Biometric Animals
First issue: 2007-07-04 - Last update: 2008-01-27
| Many
animals may be recognized by individual biometric characteristics in just
the same way as human fingerprints. Since human fingerprints are relatively
small and hidden characteristics, they cannot be used by other persons
for mutual visual identification. In contrast to human fingerprints, there
are animal skin patterns which are large enough to be used for mutual recognition
without technical aids - at least theoretically. This investigation uses
open internet sources such as Wikipedia and FishBase to find out and to
show which animals are candidates for biometric identification using large-scale
minutiae-type characteristics. Detailed information of the nature of these
characteristics are subject to deeper animal-specific investigations and
are not covered here. This contribution will be updated occasionally. The
focus is on minutiae based animal characteristics. |
Introduction
Human fingerprints
| The unique pattern of the
human fingerprint is one of the reasons, why this biometric characteristic
[1,
2] has already been used for more
than a century in criminal investigations. Today, as inexpensive electronic
sensors are available for capturing a life fingerprint, fingerprint recognition
has established as an alternative convenient and cost-saving method for
determining and verifying the identity of a human person in various applications. |
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| It is the friction ridge
structure of the skin surface especially near the finger tips which is
called fingerprint. The ridge lines are separated by valleys resp.
grooves. |
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| Human fingerprint structure |
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| Author: unknown |
License: GFDL
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| The inter-ridge distance
is nearly constant for a specific finger. What attracts attention is the
varying curvature of the ridge lines. An advantage of this structure seems
to be the support when gripping things by improved friction and an improvement
of the finger's sense of touch. Fingerprint structures are not unique for
fingers, they are also found at your toes. Furthermore, there are a couple
of animals which also show them. Examples are known for gorillas, apes,
and even opossums [3]. |
What fingerprints make distinguishable
| Fingerprints have proven
unique not even for different individuals but even for different fingers.
(To be more precise: Up today, no two fingerprints have been found which
are exactly equal.) What exactly are the characteristics which make a fingerprint
unique? When comparing fingerprints, (at least) three different types of
characteristics can be found: |
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| 1. Coarse characteristics
(loops, arch, whorls, ...) The coarse characteristics are given by
the curvature of the ridge lines. The number of different features per
finger is quite limited (at least three, generally not more than about
eight [4]). These characteristics were the first to be
used for manual classification of fingerprints since each of the ten fingers
may have different features. |
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| Fingerprint arch |
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| Fingerprint loop |
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| Fingerprint whorl |
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| 2. Fine characteristics
(minutiae)
The ridge line curvature described by the coarse characteristics
has an important consequence when we combine it with the observation that
the ridge density is nearly constant for a specific finger. For example,
when looking at the arch formation, both conditions probably only can be
fulfilled if new ridge lines are created. This could (but need not) be
an explanation for the fact that the ridges are no never-ending parallel
running lines. Instead, there are line endings and bifurcations. To each
line ending and bifurcation a point may be assigned which marks a minutia.
The arrangement of the minutiae, whose position may not be equally dense
distributed, are unique for each finger and thus for each person. This
is best visualized by the constellations in a starry sky (such as the Orion)
which build unique figures. |
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| To each minutia, subfeatures
may be attributed which provide additional unique information. Besides
position on a 2D surface, this may be the direction of the corresponding
line, the type (ending vs. bifurcation) etc. |
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| 3. Pore structure as
micro characteristics. On the crest line of the ridges, further points
can be localized which stem from the perspiratory glands (pores) of the
skin. The arrangement is as unique as the minutiae structure but is seldom
used for identification because of the difficulty to detect them reliably
under real-life conditions. |
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| Magnified pore structure in a captured
fingerprint image |
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| Author: Manfred Bromba |
License: limited to
this article
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For electronic fingerprint
recognition, minutia have proven most useful and will be mainly considered
in this article. During extraction of
the minutiae positions,
one step of electronic processing will be to deliver a binarized image
of the ridge structure which clearly shows the nature of fingerprint patterns
and its minutiae: |
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| Binarized fingerprint image |
 |
| Author: Manfred Bromba |
License: limited to
this article
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Origin: this
article
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Genotypic and randotypic characteristics
| For a deeper understanding
of the usefulness of a biometric characteristic as unique identifier it
may help to consider the origin of the differences between individuals.
