TEHUELCHESAURUS

When Tehuelchesaurus was named in 1999 by Tom Rich and colleagues, they described it as a cetiosaurid sauropod, though much of it was still encrusted with muck at the time. Over a decade later, it was fully prepared and redescribed by Carballido, Rahaut, Pol and Salgado. But even at this point, some 123 years after being coined by Richard Lyddekker, no one was sure if Cetiosauridae -- so long a wastebasket taxon for random remains from far-flung places -- was actually a bona fide sauropod family or not.

In 2012, Carballido recovered Tehuelchesaurus as a member of Neosauropoda (the "new sauropods"), specifically a camarasauromorph, which isn't a particularly useful tag because they're all non-titanosauriforme macronarians and therefore, well, just macronarians. Since then, however, at least one analysis has found a stable Cetiosauridae within Neosauropoda. Furthermore, the mamenchisaurids may belong within it, in which case Mamenchisauridae (with the family suffix "idae") would become Mamenchisaurinae (with the sub-family suffix "inae") to reflect its status as a subordinate group rather than a standalone family per se. You can't plonk an "idae"-suffixed family within an "idae"-suffixed family. At least, we don't think you can.

Originally described as hailing from the Canodon Asfalto Formation in error (it's actually from the younger Cañadón Calcáreo Formation), Tehuelchesaurus is similar to the perpetually problematic but probable Mamenchisaurus-related Omeisaurus from China, but with stouter forearms and different shaped vertebrae and hips, which bodes well for the Mamenchisaurinae within Cetiosauridae theory. We know, it's all a bit confusing, But if you're still reading: Tehuelchesaurus is from the Late Jurassic and therefore one of the oldest "new sauropods" known from South America.