Paranogmius

Overall, Paranogmius is distinguished from other plethodids by its remarkable size, with estimates placing it at 3 meters (9.8 ft) in total length with a 45 centimeters (1.48 ft) long head, making it the largest known plethodid and among the largest fish known from the Bahariya Formation.^[5]: 121 Its skull roof was relatively flat, as in other tselfatiiformes, while the snout was greatly expanded and broad. The supraoccipital bone is not enlarged whereas the parietals are, traits not found in other plethodids. Plethodid parietals, including Paranogmius', are often large, quadrangular in shape, and broadly affixed along the midline. However, those of more derived genera like Tselfatia and Dixonanogmius are broader than long and narrower at the midline. Similar to those of Bananogmius and Luxilites, the limbs forming the preopercle bone are of subequal length and strongly developed. An autapomorphy of Paranogmius is the presence of a subtemporal fossa (a depression under the temporal bone), a structure lost by most derived bony fishes and only found in the elopomoprhs and osteoglossomorphs. However, Paranogmius does lack a groove on its hypural plate (a plate at the base of the caudal fin), a groove absent in advanced plethodids' caudal (body) skeletons but present in Eoplethodus. This indicates that Paranogmius has a mix of derived and basal plethodid characteristics.^[6][2]

The jaws of Paranogmius are also unique among plethodids as the teeth are arranged in patches instead of contiguous lines like in Bananogmius. Furthermore, the border of the dentary symphysis (where the two mandibulae meet) is raised and features a spur on its dorsal (top) face. The dermopalatine, also known as the chewing plate, is large, flat, and adorned with small teeth. Its vomer is T-shaped and expands broadly at its anterior margin, another autapomorphy of the genus.^[6][2]

Weiler hypothesized that the close, "tightly pressed" association of the trunk vertebrae and quadrate from Paranogmius was a result of predation and scavenging. However, German paleontologist Werner Janensch stated that this association was the result of shallow marine waters and ocean waves.^[2] Other evidence of scavenging is known from the Bahariya Formation, such as in the holotype of the sauropod dinosaur Paralititan.^[7] As for its ecology, Weiler speculated that Paranogmius lived in freshwater environments in the Bahariya area, alongside turtles, the lungfish Ceratodus, an indeterminate polypterid, and the crocodylomorph Stomatosuchus. The short, deep vertebrae suggest that Paranogmius had a stubby yet deep body (hypsisomatic), similar to that of Tetrodon fahaka pufferfish that live in the modern-day Nile River.^[2] The anatomy of its dental plates suggest that it was a filter feeder that fed on small invertebrates. Furthermore, the lamellae, which absorb oxygen from flowing water, were surrounded by gill rakers that were adapted to filtering edible material from the water and consuming it.^[5]: 121 Paranogmius' possible synonym Concavotectum was also considered a filter feeder based on its edentulous jaws, funnel-like mouth, a deep branchial chamber, and long gill rakers, with a niche similar to that of the menhaden Brevoortia.^[8]

North Africa, during the Cenomanian stage of the Late Cretaceous, bordered the Tethys Sea, and was a mangrove-dominated coastal environment filled with vast tidal flats and waterways.^[7][9] While earlier, Albian-aged plethodids exclusively resided in Europe, the family expanded into the Tethys Sea during the Cenomanian-Turonian transition.^[4] Fossils of terrestrial and freshwater animals, including those of Paranogmius,^[2] were largely found in a lower layer of the Bahariya Formation whereas those of marine animals like plesiosaurs are more common in upper layers of the formation, indicating a change in the environment to a marine depositional one.^[10][11] A diverse fauna of freshwater bony fishes is known from this formation, some of which reached great sizes, such as the bichir Bawitius, the lungfishes Neoceratodus and Ceratodus, and the coelocanth Mawsonia. Other freshwater bony fishes found include the pycnodontid Coelodus, the enchodontid Enchodus, and the lepidotid Lepidotes.^[3]

A diverse fauna of other animals is known from the Bahariya Formation. Underwater life diversity exploded during this period in the mangroves of North Africa, represented by genera like sawskates Onchopristis and Schizorhiza,^[12] sharks like Squalicorax and Cretolamna, and a variety of invertebrates.^[11][12] Non-dinosaurian reptiles such as the early sea snake Simoliophis, turtles like Apertotemporalis and an unnamed pelomedusid,^[13] several indeterminate plesiosaurs, crocodylomorphs like the stomatosuchid Stomatosuchus and the eunotosuchian Libycosuchus,^[11][14][15] and an indeterminate pterosaur are also known from the formation.^[16] Dinosaurs are represented by the sauropods Aegyptosaurus, Paralititan, and an indeterminate titanosaur,^[7][17] the theropods Spinosaurus,^[11] Tameryraptor,^[18] Bahariasaurus, an indeterminate abelisaurid,^[16] and possibly Sigilmassasaurus and Deltadromeus.^[19][20][21]