Streptospondylus altdorfensis Meyer, 1832

Monvoisin, Evariste, Allain, Ronan, Buffetaut, Eric & Picot, Laurent, 2022, New data on the theropod diversity from the Middle to Late Jurassic of the Vaches Noires cliffs (Normandy, France), Geodiversitas 44 (12), pp. 385-415 : 392-396

? Streptospondylus altdorfensis Meyer, 1832

AXIAL SKELETON

Cervical vertebra

Material. MPV 2020.1.11, an anterior cervical vertebra ( Fig.4 ).

Stratigraphy. Lower Oxfordian marls according to the A. gregareum shells in the matrix.

The specimen is quite damaged, especially on the left lateral side, so that the prezygapophyses, the diapophyses and a part of the articular facet are missing. Only the base of the postyzagophyses and the neural spine are preserved. The latter is slightly deformed. The margins of the posterior articular facet are fractured.

The ophistocoelous centrum is laterally invaded by deep pleurocoels, as in Sinraptor and Eustreptospondylus ( Fig. 4C ). These are much less open in Allosaurus ( Madsen 1976) . The parapophyses are reduced and placed posteroventral to the anterior articular facet ( Fig. 4A ). In ventral view, the centrum is considerably compressed laterally. As in Eustreptospondylus , it is very short ( Sadleir et al. 2008). The dorsal margin of the anterior articular facet is offset from the neural canal.The neural arch represents more than half of the vertebra. The prezygapophyse extends beyond the centrum with a mediodorsally oriented facet. Posterior to the prezygapophyse and lateral to the neural canal there is a deep and oval centroprezygapohyseal fossa ( Wilson et al. 2011). Above the neural canal the spinoprezygapohyseal fossa is visible. In right lateral view, the ventrally oriented diapophysis and the prezygapophysis merge together anteriorly. Posterior to this, between the postzygodiapophyseal and centropostzygapohyseal laminae, a deep depression is present ( Fig. 4C ). This structure is similar to that in Eustreptospondylus but different from the deeply excavate postzygapophyseal centrodiapophyseal fossa of Sinraptor . A strong ridge is present extending from the lateral side of the prezygapophysis to the postzygapophysis. The extension of this ridge, as well as the centropostzygapophyseal lamina are not visible due to the break of the postzygapophysis. Yet it is possible that this ridge represents the epipostzygapophyseal lamina. In posterior view, the spinopostzygapohyseal fossa opens ventrally into the neural canal ( Fig. 4B ). However, this could be artificial and due to erosion. Based on the position of its base, it seems that the neural spine was limited to a posterior position in contrast with Allosaurus ( Madsen 1976) . The short nature of the centrum, the position of the parapophyses as well as the ventral orientation of the diapophyses indicate an anterior cervical vertebra, likely the third or fourth.

Dorsal vertebrae

Material. MNHN.F.RJN472, an anterior dorsal vertebra ( Fig. 5 ). Dorsal vertebrae MPV 2020.1.10 and B5. ( Fig.6A, B )

Stratigraphy. Oolithe Ferrugineuse de Villers according to the ferruginous ooliths of the matrix. Lower Oxfordian ( MNHN.F.RJN472and B5).Oxfordian or Callovian marls(Pen5). MNHN.F.RJN472. Only the centrum of the vertebra is present. It is anteriorly eroded as well as on the posterodorsal left side. A large opening is present on the left side of the anterior face but this seems artificial. The dorsal fracture is below most of the neural canal (except for anterior remains) as well as below the neurocentral suture, which is not visible.

The specimen is quite long (134 mm long and 126 mm wide) and ophisthocoelous ( Fig. 5A, B ). The centrum has concave ventral and lateral faces, so that it bears large pleurocentral depressions. In ventral view, the ventral face of the centrum presents a 35 mm wide plateau ( Fig. 5D ) very similar to that seen on the dorsal vertebrae of Streptospondylus ( Allain 2001). Parapophyses are poorly preserved but discernible on each side. They are anterodorsally placed, just below the neurocentral suture ( Fig. 5C ). Based on the osteology of Allosaurus and Torvosaurus ( Madsen 1976; Britt 1991) the position of the parapophyses, below the neurocentral suture, suggests an anterior dorsal vertebra, the fourth or fifth. However, the centrum is much elongated and opisthocoelous for an anterior dorsal vertebra. This is not seen in Allosaurus or Torvosaurus but is similar to Streptospondylus and Eustreptospondylus ( Sadleir et al. 2008) .

MPV 2020.1.10. Only the centrum, and the right neural arch margin are preserved ( Fig. 6C ). The right side of the centrum is also better preserved than the left one. The neural canal is visible as a concave trough filled with matrix. The base of what is interpreted as the right parapophysis is badly preserved but allows an orientation of the specimen.

