because the apical parts of
the crown were truncated (broken off). In none of
the cases in which the crowns were apically trun-
cated was the surface of the remaining part of the
crown smoothly polished, as for the Edestus minor
tooth described by Itano (2015). Others, e.g., TMM
40234-18 (Figure 4.4), have had much of the outer,
hypermineralized layer removed. On TMM 40234-
18, the outer layer is so reduced in thickness that
the darker, inner, dentine layer shows through.
FIGURE 6. Aligned and blended mosaic of 63 images of
a portion of the lateral face of TMM 40234-17. Scale bar
equals 1 mm.
FIGURE 7. 1. A scratch (red) marked on the image of
Figure A2.3, by use of the ImageJ program, and outlined
by a yellow ellipse. 2, Parameters, including position,
angle, and length, of the scratch recorded by the ImageJ
program from the mark shown in 1. The only one of
importance is the angle (in degrees) that describes the
orientation of the scratch. Zero degrees is horizontal, to
the right. The angle increases counterclockwise.
ITANO: EDESTUS MINOR MICROWEAR
8
Whether the removal of the outer layer occurred in
vivo or postmortem is not known. The other teeth
having preserved apical parts (TMM 40234-17,
TMM 40234-24, TMM 40234-25, and TMM 40234-
23) (Figures 4.3, 4.5, 4.6, and 4.7, respectively)
exhibit varying degrees of removal of the outer
layer in the region of the apices.
The tooth having the highest number of visible
scratches interpreted as having been acquired in
vivo was TMM 40234-17. The labeled side (Figure
4.3) had more scratches than the unlabeled side
and was chosen for detailed study. Figure 8 shows
a part of the surface of TMM 40234-17 that has
several shallowly incised scratches that are inter-
preted as in vivo wear. Some of these are pairs of
parallel or nearly parallel scratches separated by
approximately 45 µm to 70 µm. Most of the
scratches are roughly transverse to the deep, sinu-
ous cracks, so they are also roughly transverse to
the basal-apical axis. Figure 9 shows one of the
rare cases in which three nearly parallel scratches
are present on TMM 40234-17. The separation
between the two most widely separated scratches
is approximately 54 µm.
An unexpected observation was that the api-
ces of several of the teeth show localized wear to
the apical region, in the form of loss of some of the
outer, hypermineralized layer. The localized wear
can be seen, in varying degrees, on TMM 40234-
17, TMM 40234-18, TMM 40234-24, TMM 40234-
25, and TMM 40234-23 (Figures 4.3-7). In fact, of
all the teeth in the sample that retain their apices,
the only one that does not show some degree of
localized wear to the apical region is TMM 40234-8
(Figure 4.2).
Detailed Study of TMM 40234-17
Approximately 62% of the portion of the num-
bered side of TMM 40234-17 that has a relatively
intact surface (approximately 79 mm2 out of
approximately 130 mm2) was imaged at high reso-
lution by creating a blended mosaic of 63 images
by the method described in Appendix 1. The 63
images were arranged in nine horizontal strips of
seven images each. Figure 6 shows the blended
mosaic image. Figure 10 shows the same mosaic
image with scratches marked in red. Secondary or
tertiary scratches that are parallel to and associ-
ated with another nearby scratch are marked in
green. The images in Figures 6 and 10 are 11,951
pixels wide and 12,768 pixels high (approximately
145 megapixels, where 1 megapixel equals
1,048,576 pixels). The files have been reduced in
resolution for publication. Higher-resolution ver-
sions of Figures 6 and 10 are included as supple-
mentary material (S1 and S2, respectively). A total
of 107 scratches interpreted as having been
acquired in vivo were recorded. Sets of two or
three parallel scratches were counted as one
scratch. A file containing the parameters of the
scratches, in the format shown in Figure 7.2, is
included as supplementary material (S3).
Figure 11 shows a bidirectional rose plot of
the orientations of the 107 observed scratches
overlaid on an image of TMM 40234-17. For this
data set, L = 175.89. The null hypothesis (that the
directions of the scratches are uniform) is rejected
(p < 0.001) (Russell and Levitin, 1995, table II).
Since the directions of the scratches are not uni-
FIGURE 8. A region of the surface of TMM 40234-17
that displays several linear features interpreted as
scratches acquired in vivo. Several of these are paired.
Scale bar equals 500 µm.
FIGURE 9. A feature interpreted as caused by in vivo
wear on the surface of TMM 40234-17, outlined in yel-
low, consisting of three near-parallel scratches. Scale
bar equals 500 µm.
PALAEO-ELECTRONICA.ORG
9
formly distributed, the mean direction and the sam-
ple circular standard deviation can be calculated.
The mean direction of the scratches is 14°. The
sample circular standard deviation is 36°. The ori-
entations of the observed scratches are thus pre-
dominantly transverse to the basal-apical axis.
DISCUSSION AND CONCLUSIONS
Shallow, linear features were recorded as
scratches acquired in vivo unless they were inter-
preted as preparation marks, cracks, or some other
form of postmortem damage. Other than prepara-
tion marks, such features are expected to have
random orientations. For example, scratches
induced by tumbling in sediment, either pre-burial
or post-exposure, would have random orientations.
