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The teeth of ''Cretacladoides'' are
''Cretacladoides'' ("
, cladodont This is a typical Cladodont tooth, of a shark called ''Glikmanius''">Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius''
Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a com ...
likeness from the Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
") is a genus of chondrichthyan, possibly a falcatid, found in France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
and Austria
Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
. Known solely from teeth, mainly found in the Klausrieglerbach locality of Austria, it consists of two species, ''C. ogiveformis'' and ''C. noricum.'' Assuming a falcatid identity, it is the most recent member of the family, which otherwise became extinct at the end of the Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
.
History of discovery
The teeth of ''Cretacladoides'' were discovered on a field trip bypalaeontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Alexander Lukeneder in 2012. The limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
in which it was found yielded a diverse tooth assemblage, and was dissolved in acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
so they could be extracted. In total, 7 kg of limestone contained roughly 88 diagnosable teeth, including 41 teeth that undoubtedly belonged to elasmobranchs
Elasmobranchii () is a Class (biology), subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), Batoidea, rays, skate (fish), skates, and sawfish (superorder Batoidea). Members of this subclass are characteris ...
. While some of these had been described in a prior paper, the others were mounted on stubs, coated with gold and scanned with an electron microscope
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
at the Palaeontological Department of the University of Vienna
The University of Vienna (german: Universität Wien) is a public research university located in Vienna, Austria. It was founded by Duke Rudolph IV in 1365 and is the oldest university in the German-speaking world. With its long and rich histor ...
.Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...cladodont This is a typical Cladodont tooth, of a shark called ''Glikmanius''">Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius''
Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a com ...
, and the Greek word "εἶδος" (oides) which means "similar," or "likeness," alluding to its age and similarities to the teeth of Palaeozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and '' ...
cladodontomorph chondrichthyans.
Description
The teeth of ''Cretacladoides'' are multicuspid
The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
in structure, with a cladodont-like crown, and measure less than in width and height. The main cusp is triangular, and flanked by either two or three pairs of lateral cusplets. The first pair of cusplets is very small, while the second reaches three quarters of the main cusp's height. The third pair, when present, is roughly half the size of the second pair. The cutting edges are apparently continuous between the apex of the main cusps and the cusplets. In profile view, all cusps are inclined inwards. The labial crown face possesses either an ogive-shaped enameloid structure on the main cusp, or two converging ridges, depending on which tooth it is.
Viewed from the base, the root is D-shaped, possessing a small labial budge beneath the main cusp. From a lingual view, the root face has a well-developed protuberance below the main cusp. One pair of foramina opens laterally to this protuberance, while the second pair is below a notch which separates the second and third lateral cusplets. The aboral root face possesses two foramina, one central to the root face and the other in line with the main cusp towards the mouth.
Palaeoecology
The Klausrieglerbach locality is known to have had at least three other named chondrichthyans, of the genera ''Altusmirus
''Altusmirus'' is an extinct genus of ground shark from the Early Cretaceous age of Austria. There is only one known species, ''A. triquetrus'', named by Iris Fuchs in 2018. It was related to ''Fornicatus''.
References
{{Taxonbar, from=Q4 ...
'', '' Natarapax'' and '' Smiliteroscyllium''. The former is a ground shark, ''Smiliteroscyllium'' is a carpet shark
Carpet sharks are sharks classified in the order Orectolobiformes . Sometimes the common name "carpet shark" (named so because many species resemble ornately patterned carpets) is used interchangeably with "wobbegong", which is the common name o ...
, and ''Natarapax'' may be a ctenacanthid. The teeth of a galeomorph shark of uncertain affinities have also been found. Ammonites
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
of the genera '' Karsteniceras'' and ''Olcostephanus
''Olcostephanus'' is an extinct ammonoid cephalopod genus belonging to the family Olcostephanidae. These fast-moving nektonic carnivores lived during the Cretaceous, from the upper Valanginian to the lower Hauterivian age.Sepkoski, JacSepkoski's ...
'' have been found, with the former being represented by shells and aptychi, as well as lower beaks
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...
of an ammonite resembling '' Lamellaptychus''.Calpionellids and dinoflagellates
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
are also known from the same locality.
Late Survival
Assuming that ''Cretacladoides'' is a member of theFalcatidae
Falcatidae is a family of Paleozoic holocephalians. Members of this family include ''Falcatus'', a small fish from the Bear Gulch Limestone of Montana. The family first appeared around the start of the Carboniferous, and there is some evidence ...
, a family of symmoriiform chondrichthyans that otherwise became extinct in the Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
, it implies the existence of a ghost lineage
A ghost lineage is a hypothesized ancestor in a species lineage that has left no fossil evidence yet can be inferred to exist because of gaps in the fossil record or genomic evidence. The process of determining a ghost lineage relies on fossilized ...
. One explanation put forward by its describers is that it occupied deep-sea habitats, which allowed its line to survive the Permian–Triassic extinction event
The Permian–Triassic (P–T, P–Tr) extinction event, also known as the Latest Permian extinction event, the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, as ...
and leave very few fossils. Indeed, the deep-sea palaeoenvironment of the Klausrieglerbach locality was a dysoxic deep-sea environment, meaning it had very little oxygen.ctenacanthid, '' Natarapax trivortex'', which may indicate an additional ghost lineage in France.neoselachians instead.
References
{{Taxonbar, from=Q107304727 Symmoriiformes Cretaceous fish of Europe Fossil taxa described in 2018