For physiological characteristics such as fingerprint, there are two mechanisms
which control diversity, namely random and environmental influences during
embryonic growth and heredity. Normally, each physiological biometric characteristic
is subject to both influences. Depending on the type
of characteristic, one of the influences will dominate. For fingerprints,
coarse characteristics have strong genotypic contributions. Minutia are
predominantly randotypic in nature and cause much of the uniqueness in
a fingerprint. If random processes are responsible for the distinctiveness
of a biometric characteristic, the characteristic is called mainly randotypic
(which is related to phenotypic [Wikipedia]
in the sense that randotype is something like the difference between phenotype
and genotype)). If a biometric characteristic mainly follows hereditary
disposition, it is called mainly genotypic. (Altogether, three parts
determine the origin of each (natural) biometric characteristic in different
shares: randotypic, genotypic, and behavioral) |
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| Both
purely randotypic characteristics and purely genotypic characteristics
may theoretically approach ideal uniqueness, with only one exception: monozygotic
twins and clones. Only the randotypic part of a biometric characteristic
is able to distinguish between monozygotic twins, the genotypic parts by
definition cannot. For example, DNA as a biometric characteristic is nearly
completely genotypic. As a result, one cannot distinguish between monozygotic
twins today on the basis of DNA profiling (except in the seldom case of
mutations which are randotypic). |
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| We
have seen that a good proof for randotypic parts in a characteristic is
when even monozygotic twins have different features. But there is still
an easier method which can prove this in many cases. Most creatures have
some kind of bodily symmetry. As a rule of thumb, randotypic parts of a
biometric characteristic do not follow the body symmetry! For example,
the fingers of the right and left hand do not show the same minutiae patterns.
In this way, it should be possible to find out the nature of a characteristic
by simply investigating single individuals without need for monozygotic
twins. This will be explained using the examples in the next section. |
Morphogenesis of biometric characteristics
| Morphogenesis
[Wikipedia] is
the term used in science for the development of biological (and other)
structures and characteristics. Interestingly, for most animal characteristics
shown in this publication, there exist more and less simple models which
are able to simulate pattern formation [Wikipedia].
Such a model can be, for example, a set of differential equations or a
cellular automaton [Wikipedia].
The first model being able to describe minutiae patterns has been published
by Alan Turing [Wikipedia],
an English mathematician, logician, and cryptographer. Another model has
been proposed by A. Gierer and H. Meinhardt [Scholarpedia]. |
| Artificial pattern |
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| The
pattern above has been created by repeated blurring and sharpening
a comic image. Although such a process hardly describes the reality, the
pattern has some impressive similarities with certain animal patterns. |
| If
the pattern formation of an animal can be described by the same model or
process as for all other individuals of this species, the question arises,
why all patterns are different except for the structure type. The reason
is that the final fine pattern strongly depends on the initial conditions
and the boundary conditions. The initial condition may be a random pattern,
in which even small changes may force large variations in the final pattern,
if the model is nonlinear. (Such effects are well known from Chaos Theory
[Wikipedia].) For
an illustration see Figure 2 of [Scholarpedia].
A boundary condition may be an external environmental condition (e.g.,
temperature) or the shape of the animal. |
The Zebra
| The zebra is the most obvious
example for an animal with minutiae based markings. The minutiae are easily
recognized by human inspection. As the following images show, there is
some evidence that the pattern of the Zebra's fur has randotypic parts.
The first two images show the same Zebra from both sides. One image has
been mirrored to simplify comparison. It is easily seen that there is no
exact body symmetry in the minutiae pattern. This argues for the randotypic
nature. Nevertheless, there seem to be strong genotypic parts. This especially
effects the distribution of the minutiae density and the "ridge" density. |
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| Zebra |
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| Author: Manfred Bromba |
License: Public
Domain
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Origin: this
article
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| The next image shows a top
view of the same Zebra to verify the missing symmetry of the minutiae: |
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| Zebra |
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| Author: Manfred Bromba |
License: Public
Domain
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Origin: this
article
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| The following image shows
a different Zebra, but most probably from the same family. Again, the minutiae
pattern is different while certain "coarse" characteristics such as the
distribution of the stripe distance seem to be genotypic. Together with
the fact that this kind of Zebra has numerous minutiae, it should be possible
to uniquely identify each different Zebra. |
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| Zebra |
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| Author: Manfred Bromba |
License: Public
Domain
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Origin: this
article
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Fishes
| All the following images
show a collection of fishes as examples for minutiae based skin markings.
