The joy of finding mistakes: fewer stem dinosaurs

Finding mistakes is what I hope to do every day
in my own work, as well as that of others. Each time that happens, the data set improves. Lumping and splitting improves. The hypothetical topology of the large reptile tree (LRT, 1036 taxa) gets closer to echoing the topology of Nature itself. Science is a process of winnowing through the data and finding earlier mistakes.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Figure 1. Revision to the LRT with a focus on the Archosauria. Here taxa with a long carpus all nest within the Crocodylomorpha, following traditional thinking. Dinosaur outgroups are reduced. PVL 4597 is still the basalmost archosaur.

Today
I discovered some scoring errors among former ‘stem dinosaurs’ that turned them into basal crocodylomorphs. That’s a small shift and it involved turning some ‘absent’ scores in pedal digit 5 to ‘unknown’. It’s noteworthy that some related taxa have two tiny phalanges on pedal digit 5. A related taxon, Gracilisuchu, was illustrated by Romer (1972, Fig. 3) as a combination or chimaera of separate specimens, something I just today realized and rescored. One of those specimens is the so-called Tucuman specimen (PVL 4597, Fig 1), which nests apart from the Gracilisuchus holotype (Fig. 2) in the LRT.

Figure 1. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT.

Figure 2. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT. That fibula flange turns out to be another important trait. 

The corrected results
resolve the long proximal carpal issue in crocodylomorphs very neatly. Now, as in traditional thinking, that trait is restricted to only the crocodylomorphs and it gives us a basalmost taxon with the trait, Junggarsuchus. You might think, and it would be reasonable to do so, that phylogenetic bracketing permitted the addition of a long carpus and long coracoids with more confidence to taxa that don’t preserve this, like Gracilisuchus and Saltopus. But another related basal crocodylomorph, Scleromochlus, has small round coracoids, evidently a reversal. The carpal length is not clearly documented in Scleromochlus (Fig. 4).

Gracilisuchus

Figure 3. A basal archosaur with a very similar nasal bone, Gracilisuchus. Note pedal digit 5 here. This is how Romer 1972 illustrated it. The actual data is shown in figure 2, the Tucuman specimen, PVL 4597. The coracoid is not known in the holotype. 

Despite the short round coracoids of Scleromochlu
and its apparently short carpals, enough traits remain to nest it as a basal crocodylomorph, following the rules of maximum parsimony.

Figure 1. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. The size of the Scleromochlus hand makes it the last possible sister to pterosaurs, famous for their very large hands.

Figure 4. Scleromochlus forequarters. The yellow area shows the hand enlarged in situ. Large carpals do not appear to be present and the coracoids are not elongated. 

On a more personal note
I found out my art and a short bio were included in a paleoart website:
http://paleoartistry.webs.com while looking for information on friend and paleoartist, Mark Hallett, (wikipage here) whose website is down and I worried about his health. No worries. Mark just let his website lapse.

The author of the paleoartistry page
had both kind words and controversy for me:
“After David Peters’ excellent paintings in Giants, and A Gallery of Dinosaurs and Other Early Reptiles, as well as his own calendar, it seemed he was on his way to becoming one of the most reliable paleoartists of the 1990s, if not of all time. However, very controversial theories on reconstructing pterosaurs led to some harsh critiques obscuring Peters’ artistic brilliance.” 

That’s okay.
“Very controversial” does not mean completely bonkers (or am I reading too little into this?). It just means it inspires a lot of chatter. Or… it could mean that the author of the post follows the invalidated observations of Elgin, Hone and Frey 2010, which are the traditional views (Unwin and Bakhurina 1994), still used in David Attenborough films. If so, that would be a shame. Science is usually black and white – is or isn’t, because you can observe and test (Fig. 5) and all tests, if done the same, should turn out the same.

And you don’t toss out data
that doesn’t agree with your preconception, like Elgin, Hone and Frey did. In reality, my “very controversial reconstructions” remain the only ones built with DGS, not freehand guesswork or crude cartoonish tracings (as in Elgin, Hone and Frey 2010). The membranes (brachiopatagia and uropatagia) were documented in precise detail in Peters 2002, 2009 and here online.

Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

Figure 5. Click to animate. This is the Vienna specimen of Pterodactylus, which preserves twin uropatagia behind the knees.

