Oldest evidence of the genus Squalus in the north alpine realm with remarks on its evolution and distribution through time

Abstract

The distinct morphology of teeth of the dogfish sharks Squalus spp. allows for tracking its evolutionary history. Fossils of the genus are known since the early Cretaceous; however, fossilized teeth of Squalus from that period are scarce. Here, we report on the oldest finding of a Squalus tooth fossil (upper Campanian-lower Maastrichtian) from the north alpine realm. The tooth is assigned to S. vondermarcki based on its morphological characters. Our finding adds information on the distribution of the genus during the Cretaceous period supporting a Tethyan origin in the early Cretaceous and subsequent distribution to other ancient oceans.

Full text

Paleoichthys 2
: 1-9 (2021)
© www.pecescriollos.de 2021 - ISSN 2748-8721
Oldest evidence of the genus Squalus in the north alpine realm
with remarks on its evolution and distribution through time.
Jürgen Pollerspöck1*, Bernhard Beaury2, Nicolas Straube3 & Iris Feichtinger4,5
1
Bavarian State Collection of Zoology, Münchhausenstr. 21, 81247 Munich, Germany
2
Independent researcher. Seerosenweg 10b, 83236 Übersee, Germany
3
University Museum Bergen, Department of Natural History, Realfagbygget Allégt. 41, 5007 Bergen, Norway
4
Geological-Palaeontological Department, Natural History Museum, Burgring 7, 1010 Vienna, Austria
5
NAWI Graz Geocenter, Institute of Earth Sciences, University of Graz, Austria
*
juergen.pollerspoeck@shark-references.com
Abstract
The distinct morphology of teeth of the dogfish sharks Squalus spp. allows for tracking its evolutionary
history. Fossils of the genus are known since the early Cretaceous; however, fossilized teeth of Squalus
from that period are scarce. Here, we report on the oldest finding of a Squalus tooth fossil (upper
Campanian - lower Maastrichtian) from the north alpine realm. The tooth is assigned to S. vondermarcki
based on its morphological characters. Our finding adds information on the distribution of the genus during
the Cretaceous period supporting a Tethyan origin in the early Cretaceous and subsequent distribution to
other ancient oceans.
keywords: Cretaceous, Maastrichtian, Campanian, Squalidae, tooth morphology, chondrichthyes
Introduction
In earth history the Late Cretaceous holds a crucial role in evolution leading to modern biota. Based on
drastic climatic changes from the Cretaceous Thermal Maximum in the early-mid Turonian, the onset of a
cooling trend continued during the Campanian and culminated in the Maastrichtian (Cramer et al. 2011;
Huber et al. 2018). The significant change of climate and environmental conditions entailed both the
demise and evolution of new species of terrestrial (e.g. Condamine et al. 2021) and marine vertebrates
including speciation in cartilaginous fishes (e.g. Guinot 2013; Condamine et al. 2019; Guinot & Cavin
2020). Here, we focus on the origination of the selachian genus Squalus, which appeared in the fossil
record for the first time during the beginning of the Cretaceous Thermal Maximum, endured the severe
global cooling in the Late Cretaceous, the mass extinction event at the end of the Cretaceous and persists
until today.
The basis of this study is an isolated tooth from a building pit in Bad Adelholzen, Germany. The village Bad
Adelholzen is well known for the production of mineral water, which enabled the exposure of the complete
succession of the North Helvetic Nappe (Late Cretaceous to Late Eocene) during an expansion of the
Adelholzener Alpenquellen company in 1994. This outcrop was frequently visited by amateur collectors of
fossils, who made some extraordinary findings. The most famous is the first Bavarian Hadrosaurus
(Wellnhofer 1992). However, the more common findings are belemnites. Hence, the herein described tooth
of the order Squaliformes is the first record of sharks within this section of the Pattenau Formation and
represents the oldest evidence of this order from the north alpine realm.
Böhm (1891) and Ganss (1956) published on the fauna of the Helvetic cretaceous formations but did not
mention any shark fossils from the Pattenau Formation (“Pattenauer Mergel”). Our study documents the
first selachian fossil from this formation.

