Eocene sharks in The Limfjord area

The Chondrichthyes assemblages from the Søvind Marl Formation is compared to the Fur Formation and the Ølst Formation, from the Isle of Mors in Denmark. The fauna witnesses a dramatic shift in the Chondrichthyes fauna during around 20 ma. years, with a significant change of the environment in a very small area in the Early Eocene to Late Eocene.

HENRIK MADSEN

A new found Chondrichthyes assemblages from the Late Eocene Søvind Marl Formation (Late Priabonian) on the Isle of Mors in Denmark yielded teeth of 33 different genera/species from bulk sampling. The fauna is dominated by deepwater genera like Centrophorus, Isistius, Echinorhinus, Lamniform, Pristiophorus and Hexanchiformes. All the shark teeth are reported for the first time from the Late Priabonian, Søvind Marl Formation in Denmark.

The faunas suggests deposition in a reltive deep-water environment in subtropical waters on the middle or outer continental shelf at water depth from 100 to 400 m (Schmitz et al. 1996).

Keywords: Denmark, Søvind Marl Formation, Fur Formation, Ølst Formation, Lower Eocene, Chondrichthyes, fossil teeth.

Henrik Madsen [henrik.madsen@museummors.dk], Fossil- og Molermuseet, Museum Mors,

Skarrehagevej 8, 7900 Nykøbing Mors, Denmark.

The aim of this paper is to make a list on the chondrichthyes fossil teeth from the Søvind Marl Formation (Heilmann-Clausen 1982), on the Isle of Mors, Denmark, and compare the assemblage with the Fur Formation which is underlying the Søvind Marl Formation. Furthermore the special unformal Sundbylayer, rich in elasmobranch fossil teeth deposited between the Stolleklint Clay and the Fur Formation are used to compare the fauna before the Fur Formation and Søvind Marl Formation. This fauna, although well known by palaeontologists in Denmark, has never been described in the scientific literature. Moreover, the composition of the fauna gives information on the climate and depositional environment. The screen-washed bulk material from the layers, bonebed G1 and bonebed G2 of the Søvind Marl Formation, and the provenance of this material is therefore precisely known, dating from the Late Priabonian, Thalassiphora reticulata dinoflagellate Zone (Heilmann-Clausen 1988).The locality at Grønbjerg Klint and the material are new to science.

In the Fur Formation the assemblage of the elasmobranch only consist of 7 different genera/species. The assemblage of the chondrichthyes in the Sundbylayer consist of 20 different genera. The assemblage of the chondrichthyes in the Søvind Marl Formation,
consist of 33 different genera/species.



Fig. 1. The places were the different types of clay in this articel are found.
1: Sundby Klint, 2: Grønbjerg Klint. 3: Ejerslev molergrav. 4: Stolleklint.

Geological setting

In a distance of 7 km from Sundby Klint to Grønbjerg Klint on the Isle of Mors, it is possible to find shark teeth in these tree Geological Formations: Ølst Formation, Fur Formation, Søvind Marl Formation. The time span is around 20 ma. Age 55,8 – 34,0 ma.

Here the shark assemblage is compared in a small area in the North Sea basin were the fossils were deposited, at a time when the area went through some huge changes in climate and environment. The Paleocene-Eocene Thermal Maximum Kennett & Stott (1991) began approximately 55,8 million years before present (Röhl et al. 2007) and lasted about 170,000 years. The PETM involved more than 5 C° of warming. The Eocene Thermal Maximum 2 was another period of global warming that occurred approximately 53.7 million years before present and represents the second largest of the major Eocene hyperthermals. In the Late Priabonian, the Earth’s climate entered a phase with decreasing temperatures, culminating at the Eocene–Oligocene transition (EOT). The Late Priabonian temperature had a 10 °C temperature fall, starting at 36.1 Ma and culminating near the EOT at 33.9 Ma. (Śliwińska K.K. 2019).


Fig. 2. Paleomaps modified from Bonde 1972 and Ziegler 1990.
1: Ølst Formation, 2: Fur Formation, 3: Søvind Marl Formation.

Ølst-Formation

The shark teeth from the Ølst-Formation are rarely found in the shale, over the volcanic ash layer -33, but the far most specimens and species is from the unofficial layer Sundby-layer, that overlies the Stolleklint Clay - Age 56,0 -55,8 ma.

Fur-Formation

The shark teeth from the Fur-Formation are rarely found in the 60 meter thick diatomite called Mo-Clay. Single shark teeth are found throughout the whole formation. The striated cement stone from the level with volcanic ash layer -24 to -28, which is the lower part of the Fur Formation, have yield most shark teeth. Age 55,8-54.0 ma.

