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An identification key to elasmobranch genera based on dental morphological characters Part A: Squalomorph sharks (Superorder Squalomorphii).

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In addition to articulated, mostly formaldehyde-fixed and ethanol-preserved, taxidermy or anatomical specimens, sharks and rays are represented in scientific collections by numerous jaws and isolated teeth. These specimens often source from historical collections where existing informations about species, sex or geographic origin in many cases are scarce, incomplete or incorrect. The identification key for jaws and teeth presented herein focuses on squalomorph sharks, which comprise almost 34 % of all sharks with 179 species in 31 genera and 11 families. The key is essentially based on the following characters: vascularisation stage, labial apron, number of cusplets, distal heel, lingual ornamentation, cutting edge, and dentition kind. The key allows the identification to genus level. It is further supplemented by a comprehensive glossary of tooth morphological terms as well as an updated checklist of all currently described squalomorph sharks with indication of the distribution and the dental formula. Zusammenfassung: In zahlreichen wissenschaftlichen Sammlungen befinden sich neben formaldehyd-oder alkoholkonservierten Ganzkörper-und anatomischen Präparaten oftmals Kiefer und Zähne von Haien und Rochen. Diese Exemplare stammen häufig aus historischen Sammlungen und die vorhandenen Informati-onen über die Art, das Geschlecht oder die geografische Herkunft sind oftmals lückenhaft oder falsch. Mit der vorliegenden Arbeit wird ein Bestimmungsschlüssel für Kiefer und Zähne von squalomorphen Haien vorgestellt. Diese Überordnung beinhaltet derzeit 179 Arten in 31 Gattungen und 11 Familien und stellt damit annähernd fast 34 % aller heute bekannten Haiarten dar. Zur Identifizierung wird dabei im Wesentlichen auf folgende Merkmale zurückgegriffen: Art des Vaskularisationssystems, labiales Apron, Anzahl der Zahn-spitzen, Talon, linguale Ornamentik, Form der Schneide und Art der Bezahnung. Der Schlüssel ermöglicht die Bestimmung bis auf Gattungsebene. Ergänzt wird er durch ein umfangreiches Glossar der wichtigsten zahnmorphologischen Begriffe sowie eine aktualisierte Checkliste aller derzeit bekannten squalomorphen Haie mit Angabe der geographischen Verbreitung und der Zahnformel.
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77
Bull. Fish Biol. 18 (1/2)
Bulletin of Fish Biology Volume 18 Nos. 1/2 31.12.2018 77-105
An identification key to elasmobranch genera
based on dental morphological characters
Part A: Squalomorph sharks (Superorder Squalomorphii)
Ein auf zahnmorphologischen Merkmalen basierender
Bestimmungsschlüssel für Elasmobranchiergattungen
Teil A: Squalomorphe Haie (Überordnung Squalomorphii)
Jürgen Pollerspöck1 & Nicolas Straube2
1Benediktinerring 34, D-94569 Stephansposching, juergen.pollerspoeck@shark-references.com
2Zoologische Staatssammlung München, Münchhausenstraße 21, D-81247 München, straube@snsb.de
Summary: In addition to articulated, mostly formaldehyde-xed and ethanol-preserved, taxidermy or ana-
tomical specimens, sharks and rays are represented in scientic collections by numerous jaws and isolated
teeth. These specimens often source from historical collections where existing informations about species,
sex or geographic origin in many cases are scarce, incomplete or incorrect. The identication key for jaws and
teeth presented herein focuses on squalomorph sharks, which comprise almost 34 % of all sharks with 179
species in 31 genera and 11 families. The key is essentially based on the following characters: vascularisation
stage, labial apron, number of cusplets, distal heel, lingual ornamentation, cutting edge, and dentition kind.
The key allows the identication to genus level. It is further supplemented by a comprehensive glossary of
tooth morphological terms as well as an updated checklist of all currently described squalomorph sharks
with indication of the distribution and the dental formula.