As a precondition, the markings must show stripes. Since the circumstances
of most image shots are not accessible, scientific conclusions are hardly
possible in most cases. It will be left to other researches to prove uniqueness
of the pattern for each species. |
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| Acanthurus dussumieri |
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| Both head and body of this
Acanthurus dussumieri show minutiae-type structures, however with different
ridge density. |
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| Acanthurus lineatus |
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| The line structures of the
Acanthurus lineatus shown above and in the following two images contain
a few minutiae which seem to behave different for different fishes. |
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| Acanthurus lineatus |
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| Acanthurus lineatus |
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| Acanthurus sohal |
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| The minutiae in the line
structure are crowded on the head and top of this and the following Acanthurus
sohal. |
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| Acanthurus sohal |
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| Anisotremus virginicus |
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| The Anisotremus virginicus
seems to be a counterexample for the assumption that minutiae always must
be randotypic. At least in the above and the following images, the pattern
seems to be the same for all individuals. |
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| Anisotremus virginicus |
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| Balistapus undulatus |
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| Balistapus undulatus shows
minutiae-like structures near the eyes. |
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| Bodianus loxozonus |
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| Although the lines are broken
for this Bodianus loxozonus, a few minutiae can easily be found on the
body and the head. If the number of minutiae are sufficient for unique
identification, may be challenged. |
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| Chaetodon auriga |
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| Author: unknown |
License: SXC
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| Chaetodon auriga is a good
example for individuals with different development of biometric characteristics.
While the rear fish shows a sophisticated minutiae structure, the front
fish does only posses a regular pattern - at least at the camera side. |
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| Chaetodon capistratus |
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| Here we have a further counterexample
that not every fish with minutiae seems to have a distinct pattern. |
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| Chaetodontoplus septentrionalis |
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| Chaetodontoplus septentrionalis
show certain minutiae outside the central part of the body. |
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| Coris ballieui |
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| The drawing of Coris ballieui
suggests that all parts of the body has different minutiae-like structures. |
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| Ctenochaetus hawaiiensis |
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| Ctenochaetus hawaiiensis,
striatus, and strigosus (next two images) are beautiful examples for minutiae-rich
structures. |
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| Ctenochaetus striatus |
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| Ctenochaetus strigosus |
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| Epinephelus caninus |
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| This Epinephelus caninus
shows a very fine ridge structure which is hardly recognized. |
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| Gonioplectrus hispanus |
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| At least this specimen of
Gonioplectrus hispanus features a minutiae structure, but possibly not
distinctive enough for unique recognition. |
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| Haemulon flavolineatum |
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| From the top view of Haemulon
flavolineatum it becomes apparent that the minutiae structure of its stripe
pattern should to be mainly randotypic. |
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| Haemulon sciurus |
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| Haemulon sciurus shows minutiae
bifurcations as well as line endings. |
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| Heros serverus |
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| This most probably different
specimen of Heros serverus shows the same coarse structure than the preceding
one. That is, the question if this pattern is only accidentally equal or
shows distinctive properties remain open. |
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| Lutjanus kasmira |
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| The fine bottom structure
clearly shows minutiae behavior! |
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| Novaculichthys taeniourus |
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| It seems to be the dorsal
fin of Novaculichthys taeniourus which shows distinctive structures. |
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| Panaque nigrolineatus |
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| Panaque nigrolineatus is
characterized by a high degree of similarity of its skin pattern with the
zebra, see also next two images. |
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| Panaque nigrolineatus |
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| Panaque nigrolineatus |
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| Plectorhinchus lineatus |
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| The top minutiae pattern
of Plectorhinchus lineatus is a good candidate for unique identification |
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| Plectorhinchus orientalis / vittatus |
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| Plectorhinchus orientalis |
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| The head pattern of this
Plectorhinchus orientalis shows a higher minutiae density than the body. |
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| Pomacanthus imperator |