The overall size of the vertebra is equivalent to those of the lectotype of Streptospondylus like MNHN.F.RJN82 (MNHN 8789 in Allain 2001). Longer than high, the centrum is platycoelous to slightly amphicoelous. It is laterally and ventrally concave.There is no flat area on the centrum ventrally.On each side and below the parapophyses, pleurocentral depressions are much deeper anteriorly.This results in a second rounded depression distinct from the rest of the concavity.This feature is called here a double pleurocentral depression. This feature is similar to the condition in the dorsal vertebrae of Streptospondylus (see Fig.6A ) and Eustreptospondylus ( Allain 2001; Sadleir et al. 2008) and considered as an autapomorphy of the former. The neurocentral suture is still visible above the pleurocentral depression. Eroded but visible anteriorly, the right parapophysis is astride slightly above the neurocentral suture. This character is found on most dorsal vertebrae; therefore, a more precise positioning is not possible. Based on the position of the parapophysis, this vertebra is interpreted as a sixth or more posterior dorsal vertebra.

B5. The specimen is rather damaged, only the central part of the centrum as well as the neural arch, around the neural canal, are visible ( Fig. 6D ). The anterior, posterior and dorsal parts of the bone are highly eroded. Thus, the articular facets are poorly preserved.

Despite the erosion, some anatomical features are observable. The centrum is massive: 140 mm long and 100 mm high. This vertebra is larger than MPV V869 and should belong to a very large theropod. As in MPV 2020.1.10, and Streptospondylus and Eustreptospondylus dorsal vertebrae, it is laterally excavated by an anteriorly double pleurocentral depression. Foramina 3 mm in diameter are visible in the middle of the depressions. There are three on the right side and one on the left side. The ventral part of the centrum is flat so that it forms a 70 mm wide plateau. This feature is visible in MPV V869, MNHN.F.RJN472 and the dorsal vertebrae of other Megalosauroidea , such as Streptospondylus ( Allain 2001). In right lateral view, two eroded areas anterior and posterior to the neural canal are likely remains of the anterior and posterior centrodiapophyseal laminae.

APPENDICULAR SKELETON

Tibia

Material. MPV 2020.1.2, a proximal end of a left tibia ( Fig. 7 ).

Stratigraphy. Callovian or Oxfordian marls.

The specimen is quite well preserved.The proximal articular surface is slightly fractured and eroded. The proximal side is 110 mm long and 65 mm wide. In posterior view, the lateral condyle is more distal than the medial one. Thus, the articular face is laterodistally oriented, as in Eustreptospondylus ( Sadleir et al. 2008) ( Fig. 7E ). Both condyles are equivalent in size, and a groove separates them posteriorly. Their shape is also reminiscent of Eustreptospondylus , especially the lateral one that is flat to slightly concave in proximal view. In dorsal view, the cnemial crest is anterolaterally placed ( Fig. 7C ). Its anterolateral end is proximally directed in lateral view. A crest is present along its lateral side. This structure forms the anterior margin of the incisura tibialis which separates the cnemial crest from the lateral condyle. This anterior depression allows the proximal contact with the fibula. In contrast with Allosaurus , in which the incisura tibialis is rectangular and deep, that of MPV 2020.1.2 is shallow, as in Megalosaurus and Eustreptospondylus ( Sadleir et al. 2008; Benson 2010). There is a bony blade extending along the distal half of the specimen corresponding to the crista fibularis ( Fig. 7A, D ). This crest is in a central position on the diaphysis. The structure does not extend to the proximal surface of the tibia. The size of the specimen is small and equivalent to that of OUMNH J.13558, the juvenile type of Eustreptospondylus that is smaller than Streptospondylus ( Allain 2001; Sadleir et al. 2008).

Figures

FIG. 4. —?Streptospondylus altdorfensis, anterior cervical vertebra (MPV 2020.1.11), Oxfordian marls, in anterior (A), posterior (B) and right lateral (C) views. Abbreviations: ags, Actinostreon gregareum shell; cpol, centropostzygapophyseal lamina; cprf, centroprezygapophyseal fossa; dp, diapophysis; ns, neural spine; plr, pleurocoele; podl, postzygodiapophyseal lamina; pp, parapophysis; pr, prezygapophysis; spof, spinopostzygodiapophyseal fossa; sprf, spinoprezygapohyseal fossa. Scale bar: 5 cm.

FIG. 5. — Specimen MNHN.F.RJN472, anterior dorsal vertebra of Streptospondylus altdorfensis from Oolithes Ferrugineuse de Villers, in left lateral (A), posterior (B), dorsal (C) and ventral (D) views. Abbreviations: pcd, pleurocentral depression; pp, parapophysis; vp, ventral plateau. Scale bar: 5 cm.

FIG. 6. — Dorsal vertebrae of Streptospondylus altdorfensis from Vaches Noires cliffs. Specimen MNHN.F.RJN82 of the type specimen of Streptospondylus altdorfensis in right lateral (A) and ventral (B) views. Specimen MPV 2020.1.10 (Callovian or Oxfordian marls) in right lateral (C) and ventral (D) views. Specimen B5 (Oolithes Ferrugineuse de Villers),in right lateral (E) and ventral (F) views.Abbreviations:ddpc, double pleurocentral depression;vp, ventral plateau.Scale bars:5 cm.

FIG. 7. — Specimen MPV 2020.1.2, proximal end of left tibia of?Streptospondylus altdorfensis from Callovian or Oxfordian marls,in anterior (A), medial (B), proximal (C), lateral (D), posterior (E) views. Abbreviations: cnc, cnemial crest; fc, fibular crest; ict, incisura tibialis. Scale bar: 5 cm.