Key words: Dentition, Elasmobranchii, single-access key, teeth
Zusammenfassung: In zahlreichen wissenschaftlichen Sammlungen benden sich neben formaldehyd- oder
alkoholkonservierten Ganzkörper- und anatomischen Präparaten oftmals Kiefer und Zähne von Haien und
Rochen. Diese Exemplare stammen häug aus historischen Sammlungen und die vorhandenen Informati-
onen über die Art, das Geschlecht oder die geograsche Herkunft sind oftmals lückenhaft oder falsch. Mit
der vorliegenden Arbeit wird ein Bestimmungsschlüssel für Kiefer und Zähne von squalomorphen Haien
vorgestellt. Diese Überordnung beinhaltet derzeit 179 Arten in 31 Gattungen und 11 Familien und stellt damit
annähernd fast 34 % aller heute bekannten Haiarten dar. Zur Identizierung wird dabei im Wesentlichen
auf folgende Merkmale zurückgegriffen: Art des Vaskularisationssystems, labiales Apron, Anzahl der Zahn-
spitzen, Talon, linguale Ornamentik, Form der Schneide und Art der Bezahnung. Der Schlüssel ermöglicht
die Bestimmung bis auf Gattungsebene. Ergänzt wird er durch ein umfangreiches Glossar der wichtigsten
zahnmorphologischen Begriffe sowie eine aktualisierte Checkliste aller derzeit bekannten squalomorphen
Haie mit Angabe der geographischen Verbreitung und der Zahnformel.
Schlüsselwörter: Bezahnung, Elasmobranchii, dichotomer Bestimmungsschlüssel, Zähne
1. Introduction
Besides numerous synapomorphies, sharks,
skates and rays (Elasmobranchii) are character-
ized by the outstanding feature of being able
to produce teeth only within the dental lamina
and constantly replace jaw teeth throughout
their lifetime (Reif 1978; Smith et al. 2013;
UndeRwood et al. 2016). The elasmobranch
dentition often reects feeding habits and allows
for tracing ecological characteristics of its bearer
(Reif 1976; motta 2004). Due to these speciali-
zations, dental morphological characters are
further useful on numerous taxonomic levels,
78
in many instances even for species level identi-
cation (Sáez & PeqUeño 2010; Shimada 2002,
2005; Voigt & webeR 2011). Therefore, dental
characters of extant species are also decisive for
the identication of extinct species. The reason
for that lies in the fact that the fossil record
of elasmobranchs mainly comprises fossilized
teeth. Contrasting a rather detailed record of
fossil teeth, articulated fossils of elasmobranchs
are rather scarce, as Elasmobranchii have a
cartilaginous skeleton, which is less prone for
fossilization. Therefore, numerous fossil taxa
are described based on dental characters only
(e.g. CaPPetta & CaSe 2016; ebeRSole & ehRet
2018; PolleRSPöCk & StRaUbe 2017; Shimada
et al. 2017; welton 2016).
Recently, gUinot et al. (2018) and mollen
(2019) pointed out the importance of morpho-
logical descriptions of teeth in newly described
extant elasmobranch species as references for
the fossil record. Today, in most descriptions of
extant species, the dental formula and images of
upper and lower teeth are reported (e.g. kawaUChi
et al. 2014; StRaUbe et al. 2011; weigmann &
kaSChneR 2017; white et al. 2017). Apart from
few exceptions (e.g. gUtteRidge & bennett
2014; PSomadakiS et al. 2009; Rangel et al. 2016;
StRaUbe et al. 2007), ontogenetic and sexual varia-
tion of dental characters mostly remain unknown.
Living squalomorph sharks are characterized
by numerous distinct specializations of denti-
tions allowing for a species-level identication
in several examples such as Trigonognathus kabeyai
or Chlamydoselachus anguineus (CaPPetta & adnet
2001; Pfeil 1983). Apart from the highly diverse
angel sharks (Squatiniformes), many squalo-
morphs are deep-water inhabitants (kyne &
SimPfendoRfeR 2007), a habitat supporting the
development of specialized dentitions (adnet
& CaPPetta 2001). Their distinctive dental
features further allow clear identication of the
fossil record (e.g. maiSey 2012).
As scientic collections of both extant and
extinct elasmobranchs often hold jaws and/or
teeth only, in this study we aim for providing den-
tal morphological characters of the superorder
Squalomorphii as a rst step to summarize known
dental characters used for identication of taxa.
