Restoring Pisanosaurus

Updated March 24, 2015 with a newly restored Pisanosaurus pelvis.

Pisanosaurus (Casamiquela 1967) is widely considered the most basal ornithischian dinosaur. Unfortunately Pisanosaurus is only known from a few bones. So we rely on sister taxa to help restore the missing bits and pieces.

But first, a minor problem. 
Only the central portion of the Pisanosaurus pelvis  (Fig. 1) is known, the area surrounding the open acetabulum. So the outline shape of the Pisanosaurus pelvis, a key trait in the identification of ornithischian dinosaurs, is not known.

Figure 1. Pelves of Haya, a typical ornithischian, and what remains of the pelvis of Pisanosaurus.

Figure 1. Pelves of Haya, a typical ornithischian, and what remains of the pelvis of Pisanosaurus. The two pelves do no appear to be completely similar.

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I’m not sure about this…
But the placement of the possible obturator foramen and tab-like contribution of the pubis make it appear that the Sereno pelvic elements might have been misidentified — but then the other elements look correct in the Sereno orientation. Contradicting clues make this a difficult problem. Perhaps a photo or firsthand observation would show where the problems are in the drawing. Published data do not indicate where the pelvis was found in relation to the rest of the body, but I can only assume it was correctly oriented, favoring the  Sereno model.

Figure 2. Pisanosaurus pelvis restored the Sereno way (on the right) and like Haya (on the left). Note the possible placement of the obturator foramen, a pubis trait on the alternate orientation. And note the tab-like shape of the pubic contribution of the pubis (compare to figure 1).

Figure 2. Pisanosaurus pelvis restored the Sereno way (on the right) and like Haya (on the left). Note the possible placement of the obturator foramen, a pubis trait on the alternate orientation. And note the tab-like shape of the pubic contribution of the pubis (compare to figure 1).

Skulls
When the Pisanosaurus skull is restored to resemble the skull of Haya, the resemblance is striking. Not much difference here in the preserved elements.

Figure 3. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

Figure 3. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

The pes of Haya and Pisanosaurus
The phalanges are shorter in Haya, but the pedal morphology is otherwise similar to what we know of Pisanosaurus (Fig 4).

Figure 4. The pedes of Haya and Pisanosaurus compared. The patterns are similar despite the shorter phalanges of Haya.

Figure 4. The pedes of Haya and Pisanosaurus compared. The patterns are similar despite the shorter phalanges of Haya.

Pisanosaurus is a problem, but not an unsurmountable problem
Perhaps just enough clues are available. All workers nest Pisanosaurus at the base of the Ornithischia.

The origin of the predentary bone preceded Pisanosaurus, and the missing mandible tip probably marks it’s border.  Even so, in the fossil a line of demarcation is present. Not sure what to make of it. It is colored yellow here (Fig. 6).

Figure 6. The restored skull of Pisanosaurus. Note the openings of the mandible are not where the former fenestra was placed, so they are artifacts. The predentary of ornithischians is a novel and separate bone, and is probably missing here. Nevertheless, a line of demarcation found on the fossil is shown here.

Figure 6. The restored skull of Pisanosaurus. Note the prominent openings of the posterior mandible are not where the former fenestra was placed, so they are artifacts. The mandibular fenestra is below the second to last tooth, where the (yellow) splenial is showing through. The predentary of ornithischians is a novel and separate bone, and is missing here. A line of demarcation found on the fossil is colored yellow here.

References
Bonaparte JF 1976. Pisanosaurus mertii Casamiquela and the origin of the Ornithischia. Journal of Palaeontology 50(5):808-820.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007a. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Irmis RB, Parker WG, Nesbitt SJ and Liu J 2007b. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218
Casamiquela RM 1967. Un nuevo dinosaurio ornitisquio triásico (Pisanosaurus mertii; Ornithopoda) de la Formación Ischigualasto, Argentina. Ameghiniana 4 (2): 47–64.
Sereno P 1991. Lesothosaurus, “Fabrosaurids,” and the early evolution of Ornithischia. Journal of Vertebrate Paleontology 11:168-197.

wiki/Pisanosaurus

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2 thoughts on “Restoring Pisanosaurus

  1. Dear David, I love these posts. I live in the Buffalo New York area USA. It is blowing snow and very cold. This is getting me through this winter!! I’m learning a great deal from you. Keep up the great work.

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