Atychodracon Smith, 2015
'Rhomaleosaurus' megacephalus deserved generic separation from Rhomaleosaurus (Smith and Dyke, 2008) and so a new genus was erected to accommodate it by Smith (2015): Atychodracon. A. megacephalus is closely related to Eurycleidus and some previous authors have regarded A. megacephalus as a distinct species of Eurycleidus. The original holotype specimen was housed in the Bristol City Museum and Art Gallery but it was destroyed during the Second World War. Surviving plaster casts of the holotype skull and forelimb allow for diagnosis of the taxon.
A replacement neotype specimen (now considered a referred specimen) of A. megacephalus nicknamed the 'Barrow Kipper' (Taylor and Martin, 1990) after the location where it was discovered is on display at the New Walk Museum in Leicester, UK. The skull was described extensively by Cruikshank (1994b) and is also on display at the New Walk Museum in Leicester, UK.
Cruickshank et al. (1991) proposed a specialised plesiosaur olfaction ('smelling') system based on A. megacephalus, which may have been a common adaptation among plesiosaurians (Brown and Cruickshank, 1994). The anteriorly placed internal nostrils on the palate are associated with grooves that may have channelled water into them. The flow of water might have been maintained by hydrodynamic pressure over the posteriorly placed external nares (on the top of the skull) as the animal swam. The water could have been 'tasted' by olfactory epithelia during its passage through the nasal ducts.
A. megacephalus Stutchbury, 1846
Type specimen: BRSMG Cb 2335, complete skeleton, destroyed during the Blitz. Plaster casts of the skull and limb are housed in the Natural History Museum, London (NHMUK R1309/1310); the Geology Museum, Trinity College Dublin (TCD.47762a, TCD.47762b; Wyse Jackson, 2004) and in the British Geological Survey, Keyworth, Nottingham (BGS GSM 118410).
Referred material: Smith (2015) provided a list of referred material: LEICS G221.1851 (the neotype specimen) from Barrow-upon-Soar, Leicestershire, UK (Cruickshank, 1994a, 1994b); NMING F10194, a partial skeleton including the skull (but no mandible) from Street (Smith, 2007; Benson et al., 2012); NMING F8749, a partial skeleton including a damaged skull and suffering from pyrite decay, also from Barrow-upon-Soar (Smith, 2007). A complete skeleton from Wilmcote, Warwickshire, UK, sometimes referred to ‘P.’ megacephalus (WARMS G10875, Wright, 1860; Cruickshank, 1994a) represents a new species (Smith, 2007).
Age and Location
Lowermost beds of the Blue Lias Formation (Lower Lias, Hettangian) of Street-on-the-Fosse, a village about 14 km ENE of Street, Somerset, UK.