2. Material and Methods
The identification key is based primarily on
the information in the scientific literature
and was supplemented in part by research of
Polle RS PöCk et al. (2018). The valid species
and the classification listed in the checklist
(tab. 1) were downloaded from the database
www.shark-references.com (PolleRSPöCk &
StRaUbe 2019). The information on dental
formula and distribution contained in the
checklist is derived from the first descriptions
of the species or from the references listed
in table 1 (column “remarks”). Distribution
data were encoded using data from the Food
and Agriculture Organization (FAO) Fish-
eries and Aquaculture Department (http://
www.fao.org/fishery/area/search/en) (fig.
1, tab. 2).
The taxonomy of the superorder Squalo-
morphii is following PolleRSPöCk & StRaUbe,
2019 and is shown in table 3. In addition,
the maximum total length of the specimens
derived from ebeRt et al. (2013) was rounded
to the nearest full 10 cm to have an approx-
imate size. This can be useful for excluding
specimens beforehand or double-check, if a
specimen falls into a size range known from
literature. Further, we specied for each ge-
nus an approximate maximum width of the
jaws. For this, the values for the mouth width
were determined from available publications
listed below and the following average values
as percentage of standard length were used.
These data should be used as reference values
only: family Pristiophoridae: 5% (weigmann
et al. 2014: 4,3%-5,9%TL, ebeRt & wilmS,
2013: 3,6%-4,0%TL; yeaRSley et al. 2008:
4,4%-4,9%TL); family Squatinidae: 12% (Vaz
& de CaRValho, 2013: 10.8%-15.6%TL,
9.9%-15.1%TL, 13.7%-15.4%TL); all oth-
er families: 10% (e.g. StRaU be et al. 2011
for Etmopterus spp.: 10,23%TL, laSt et al.
2007a,b for Squalus spp.: 6.9%-7.7%TL, 7.8%-
8.6%TL, 8.1%-8.4%TL; white et al. 2013 for
Centrophorus spp.: 6,8%-10,4%TL, yano et
al. 2004 for Somniosus spp.: 7.2%-13.9%TL,
7.9%-10.9%TL, 6.5%-11.3%TL).
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Bull. Fish Biol. 18 (1/2)
Tab. 1: Checklist of sharks of the superorder Squalomorphii (status as of 01. January 2019).
Tab. 1: Checkliste der Haie der Überordnung Squalomorphii (Stand: 01. Januar 2019).
Remarks: All data have been extracted from the original descriptions of the species, except in cases where the
column „Remarks“ shows a different reference. The geographical distribution is indicated by the FAO shing
areas (http://www.fao.org/shery/area/search/en). This list is included here to allow for narrowing down
the number of possible species, if the collection locality is known. Further, including geographic informa-
tion may allow a more detailed identication compared to the identication based on jaws and teeth alone.
80
Tab. 1: Continued.
Tab. 1: Fortsetzung.
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Tab. 1: Continued.
Tab. 1: Fortsetzung.
82
Tab. 1: Continued.
Tab. 1: Fortsetzung.
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Tab. 1: Continued.
Tab. 1: Fortsetzung.
84
Tab. 1: Continued.
Tab. 1: Fortsetzung.
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Bull. Fish Biol. 18 (1/2)
Tab. 1: Continued.
Tab. 1: Fortsetzung.
Fig. 1: Map of the FAO Major Fishing Areas (http://www.fao.org/shery/area/search/en).
Abb. 1: Karte der Hauptschereigebiete der FAO (http://www.fao.org/shery/area/search/en).
3. Morphological identication key to
teeth of squalomorph sharks
The following key has been developed for
identication at the genus level for complete
specimens or isolated jaws, but can be used
in many cases for isolated teeth as well. When
selecting the morphological characters of teeth,
we focused on using characters that can be iden-
tied without removing teeth from the jaws. In
particular, no lingual root features were used.
Specic groups of teeth, such as symphyseal
teeth or commissural teeth have not been taken
into consideration. This key is most useful when
teeth from the lateral area of the jaws are used.