Experimental studies have shown that the main
effect of abrasion of teeth by tumbling in sediment
is to obliterate microwear features rather than to
modify or to create new ones (King et al., 1999). In
particular, generation of microwear features having
a preferred orientation was not observed in those
experiments. Inclusion of scratches with random
orientations in the data set should not bias the cal-
culated mean direction but would increase the cir-
cular standard deviation. The lengths of the
features, though recorded, were not thought to be
of significance, particularly since many, if not most,
of the scratches could have been reduced in
apparent length by postmortem weathering or
abrasion. Positional dependence on the tooth of
scratches acquired in vivo is to be expected. How-
ever, the sample size was too small to divide into
subsets from different regions of the examined
tooth surface.
One of the few mechanisms that could lead to
linear features having a preferred orientation is
preparation with a sharp tool. Preparation-related
features would be of recent origin and hence would
have sharp edges and be unworn. A few marks fit-
ting this description are present, as in Figure 5.1,
but these are limited to a small part of the surface.
More commonly, the linear features thought to be
scratches acquired in vivo show signs of weather-
ing or abrasion, as in Figures 5.3, 8, and 9. Also,
the double and triple scratches, which have varying
amounts of separation, are difficult to attribute to
tool marks.
The sharp, serrated teeth of Edestus strongly
suggest that it was a predator. If the prey were
other fish, then the scratches might have been
caused by contact with dermal denticles or scales
on the skin of such prey.
FIGURE 10. Same mosaic image as in Figure 6, with
scratches marked in red. Secondary or tertiary
scratches that are parallel to and associated with
another nearby scratch are marked in green. Scale bar
equals 1 mm.
FIGURE 11. Rose plot (yellow) of angles of orientation of
107 scratches observed on surface of TMM 40234-17,
overlaid on image of the same tooth. Scale bar equals 5
mm.
ITANO: EDESTUS MINOR MICROWEAR
10
The observed localized wear to the apices of
some teeth is unexplained but might be a result of
the apices being abraded by repeatedly being
dragged through the outer covering of prey. Such
wear would be consistent with the use of the tooth
whorls to slash. In order for such wear to occur, the
prey would have had to have been relatively heavy.
Such a mode of predation would tend to cause an
increase in the density of scratches toward the
tooth apices. Such an increase in scratch density
might be observable if more and better-preserved
material can be located.
Due to the paucity of information on the paleo-
environment and fauna associated with these
teeth, the monograph by Zangerl and Richardson
(1963) on the paleoecology of two Pennsylvanian
black shales might be informative. The invertebrate
fauna of these shales indicates marine conditions.
Edestus remains, including those of juveniles, are
known to occur in these shales (Zangerl and Rich-
ardson, 1963; Taylor and Adamec, 1977; Zangerl
and Jeremiah, 2004). Zangerl and Richardson
(1963, p. 136-137) noted the presence in these
shales of remains of fish, mainly chondrichthyans
and “palaeoniscoids,” that showed evidence of
damage due to predation. They noted “essentially
whole individuals, near-perfectly articulated, except
for local, usually linear, areas of disturbance.”
Often, body parts were nearly severed, but appar-
ently still connected to each other by connective
tissue. In addition to noting the fish having linear
wounds, they remarked on the presence of many
specimens of “near-perfectly articulated partial
individuals.” These consist of separated heads and
tails or bodies lacking heads, tails, or both. There is
no proof that the “amputation” observed is not the
result of ordinary taphonomic processes, e.g.,
decay. However, that seems unlikely, since the par-
tial bodies are described as being near-perfectly
articulated. Both the linear wounds and the ampu-
tated remains might be the result of predation by
Edestus, either by a bite with the inner, lingual
parts of the tooth whorls, or by a sweeping blow
with the outer, labial parts. Predation by the former
mode would tend to create scratches on the Edes-
tus teeth oriented mainly parallel to the basal-api-
cal axis (Figure 3.1), while the latter mode would
tend to create scratches oriented mainly perpen-
dicular to that axis (Figure 3.2). Since the partial
bodies are articulated, they may represent prey
that was cut, but not ingested, by the predator.
The observation that scratches on a lateral
face of a crown of an Edestus tooth are oriented
transversely to the basal-apical axis supports the
hypothesis that the tooth whorls were used to kill or
disable prey by slashing them, rather than to cut
prey caught between the two whorls. However, the
teeth might have served other functions, e.g., for
the few most lingual teeth, cutting prey trapped
between the jaws. The exploratory nature of this
study, based mainly on examination of a single
tooth, is acknowledged. Alternative interpretations
of the same observations are possible, even if the
scratches were acquired in vivo rather than post-
mortem.
Two such alternative interpretations are:
1) “Reciprocating saw” hypothesis: Zangerl and
Jeremiah (2004) hypothesized that the lower
jaw of Edestus might have been capable of
linear forward and backward motions, so that
it could operate like the human tool, the recip-
rocating saw, to cut prey trapped between the
jaws. Such a mode of predation could result in
tooth microwear consisting of scratches ori-
ented transversely to the basal-apical axis,
either from interaction between the teeth and
the prey or between teeth of opposing jaws.