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Geographical and geological settings
Bad Adelholzen is located about 100 km south-east from Munich belonging to the municipality of Siegsdorf
(Upper Bavaria) near the northern edge of the Alps (fig. 1A). Cretaceous sediments were only accessible
during construction works. It must be mentioned that the sketch of the outcrop and the corresponding
stratigraphic horizons of figure 1 rely on informal notes from the one of the authors (BB) during 1994 with
only some rough measurements. During the Cretaceous to the Late Eocene, sediments were deposited on
the southern continental shelf of Europe in the Tethys Ocean (Helvetic Unit). Hagn (1960) assumed the
Tethys Sea to comprise two sea basins divided by the Ultrahelvetic Ridge. This ridge was formed regionally
differently as an island chain or as a submarine bar (Heyng 2012). Therefore, these sediments are divided
in a southern (South Helvetic Unit) and a northern part (Northern Helvetic Unit), respectively (Hagn 1960).
The described outcrop comprises only sediments of the Northern Helvetic Unit. Bad Adelholzen is
geographically located in the collision zone of the Helvetic nappe and the North Alpine Foreland Basin.
fig. 1.
Geographical and geological settings. A: The locality Adelholzen (star) in the very south-east of Germany. B: Simplified
geological setting. Locality marked by star. C: Sketch of the geological cross section after completion of construction.

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Consequently, the North Alpine Foreland Basin has been successively overthrusted by the Helvetic nappe
during alpine orogenesis (Hagn 1960).
Simplified, all strata are running more or less in east-west direction. From north to south, sediments from
the Oligocene are found first in the north of the company site, followed by the Northern Helvetic nappe in
the south. The contact zone was never accessible due to a Pleistocene glacier outflow of the Chiemsee
glacier, removing the autochthonous sediments and replacing them with allochthonous gravel or clay.
The accessible succession started with the Pattenau Formation (Campanian-Maastrichtian) in the north of
the ancient outcrop (fig. 1B, C) and is followed by the Gerhartsreit Formation (Maastrichtian). Sediments
from the Palaeocene and lower Eocene sediments are missing due to a rather large hiatus. Consequently,
the Adelholzen Formation (type locality) follows the Gerhartsreit Formation at this site, which represents
sediments from the middle to upper Eocene. The top of autochthonous sedimentation is represented by the
deposition of the Stockletten. The sketch (fig. 3B, C) is showing the former geological exposure overlayed
on today’s situation. Hagn et al. (1981) described the formation of interest, Pattenau Formation, as “light
grey, calcareous, chunky marls with a tinge of blue or green”. Throughout the section, several layers with
fossil accumulations could be observed, dominated by belemnites, molluscs (Inoceramus), and echinoids
among others.
Material & methods
The tooth-bearing sediments from the Pattenau Formation (5 kg) were collected by one of the authors (BB)
in 1994. The tooth was extracted from the sediment in 2013 by using diluted hydrogen peroxide in
combination with screen-washing down to a mesh size of 300µm. The accompanying fauna consists
particularly of belemnites as well as a rich micro fauna. The tooth analyzed herein is deposited in the
Natural History Museum (NHM) Vienna with the inventory number NHMW/2021/0136/0001.
fig. 2.
Squalus vondermarcki Müller & Schöllmann, 1989, Pattenau Formation, Collection No. NHMW/2021/0136/0001
A: lingual view, B: labial view, C: basal view, D: occlusal view.

