Strange Bedfellows – Nesbitt (2011) – part 3 – Euparkeria

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. We started at the base with Mesosuchus. Yesterday we looked at Vancleavea. Today we look at Euparkeria, surrounded by Tropidosuchus + Chanaresuchus on primitive side and the phytosauria led by Parasuchus on the derived side (Fig. 1).

The nesting of Euparkeria in Nesbitt (2011) surrounded by Tropidosuchus + Chanaresuchus and the Phytosauria, including Parasuchus.

Figure 1. The nesting of Euparkeria in Nesbitt (2011) surrounded by Tropidosuchus + Chanaresuchus and the Phytosauria, including Parasuchus.

Here (Fig. 2) are the selected Nesbitt (2011) sisters for visual comparison. They don’t look like sisters to me with their disparate shapes and proportions.
Surrounding Euparkeria in the Nesbitt (2011) tree are Tropidosuchus and Parasuchus, as shown here. The first and third have dorsal nares and a long narrow rostrum, among other traits. Euparkeria does not.

Figure 2. Surrounding Euparkeria in the Nesbitt (2011) tree are Tropidosuchus and Parasuchus, as shown here. The first and third have dorsal nares and a long narrow rostrum, among other traits. Euparkeria does not. If >I< were to propose these three as closest kin, I would have been laughed out of the city. Tropidosuchus is relatively close to Parasuchus in the large reptile tree, but several taxa, including Chanaresuchus and both the large and small Proterochampsa intervene.

Euparkeria does not fit here.
While Tropidosuchus and Parasuchus do share a suite of characters (dorsal naris, long narrow rostrum among them), several intervening taxa, like Chanaresuchus and Proterochampsa are missing here. Even with this distance, Euparkeria shares very little with these two and belongs with erythrosuchids and primitive rauisuchians. Here they are (Fig. 3), as promised yesterday.
Figure 3. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus following the nestings recovered by the large reptile tree. All three share a suite of traits that do not include a long narrow rostrum and a dorsal naris, among other traits.

Figure 3. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus following the nestings recovered by the large reptile tree. All three share a suite of traits that do not include a long narrow rostrum and a dorsal naris, among other traits. Overall and in most details, these three look alike. Here, oddly enough, the much larger taxon has the juvenile trait of a larger skull and shorter tail!!

Euparkeria fits better here.
Matching the Nesbitt (2011) tree, Euparkeria nested with the Garjainia (and Erythrosuchus) and Ornithosuchus in the large reptile tree (Fig. 3). Being surrounded by two pararchosauriforms (Fig. 2) is quite odd. They share very few traits not more closely shared by other taxa.  This should have raised red flags and should have been cause for concern regarding the scoring of Nesbitt’s (2011) characters, no matter how many he used. In real evolution, sister taxa should look alike (Fig. 3) with slight variation. In real evolution, one should be able to trace a gradual accumulation of character traits, as we do with fossil hominids. The rules don’t change with reptiles. You need to take the shortest path, the one with the fewest changes, to nest sister taxa. One look at these results brings immediate understanding that there’s something wrong in the Nesbitt (2011) matrix that produces such strange bedfellows.

Youngina BPI 2871 and its descendants, according to the large reptile tree, the choristodere Cteniogenys and the chanaresuchid, Gualosuchus.

Figure 4. Youngina BPI 2871 and its descendants, according to the large reptile tree, the choristodere Cteniogenys and the chanaresuchid, Gualosuchus.

Choristodera and the Chanaresuchidae
While Tropidosuchus is on our minds… previously overlooked, the choristoderes were descendants of Youngina and a basal taxon produced parasuchians and chanaresuchians, according to the results recovered from the large reptile tree. Comparing the the choristodere, Cteniogenys, with the chanaresuchid, Gualosuchus, is instructive. The former lacks an antorbital fenestra, but it developed independently in the common ancestor of parasuchia and chanaresuchidae,  the BPI 2871 specimen of Youngina, a taxon not far from Gualosuchus.

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.

9 thoughts on “Strange Bedfellows – Nesbitt (2011) – part 3 – Euparkeria

  1. Although I have nothing worthwhile to say concerning the cladistic details or arguments, putting Euparkeria with Erythrosuchus and Ornithosuchus is music to my ears. (Does that carry any weight?)

    However, I don’t understand your point about the juvenile traits in Fig 3. Based on the m-scales in the figure, Ornithosuchus looks biggest. It has a big, but maybe not the biggest, skull, but also the longest neck and tail, Also, of course, it’s well along the path toward obligatory bipedality.

      • But isn’t Ornithosuchus larger? Your renditions of the two animals are equal in length but at different scales. If you applied the Garjainia scale to Ornithosuchus, the latter’s tail would extend outside the figure.

      • Typically, as in the case of Ornithosuchus, the head of the larger reptile is relatively smaller. The opposite occurs in Garjainia, which is why the topic was raised.

  2. Is it possible that the general morphological similarities between phytosaurs and proterochampsians are examples of convergent evolution? Proterochampsians were in decline prior to the appearance of phytosaurs in the fossil record, perhaps phytosaur filled their niche sometime during the Carnian, much like how specific crocodylomorphs acquired the niche in the Jurassic.
    When discussing relations, it’s always wise to bring up subtle anatomical characteristics which would not be affected by the acquisition of a specific lifestyle. Where would we be now if early phytosaur-oriented paleontologists were too distracted by the similarities between phytosaurs and crocodilians to see the truth? It’s the subtle traits that matter, and I’d like to hear which synapomorphies you have found to link phytosaurs and proterochampsians together. Just a little food for thought.

    • Currently in the LRT phytosaurs and proterochampsians have a last common ancestor in Elaphrosuchus or perhaps Diandongosuchus, depending on how one reads the tree. The traits, subtle and obvious, can be found by reading the MacClade file at your leisure, available by request, reminding one and all that this is a hypothesis of relationships taking in a larger number of pertinent taxa than in smaller studies, and thus is less likely to overlook pertinent specimens. Looking at the tree I note that most of the taxa in your interest are terminal taxa, with few interrupting the basal branches. So more direct ancestors and transitional taxa are waiting to be discovered and added to the LRT.

      • Thank you. If by chance a new transitional taxa is discovered that completely alters your tree, what would you do? Would you reinterpret the new taxa to fit your results or reinterpret your results to fit the new taxa?

      • You are welcome to wait for a change, and I would welcome a massive change–if it was warranted. Listen. The LRT was more or less established after the original 260 taxa (not counting pterosaurs and therapsids). Since then over 1000 taxa have been added and the tree topology has not changed, except for drepanosaurs + Jesairosaurus nesting closer to basal lepidosauriformes and poposaurus nesting further from orinithischians. Both reasonable given their morphology. If a change was going to happen, it would have happened earlier, with fewer taxa. Nowadays, statistically every new taxon is ‘worth’ less than one-tenth of one percent of the entire tree. So change is less likely as the rest of the tree has been strongly cemented with every new taxon neatly tucking between two others already nested. That’s the value the LRT brings. It minimizes the effect of taxon exclusion because it includes so many taxa from such a wide gamut.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.