Søvind Marl Formation

The shark teeth from the Søvind Marl Formation at Grønbjerg Klint are from the Late Priabonian overlies the Fur Formation that is Early Ypresian, and on this locality the author has observed arround 6 meters of unknown layers, that expands the Fur Formation. On top of these new layers is visible. The layers are not identical with Søvind Marl, but are equivalent in age to the layers from this Formation. - Age 34,0 ma.

Fig. 3. Modified from Stokke et. al. 2020.

Grønbjerg Klint is a coast cliff in Northern Jutland on the Isle of Mors, near the small village of Flade (Fig. 1). During the Eocene, the Danish area was covered by the North Sea and clays and marls were deposited. When the Søvind Marl Formation was deposited, in a period where the English Channel was open, and the warm Atlantic Ocean made the sea level higher than when the Stolleklint Clay and Mo-clay sediments were deposited. The fine-grained clays of the Søvind Marl Formation and the Moclay are exposed in outcrops on the N-coast of Mors. Small outcrops of Stolleklint Clay and Holmehus Clay with the Paleocene-Eocene boundery have been observed on the beach at Sundby Klint. The Søvind Marl Formation, is only known from this locality in the Limfjord area.

Stratigraphy

The Søvind Marl Formation has been logged by Heilmann-Clausen et al. (1985) It is restricted to this locality in the western Limfjord area.

At Grønbjerg Klint the Søvind Marl Formation layers is different than the layers in the rest of Denmark. The stratigraphy of the Søvind Marl Formation is illustrated by Heilmann-Clausen et al. 1985. At Grønbjerg Klint 4 meter is more or less exposed in a landslide west of the mo-clay cliff. It is also overlaying the moclay with 36 cm red-brown clay on top of the Grønbjerg Klint. Søvind Marl Formation at Grønbjerg Klint, is red-brown, green, gray and grey-green, glauconitic fine-grained waxy clay, with light yellow and grey burrows preserved as small calcareous concretions.


Fig. 4. The landslide area with the Søvind Marl Formation at Grønbjerg Klint.


Fig. 5. The aurthor Henrik Madsen with the G2 layer at Grønbjerg Klint.

In the two measured profiles in the big landslide profile A, is 1,5 meter high and 15 meter in length. Furthermore a excavated ditch presents 2,4 meter green and brown clay below the glauconitic layer (G 1). In a slide a few meters behind and above this profile, the glauconitic layer G 2 is visible. Profile B is a 3,3 meter high and 10 meter wide profile, with the two glauconitic rich layers present (G 1 and G 2). At Grønbjerg Klint the Søvind Marl Formation is overlain by up to two meters glacial sand and pebbels.


Fig. 6. Drawing of the layers at Grønbjerg. In total, the thickness of the clay is over 484 cm.

Nanoplankton sample

The nanoplankton sample contains these dinoflagellates cysts:
Phthanoperidinium comatum,
Homotryblium floripes,
Areosphaeridium dictyoplokus,
Deflandrea phosphoritica,
Hystrichokolpoma cinctum,
Thalassiphora pelagica,
Wetzeliella sp.,

These specimens are all characteristic for the Areosphaeridium arcuatum
and Thalassiphora reticulata Zone (Heilmann-Clausen 1988).
This zone is in the upper part of the Søvind Marl Formation

The NP sample also contains these dinoflagellates cysts:
Eatonicysta ursulae,
Deflandrea oebisfeldensis,
Cordosphaeridium cantharellus,
Glaphyrocysta semitecta,
Enneadocysta arcuata.
Areoligera cf. senonensis.
The sampling work was done by Karen Dybkjær at The Geological Survey of Denmark and Greenland (GEUS).

Coccolites sample
The coccolite samples from the clay at Grønbjerg klint, contained the index coccolite Isthmolithus recurvus, that is unik for the Upper Søvind Marl Formation - NP 19-20.
The sampling work was done by Claus Heilmann Clausen.