References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.
Romer AS 1972. 
The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

wiki/Gracilisuchus
paleoartistry.webs.com/1980s.htm

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The Nesbitt 2011 Tree – Mixes and Matches

A few years ago Sterling Nesbitt (2011) recovered a tree of the Archosauria (Fig. 1) using several dozen taxa and several hundred traits. This is laudable. Unfortunately, Nesbitt’s inclusion set did not follow a larger gamut analysis (like the large reptile tree) to determine which taxa to include and which to exclude. So Nesbitt’s tree included several taxa that were not at all related to Archosauria and their ancestors, according to the larger gamut results. These outliers included Mesosuchus and pterosaurs (both nesting on the new Lepidosauromorpha branch, far from the archosaurs) and Vancleavea (a thalattosaur).

Figure 1. Click to enlarge. On the left is the Nesbitt (2011) tree. On the right is a subset of taxa from the large reptile tree. Pink double arrows, and there are lots of them, are pretty good matches. Green double arrows are mismatches.

Figure 1. Click to enlarge. On the left is the Nesbitt (2011) tree. On the right is a subset of taxa from the large reptile tree. Pink double arrows, and there are lots of them, are pretty good matches. Green double arrows are mismatches. The lack of resolution in the Peters Partial Tree reflects the lack of real relationships among those many “by default” nested sisters. Eoraptor was inadvertently  pruned from the Peters tree, but nested with Saturnalia.

In an attempt at testing Nesbitt’s tree, I included as many of the same taxa, massively pruning the large reptile tree to do so. There are also several taxa in the Nesbitt tree that are not found in the large reptile tree, chiefly from the higher crocs, the higher dinos, the partial rauisuchians and a few odds and ends known from very incomplete material. The results (Fig. 1) largely echoed the Nesbitt tree, but several mismatches also arose.

Mismatch: Pterosaurs
Among the tree mismatches are pterosaurs, which nest close to dinosaurs in the Nesbitt tree but nest with Vancleavea in the large reptile tree after pruning the real sisters of pterosaurs among the lepidosaur / tritosaur / fenestrasaurs.

Lagerpeton
Lagerpeton is at the base of the dinosaurs in the Nesbitt tree, but nests with Tropidosuchus in the Peters tree. Lagerpeton has many ankle traits in common with dinos, which were treated in the Peters tree, but emphasized in the Nesbitt tree.

Lewisuchus
Lewisuchus nests at the base of the Silesauridae, the outgroup to the Dinosauria, in the Nesbitt tree, but at the base of the Archosauria in the Peters tree. Nesbitt excluded the Lewisuchus sisters Pseudhesperosuchus and Decuriasuchus found by the Peters tree.

Turfanosuchus and Gracilisuchus
These two nest close to the Ornithosuchia (basal Pseudosuchia) in the Nesbitt tree, but at the base of the Archosauria/Crocodylomorpha in the Peters tree. Not sure why these two nest so far from the basal crocs in the Nesbitt tree, but the lack of the basal archosaurs and Gracilisuchus sister taxa, Scleromochlus SaltopusPseudhesperosuchus and Decuriasuchus may have something to do with it.

Poposaurs
Nesbitt nests poposaurs (those “dinosaur-like pseudosuchians”) with rauisuchians. Peters nests them with dinosaurs (despite the calcaneum tuber) and includes in their number Sacisaurus and Silesaurus. Nesbitt, like Mortimer, nests beaked Sacisaurus and beaked ornithischian dinosaurs like Lesothosaurus, and other plant eaters, like Saturnalia, basal to non-beaked theropod dinosaurs, which appears to be due to the creation of an upside-down topology (correct but inverted) and far from Marasuchus, another theropod, according to the large reptile tree.

The differences between the two trees arise from the choice of taxa and characters.
The Peters tree uses many more taxa. This allows pterosaurs, Mesosuchus and Vancleavea to nest more parsimoniously elsewhere and to separate parasuchians, chanaresuchians (including Lagerpeton) to separate from the rest. Nesbitt did not employ any younginids or choristoderes, which nest at the base of the Archosauriformes.

