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Main » 2008»July»9 » Notes on the remains of archosaurian reptiles, mostly basal sauropodomorph dinosaurs, from the 1834 fissure fill (Rhaetian, Upper Triassic)
Notes on the remains of archosaurian reptiles, mostly basal sauropodomorph dinosaurs, from the 1834 fissure fill (Rhaetian, Upper Triassic)
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Many of the best preserved teeth and bones of archosaurian reptiles found in 1834 in an Upper Triassic Rhaetian fissure fill on Durdham Down in Clifton (now in Bristol), southwest England were destroyed in 1940. Based on an 1875 map, the site is positively identified as within Quarry Steps Quarry. This paper includes an annotated catalogue, copies of most of the illustrations from 1840 to 1908, and photos of important extant specimens. Most of the recognizable, mostly unassociated and incomplete bones have long been referred to the basal sauropodomorph dinosaur Thecodontosaurus Riley & StutchbuRy, 1836 (as T. antiquus MoRRiS, 1843), with gracile and robust morphs of several of the appendicular bones as a sexual dimorphism. The deltopectoral crest of unassociated Clifton humeri is plesiomorphic for basal sauropodomorphs, being anteroposteriorly high and markedly asymmetrical in lateral view with a short edge distal to the very prominent apex. The apex is at 40% (measured perpendicular to long axis of humerus) of total length in gracile ones and +50% in robust ones of the same size. However, the former position is plesiomorphic for sauropodomorphs, the latter derived, and no other basal sauropodomorph species has such a marked dimorphism. The only partial skeleton from Clifton, which includes a forelimb and girdle, has a third humeral morph with a low symmetrical deltopectoral crest with a rounded apex at 25% of length. Whatever the status of the gracile and robust morphs, the characters of referred postcranial bones from Clifton cannot be used to distinguish the species of Thecodontosaurus Riley & StutchbuRy, 1836 that, along with T. antiquus Riley & StutchbuRy vide owen, 1842, may be a nomen dubium. However, T. antiquus is retained for the slender humeral morph pending the description of referred material from a Rhaetian fissure fill at Tytherington Quarry, Avon. In the humerus of Pantydraco (Thecodontosaurus) caducus (Upper Triassic/Lower Jurassic, Wales) the apex of the asymmetrical deltopectoral crest is at 40% of the length and the process is low, a morph that is not represented at Clifton. The Clifton forelimb and girdle is made the holotype of Asylosaurus yalensis n. gen. et sp. The manus shows lateral reduction, so phalangeal formula is 2-3-4-2-?1, and the humerus has a large medial tubercle (small in Welsh humerus).
The other Clifton bones are identified as either : A. very basal Sauropodomorpha indet (could be Asylosaurus or Thecodontosaurus, includes slender morph bones) ; B. Anchisauria indet (more derived than A, includes robust morph bones) ; or C. basal Sauropodomorpha indet (could be A or B).
Teeth of carnivorous archosaurs from Clifton (A-N, Q-W) and Coombe Hill (O-P). A-N: heterodont crurotarsal phytosaur Rileyasuchus (Palaeosaurus) platyodon: A-P: Palaeosaurus platyodon riley & StutcHBury, 1840: A-G: holotype BRSMG *Ca7448/3 in A-E: medial (lingual) view; F: detail of serrations on mesial (anterior) edge and G: cross sectional view of root. H-N: referred tooth BMNH R16119 in H: mesial; I-J: lingual and K: distal (posterior) views; L-M: detail of serrations on L: distal and M: mesial edges, and N: cross-section of base of crown. O-P: Palaeosaurus stricklandi daviS, 1881, holotype BGS GSL4498 in: O: cross sectional view at lowest level of complete crown and P: lingual view. Q-U: Palaeosauriscus (Palaeosaurus) cylindrodon (riley & StutcHBury, 1840), holotype BRSMG *Ca7449/4♦ in Q, R, T: side view; S: cross section of base of crown and U: detail of serrations of distal edge. V-W: Theropoda indet, BMNH 49884e♦ in V: side view with W: detail of serrations on distal edge. A, Q from riley & StutcHBury (1840), B from Owen (1841), C from lydekker (1888), D from Zittel (1890), E-I, M, S-U from Huene (1908a), J-L, N from Huene (1908b), O, P from daviS (1881), R from Huxley (1870), V, W from Huene (1906); scale bars = 1 mm.
An ilium and two femora are very basal Theropoda (or possibly Dinosauriformes) ; other theropod remains include a small tooth crown with fine perpendicular denticles, a metacarpal I, a slender recurved manual ungual, and an astragalus. A dorsal centrum may be from an ornithischian dinosaur. Rileyasuchus Kuhn, 1961 (type species Palaeosaurus platyodon Riley & StutchbuRy, 1840), a nomen dubium, is a heterodont crurotarsal phytosaur now represented by two teeth and two humeri. The denticles are angled slightly apically on the expanded mesial blade and perpendicular to the distal edge. Palaeosauriscus Kuhn, 1959 (type species Palaeosaurus cylindrodon Riley & StutchbuRy, 1840) is based on lost teeth ; it is archosauria indet but may be a valid taxon based on the subcircular cross-section and fine, obliquely inclined denticles. A few bones are none of the above and are Archosauria indet (dentary with teeth, scapula-coracoid) and even Reptilia indet (?prootic, parietal, distal femur, tibia, metapodial).
Associated bones of very basal sauropodomorphs from Clifton. A-D : associated forelimb and girdle, dorsal ribs and other bones, YPM 2195, holotype of Asylosaurus yalensis, n. gen. et sp. A-C : main block at same magnification (~75%) : A : main side and B : bone bearing part of other side ; C : distal left femur repositioned using painted guidelines on B (in area q). D : distal right tibia in posterior view (has impression of rib on other side so probably from side B of block). E-G : YPM 56719 : E : dorsal ribs and gastralia ; F : disarticulated incomplete metacarpals and G : metacarpal V. a = distal right femur (Figs 25D-F) repositioned on block ; b = right distal scapula blade (Figs 13B-D, 14I) ; c = left scapula blade (Figs 13E-G, 14J) ; d = proximal left humerus (Fig. 15N) ; e = right humerus (Figs 13A, I-K, 15A-M), bone in lateral view in A and proximal end in posterior view in B ; f = fragment of shaft of left radius (Figs 17A-C) ; g = left ulna (Figs 13A, L-Q, 17A-G) ; h = digit I of left manus (Figs 13A, 19A-D, G, H) ; i = mid-cervical vertebra (Figs 7B-F) ; j = proximal caudal vertebra (Fig. 11A) ; k = proximal caudal vertebra (Figs 11B, C) ; l = gastralia (Figs 8D, F) ; m = left manus (Figs 13A, R, S, 19) ; n = distal left ulna (cf. g) ; p = ends of diapophyses of two dorsal vertebrae ; q = attachment area for matrix with distal left femur shown in C (Figs 25A-C) ; r = dorsal ribs (Fig. 8D) ; scale bars = 10 mm.
