Poposaurs to scale and the chronological Lotosaurus problem

Updated April 22, 2014 to reflect the new basal archosaur position of poposaurids.

Adding Sacisaurus (Fig. 1) as a basal member of the poposaur list adds a certain perspective.  It calls into question the early Triassic appearance of Lotosaurus (Fig.1) since all other poposaurs are Late Triassic. Either the geological setting for Lotosaurus was poorly calibrated, or these poposaurs all had a much earlier origin, in the Permian, which appears unlikely. The other possibility is that Lotosaurus is not a poposaur after all, but an offshoot of another Permian root. This might be interesting…

Poposaurs now nest as basal archosaurs. So the chronology problem goes away.

Figure 1. Poposaurs to scale and in phylogenetic order (top to bottom). Sacisaurus is at the base. Silesaurus and Lotosaurus are derived. Poposaurus is one of the largest, along with Lotosaurus.

Figure 1. Poposaurs to scale and in phylogenetic order (top to bottom). Sacisaurus is at the base. Silesaurus and Lotosaurus are derived. Poposaurus is one of the largest, along with Lotosaurus. Pisanosaurus, basal ornithischian, does not belong in this clade.

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