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Results
1. Systematic palaeontology
cohort
EUSELACHII
Hay, 1902
subcohort
NEOSELACHII
Compagno, 1977
order
Squaliformes
Compagno, 1977
family Squalidae Blainville, 1816
genus
Squalus
Linné, 1758
type species
S. acanthias
Linné, 1758 | by subsequent designation
Squalus vondermarcki Müller & Schöllmann, 1989
1977 Squalus cfr. latidens - Herman: 139, pl. 5 fig. 9
1982a Centrosqualus appendiculatus - Herman: 133-134 (partim), pl. 1 fig. 4a
figure 2 A-D
material: 1 tooth (NHMW/2021/0136/0001).
size: height: 1.90 mm; width: 3.03 mm.
distribution: Germany, Maastrichtian-Campanian (Müller 1989, 1991; Müller & Schöllmann 1989; Thies
& Müller 1993; Zacke 2003), Angola (Antunes & Cappetta 2002), ?Canada (Cappetta et al.
2019).
2. Description
The tooth is strongly labio-lingually compressed. Its width is 3.02 mm, the height is 1.93 mm and the angle
of inclination of the main cusp measures 28.4°. The broad, triangular main cusp is strongly bent distally.
The crown is smooth and biconvex. Folds or ornamentations are absent. The mesial cutting edge shows no
serration, is convex in the lower two-thirds and straight near the tip of the cusp. The short distal cutting
edge is weakly convex. The semi-circular distal heel takes up about a quarter of the total width. The labial
short and approximately rectangular apron overhangs insignificant the base of the root. Several small
foramina are located on both sides of the apron directly below the crown base. The lingual side of the tooth
shows a prominent, high medially uvula with a central infundibulum. Similar to the labial side of the tooth
there are several small foramina on both sides of the uvula. The compressed and narrow root shows a flat
basal face and a well marked lingual bulge.
3. Remarks
The tooth described here shows great similarity with the tooth illustrated by Müller & Schöllmann (1989, fig.
4) and described as Squalus vondermarcki. The morphological differences from the valid species
mentioned below are described in detail in Antunes & Cappetta (2002). Cappetta et al. (2019) reported S.
vondermarcki from the Campanian of Hornby Island, British Columbia, Canada. It is remarkable that, in
contrast to the teeth from the Campanian of Northern Germany and the tooth shown herein, the teeth from
Hornby Island possess aprons that distinctly overhang the bases of roots. Müller & Schöllmann (1989) write
in their species diagnosis that the apron generally slightly overhangs the base of the root, however, not as
distinct as shown in Cappetta et al. (2019). We therefore suggest a taxonomic re-analysis of fossil teeth
from Hornby Island.
In addition to the genera Squalus and Cirrhigaleus, the extinct genera †Centrosqualus Signeux, 1950,
†Protosqualus Cappetta, 1977, †Megasqualus Herman, 1982b, and †Centrophoides Davis, 1887, are
included in the family Squalidae. Apart from S. vondermarcki, the following valid Squalus species are
currently known from the Cretaceous: S. worlandensis Case, 1987, S. huntensis Case & Cappetta, 1997,
S. ballingsloevensis Siverson, 1993, S. balsvikensis Siverson, 1993, S. gabrielsoni Siverson, 1993, S.
nicholsae Cappetta, Morrison & Adnet, 2019, S. argentinensis (Bogan, Agnolín & Novas, 2016), and S.
chiconis (Jordan, 1907).
Squalus chiconis (Jordan, 1907) was originally described as Hemipristis chiconis Jordan, 1907 and later
placed in Notidanion chicone (Jordan & Hannibal, 1923). The holotype was examined by Welton &
Alderson (1981) and clearly identified as Squalus. Due to the only fragmentary preservation and the lack of
the complete root, the morphological characteristics decisive for species identification are missing and the
species has to be evaluated as a nomen dubium.

