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Paraorthacodus is an extinct genus of shark. It a member of the family Paraorthacodontidae[1][2] (though it was formerly regarded as a member of the family Palaeospinacidae[3]), which is either placed in Hexanchiformes[2] or in Synechodontiformes.[1] It is known from over a dozen named species[4] spanning from the Early Jurassic[4] to the Paleocene,[4] or possibly Eocene.[3] Almost all members of the genus are exclusively known from isolated teeth, with the exception of P. jurensis from the Late Jurassic-Early Cretaceous of Europe, which is known from full body fossils from the Late Jurassic of Germany,[5] which suggest that juveniles had a robust body with a round head, while adults had large body sizes with a fusiform profile.[1] There was only a single dorsal fin towards the back of the body without a fin spine.[3] The dentition had teeth with a single large central cusp along with shorter lateral cusplets,[3] which were designed for clutching.[1] The teeth are distinguished from those of Synechodus by the lateral cusplets decreasing in size linearly away from the central cusp rather than exponentially as in Synechodus.[3]
| Paraorthacodus Temporal range: | |
|---|---|
 | |
| Paraorthacodus jurensis holotype specimen | |
 | |
| Paraorthacodus jurensis full-body specimen | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Family: | †Paraorthacodontidae |
| Genus: | †Paraorthacodus Glückman, 1957 |
| Species | |
|
P. andersoni | |
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- Paraorthacodus andersoni (Case, 1978) Late Cretaceous (Santonian and Campanian)
- Paraorthacodus antarcticus Klug et al., 2008 Late Cretaceous (Campanian)
- Paraorthacodus clarkii (Eastman, 1901) Paleocene (Thanetian)
- Paraorthacodus conicus (Davis, 1890) Late Cretaceous (Coniacian to Campanian)
- Paraorthacodus eocaenus (Leriche, 1902) Paleogene (Thanetian to Ypresian according to,[3] exclusively Thanetian according to,[4] considered a synonym of P. clarkii by[6])
- Paraorthacodus jurensis (Schweizer, 1964) Late Jurassic (Kimmeridgian)
- Paraorthacodus nerviensis (Leriche, 1929) uppermost Cretaceous
- Paraorthacodus patagonicus (Ameghino, 1893) Late Cretaceous (Coniacian)
- Paraorthacodus recurvus (Trautschold, 1877) Cretaceous (Albian-uppermost Cretaceous)
- Paraorthacodus sulcatus (Davis, 1888) Late Cretaceous (Campanian)
- Paraorthacodus validus (Chapman, 1918) from the Cretaceous
- Paraorthacodus turgaicus Glickman, 1964, Paleocene (Thanetian)
- Paraorthacodus helveticus (De Beaumont 1960) Early Jurassic (Sinemurian)
- Paraorthacodus arduennae Delsate, 2001) Early Jurassic (Pliensbachian)
- Paraorthacodus kruckowi (Thies 1983) Middle Jurassic (Aalenian)
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