Back to Vancleavea

Several years ago we looked at Vancleavea campi (Figs. 1,2 ), a Triassic aquatic reptile described by Nesbitt, et al. 2008 as an archosauriform nesting with Erythrosuchus, Euparkeria, Turfanosuchus and Doswellia (according to Wikipedia, based on published work listed above). Unfortunately, Vancleavea shares few traits with these archosauriforms. It has no antorbital fenestra, no upper temporal fenestra and no mandibular fenestra.

Figure 1. Vancleavea surrounded by purported sister taxa as figured by Nesbitt and Wikipedia. None of these taxa share more traits with Vancleavea than does Helveticosaurus, a taxon ignored since it was proposed here.

Figure 1. Vancleavea surrounded by purported sister taxa as figured by Nesbitt and Wikipedia. None of these taxa share more traits with Vancleavea than does Helveticosaurus, a taxon ignored since it was proposed here.

Not yet tested in academic publications,
the thalattosaur, Helveticosaurus, shares more traits with Vancleavea than 569 other tested taxa in the large reptile tree.

Figure 2. Vancleavea with its sister, Helveticosaurus.

Figure 2. Vancleavea with its sister, Helveticosaurus.

This counter argument
was made more than 4 years ago. To date no one else has supported or refuted the argument. Nevertheless, in the last four years Vancleavea has appeared in several cladograms without Helveticosaurus. Unfortunately this demonstrates that paleontologists are really not interested in its correct nesting node, but would rather just add new taxa to existing flawed analyses and cladograms. Testing prior work is not their strong suite. Discovery is.

Vancleavea campi  (Nesbitt et al. 2009) Late Triassic,~210 mya, ~1.2 meters in length, was originally considered a very weird archosauriform close to DoswelliaTurfanosuchusChanaresuchus and Erythrosuchus, but that’s because the authors did not compare it to Helveticosaurus with which Vanclevea shares more traits. It turns out that Vanclevea was a not-so-weird thalattosaur and a prime example of what happens when the gamut of the inclusion set is decided prior to the analysis. Vancleavea was the last in its lineage. Unlike other thalattosauriforms, Vancleavea was armored with a variety of ossified scales covering the body.

There must be dozens
of Vancleavea-like thalattosaurs yet to be discovered, judging by the variation present between it and Helveticosaurus. Even so, after adding hundreds of taxa to the large reptile tree, these two still nest together.

Not the only time a taxon’s correct nesting ignored.
These taxa are also traditionally incorrectly nested based on the results of the large reptile tree.

  1. Turtles
  2. Pterosaurs
  3. Fenestrasauria and Tritosauria
  4. Snakes
  5. Caseasauria
  6. Mesosauria
  7. Poposauria
  8. Rhynchosauria
  9. Synapsida
  10. Chilesaurus and Daemonosaurus
  11. Gephyrostegus
  12. Procolophon
  13. Cartorhynchus
  14. Youngina and Youngoides
  15. Xianglong
  16. Tetraceratops
  17. Eudibamus
  18. Doswellia
  19. Revuletosaurus
  20. Scleromochlus
  21. Pseudhesperosuchus
  22. Marasuchus
  23. Lagerpeton
  24. Teraterpeton
  25. Ticinosuchus
  26. and whatever else I’ve forgotten to list here

References
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
Parker WG and Barton B 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11 (3): 20p.

wiki/Vancleavea

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Vancleavea occiput and comments

The original Vancleavea paper (Nesbitt et al. 2009) illustrated the occiput of Vancleavea (Fig. 1), but from oblique angles of the in situ scattered bones. The skull was removed from the matrix, but the occiput was not shown in straight-on, reconstructed occipital view. Here, trying to remedy that, I attempt to reconstruct the Vancleavea occiput from the published data.

Vancleavea is a derived thalattosaur, close to Helveticosaurus and Eusaurosphargis which, due to their crushed and scattered fossils, provide few clues to guide the reconstruction. In fact thalattosaurs as a group provide few clues as to how the occiput blueprint comes together. So, even if this reconstruction is correct, there is little to nothing to compare it to.

Figure 1. Vancleavea occiput gleaned from several oblique views of cranial elements.

