MFSN 19864 is a Triassic pterosaur tail. Well… I imagine it’s a pterosaur tail. We don’t know the rest of this specimen. Compared to another basal pterosaur, MPUM 6009, MFSN 19864 is longer and more robust with what appears to be a tiny vane at the tail tip (Fig.1).

Figure 1. Click to enlarge. MFSN 19864 compared to MPUM 6009 another pterosaur with an attenuated tail without ossified reinforcements.
Dalla Vecchia (2003) noted that this tail had no ossified reinforcing “bundles” of pre- and post-zygopophyses, although such “bundles” were probably present and unossified. This appears to have been a larger pterosaur based on the size of the proximal caudals.
Earlier we looked at other Triassic bits and pieces here, here and here.
References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.