Material and methods

The present paper is based on one collection. The examined part of the collection consists of a total of more than 6000 teeth. The majority of the teeth are from Lamniformes. Of the total number of teeth, ?% are identified to genus or species, ?% are identified only to family or order, and the remaining ?% of the teeth are so damaged that identification was not attempted. The precise stratigraphic origin of these teeth is from layer bed G1 and bed G2. (GPS coordinates: 56°54'05.6"N 8°47'55.2"E. in October 2020, but will in time slide towards the Limfjord). The bulk material was collected in 2020 and a total of approximately 1100 kg of clay has been processed. 850 kg from bed G1 and 250 kg from bed G2. The clay was dried, dissolved in water three times and screen washed through two different mesh sizes, where the coarse sieve has 2.0 mm meshes, and the smallest one has 0.5 mm. The 250 kg from G2 was reduced to 2,0 kg. The reduced material contain a lot of glauconite, some pyrite, grains of sand and borrows of chalk. The residues were searched for sharkteeth by HM using a binocular microscope (Euromex). About ?? % of the teeth are identified to genus or species. All illustrated fossils are housed in the Fossil- and MoclayMuseum, under the catalogue numbers, Specify xxxx. Teeth larger than 5 mm have been photographed with a Nikon D7000. Smaller teeth have been photographed with a binocular microscope. Besides the shark teeth, the bulk samples contained a large amount of teeth and bones of bony fish. They are not the subject of this work.

The The Søvind Marl Formation is generally poor in makrofossil material, but extensive sampling in Søvind Marl Formation in 2020, has revealed a variety of fossils including remains of bony fishes, sharks, rays and chimaera teeth. – Birdsbones, gastropods, bivalves, corals, ostracods, foraminiferas, seaurhcin and calcareous burrows produced by different animals are present both G1 and G2.

The fossils from sharks are mainly teeth, some dermal denticles, coprolites and few vertebrae. The morphology of the dermal denticles is very varied from one family to another and often from one genus to another within a family. Therefore one must be careful when denticle morphology is used to characterize a species. (Cappetta 2012).

Dermal denticles, coprolites and vertebrae are not used to characterize the species in this article.

Presevation of the fossils

Fig. 7: Cropolite from shark. B: Dermal denticle. C: Transparant tooth with fine details.

Sharks from the Søvind Marl Formation

Order Lamniformes Berg 1958
Family Mitsukurinidae Jordan 1898
Genus Mitsukurina Jordan 1898 - Common name DK: Troldhajer / GB: Goblin shark
Mitsukurina sp.


Fig. 8. Mitsukurina sp.. A, labial view; B, profile; C, lingual view; 10,0 mm high – Bed G2

Family Lamnidae Müller and Henle 1838
Genus Isurolamna Cappetta 1976 - Common name DK: Makrelhajer / GB: Macerel shark
Isurolamna inflata (Casier 1946)


Fig. 9. Isurolamna inflata. A, labial view; B, profile; C, lingual view; 8,8 mm high – Bed G2

Genus Macrorhizodus Glikman 1964b - Common name DK: Makrelhajer / GB: Macerel shark
Macrorhizodus sp.


Fig. 10. Macrorhizodus sp. A, labial view; B, profile; C, lingual view; 30,0 mm high – Bed G1
D, lingual view; E, labial view; F, profile; 20,0 mm high – Bed G1

Genus Xiphodolamia Leidy 1877 - Common name DK: Makrelhajer / GB: Macerel shark
Xiphodolamia ensis (Casier 1946)


Fig. 11. Xiphodolamia ensis. A, anterior tooth, labial view; 20,0mm high B, lateral tooth, lingual view; 8,0mm high – Bed G2

Family Alopiidae Bonaparte 1838
Genus Alopias Rafinesque 1810 - Common name DK: Rævehajer / GB: Thresher sharks
Alopias crochardi Ward 1978


Fig. 12. Alopias sp.. A, labial view; B, profile; C, lingual view; 5,3 mm high – Bed G2.

Genus Usakias Zhelezko & Kozlov 1999 - Common name DK: Rævehajer / GB: Thresher sharks
Usakias sp.


Fig. 13. Usakias sp. A, labial view; B, profile; C, lingual view; 10,0 mm wide – Bed G1

Family Odontaspididae Müller & Henle 1839
Genus Hypotodus Jaekel 1895 - Common name DK: Sandhajer / GB: Sand Tiger sharks
Hypotodus verticalis


Fig. 14. Hypotodus sp. A, labial view; B, lingual view; C, profile; 7,3 mm high – Bed G2.

Genus Brachycarcharias Cappetta & Nolf, 2005 - Common name DK: Sandhajer / GB: Sand Tiger sharks
Brachycarcharias lerichei Casier, 1946


Fig. 15. Brachycarcharias lerichei. A, labial view; B, profile; C, lingual view; 10,3 mm wide – Bed G1

Genus Carcharias Rafinesque 1810 - Common name DK: Sandhajer / GB: Sand Tiger sharks
Carcharias sp.


