[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Megalosaurus = Torvosaurus in Europe -- additional data for Mr. Mortimer



     Megalosaurus nethercombensis...which is not Magnosaurus. Jurassic, Aalenian-Bajocian. OUM J12143, paired dentaries, cranial dorsal, caudal dorsal, proximal caudal, proximal pubes, femora, left tibia + distal fibula fragment. A Megalosaurus differing from the further derived M. bucklandii in that the jaw is but half so deep, the chin more  pointed, and is depressed at alveolus 7 so that the chin is heavier; the teeth are more recurved and have a slight mesiolateral bulge; the labial parapet is more pronounced; the rugosae are higher, the notches extending well below the nutrient groove; the splenial groove runs much farther rostrally, rounding onto the very tip of the dentary; it ends similarly below alveolus 10; the lingual bar is much shallower, the bar below the groove shallower and rounder; the two foramina at the fro! ! nt of the splenial groove are farther apart; the caudal dorsal is 70 mm high x 62 mm wide vs. 104 x 99 mm for OUM J13577 and is more slender and smaller; the proximal caudal is 64 x 55 mm vs. 100 x 119 mm for OUM J13578, and is also smaller and thinner; the pubis lacks the distal expansion; the femoral distal end has the condyles running farther up the shaft, the intercondylar fossa is deeper; the tibia is more slender, the tuberosity weaker as is the fibular flange, there is no distomedial shoulder; the fibula distal end differs greatly in detail.
      Another taxon to be mentioned is Proceratosaurus bradleyi BMNH R4860. In my analyses (with which Sam Welles agreed), this is not a ceratosaur, not Megalosauridae, but is the tentative sister taxon to Ornitholestes. The circular, pronounced maxillary fenestra and antorbital tooth row are diagnostic of Tetanurae, removing BMNH R4860 from Ceratosauria. The shallow surangular removes BMNH R4860 from non-tyrannosaur tetanurine clades. As preserved, BMNH R4860 has the following combination of character states: Pm 4 / M 18 / D 13; teeth sharply recurved with distal basal swelling; premaxillary teeth small, thick, slightly recurved, distal edge serrated to base, lateral face grooved vertically; maxillary tooth 1 similar to premaxillary teeth; following teeth compressed, recurved, mesial edge blunt and finely serrated, distal edge sharper, more coarsely serrated; 3 mesial dentary teeth small and similar to predentary teeth, ! ! subsequent teeth similar to those of maxilla; naris elongate; premaxilla square-like; maxilla without preantorbital fenestra, its depression with two deeper areas below nasal ramus; nasal with vertically groove rostroproximal region; dentary low and delicate; mandibular fenestra tear-drop shaped. Compared with Monolophosaurus jiangi, as preserved the rostroproximal bulge above the nasal bar arises abruptly vs. the gradual medial crest,although it is probable BMNH R4860 had a similar crest and not a horn core. Compared with Ornitholestes AMNH 619, the short stout squamosal and quadratojugal processes are similar; the premaxillae are similarly rostrocaudally short. The elongate external naris is similar, as are the maxilla, two preorbital fenestrae, preorbital depression, jugal, and lacrimal. The orbit is smaller, the muzzle longer. The flaring at the base of the bulging nasal process is similar. The mandibles are slender vs. deep, caudally short vs. long, the dent! ! ary elongate and slightly upcurved vs. short and downcurved. The teeth are conical and small, with reduced mesial serrations, but those of BMNH R4860 are less heterodont. Compared with Dromaeosaurus albertensis AMNH 5356, in lateral view the low profile is similar. The quadraomandibular articulation is similar, as are the wide orbits, wide laterotemporal fenestrae, and possibly lateral exposure of the splenial. The palate is similarly not highly arched; it has a wide fenestra between medial and lateral areas of the pterygoid-palatine joint. The median ramus of the palatine is more slender. The antorbital fenestra differs in being larger than the orbit. The marginal dentition is not reduced. The splenial has a similar lateral exposure.
      Compared with the maxilla of Megalosaurus bucklandii, OUM J13506, Proceratosaurus differs in having a depression, a much wider nasal process, and a very slender caudal bar. Compared with the dentary OUM J13505, BMNH R4860 has fewer teeth, the mandible is much more delicate, the chin pointed, the mesial dentary teeth very small. The homologous parts are very different.
      Compared with Ceratosaurus USNM 4735, it is much smaller, snout to quadrate 259 vs. 464 mm, and is much lower relative to length; reduced to scale, the premaxilla is rostrally concave, more vertical, extending farther back below the naris; the nasal process is longer and much higher; the naris is much longer; the maxilla has a double depression, the caudal ramus is much lower; the antorbital fenestra is longer, the orbit much longer ventrally; the temporal fenestra is shorter; the quadrate is more vertical and much shorter; the quadratojugal has a thicker vertical ramus and a much shorter jugal process; the nasal prominence as preserved is dorsorostral to the maxilla vs. farther back, its rostral edge higher and dipping steeply caudally; the dentary is much more delicate, lower, pointed rostrally, its rostrodorsal edge dipping forward; the mandibular fenestra is pointed rostrally vs. oval; the teeth differ greatly in detail and n! ! umber, 4 Pm / 18 M / 13 D vs. 3 Pm / 15 M / 15 D; except for the nasal construction, the two taxa are very different. Proceratosaurus is not Ceratosauria.