Figure 1. Vancleavea occiput gleaned from several oblique views of cranial elements. If you have better data, please send it along.

The Vancleavea occiput
is dominated by a large supraoccipital plate bordered by post parietals fused to the roofing parietals. It’s fairly solid with a single opening for the spinal chord above the single-headed occipital condyle and paired openings on either side of the condyle, set not much higher than the ventral quadrates.

Not (m)any thalattosaur occiputs are known to compare this to.

This is also a great time
to respond to David Marjanovic’s notes on why Vancleavea is not a thalattosaur published in the Dinosaur Mailing List here.

One key to understanding the several arguments offered by Marjanovic is the nesting of Vancleavea with the odd thalattosaur sister to Vancleavea, Helveticosaurus and Eusaurosphargis, which are not even considered by Marjanovic. He compares Vancleavea to Askeptosaurus and Miodentosaurus among others.

The other key to understanding is the identification of several breaks in the skull of Vancleavea that look like sutures and vice versa. Remember, Vancleavea was described as the oddest of all archosauriformes in that it lacked an antorbital fenestra, upper temporal fenestrae and mandibular fenestra, among several other noteworthy traits otherwise common to archosauriforms. So the cracks that fit that interpretation were identified as sutures. David Marjanovic’s comments are identified as DM. I am DP.

DM: Judging *Vancleavea* from the illustrations here [link no longer active]: Thalattosaurs retain the supratemporal. *Vancleavea* lacks it.

DP: The supratemporal of Askeptosaurus is a vestige and that bone is also indistinct or lacking in Eusaurosphargis and Helveticosaurus. So indeed Vancleavea lacks the supratemporal, as does its closest sister taxa.

DM: – Thalattosaurs have an open lower temporal arch (the caudal process of the jugal doesn’t reach very far back, so the lower temporal fenestra is open ventrally); I’m not even sure if they have a quadratojugal at all (none is in any case preserved in *Miodentosaurus*). It’s closed in *Vancleavea*, the qj is large, and the caudal process of the j is very broad dorsoventrally, much unlike the very delicate T-shaped jugals of thalattosaurs.

DP: Helveticosaurus likewise does not have an open lower temporal arch, the quadratojugal is large and the caudal process of the jugal is very broad dorsoventrally. Eusaurosphargis is too scattered to determine but my guess, based on the brevity of the jugal posterior process, is the quadratojugal is a trait shared by only Helveticosaurus and Vancleavea.

DM: – The maxilla contacts the naris in thalattosaurs. In *V.*, they are separated by a huge caudodorsal process of the premaxilla.

DP: This is a misinterpretation based on a bone break, coincidentally on both side of the skull. These are not sutures. The actual sutures are visible at the bases of this purported process on both sides. On the same subject, Nesbitt nested Vancleavea between Erythrosuchus, which has these caudodorsal process of the premaxilla, and Chanaresuchus + Tropidosuchus, which do not.

DM: – Thalattosaurs have a very large pineal foramen. *V.* lacks any trace of it.

DP: The size of the pineal foramen varies within thalattosaurs, larger in Anshunsaurus and Miodentosaurus, smaller in Endennasaurus. Nesbitt et al. 2009 overlooked the pineal foramen in Vancleavea, perhaps because the parietals are split apart.

Figure 1. Vancleavea pineal foramen.

Figure 2. Vancleavea pineal foramen.

DM: – Thalattosaurs retain caudal ribs — real free mobile ribs on the first few tail vertebrae. Can’t see such a thing in the low-resolution reconstruction of *V.*

DP: In like fashion Helveticosaurus and Eusaurosphargis also lack caudal ribs. Askeptosaurus has four. Miodentosaurus has two. So these taxa show this trait gradually disappearing.

DM: *V.* shares all these character states with all other archosauriforms, except for the thin jugal of… maniraptoriforms or something. Both, however, have a single bone called the “postorbital” in *V.* and the “postfrontal” in thalattosaurs…

DP: Indeed this bone convergently results from the fusion of the postorbital and postfrontal, not the disappearance of one or the other, which remain separate in Askeptosaurus, fused in Helveticosaurus and Vancleavea, separate in Erythrosuchus, fused in Tropidosuchus.