Key to squalomorph genera based on dental
characters: the number in brackets after genera
names indicates the number of valid species
(PolleRSPöCk & StRaUbe 2019), for monospeci-
c genera the corresponding species is indicated.
86
Tab. 2: FAO Major Fishing Areas (http://www.fao.org/shery/area/search/en).
Tab. 2: Hauptschereigebiete der FAO (http://www.fao.org/shery/area/search/en).
3.1. Glossary (tooth morphological char-
acters, after Casier 1961; Ledoux 1972;
Cappetta 2012)
3.1.1. Glossary: orientation
Apical: direction towards the root tip (g. 2).
Basal: direction towards the crown tip (g. 2).
Distal: direction to roof of the mouth (g. 2).
Labial: direction to mouth opening, outer face.
Lingual: direction to throat, inner face (g. 2).
Mesial: direction towards the anterior midline
of the jaw (g. 2).
Occlusal: direction towards the biting surface.
Symphyseal tooth: usually one symmetrical
tooth, crown mostly erected, position exact-
ly midway between the two jaw halves (e.g.
sometimes in the lower jaws of hexanchids or
squalids).
Parasymphyseal tooth: rst tooth of the right/
left jaw side, reduced in size, distorted cusp,
asymmetrical root.
Anterior teeth: teeth in the anterior region
of the jaw, often characterized by a strongly
erected crown; anterior squalomorph shark
teeth are often less wide but higher compared
to posterior teeth.
Posterior teeth: teeth in the posterior region of
the jaw, often characterized by a distally inclined
crown; posterior squalomorph shark teeth are
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Bull. Fish Biol. 18 (1/2)
Tab. 3: Taxonomy of the superorder Squalomorphii.
Tab. 3: Taxonomie der Überordnung Squalomorphii.
Fig. 2: Terms of orientation; lower teeth of Centroscymnus coelolepis.
Abb. 2: Begriffe der Orientierung; Unterkieferzähne von Centroscymnus coelolepis.
88
often wider and lower compared to anterior
ones (g. 2).
Commissural tooth: teeth near the corner of the
mouth, in squalomorphs, especially in the lower
jaw, one single commissural tooth is present and
differs very clearly from the posterior one in its
morphology (g. 2).
3.1.2. Glossary: characters of tooth crown
Apron (Apr, g. 3): also referred to as tablier,
a variable long and thick labial expansion of
the cusp (consist of an enameloid covered part
of the root, e.g. species of the genera Squalus
spp., Squatina spp.). Absent in various species
of the genera Hexanchus spp., Heptranchias spp.,
Echinorhinus spp.
Distal/mesial cusplets: small, left and/or right
arranged cusplets (e.g. at the upper jaw teeth
of Etmopterus spp. or the upper/lower teeth of
Centroscyllium spp.).
Distal/mesial cutting edge: enameloid margin of
the tooth; the cutting edge can e.g. be absent,
partially present or ranging from the top to the
crown base.
Comb- or sawblade-like tooth: multicuspid tooth
with the distinctive character that the rst mesial
cusp is always the largest and size of consecutive
cusps decrease gradually towards distal.
Talon or mesial/distal heel (Dih, Mhe, g.
3): squalomorph teeth without cusplets often
show mesially and/or distally prolonged more
or less marked enameloid heels at the bases
of the cusp.
Fig. 3: Squalomorph tooth forms; abbreviations: Apr (apron); Nug (nutritive or basal groove), Bfr (basal
face of the root), Lar (labial face of the root), Lfr (lingual face of the root), Dih (distal heel or talon), Uvl
(uvula), Dlih (distolingual hollow or overlapping surface), Inf (infundibulum or central lingual foramen),
Lbr (lingual bulge of the root). © drawings: Helmut Bracher, Altdorf.
Abb. 3: Squalomorphe Zahnformen; Abkürzungen: Apr (Apron); Nug (Basalfurche), Bfr (basale
Wurzeläche), Lar (labiale Wurzeläche), Lfr (linguale Wurzeläche), Dih (distaler Höcker, Talon), Uvl
(Uvula), Dlih (distolinguale Überlappungsäche), Inf (Infundibulum oder zentrales linguales Foramen),
Lbr (lingualer Wurzelgrat). © Zeichnungen: Helmut Bracher, Altdorf.