The Nesbitt tree uses more and different characters, many too small or hidden to be observed in a typical reconstruction (though they may and are still important!), which is the prime source for the Peters characters.

In the Peters tree all taxa share a large number of traits. In other words, very few traits separate sisters. They could have evolved from one another.

The Nesbitt tree ignores the strange bedfellows it produces in which sister taxa share very few traits, but nest by default, as some do in the pruned Peters tree.

Most sisters in the Nesbitt tree are also sisters in the Peters tree, providing confirmation for those relationships in both studies.

The Peters tree finds that enough taxa are known to produce a gradual accumulation of traits in derived taxa and a gradual spectrum of morphologies.

The Nesbit tree assumes (or hopes) that there are large numbers of taxa that will someday fill out and blend in the disparate morphologies among putative sisters. In many cases, these taxa are indeed known, just not used by Nesbitt.

There are also some irreversible reversals in the Nesbitt tree that are absent in the Peters tree when you get down to details. More plesiomorphic taxa can be found in basal positions in the complete Peters tree (the large reptile tree), like the many younginids missing from the base of the Nesbitt tree.

Late News Item:
Nesbitt (2011) nested Eoraptor with theropods. The large reptile tree nested Eoraptor with basal phytodinosaurs like Pampadromaeus and Panphagia. Today’s paper by Sereno et al. (2013) confirms the large reptile tree nesting.

A shorter Scelidosaurus skull

Scelidosaurus nests next to Daemonosaurus as the most basal ornithischian in the large reptile tree. It’s obviously quite a bit more derived than Daemonosaurus with those plant-eating teeth and tiny antorbital fenestra (Fig. 1). Probably more bulky, too (Fig. 2).  But no other taxon in the large reptile tree (338 taxa) is closer with the exceptions of Heterodontosaurus (Fig. 2) and Hexinlusaurus.

This is one of the dinosaurs I rescored a few weeks ago. I was under the impression that it had a longer rostrum. I’d like to see some papers on this.

Figure 1. Scelidosaurus in situ with bones traced and colorized. Only the left half of the dorsal skull has been traced. The break in the rostrum occurs right where Daemonosaurus and Heterodontosaurus have dentary fangs, so, with phylogenetic bracketing, one has to wonder whether Scelidosaurus had them too.

Figure 1. Scelidosaurus in situ with bones traced and colorized. The naris is not clear. Only the left half of the dorsal skull has been traced. No palpebral? This skull is somewhat distorted, taken with a wide-angle lens. 

A shorter skull gives Scelidosaurus something of a new look.

Figure 2. Basal ornithischia and Pampadroameus, a sister to their common ancestor. Daemonosaurus likely resembled Pampadromaeus, with its long neck.

Figure 2. Basal ornithischia and Pampadroameus, a sister to their common ancestor. Daemonosaurus likely resembled Pampadromaeus, with its long neck.

So, the origin of the Ornithischia remains in that gray unknown area represented by the unknown postcrania of Daemonosaurus. Scelidosaurus and Heterodontosaurus have the basic ornithischian pelvis. Pampadromaeus probably doesn’t since it is also basal to sauropods. Daemonosaurus is apparently where the magic transformation takes place in the pelvis.

Figure 3. Daemonosaurus and kin. Here a selection of basal dinosaurs is divided into clades. Yet, note the resemblances. These taxa are not too far from one another.

Figure 3. Daemonosaurus and kin. Here a selection of basal dinosaurs is divided into clades. Yet, note the resemblances. These taxa are not too far from one another.

Addendum
Mike Hanson has kindly sent a less distorted side view skull. Here it is (Figure addendum). Thank you, Mike.This is to demonstrate that I make mistakes (this one more or less on purpose to encourage the reception of better data, see above) and that I correct them once revealed, as I have done before. Even with the distortion adjustment, the skull is still shorter and smaller in the rostrum than the data I had before. All I want is the best data. Again, thank you, Mike. Keep it coming. 

The revised skull of Scelidosaurus taken from more distance for less distortion.

Figure addendum. The revised skull of Scelidosaurus taken from more distance for less distortion.