Fig. 16. Carcharias sp.. A, labial view; B, profile; C, lingual view; upper lateral tooth. 7,3 mm high – Bed G2

Order Carcharhiniformes Compagno, 1977
Family Scyliorhinidae Gill 1862
Genus Megascyliorhinus Cappetta & Ward 1977 - Common name DK: Rødhajer / GB: Cat sharks
Megascyliorhinus cooperi


Fig. 17. Megascyliorhinus sp. A, labial view; B, profile; C, lingual view; lateral tooth. 5,3 mm high – Bed G2.

Genus Premontreia Cappetta 1992 - Common name DK: Rødhajer / GB: Cat sharks
Premontreia sp.

Fig. 18. Premontreia sp.. A, labial view; B, lingual view; 2,8 mm high – Bed G2.

Genus Physogaleus Cappetta 1980a - Common name DK: Gråhajer / GB: Sharpnose sharks
Physogaleus secundus Winkler 1876b


Fig. 19. Physogaleus sp. A, labial view; B, lingual view; 6,0 mm high – Bed G1

Family Triakidae GRAY 1851
Genus Triakis MÜLLER & HENLE 1838 - Common name DK: Gråhajer / GB: Hound sharks
Triakis wardi CAPPETTA, 1976


Fig. 20. Triakis sp. A, labial view; B, lingual view; 1,4 mm high – Bed G2

Genus Mustelus LINCK 1790 - Common name DK: Glathajer / GB: Smooth Hound
Mustelus aff. M. vanderhoefti Herman, 1982


Fig. 21. Mustelus aff. vanderhoefti. A, occlusal face; B, lingual face; 1,4 mm wide – Bed G2

Order Hexanchiformes F. de Buen, 1926
Family Chlamydoselachidae Garman 1884
Genus Rolfodon Cappetta, H. & Morrison, K. & Adnet, S. (2021)
Common name DK: Kravehajer / GB: Frilled sharks
Rolfodon fiedleri


Fig. 22. Rolfodon sp. A, labial view; B, lingual view; C, detail of small cusps on the middle tooth;
D, basal view;. 5,0 mm high – Bed G1. Rolfodon fiedleri. E, labial view; 3,0 mm high Bed G2


Fig. 23. Chlamydoselachus sp. A, labial view; B, lingual view; C, profile view; 5,5 mm high Bed G2

Family Hexanchidae J. E. Gray, 1851
Genus Heptranchias Rafinesque, 1810 - Common name DK: Seks- syvgællehajer / GB: Cow sharks
Heptranchias howelli


Fig. 24. Heptranchias howelli. A, Lower tooth, labial view; 10,0 mm wide – Bed G2.
B, Upper tooth, labial view; 5,0 mm high – Bed G2

Genus Hexanchus Rafinesque, 1810 - Common name DK: Seks- syvgællehajer / GB: Cow sharks
Hexanchus agassizi


Fig. 25. Hexanchus agassizi. A, Lower tooth. lingual view; 12,0 mm wide – Bed G1.
B, Upper tooth, lingual view; 5,0 mm high – Bed G2.

Genus Notorynchus Ayres, 1855 - Common name DK: Seks- syvgællehajer / GB: Cow sharks
Notorynchus serratissimus Agassiz, 1843


Fig. 26. Notorynchus sp. A, Lower tooth. Lingual view; 10,0 mm wide – Bed G1.
B, Upper tooth. Lingual view; 5,0 mm high – Bed G1.

Order Squaliformes Compagno, 1973
Family Centrophoridae Bleeker, 1859
Genus Centrophorus J. P. Müller & Henle, 1837 - Common name DK: Pighajer / GB: Gulper shark
Centrophorus aff. granulosus


Fig. 27. Centrophorus aff. granulosus. A, labial view; B, lingual view; 3,5 mm high – Bed G1.

Family Squalidae Blainville, 1816
Genus Squalus Linnaeus, 1758 - Common name DK: Pighajer / GB: Spiny dogfish
Squalus minor Daimeries, 1888


Fig. 28. Squalus sp. A, lingual view; B, labial view; 2,8 mm wide – Bed G1.

Genus Megasqualus Herman 1982 - Common name DK: Pighajer / GB: Spiny dogfish
Megasqualus sp.


Fig. 29. Megasqualus sp. A, labial view; B, lingual view; 6,1 mm wide – Bed G1.

Family Dalatiidae Gray 1851
Genus Isistius Gill 1865 - Common name DK: Cigarhajer / GB: Cookiecutter shark
Isistius trituratus Winkler 1876b


Fig. 30. Isistius trituratus. A, lingual view; B, labial view. 3,0 mm high – Bed G2.