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tab. 1.
Fossil records of the genus Squalus.
fig. 3.
Paleogeographic records of the genus
Squalus during the Cretaceous indicated
by red stars, big star (n>100), medium star
(n>20<100), small star (n<20)
(Palaeomaps after Scotese 2014).
Species Age Number of specimens County O cean Reference
Squalus sp. Maastrichtian 1Chile East Pac ific Muñoz-Ramírez et al. 2007
Squalus gabrielsoni Siverson, 1993 Maastrichtian 36 Denmark N orth Atlantic Adolfssen & Ward 2014
Squalus ballingsloeve nsis Siverso n, 1993 Maastrichtian >100 Sweden North Atlantic Siverson 1993
Squalus balsvikensis Siverson, 1993 Maastrichtian severa l hundred teeth Sweden North Atlantic Siverson 1993
Squalus gabrielsoni Siverson, 1993 Maastrichtian about 50 teeth Sweden North Atlantic Siverson 1993
Squalus huntensis Case & C appetta, 1997 Maastrichtian 1US, Nort h Carolina North East Atlantic Case et al. 2017
Squalus chiconis (=sp.) (Jo rdan, 1907) Maastrichtian 1US, Calif ornia Ost Pacific Jordan 1907
Squalus argentinensi s (Boga n, Agnolin & Novas, 2016) Maastrichtian 18 Argentina So uth East Atlantic Bogan et al. 2016
Squalus sp. Maastrichtian 1Germany T ethys Pollerspöck & Beaury 2014
Squalus vondermarcki Müller & Schöllmann, 1989 Maastrichtian 5Germany T ethys Zacke 2003
Squalus sp. Maastrichtian ?Maroc T ethys No ubhani & Cappe tta 1997
Squalus ballingsloeve nsis Siverso n, 1993 Maastrichtian 153 US, Nort h Dakota Western Interio r Seaway Hoganson et al. 2019
Squalus sp. Maastrichtian 4US, Nort h Dakota Western Interio r Seaway Hoganson et al. 2019
Squalus huntensis Case & C appetta, 1997 Maastrichtian 2US, Te xas Western Interior Seaway/East Atlantic C ase & Cappetta 1997
Squalus nicholsae Cappe tta, Morriso n & Adnet, 2019 Campanian 154 CA, British Columbia East Pacific Cappetta et al. 2019
Squalus sp. Campanian 1CA, British Columbia East Pacific Cappetta et al. 2019
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian 343 CA, British Columbia East Pacific Cappetta et al. 2019
Squalus sp. Campanian 2US, California East Pacific Welton & Alderson 1981
Squalus vondermarcki Müller & Schöllmann, 1989 Early Camp./Late Maastr. 10 Angola South West Atlantic Antunes & Ca ppetta 2002
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian >50 Germany Te thys Müller 1989
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian 6 (plus fra gments) Germany Te thys Müller & Schöllmann 1989
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian 2Germany Te thys Thies & Müller 1993
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian 20 Germany Te thys Müller 1991
Squalus vondermarcki Müller & Schöllmann, 1989 Campanian 1Germany Te thys this study
Squalus sp. Campanian ?Israel Te thys Lewy & Ca ppetta 1989
Squalus worlandensis (Case, 1987) Campanian 4CA, Alberta Western Interio r Seaway Cook et al. 2017
Squalus sp. Campanian >200 US, Sout h Dakota We stern Interior Seaw ay Martin & Fox 2007
Squalus worlandensis (Case, 1987) Campanian numerous teeth (100 ?) US, Wyo ming Wes tern Interior Seawa y Case 1987
Squalus worlandensis (Case, 1987) Campanian ?US, Wyoming Western I nterior Seaway Demar & Breithaupt 2006
Squalus sp. Turonia n (?, one f in spine) Ge rmany Tet hys Fischer et al. 2017
Squalus sp. Cenoma nian 1L ithuania n North Atlantic Adnet et al. 2008
Squalus sp. Cenoma nian >10 Kazakhstan Tethys Kennedy et al. 2008
Squalus sp. Cenoma nian ?Russia Te thys Popov & Lapkin 2000
Squalus sp. Cenoma nian 2U nited Kingdom Tethys Underwood & Mitchell 1999