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Bull. Fish Biol. 18 (1/2)
Uvula (Uvl, g. 3): like an apron, mostly short
and conical, only at the lingual side of the tooth
and sometimes very distinctive (e.g. Squalus
spp., Deania spp., Centrophorus spp.). Absent in
various genera (e.g. Hexanchus spp., Heptranchias
spp., Echinorhinus spp.).
3.1.3. Glossary: characters of the tooth root
Basal face of the root (Bfr, g. 3): the part of
the root with which the tooth is connected
to the jaw, in several studies (e.g. kitamURa
2013; welton 2016), this part of the root
is falsely referred to as the lingual root face,
in squalomorph teeth, the basal root face is
often separated by a horizontal ridge (= lin-
gual bulge of the root) from the lingual face
of the root.
Nutritive or basal groove (Nug, g. 3) or Sul-
cus: lingual pronounced groove, which usually
begins at the base of the root and ends in a
central foramen.
Foramen: Openings for e.g. blood and nerve
vessels, the foramen are differentiated according
to their location (labial/lingual/mesial/distal/
axial or central) and size.
Labial face of the root (Lar): see gure 3.
Lingual face of the root (Lfr): see gure 3.
Root vascularization: how the tooth is sup-
plied with the necessary nutrients. There are
four basic evolutionary systems (after CaSieR
1961):
a) anaulacorhizid stage: several, mostly smaller
and irregularly scattered foramina are present
on both sides of the root (e.g., in hybodon-
toids, notidanoids and presquatinoid tooth
types); according to CaSieR (1961) squaliform
sharks teeth belong to the anaulacorhizid
stage.
b) Hemiaulacorhizid stage: medial vascular
canal opens into a centralized foramen at the
basal face of the root. This face is more or less
perpendicular to the axis of the crown (typical
of squatinoid, orectoloboid or chlamydoselachid
tooth types).
c) Holaulacorhizid stage: central foramen ends
in a nutritive or basal groove that divides the
basal surface of the root into two areas (typi-
cally at scyliorhinoid or rhinobatoid tooth types,
e.g. order Lamniformes, Carcharhiniformes,
Rajiformes, Torpediniformes and some mylio-
batiforms).
d) Polyaulacorhizid stage: transverse enlarge-
ment of the root, which is often separated by
more or less wide and deep parallel laminae
with several small foramina, is developed.
This stage especially occurs in myliobatoid
tooth types.
Button hole or Boutonnière: this hole of the
root is created by the union of a central lingual
and labial foramen. According to CaSieR (1961)
this character is present especially in Dalatias licha
and Isistius spp.
Infundibulum: central labial and lingual foramen
merged to a central labial foramen, e.g. Somniosus
spp., Squalus spp., Centrophorus spp.
Mesial labial hollow/distal lingual hollow or
overlapping surface: typical character that occurs
essentially only in squaliform lower teeth and
differs greatly within the different genera. With
the exception of the last tooth in the dentition
(commissural tooth), all lower jaw teeth have
two overlapping surfaces.
Root lobes: root split in two long and distinct
branches; usually not present in lower squalo-
morph shark teeth, typical for e.g. galeomorph
shark teeth.
3.1.4. Glossary: heterodonty/homodonty
Dignathic heterodonty: present, when teeth
of upper and lower jaws have different mor-
phologies.
Disjunct monognathic heterodonty: different
type of teeth present in one jaw, e.g. symphyseal,
parasymphyseal, anterior, lateral or posterior
teeth.
Gradient monognathic heterodonty: tooth
morphology changes continuously from row
to row within one jaw.
Gynandric or sexual heterodonty (sexual dimor-
phism): present if teeth of both sexes differ in
morphology.
Homodonty: teeth in the upper and lower jaws
show a very similar morphology.
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3.2. Morphological identication key
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Mochizuki & Ohe
de Buen
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Bonnaterre
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Acknowledgments
Many thanks to Helmut bRaChe R, Altdorf,
for the permission to use his drawings of
squalomorph shark teeth. We would like to
acknowledge two anonymous reviewers for their
constructive criticism.