This interpretation, while not ruled out by the
observations, suffers from the same drawback
as the “scissors” mode, which is that only a
few of the innermost teeth seem to be effec-
tive in cutting, while the majority of the teeth
do not seem to be functional, despite the fact
that they carry a cost in terms of weight and
water resistance. A true “circular saw” action,
which might make use of more of the teeth, is
difficult to imagine.
2) Substrate interaction: it has been hypothe-
sized that the Edestus tooth whorls might
have been used to plow through the substrate
to locate prey (Eaton, 1962). There seems to
be no way to definitively refute this hypothe-
sis. However, the sharply-pointed, serrated
teeth of Edestus would seem to be better
adapted to slice through flesh than to plow
through sediment. In particular, there would
seem to be no need for serrations if the teeth
were to be used for the latter function. That
does not rule out probing through the sub-
strate as a secondary function.
ACKNOWLEDGMENTS
H. Blom (University of Uppsala) first sug-
gested that tooth microwear might indicate how
Edestus teeth were used. I thank J.C. Sagebiel
(TMM) for the loan of specimens. I thank two anon-
ymous reviewers and the Handling Editor for their
comments, which led to improvements in the man-
PALAEO-ELECTRONICA.ORG
11
uscript. Photographic equipment and software
were purchased with the aid of a Karl Hirsch
Memorial Research Grant from the Western Inte-
rior Paleontological Society (Denver). SEM imag-
ing was performed by D.K. Elliott (Northern Arizona
University). Photoshop is a registered trademark of
Adobe Systems International.
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APPENDIX 1
Procedure for generating a single, optimally-focused image from a two-dimensional grid of over-
lapping images.
In order to acquire an
image of such a large
area (approximately 79
mm2) at sufficiently high
resolution to observe
microwear, the apparatus
shown in Figure A1 was
assembled. The number
given for the imaged area
excludes regions where
the outer, hypermineral-
ized surface layer is not
preserved and areas that
were out of focus in the
final image (on the upper
right of Figure 6). The
object to be photo-
graphed is placed on a
precision, micrometer-
driven XY translation
stage. In actual practice,
unlike in Figure A1, the
camera lens is placed
very close to the object,
so that only a small part
of the object is imaged.
Keeping the camera in a
fixed position, the object
is translated so that over-
lapping images can be
acquired in a two-dimensional grid. Merging the grid of overlapping images into a single, opti-
mally focused image was carried out with the use of the Adobe Photoshop ™ program (version
CC 2015 -16.0).
Figure A2.1-3 illustrates the method for a simple, one-dimensional case. Figure A2.1 shows
three overlapping images of a part of TMM 40234-17 that were obtained by horizontally translat-
ing the tooth while keeping the position of the camera fixed. Figure A2.2 shows the three images
overlaid by use of the Auto-Align Layers function. In order for this procedure to function properly,
it is important that the object be translated but not rotated, as this function cannot compensate
for a rotation. Figure A2.3 shows the result of applying the Auto-Blend Layers function to the
aligned images. For every region of the combined image, this function selects the image with the
clearest focus. This function is more often used to blend several images having the same field of
view, but different focus settings, and is called “focus-stacking.” Figure A2.3 is a seamless, single
image with improved overall focus.
The extension to a two-dimensional grid is straightforward. A series of overlapping images is
acquired by translating the object horizontally. These images are aligned and blended as previ-
ously described. The object is then translated vertically, and another series of overlapping
images is acquired that is again aligned and blended. This process is repeated, so that a set of
vertically overlapping strips is obtained. These strips are then aligned and blended to obtain a
single image. The complete image can then be imported into ImageJ, where the scratches can
be marked and recorded.
FIGURE A1. Apparatus for optical imaging of an object in a two-
dimensional grid utilizing a compact digital camera and a precision,
micrometer-driven XY translation stage.
PALAEO-ELECTRONICA.ORG
15
FIGURE A2. Method of generating a mosaic image from several overlapping images and then marking and measuring
linear features on the mosaic image. A region of TMM 40234-17 around that shown in Figure 5.1 is used as an exam-
ple. 1, Three overlapping images. The same region is in better focus in some images than in others. 2, The three
images aligned and overlapped. 3, The three images blended into a single image, with the best-focused image
selected for each region.
ITANO: EDESTUS MINOR MICROWEAR
16
SUPPLEMENTAL MATERIAL
S1. 831_mosaic.jpg (Blended mosaic image of TMM 40234-17 available for download at https://
palaeo-electronica.org/content/2019/2603-edestus-minor-microwear. Higher resolution version
of Figure 6.)
S2. 831_marked.jpg (Blended mosaic image of TMM 40234-17 with scratches marked available
for download at https://palaeo-electronica.org/content/2019/2603-edestus-minor-microwear.
Higher resolution version of Figure 10.)
S3. 831_sup_3.xlsx (Spreadsheet containing scratch-angle data from TMM 40234-17 for down-
load at https://palaeo-electronica.org/content/2019/2603-edestus-minor-microwear.)
