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Janenschia vs Tendaguria - new sauropod paper




I just skimmed thru the paper which tries to make sense of the unassociated sauropod material lumped into the genus _Janenschia_.


The paper (mentioned by George some weeks back):

Bonaparte, J. F., Heinrich, W.-D. & Wild R., 2000. "Review of _Janenschia_ Wild, with the description of a new sauropod from the Tendaguru beds of Tanzania and a discussion on the systematic value of procoelous caudal vertebrae in the Sauropoda," Palaeontographica A 256: 25?76

A few interesting tidbits came up.

Scratch _Janenschia robusta_ as the earliest known member of the
Titanosauroidea. Bonaparte et al. (2000) restrict the hypodigm of this genus and species to the holotype hindlimb (SMNS 12144) and comparable limb material (fore- and hind-) from the Upper Saurian Bed (Kimmeridgian), Tendaguru Beds, Tanzania. Based on the limb bones, _Janenschia_ might be a camarasaurid. The vertebrae (including the proximally procoelous caudals) and hip elements are excluded from _J. robusta_.


Two heavy dorsals (MB.R.2092.1 and MB.R.2092.2), probably from the Upper Saurian Bed and previously referred to _J. robusta_, are made the holotype of a new sauropod genus and species, _Tendaguria tanzaniensis_. These are very distinctive, with extremely low neural spines and very big transverse processes. A cervical is provisionally referred to _T. tanzaniensis_. The vertebrae MIGHT belong to _J. robusta_ (after all, the limb bones, like the dorsals, are rather heavily-constructed), but since association cannot be proven, Bonaparte et al. believe that it is better to give them there own
genus. As noted by McIntosh (1990), the dorsals are VERY distinctive.


Among sauropods, Bonaparte et al. suggest that _Janenschia_ is most closely related to _Camarasaurus_. _Tendaguria_'s affinities are not clear, but it apparently does not belong in any previously described family. Bonaparte et al. grant _Tendaguria_ its own sauropod family (Tendaguriidae). (Bonaparte has erected quite a few new sauropod families in the last year or too - also Haplocanthosauridae, Apatosauridae, Agustiniidae.)

As for the procoelous vertebrae, which was the main reason for allying
_Janenschia_ with the titanosaurids... Bonaparte et al. contend (and I agree) that, by itself, procoely in the proximal caudal vertebrae is a poor yardstick for determining the relationships of sauropods. For example, they are also exhibited by _Mamenchisaurus_ and _Bellusaurus_. In these Asian genera, I'm not sure if the proximal caudals have the strong ball-and-socket (deeply convex/concave) procoely of titanosaurid caudals or the weaker type of procoely (flat or weakly convex/concave articular surfaces) seen in certain basal titanosauriforms (like _Sonorasaurus_). I'll have to check.
However, I have read elsewhere that the proximal caudals of the diplodocid _Supersaurus_ exhibit strong (ball-and-socket) procoely, and this genus is certainly non-titanosaurian.




Tim
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