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Received: 20.01.2019
Accepted: 24.03.2019
... Stone & Shimada (2019) examined the skeletal anatomy of the specimen from Humphreys et al. (1989). Pollerspöck & Straube (2020) described the tooth morphology of all lamniform sharks, and provided an identification key based on those characters. All studies confirmed the presence of a pair of cusplets on each side of the cusp. ...
... Morphometric measurements were in centimeters (cm), and body proportions are expressed in terms of total length (TL). Tooth count and dental formula followed Pollerspöck & Straube (2020). Lateral and posterior teeth were combined due to the difficulty to distinguish between the two types of teeth. ...
... The number of cusplets on the tooth was recognized a useful character to distinguish O. noronhai from O. ferox, as the former has only one per side, but the latter has two to three (Humphreys et al. 1989;Kerstetter & Taylor 2008;Pollerspöck & Straube 2020). However, our specimen does not match this character. ...
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... Th ese features closely match the condition that can be observed in typical Dalatias lower teeth (e. g., Cappetta, 2012;Carrillo-Briceño et al., 2015, 2016, 2020. Lastly, this specimen possesses a button-shaped foramen surrounded by mesial and distal aprons, which is a character that is present especially in species of Dalatias and Isistius according to Pollerspöck and Straube (2018). CNUNHM-F279 can be easily distinguished from the lower teeth of Isistius by its much larger size, distinctively developed serrations and the presence of the distal heel (Cappetta, 2012;Suzuki, 2015;Pollerspöck and Straube, 2018). ...
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... Tooth replacement occurs from several days per tooth row (e.g., in the dusky smooth-hound Mustelus canis and in the lemon shark Negaprion brevirostris) to several weeks (e.g., in S. canicula and in the horn shark Heterodontus francisci) [Ifft and Zinn, 1948;Applegate, 1967;Moss, 1967;Märkel and Laubier, 1969;Luer et al., 1990]. Moreover, because enameloid and dentine are very hard to decay -as opposed to calcified cartilage-, most fossil remains of elasmobranchs are teeth [Shimada, 2005b;Pollerspöck and Straube, 2019]. The identification of isolated teeth is thus largely based on characters such as the location, number and size of root foramina, the presence and extension of cutting edges on the crown, the occurrence of accessory cusps, and homodonty and heterodonty patterns [Herman et al., 1989[Herman et al., , 1990Cappetta, 2012;Pollerspöck and Straube, 2019]. ...
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Teeth are serial structures whose evolutionary and developmental history is intricately linked with the emergence of mineralised tissues in vertebrates. Teeth display a broad range of forms and differ in developmental patterns in extant vertebrates, making them remarkable elements to study species diversification. Selachian teeth renew permanently and display morphologies that are correlated with mating and trophic behaviours.This work first assesses the variation of tooth forms in two scyliorhinids by using 3D geometric morphometrics and machine learning. The emergence of gynandric heterodonty is detailed for the first time along the ontogeny of sharks and it is demonstrated that this natural variation should be first assessed before performing species discrimination.This work also questions the role of specific proteins on the acquisition of a shark tooth form over development. Functional tests suggest an impact of Shh and Fgf3 in the cusp morphogenesis and in the mineralisation process. These proteins are promising explanatory variables to the inter- and intraspecific tooth differences observed, leading to hypotheses on their role in the evolution of structures with speciation and trophic and mating behaviours.Histological data on extant chondrichthyan vertebrae finally highlight the unsuspected proportion of extant elasmobranchs exhibiting fibrous mineralisation in the neural arches, a bone-like tissue which occurrence had long been refuted in this group. Evolutionary considerations are discussed in the light of the evolution of jawed vertebrates and question on the ecological factors that led particular tissues to be restricted to specific shark and batoid groups.
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... and the morphology of the oral teeth (poorly developed labial apron in Pristiophorus and rectangular apron in Pliotrema)(Pollerspöck & Straube, 2019).Identification to species can be achieved in both genera based on the relative position of the barbels along the rostrum(Ebert & Wilms, 2013;Weigmann et al., 2020). Some species have the barbels positioned closer to the nostrils and others around the mid-point of the rostrum. ...
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