[D] Mantellisaurus atherfieldensis [sG] [T]
Cretaceous Early Valanginian Hauterivian Barremian Aptian
Ornithischia Ornithopoda Iguanodontia Iguanodontidae
Wealden Beds, Isle of Wight, West Sussex, East Sussex, Surrey, Kent, Lower Green-sand-Formation, Kent, England; Wealden Beds, Province de la Hainaut, Belgium; Wealden Beds, Nordrhein-Westphalen, Germany; Las Zabacheras Beds, Provincia de Teruel, Spain
Mantellisaurus atherfieldensis (Paul, 2006) > Iguanodon atherfieldensis (Hooley, 1924) > Iguanodon mantelli (Meyer, 1832) Vectisaurus valdensis (Hulke, 1879) Therosaurus mantelli (Fitzinger, 1840) Sphenospondylus gracilis (Seeley, 1882) Heterosaurus neocomiensis (Cornual, 1850 partim).
BMNH R5764. Holotype horizon, locality, age. Upper Vectis Formation, Isle of Wight, earliest Aptian.
Referred specimen. BMNH 3741. Horizon, locality, age. Lower Lower Greensand Formation, England, early Aptian.
(Paul, 2007) Probably modest sized as adults. Overall lightly constructed. Premaxillary tip to anterior orbital rim/latter to paraoccipital process tip length ratio ~1.25; dentary pre-coronoid process length/minimum depth ratio under 5. Rostrum subtriangular in lateral view. Maxillary process of premaxilla shallow. Dorsal apex of maxilla set posteriorly. Antorbital fossa and fenestra reduced. Lacrimal short, does not contact nasal. Lateral temporal fenestra moderate in size. Posterior portion of jugal short. Quadratojugal short. Quadrate tall, transversely narrow, shaft curved, lateral foramen set high, dorso-posterior buttress small. Diastema absent.
Tooth positions 23 in maxilla, 22 in dentary. Dorso-sacral/hindlimb length ratio ~1. Posterior dorsal centra not compressed antero-posteriorly. 7 fused sacrals. Scapula blade narrow and constricted at middle of blade, base rather narrow, acromion process placed rather dorsally and directed anteriorly. Forelimb ~50% of hindlimb length. Deltopectoral crest of humerus distally placed, fairly large and incipiently hatchet shaped. Manual phalanx 1 of digit I absent, pollex spike and other unguals moderate in size. Pelvis relatively large. Main body of ilium deep. Prepubic process of pubis deep. Femoral shaft curved. Metatarsal I present, II short. Distal phalanges of toes not strongly abbreviated.
Carpenter & Ishida (2010) Early and “Middle” Cretaceous Iguanodonts in Time and Space Journal of Iberian Geology 36 (2) 145-164
Mantellisaurus atherfieldensis (Hooley 1925) =Iguanodon atherfieldensis Hooley 1925
Atherfield, Isle of Wight, England
Barremian- lowermost Aptian (Anderson 1967;Martill, personal communication, 2010)
The considerable differences between Iguanodon bernissartensis and Iguanodon atherfieldensis has long been known (Hooley, 1925; Norman, 1986), although the possibility that these were sexual dimorphs has been suggested (Hooley 1912; Carpenter, 1999). However, as shown by Paul (2006), the differences between the taxa are considerable and warrant separate generic designation. Godefroit et al. (2009: 549) has questioned the splitting of the two taxa into separate genera because no phylogentic analysis was conducted to demonstrate the two species were paraphyletic.
However, two closely related genera could show a sister-group relationship, thus making the point of Godefrot et al., irrelevant. The case for separating the two taxa generically had been anticipated by Seeley (1887a: 83): “I therefore find myself differing from M. Dollo, not so much upon he results of his own work, as upon matters in which he depends upon and has the support of one of our most accomplished and most cautious comparative anatomists
But when the value of the characteristics of these two Iguanodon types [Iguanodon bernissartensis and Iguanodon mantelli], which M. Dollo has so well contrasted, will estimated, I am tempted to ask, is there any living reptilian genus which in the skeletons of its species comprises so wide and varied an assemblage of differential characters?
If the differences were limited to one series of characteristics, or to one region of the body, we might accept them as specific; but when they range through all parts of the skeleton, so as to imply many differences in the soft parts of the body, I cannot but reiterate ... my earlier belief that the larger Belgian type constitutes a new genus.” Unfortunately, as noted above, the ruling of the ICZN makes it necessary to change the smaller Belgian type as a different genus.
If anything Paul (2008) did not go far enough because it is clear that Early Cretaceous iguanodontid genera were far more diverse than generally realized, as shown by Cedar Mountain discoveries, and that the genus Iguanodon is a waste-basket of medium to large ornithopods. How Iguanodon became a waste basket is considered later.
A number of ilia are referred to this taxon based on their overall similarities in the framework of the variation seen in Camptosaurus ilia. Variation is seen in the ventral deflection or angle of the preacetabular process, acuteness of the postacetabular process, and prominence of the postacetabular notch. The ilium has a long, slender preacetabular process, short, triangular postacetabular process, short lateral iliac crest, shallow suprailiac notch, wide preacetabular notch, and shallow postacetabular notch. The ischial peduncle is well expanded onto the lateral surface of the ilium.