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This is first seen in Janenschia, in which a thumb claw was present, but it’s also the case in various other taxa, including Andesaurus and Argyrosaurus.
With the exception of the controversial Jurassic form Janenschia (and probably a few basal taxa from the Cretaceous), titanosaurs were all devoid of thumb claws.
In Janenschia, a raised lip around the outer surface of the first metacarpal’s distal end is very nearly in contact with the dorsoproximal part of the claw.