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The oldest records of teeth assigned to the genus Squalus come from the Cenomanian (North East
England, Underwood & Mitchell 1999; Russia, Popov & Lapkin 2000; Lithuanian, Adnet et al. 2008;
Kazakhstan, Kennedy et al. 2008). Both Underwood & Mitchell (1999) and Adnet et al. (2008) documented
a striking dominance of the genus Protosqualus relative to the genus Squalus at these sites (470/2 in
Underwood & Mitchell 1999, and more than 150/1 in Adnet et al. 2008).
Protosqualus differs essentially from Squalus in having two separate lingual foramina, whereas the genus
Squalus usually has one infundibulum. However, Cappetta (1977) already notes in the genus diagnosis of
Protosqualus that three out of 18 tooth specimens have an infundibulum. The second difference is the
shape of the apron. While the apron of Protosqualus is usually very broad at the base and continuously
tapers towards the bottom, the apron of Squalus is usually formed with parallel edges (Underwood &
Mitchell 1999). Protosqualus has been recorded mainly from the central Tethys (Europe, Russia, Cappetta
2012). It has been reported from Australia (Kemp 1991; Berrell et al. 2020) and India (Underwood et al.
2011). To date, there are no records from North America.
Discussion
Teeth of the genus Squalus are relatively rare in Late Cretaceous sediments. A database search at
www.shark-references.com (Pollerspöck & Straube 2021a) revealed 832 publications dealing with Late
Cretaceous elasmobranch faunas. Of these, 9,85 % report on squaliform tooth fossils. Only 4,69 % of the
articles documenting squaliform diversity report on Squalus fossils (tab. 1).
Figure 3 summarises the findings of the genus Squalus published to date. Contrary to the description in
Adnet et al. (2008, fig. 5), which suggests a continuous record of the genus Squalus from the Cenomanian
to the present day, records are still missing from the Turonian to the Santonian. (tab. 1, fig. 3).
According to current knowledge, the genus Squalus appears in the Cenomanian in the area of the Central
Tethys, is common in the Campanian in North America both on the Pacific coast and at Western Interior
Seaway, but has also already been recorded in the southern Atlantic (Angola) (fig. 3). The geographical
distribution continues in the Maastrichtian with first records from the South-East Pacific (Chile). Today, with
37 species (Pollerspöck & Straube 2021b), the genus is distributed almost worldwide in boreal, temperate
and tropical seas and is one of the most diverse genera of the order Squaliformes.
Assuming the genus Squalus originated in the Central Tethys, it appears to have expanded from there to
the Campanian both eastward (Israel, Lewy & Cappetta 1989) and southward along the African continent
(Angola, Antunes & Cappetta 2002) and westward (North America). The numerous abundance in the area
of the Western Interior Seaway is remarkable (Case 1987; Martin & Fox 2007), since only few specimens
were documented from other sites (tab. 1). In the Western Interior Seaway, water depth increased steadily
westward, reaching several hundred meters in the Utah area (Kauffman 1984). The two sites mentioned
above were located in the central and eastern areas of this sea, respectively, and thus in much shallower
waters. The sediments in which the teeth of the fossil S. worlandensis (Case, 1987) were found are even
attributed to the estuarine phase of the Mesaverde Formation. Comparably shallow habitats as estimated
for the Mesaverde Formation are occupied today only by Cirrhigaleus asper, S. acanthias, and S. suckleyi.
In contrast, several recent representatives of the family Squalidae usually inhabit depths of 600m and
below (Ebert et al. 2013). Squalus acanthias and S. suckleyi are known to reproduce in shallow nearshore
areas (Ebert et al. 2013). The numerically frequent occurrence of Squalus fossils in shallow water deposits
of the Maastrichtian may indicate at least temporary shallow habitat occupancy.
However, the numerically largest occurrence of fossil Squalus teeth is reported from large deep-water
submarine fan complexes at the North American Pacific Coast region (Cappetta et al. 2019). Since there
was no connection between the Pacific and the Western Interior Seaway in the Maastrichtian, the genus
likely spread along the North American Pacific coast via the Central American Seaway. Records from Chile
provide further datapoints allowing speculation on a worldwide distribution already in the Maastrichtian.
Acknowledgments
The authors would like to thank the two reviewers Sylvain Adnet and Dirk Hovestadt for their constructive
criticism.
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© www.pecescriollos.de 2021 - ISSN 2748-8721
Pollerspöck, J., B. Beaury, N. Straube & I. Feichtinger (2021):
Oldest evidence of the genus Squalus in the north alpine realm with remarks on its evolution and distribution through time.
Paleoichthys 2: 1-9
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authors’ IDs & affiliations
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