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|
| Author: Manfred Bromba |
License: Public
Domain
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Origin: this
publication
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| From the Pomacanthus imperator
above it was possible to take a shot from both sides. Obviously, the minutiae
pattern does not follow bodily symmetry, thus being a candidate for randotypic
formation according to our rule of thumb. |
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| Pomacanthus imperator |
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| Pomacanthus imperator is
a good example for the fact that certain individuals only show a small
number of distinctive markings compared to other ones. The drawings above
even show different coarse characteristics similar to those of fingerprints! |
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| Pomacanthus imperator |
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| Pygoplytes diacanthus |
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| Author: unknown |
License: SXC
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| This Pygoplytes diacanthus
shows minutiae structures in the red line structure at its anal fin. (The
red color seems not to be typical for all members of this species.) |
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| Sarpa salpa |
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| Sarpa salpa is a nice example
for a minutiae-like structure with low individuality. That is, in contrast
to fingerprint there need not be a tight correspondence between randotype
and minutiae and ridge structure! |
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| Siganus doliatus |
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| This specimen of Siganus
doliatus provides a very clear minutiae structure. |
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| Symphorichthys spilurus |
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| The line structure of Symphorichthys
spilurus shows some similarity with Haemulon sciurus. |
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| Symphorichthys spilurus |
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| Symphorichthys spilurus |
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| Symphorichthys spilurus |
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| Symphysodon aequifasciatus |
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| Author: Anka Zolnierzak |
License: SXC
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| Symphysodon aequifasciatus
as well as Symphysodon discus possess a rich minutia pattern, see the following
pictures. |
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| Symphysodon aequifasciatus |
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| Symphysodon aequifasciatus |
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| Symphysodon aequifasciatus |
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| Symphysodon aequifasciatus |
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| Author: M. Kraus |
License: GFDL
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| Symphysodon discus |
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| Thalassoma lunare |
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| It's not know to the author
if this and the following Thalassoma lunare are the same individual. At
least the pattern upside the eye seems to show a significant difference. |
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| Xanthichthys auromarginatus |
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| Although Xanthichthys auromarginatus
only shows a dotted line structure, minutiae are easily located. |
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| Thalassoma lunare |
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| Zebrasoma desjardinii |
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| Zebrasoma desjardinii which
bears the Zebra in its name, shows a fine pattern with minutiae-type line
pattern. Both bifurcations and line endings appear. |
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| Zebrasoma desjardinii |
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| If this and the next Zebrasoma
desjardinii are the same individual, this would suggest a randotypic origin
of the pattern since there is no symmetry found. |
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| Zebrasoma desjardinii |
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| Zebrasoma xanthurum |
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| This image shows two Zebrasoma
xanthurum. Remarkable is the fact that the specimen to the right, in contrast
to the second one, has only a weak minutiae-type pattern available. To
see the difference more clearly, the Zebrasoma xanthurum to the left has
been zoomed in, see next photo. This corresponds to human biometric characteristics
which, in minor cases, are also not such developed that they can be measured
without problems. |
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| Zebrasoma xanthurum
(zoomed in) |
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Fingerprint Cyphoma
| The fingerprint cyphoma
(cyphoma signatum) is a snail with shell. The mellow body and especially
the shell shows minutiae structures in highest perfection and unique beauteousness.
As most snail shells, there is no bodily symmetry which may apply to our
rule of thumb for randotypes. Following, the best images from the internet
have been collected. |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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| Cyphoma signatum |
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Open questions
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Are there animals which use
the minutiae-type biometric characteristics of their conspecifics to distinguish
each other?
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How unique are animal characteristics?
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What other types of geometric
patterns can be used as biometric characteristics? (giraffes, tigers, fish,
cows, whales [5, 6], gorillas [7],
sheep [8], etc.)
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What is the genotypic fraction
in these characteristics?
Acknowledgment
| The author would like to
thank all photographers for their personal or general permission to publish
their photos in this article. All rights remain with the contributors. |
|
| Henry
Boitel, editor of the Biometrics Discussion Group, gave me the great hint
to have a look at the Fingerprint Cyphoma. |
Literature
|