DM: The quadrate looks similar, too, differing from the pillar dinosaurs have, but I’m not familiar with enough diapsid quadrates to tell what that means.

DP: The quadrate leans anteriorly like most thalattosaurs and archosauriforms, like Erythrosuchus.

DM: – In thalattosaurs the rostral margin of the orbit is formed by the maxilla. In *Vancleavea*, the prefrontal does that, and (perhaps because the orbit is so remarkably small) it even contacts the jugal, excluding the maxilla from the orbit altogether. Or is the “prefrontal” of *V.* actually the lacrimal, which is altogether missing in thalattosaurs (or at least *Miodentosaurus*)?

DP: It appears the lacrimal is tiny, at the base of the prefrontal in Vancleavea. Similar structure in Helveticosaurus, reduced from the larger bones in Eusaurosphargis and Miodentosaurus.

DM: – *V.* has very long hemal spines. Thalattosaurs never.

DP: These spines are longer in Anshunsaurus and even longer in Helveticosaurus.

DM: – *V.* has considerably smaller limbs, especially hands & feet, than thalattosaurs.

DP: Vancleavea does have smaller limbs than other related thalattosaurs. Askeptosaurus, Concavispina and Xinpusaurus, not closely related to Vancleavea, also have smaller limbs.

DM: Finally, *V.* is much smaller than *Miodentosaurus*. This means that things like the relatively much smaller orbit of *V.* (complete with taller jugal and maxilla) or its relatively much shorter extension of the jaw joints caudal to the occiput cannot be size-related — the opposite relationship would be expected.

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

Figure 3. Askeptosaurus, Vancleavea and Helveticosaurus for comparison and to illustrate points brought out in the text above.

DP: Helveticosaurus also has a similar small orbit.

Okay,
so Vancleavea is not like the majority of thalattosaurs. It’s like Helveticosaurus, which is also distinct from the majority of thalattosaurs, but even more unlike any of the 359 other reptiles tested in that matrix.

And selecting even several distinct traits from a list of 228 is like pulling a Larry Martin (famous for challenging birds-are-dinosaurs people to name one, just one trait, that links birds to dinosaurs). Everyone who deals with phylogenetic analysis knows there can be massive convergence and it is the suite of traits that nests taxa, not just a few or even a dozen traits.

Phylogenetic analysis
Vancleavea nests with Helveticosaurus. Removing Helveticosaurus and all the thalattosaurs does not change the remaining tree topology. Removing all the enaliosaurs does shift Vancleavea and also the proterosuchid Fugusuchus next to the choristodere Doswellia, not far from Erythrosuchus. But that takes a lot of deletion to make this work.

References
Nesbitt SJ, Stocker MR, Small BJ and Downs A 2009. 
The osteology and relationships ofVancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157 (4): 814–864. doi:10.1111/j.1096-3642.2009.00530.x.
Parker WG and Barton B 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Palaeontologia Electronica 11 (3): 20p.

wiki/Vancleavea

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.

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.

Nesbitt (2011) and his Characters – part 3 – Vancleavea + Archosauria

Following remarks from fellow paleontologists asking for my study to include more Nesbitt (2011) characters in the large reptile study, I thought we should dive right into them, taking a few days to digest them all — a bite at a time. Earlier we considered more basal clades in part 1 and part 2.

Nesbitt Characters for Vancleavea + Archosauria
Sterling Nesbitt (SN) reported, (1) Postparietal(s) absent (146-1). Postparietals are absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(2) Postaxial intercentra absent (177-1). Postaxial intercentra are absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(3) Ectepicondylar flange of the humerus absent (234-1). An ectepicondylar flange is absent in pterosaurs (Bennett, 1996).
Note: As in certain lepidosaurs, including all fenestrasaurs.

(4) Distal condyles of the femur not projecting markedly beyond shaft (318-1). Distal condyles of the femur not projecting markedly beyond shaft in basal pterosaurs.
Note: As in certain lepidosaurs, including all fenestrasaurs.

Long time readers will remember that Vancleavea nests as a thalattosaur close to Helveticosaurus, not an archosauriform, as recovered by the large reptile tree.

Tomorrow: Crurotarsi (Phytosauria + Crocodylomorpha)

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.