The manus of Effigia revisited

The manus of Effigia is tiny.

Figure 1. Effigia. Note the tiny hands.

Figure 1. Effigia. Note the tiny hands.

Really tiny.
Even so, it is one of the few manus examples from a wide range of post-Proterosuchus and pre-Herrerasaurus taxa. The Effigia manus (Figs. 1, 2) includes only 3 metacarpals and 2 phalanges, plus two carpals. Another metacarpal, one that looked like mc1 of Coelophysis and measuring 12×5.5 mm was described by Nesbitt (2007).

Not much to go on, but PILs and sister taxa (even distantly related) can help (Fig. 1) make the restoration — in this case two restorations: one if you switch the two longest metacarpals, one if you don’t. I think you should, to match another poposaurid manus, that of Poposaurus (Fig.1), which we looked at earlier here so metacarpals 1-3 align. In either case, tiny digit 5 appears to be missing, so the known digits are 2-4, not 3-5.

Figure 1. The manus of Effigia reconstructed. Metacarpal 1 was described with measurements. Here two possible hands can be restored, but only when one switches the longest metacarpals. That's the one I think will prevail.

Figure 1. The manus of Effigia reconstructed. Metacarpal 1 was described with measurements. Here two possible hands can be restored, but only when one switches the longest metacarpals. That’s the one I think will prevail.

From Nesbitt (2007):
“Portions of the right manus were recovered somewhat articulated with both the radius and the ulna. Metacarpals III, IV, and V were found articulated together and a potential metacarpal I and the carpals were found together nearby. Unfortunately, the identity of the two carpals cannot be determined with certainty. The proposed metacarpal I proximal portion is broken, shifted ventrally, and appressed against the shaft. Metacarpal I is estimated to have been 12 mm long and 5.5 mm wide. It has a dorsoventrally compressed shaft and the distal end is asymmetrical; only the medial side bears a rounded articular surface; the lateral side tapers to a sharp edge. The morphology is strongly reminiscent of metacarpal I of Coelophysis and other theropods. Metacarpal II was not preserved.

“A much more robust phalanx is also present and may belong with either metacarpal III or metacarpal I. This phalanx indicates that at least one of the digits was not as reduced as much as digit I.”

If you shift the two longest metacarpals and add appropriate phalanges that fit the few established PILs, then you get a very poposaur-ish manus. If you don’t, you get an odd sort of manus, very autapomorphic. The carpals were matched to those of aetosaurs, Lotosaurus and Herrerasaurus, the closest known sisters with known carpals. If tiny distal carpals were present, they were not recovered.

On a side note,
the manus of Lotosaurus is looking ‘funky’ when compared to other popoosaurs. If anyone has good data on that piece of anatomy, please send it.

References
Nesbitt SJ and Norell MA 2006. Extreme convergence in the body plans of an early suchian (Archosauria) and ornithomimid dinosaurs (Theropoda). Proceedings of the Royal Society B 273:1045–1048. online
Nesbitt S 2007. The anatomy of Effigia okeeffeae (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. Bulletin of the American Museum of Natural History, 302: 84 pp. online pdf
wiki/Effigia

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