Strange Bedfellows – Nesbitt (2011) – part 2 – Vancleavea

Sometimes we miss the big picture. 
Here then, for your approval and disapproval are comparisons between closest kin found by the Nesbitt (2011) tree versus those found by the large reptile tree. Yesterday we started at the base (Fig. 1) and the ill-advised inclusion of Mesosuchus. Today we reexamine the mistaken inclusion of Vancleavea (we did this several months ago, but differently).

The base of the Nesbitt (2011) tree

Figure 1. The base of the Nesbitt (2011) tree with featured taxa in yellow.

Nesbitt (2011) included the new Triassic reptile, Vancleavea, in his list of Archosauriform taxa. It nested between Erythrosuchus and Tropidosuchus + Chanaresuchus (Figs. 1, 2). Since evolution works in minute steps, you may rightly ask, what’s wrong with this picture?

Figure 1. Closest known taxa recovered by the Nesbitt (2011) study. Here Vancleavea nested between Erythrosuchus and Tropidosuchus.

Figure 2. Closest known taxa recovered by the Nesbitt (2011) study. Here Vancleavea nested between Erythrosuchus and Tropidosuchus.

For comparison
The much larger and more inclusive large reptile tree, recovered Vancleavea with the thalattosaurs, Helveticosaurus and Askeptosaurus (Fig. 3). Nesbitt’s 2011 study did not include these sisters.

 

Figure 3. The closest kin of Vancleavea recovered by the large reptile tree. Askeptosaurus, Vancleavea and Helveticosaurus, all thalattosaurs unrelated to archosauriforms.

Figure 3. The closest kin of Vancleavea recovered by the large reptile tree. Askeptosaurus, Vancleavea and Helveticosaurus, all thalattosaurs unrelated to archosauriforms.

Tropidosuchus and Chanaresuchus

The large reptile tree also recovered Tropidosuchus with Chanaresuchus (matching Nesbitt 2011) and Lagerpeton (Fig. 4), which nests closer to dinos in the Nesbitt (2011) tree. That’s pretty far from Erythrosuchus. So the three putative sisters found by Nesbitt (2011) are all strange bedfellows.

Figure 3. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Figure 4. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton. Note the distinct sizes, the shape of the pelvis nd the evolution of the foot.

Erythrosuchus
I’ll show pix of erythrosuchids and kin in a blog or two.

Remember
Fewer anatomical differences signal a closer relationship. Conversely, that means sister taxa share are a larger suite of traits. Our trees should recover sisters with a large suite of traits. By not including thalattosaurs, Vancleavea was inappropriately nested with archosauriforms by Nesbitt (2011).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Nesbitt SJ 2011.
 The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

12 thoughts on “Strange Bedfellows – Nesbitt (2011) – part 2 – Vancleavea

  1. Sorry, Dave, but I gotta point this out:

    Since evolution works in minute steps, you may rightly ask, what’s wrong with this picture?

    Indeed, the effects of evolution are gradual, incremental, and small. But the fossil record does not preserve it all, nor do we have a perfect reflection of the record that is preserved available to us. It is problematic to insist that the phylogenetic analysis is not correct when making a simple gorss-appearance comparison. Not only do aquatic taxa arise multiple times in multiple different diapsid clades, but they also produce similar animals from very, very different starting points. So it stands to reason that the two groups that bracket Vancleavea campi look little like it — in gross appearance. It is just as useful to say that whales look nothing like pigs, hippos or ruminants, but it sure is related to them more than other mammals, and details of the limbs (such as a particular hinge in the proximal tarsals) show that a feature is being retained through deep time regardless of lack of functionality. That’s what Gould called spandrels, and argued that they are more useful to evolution than gross morphologic similarities were.

  2. Jaime, you’ve got your blinders on. I provided two closer sister taxa to Vancleavea and you can test them yourself or ask for my matrix. This is science. Throw them into the same pot and see which ones float together. Keep them separate and you’ll never know. BTW, whales DO look more like hippos and ruminants (as many studies have shown), when you consider ALL the whales, or even just the most primitive whales, compared to any other clade. That’s the point.

  3. When you are saying that these taxa don’t fall out the same way in your reptile tree is this your previously recovered tree or the tree including new characters from Nesbitt?

      • I am curious if inclusion of new characters from Nesbitt’s paper causes any shifts in the included taxa.

      • That’s going to take awhile considering the number of taxa, the focus on archosaurian traits, and the relative difficulty of judging so many characters that do not have an IS/IS NOT dichotomy. Don’t hold your breath. I’m doing my best to work around that train wreck and show it for what it is.

  4. I’m only an amateur paleontologist, but I have spent a few weeks digging at Ghost Ranch and working in Alex Downs’ lab, and have seen the Vancleavea specimen up close several times. It’s fairly complete and very well-articulated, including even relatively delicate features like the tiny dewlap osteoderms. The skull is compressed (flattened side-to-side) relative to other recovered jaws, and the spine is broken in an acute angle in one place, but there’s really not much missing. One can open the skull (and I have); the brain cavity is the size of a small raisin.

    I’m not going to venture an opinion on whether Nesbitt et al. got the classification wrong, but I do find it rather hard to believe that they miscounted vertebrae (as claimed at reptileevolution.com: “Nesbitt et al. (2009) estimated too few dorsal vertebrae. The actual number appears to have been 35 or so, similar to Miodentosaurus. The number of cervicals was likely ~10, as in Miodentosaurus and Helveticosaurus.”) given the quality of the fossil. DISCLAIMER: I know 4 of the Vancleavea-related authors (Nesbitt, Irmis, Downs, Small).

    P.S. I have pretty good photos if you want them. (https://www.facebook.com/photo.php?fbid=100685568213 is one, but not nearly the best.)

  5. The number of vertebrae is highly variable in that section of the clade with Eusaurosphargis having a very low number just outside of the Helveticosaurus/Vancleavea clade. I did not know about Eusaurosphargis at the time, so I wrote what I wrote. But I’ll be glad to refigure that number with solid data. BTW, is anyone over there phylogenetically retesting Vancleavea with the inclusion of Helveticosaurus and thalattosaurs?

    Dave

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