Drepanosaur pectoral girdle, bones identified

Along with the recent abstract on desert drepanosaurs, an earlier paper (Harris and Downs 2002) reported on a 3D drepanosaur pectoral girdle (Fig. 1).

Figure 1. 3D drepanosaur pectoral girdle. Green = clavicles, lavendar = interclavicle, pink = scapula, yellow = coracoid, blue = sternum.

Figure 1. 3D drepanosaur pectoral girdle. Green = overlapping clavicles, lavendar = interclavicle, pink = scapula, yellow = coracoid, blue = sternum.

Harris and Downs (2002) accurately reported on most of the elements here. But they overlooked the big one in the middle. They either overlooked the interclavicle binding all the other pectoral elements together, or else they considered it part of the scapulocoracoid. They also did not notice the right clavicle overlapped the left one.

These color images were created using a very simple version of DGS, digital graphic segregation, which also involves phylogenetic analysis and phylogenetic bracketing.

Drepanosaurs are tritosaur lepidosaurs. Earlier we looked at several other tritosaur pectoral girdles. Tritosaurs do weird things with their interclavicle/sternum.

Figure 2. Drepanosaur pectoral girdles

Figure 2. Drepanosaur pectoral girdles

Here (Fig. we see in ventral view the interclavicle and overlapping clavicles of Jesairosaurus, the mother of all drepanosaurids. Cosesaurus, likewise, has these overlapping clavicles, as does Longisquama and the Pterosauria, as part of their sternal complex.

Figure 2. The broad, yet T-shaped interclavicle of Jesairosaurus at the base of the drepanosaurids.

Figure 3. The broad, yet T-shaped interclavicle of Jesairosaurus, an ancestral taxon at the base of the drepanosaurids.

Hypuronector (Fig. 4 ) is also ancestral to drepanosaurids, nesting between Vallesaurus and Jesairosaurus.

Figure 3. Hypuronector pectoral girdle. Scapula = pink. Clavicle = yellow. Interclavicle  = lavender. Sternum = blue. Clavicle = green.

Figure 4. Hypuronector pectoral girdle. Scapula = pink. Clavicle = yellow. Interclavicle = lavender. Sternum = blue. Clavicle = green. Hypuronector is also ancestral to drepanosaurs.

Vallesaurus is represented by a crushed specimen in which the interclavicle appears to be broken at or near the midline during crushing. The clavicles and sterna are likewise split medially.

Vallesaurus pectoral girdle. Here the interclavicle (in lavender/puple), if that is what it is, is neatly split in half.

Vallesaurus pectoral girdle. Here the interclavicle (in lavender/puple), if that is what it is, is neatly split in half along with the clavicles and sterna.

Dr. Seuss had it right
This clade of tritosaur lepidosaurs (drepanosaurs, tanstropheids, fenestrasaurs, pterosaurs) are indeed a bizarre bunch of the most unusual reptiles known to science.

References
Harris JD and Downs A 2002. A drepanosaurid pectoral girdle from the Ghost Ranch (Whitaker) Coelophysis quarry (Chinle Group, Rock Point Formation, Rhaetian), New Mexico. Journal of Vertebrate Paleontology 22(1):70-75.

10 thoughts on “Drepanosaur pectoral girdle, bones identified

  1. “These color images were created using a very simple version of DGS, digital graphic segregation, which also involves phylogenetic analysis and phylogenetic bracketing.”
    This confuses me. You are using phylogenetic analyses to inform what you highlight? Is that correct?

  2. Yes. Where an animals nests helps one to identify bones more accurately in photos. This is not circular reasoning because nestings are created by a suite of several hundred traits. Corrections on individual traits nearly always further cement relationships. This helps avoid mistakes.

    In this case the interclavicle was not mentioned by Harris and Downs, but sister taxa have an interclavicle. So I looked for it and there it was. Mistakes identified, if valid, will be corrected.

  3. But aren’t you using these DGS-found traits to help code the matrix you use to develop the LRT? And if that tree then creates nestings that help you find more characters through DGS that will then be used in the self-same tree, how is that not circular?

  4. That assumes that what I find on DGS is invalid. And what I cross reference in the literature is invalid. Just the opposite. Sure I make mistakes, but the corrections almost always further cement relations. The beauty of Science is, you can look at the same fossil and come up with your own interpretation, reconstruction and nesting. Please do and get back to me if we don’t match.

  5. The statement makes no assumptions about whether DGS produces valid results. A methodology should be confirmed independently. You are expecting a certain trait to be present in a specimen based on the DGS-informed nesting. You see features and interpret them based on your preconceived notions of where it nests (based on your DGS codings). This is why, “corrections almost always further cement relations.” You are a priori assuming that the DGS-based tree is correct and are using your DGS observations to bolster existing observations. That’s not an actual test – that’s self-confirmation.

  6. To clarify about my last comment: in that post you reidentified a bone that was not identified in the original publication. You did this based on its nesting. This nesting is based on DGS. You used DGS to “recover” this element, which will now go into the phylogeny. The phylogeny will drive further DGS identifications. Further DGS IDs will go back into the matrix. Ad infinitum. How is that not circular?

  7. Please tell me which observation (whether based on DGS or the literature) you have another solution for? I want to help you, but you also have to understand your need to dismantle a technique that is becoming widely used (see the most recent JVP Palci et al. 2013 on the reevaluation of snake limbs, jugals, etc.) and to good effect.

    • Not having a solution is okay if the other option is based on a circular argument. The reason I am wary of this methodology is, basically, Revueltosaurus. People assumed the teeth were from an ornithischian. That colored their view of other fossils and people fit their interpretation to fit their preconceived notion. Having ornithischians in the Chinle meant you could find ornithischians in the Chinle, so any archosaurian herbivore teeth were ornithischian, which “proved” that ornithisichians were in the Chinle…etc. etc. etc. This sort of big problem can occur any time you aren’t independently testing the robustness of your conclusions.

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