 

 

References
Norman D 2001. Scelidosaurus, the earliest complete dinosaur in The Armored Dinosaurs, pp 3-24. Bloomington: Indiana University Press.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B, published online 
Thulborn, RA 1977.
 Relationships of the lower Jurassic dinosaur Scelidosaurus harrisonii. Journal of Paleontology. 51: 725-739

wiki/Daemonosaurus
wiki/Scelidosaurus

The Skull of Lotosaurus (the finback poposaurid dinosaur)

The skull of Lotosaurus color coded.

Figure 1. The skull of Lotosaurus color coded. This toothless poposaurid nests with the herbivorous Silesaurus and Pseudolagosuchus (Fig. 2), neither of which have a fin. This is a DGS tracing.

Lotosaurus is interesting and mysterious because it is so big and so derived, yet appears so early (early Middle Triassic), essentially earlier than all other known dinosaurs. If phylogeny is a guide, then dinosaurs, notably theropods, originated earlier than this. Maybe there was a dino explosion in the early Triassic matching the placental explosion in the early Paleocene. We just haven’t found evidence for it yet.

Lotosaurus really needs a fresh new paper and a complete redescription. To that point, Nesbitt (2011) reports, A full description of Lotosaurus is currently underway.” We’ve seen recent papers on Arizonasaurus (Fig. 1, an unrelated rauisuchian) and Ctenosauriscus (Fig. 2, too soon to know what it is), but really nothing recent on Lotosaurus (Zhang 1975), which currently nests with poposaurid dinosaurs. It would be nice to know what’s real and what isn’t, how many specimens we have (Wiki says 10), and if new data changes hows it currently nests.

Earlier we looked at other finbacks and possible sister taxa. The skull of Silesaurus is a pretty close match to that of Lotosaurus, sans the teeth and adding some bulk. The rest of the changes in morphology appear to reflect the return to a quadrupedal stance along with greater bulk and loss of teeth.

Figure 3. Lotosaurus compared to sister taxa and other finback archosaurs.

Figure 3. Lotosaurus compared to sister taxa and other finback archosaurs.

Nesbitt (2003) reported on Arizonasaurus. He wrote, Characterisitics of the skeleton of Arizonasaurus show that it belongs to a poorly known group of Middle Triassic (240–230 Myr ago) archosaurs called the ctenosauriscids, and that ctenosauriscids are or are closely related to poposaurs. Furthermore, many characteristics of Arizonasaurus provide evidence that poposaurids and ctenosauriscids are derived rauisuchians.”

Dinosaurs are also derived from basal rauisuchians, but that’s not what Nesbitt meant. Nesbitt considered Arizonasaurus a derived rauisuchian, but the large reptile tree nested it close to the basal taxon, Vjushkovia. Nesbitt’s (2003) analysis did not include Lotosaurus, but his 2011 study did, nesting it between Poposaurus and Sillosuchus, Effigia and Shuvosaurus, with rauisuchians and far from Silesaurus, which Nesbitt (2011) nested just outside the Dinosauria. We earlier discussed problems with Nesbitt (2011) and his “strange bedfellows” in a nine-part  series. It’s worthwhile to also recall that certain poposaurs developed a new calcaneal tuber, convergent with the development of a calcaneal heel in crocodylomorphs. Such a structure traditionally removes poposaurids from the Dinosauria, but phylogenetic analysis puts them back in. Lotosaurus had a very small calcaneal tuber, if any. It’s hard to see on existing data.

I’ll be out for a week on family business. See you again after the 25th.

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
Butler RJ, Brusatte SL, Reich M, Nesbitt SJ, Schoch RR, et al. 2011. The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation. PLoS ONE 6(10): e25693. doi:10.1371/journal.pone.0025693 Plos One paper
Nesbitt SJ 2003. Arizonasaurus and its implications for archosaur divergence
Sterling J. Nesbitt Proceedings of the Royal Society, London B (Suppl.) 270, S234–S237. DOI 10.1098/rsbl.2003.0066
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.
Weinbaum JC and Hungerbuhler A 2007. A Revision of Poposaurus gracilis (Archosauria: Suchia) based on two new specimens from the Late Triassic of the southwestern USA. Palaeontologische Zeitschrift 81(2):131-145.
Zhang F-K 1975. A new thecodont Lotosaurus, from Middle Triassic of Hunan. Vertebrata PalAsiatica 13:144-147.

wiki/Lotosaurus