Genus Eosqualiolus ADNET 2006 - Common name DK: Chokoladehajer / GB: Kitefin shark
Eosqualiolus aturensis

Genus Dalatias Rafinesque, 1810 - Common name DK: Chokoladehajer / GB: Kitefin shark
Dalatias sp.


Fig. 31. Eosqualiolus aturensis. A, labial view; B, lingual view. 1,7 mm high – Bed G2.
Dalatias sp. C. labial view; 1,7 mm high – Bed G1

Family Etmopteridae Fowler, 1934
Genus Etmopterus Rafinesque, 1810 - Common name DK: Lanternhajer / GB: Lantern shark
Etmopterus sp.


Fig. 32. Etmopterus sp.. A, lingual view; B, labial view. 6,5 mm high – Bed G2.
Etmopterus sp.. C, labial view; D, lingual view. 2,8 mm high – Bed G1.

Genus Orthechinorhinus Adnet 2006 - Common name DK: Lanternhajer / GB: Lantern shark
Orthechinorhinus pfeili Adnet 2006


Fig. 33. Orthechinorhinus pfeili. A, labial view; B, lingual view; 1,1 mm high – Bed G2.

Genus Orthechinorhinus Adnet 2006 - Common name DK: Lanternhajer / GB: Lantern shark
Orthechinorhinus sp. Adnet 2006


Fig. 34. Orthechinorhinus sp. A, labial view; B, profile; C, lingual view; 3,0 mm wide – Bed G2.

Order Echinorhiniformes Buen 1926
Family Echinorhinidae Gill 1862
Genus Echinorhinus Blainville 1816 - Common name DK: Sømhajer / GB: Bramble shark
Echinorhinus cf. priscus Arambourg 1952


Fig. 35. Echinorhinus cf. priscus. A, lingual view; B, labial view. 5,3 mm wide – Bed G1.
Echinorhinus cf. priscus. C, Lateral tooth lingual view; D, labial view. 2,2 mm wide – Bed G1.

Order Pristiophoriformes Berg 1958
Family Pristiophoridae Bleeker 1859
Genus Pristiophorus Müller & Henle 1837 - Common name DK: Savhajer / GB: Sawshark
Pristiophorus cf. lanceolatus Davis 1888


Fig. 36. Pristiophorus cf. lanceolatus. Rostral tooth A, labial view; B, lingual view; C, profile view; 7,0 mm high – Bed G2

Order Orectolobiformes Applegate 1972
Family Orectolobidae JORDAN & FOWLER 1903
Genus Orectoloboides sp. CAPPETTA 1977b - Common name DK: Tæppehajer / GB: Wobbegong
Orectoloboides sp. CAPPETTA 1977b


Fig. 37. Orectoloboides sp. A, labial view; B, Root from above; 3,3 mm high – Bed G2.
Orectoloboiformes sp. C, labial view; D, lingual view; 2,0 mm wide – Bed G2.

Family Rhincodontidae Garman 1913
Genus Palaeorhincodon HERMAN 1974a - Common name DK: Hvalhajer / GB: Waleshark
Palaeorhincodon wardi HERMAN 1974a


Fig. 38. Palaeorhincodon wardi. A, labial view; B, lingual view; C, profile view; 1,9 mm high – Bed G2

Order Heterodontiformes Berg 1937
Family Heterodontidae J. E. Gray, 1851
Genus Heterodontus Blainville, 1816 - Common name DK: Hornhajer / GB: Bullhead sharks
Heterodontus sp.


Fig. 39. Heterodontus sp. A, Toot seen from above ; B, labial view; 13,0 mm wide – Bed G1.


Fig. 40. Heterodontus sp. A, lingual view; B, occlusal view; C, labial view 3,0 mm wide – Bed G2.

Superorder Batomorphii Cappetta 1980b
Order Myliobatiformes Compagno 1973
Superfamily Dasyatoidea Jordan 1888
Family incertae sedis
Genus Coupatezia Cappetta 1982 - Common name DK: Pigrokker / GB: Stingrays
Coupatezia miretrainensis Adnet 2006a


Fig. 41. Coupatezia sp. A, lingual view; B, distal view; C, labial view. 3,0 mm high – Bed G2.

Order Chimaeriformes Obruchev 1953
Family Chimaeridae Bonaparte 1831
Genus Chimaera Linnaeus 1758
Elasmodus sp. Egerton 1843


Fig.42. Elasmodus sp.?. All from the same tooth. Largest fragment is 10,0 mm.