Dr. Baron tip-toes around the radiation of dinosaurs

Last year, Dr. Matthew Baron,
not even a year out from his PhD thesis, placed himself in the middle of controversy when Baron, Norman and Barrett 2017 resurrected the clade Ornithoscelida, wrongly uniting plant-eating Ornithischia with meat-eating Theropoda to the exclusion of plant-eating Sauropodomorpha, an invalid (due to taxon exclusion) hypothesis of relationships, we discussed earlier here.

Dr. Baron guessed,Maybe Ornithischia is actually so far removed from the base of the dinosaur tree that no studies, including my own, have been able to properly place them… Its an intriguing thought and one that needs examining properly.” By his own words, Dr. Baron is not yet an authority on the subject. That authority can only come from a wide gamut analysis that minimizes taxon exclusion, like the large reptile tree (LRT, 1236 taxa), which is something that anyone can produce. As noted last year (see citations below), Dr. Baron’s team excluded several relevant taxa.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha.

Figure 1. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal phytodinosauria.

Later Langer et al. 2017 argued against the Baron, Norman and Barrett interpretation. Baron, Norman and Barrett agued back, stating in Baron’s summary, “Langer et al.’s response showed that the alternative arrangement, that preserved the traditional model, was not statistically significantly different to our own hypothesis, and that was with much of our data having been altered, in ways that we perhaps disagree with strongly.”

Baron is correct is noting that Seeley’s original division, uniting sauropodomorphs with theropods based on pelvis orientation “just because a subgroup have gone on to lose a feature that was the ancestral condition for the wider group, it does not mean that we can then say that the other subgroups who have ‘hung on’ to the feature should be grouped together to the exclusion of the experimental group, at least based on that feature’s absence/presence, without other evidence.” Plus it would be one more example of pulling a Larry Martin.

Unfortunately
Dr. Baron pulls out a bad example as his example of the above. He states, “In fact, Cetacea is more closely related to Carnivora than either group are to the Primates.” In counterpoint, in the large reptile tree (LRT, 1236 taxa) there is no clade “Cetacea.” Odontoceti arise from tenrecs and elephant shrews. Mysticeti arise from hippos and desmostylians. Carnivora split apart in the first dichotomy in Eutheria. Thus all other eutherians, including primates, odontocetes and mysticetes have a last common ancestor that is not a member of the Carnivora.

Unfortunately
Dr. Baron bases the above quote on a phylogenetic error when he states, “Like I said before, you need to look at TOTAL EVIDENCE to come to this quite obvious conclusion, which means focusing on more anatomical evidence.” While this may sound reasonable and correct, a focus on anatomical evidence may lead to confusion due to convergence. Bottom line, it is more important to look at the phylogenetic placement of a taxon in order to determine what it is. This has to be done in the context of a wide gamut analysis that minimizes taxon exclusion using at least 150 (sometimes multi-state) characters (the LRT uses 238). Otherwise you’re cherry-picking taxa, something Baron, Norman and Barrett were guilty of by excluding bipedal crocs and several basal dinosaurs from their study (and we know this since the LRT includes them). Baron also cherry-picks traits in part 3 of his argument, pulling a Larry Martin several times in doing so. In a good phylogenetic analysis, like the LRT, you’ll see a gradual accumulation of traits. That means you’ll get a pubis with a transitional phase, a tiny predentary and other traits in gradual accumulation among the outgroups to Ornithischians.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 2. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Baron promises
“I will eat my shoes!” if Seeley’s dichotomy is correct. That’s an easy promise to make knowing there is a third hypothesis out there: the Theropod/Phytodinosaur dichotomy presented by Bakker (1986) and confirmed by the LRT in 2011.

Pertinent to this discussion
sometimes what a paleontologist does not say about a particular subject can be more important that what a paleontologist does say. I lump taxon exclusion and citation exclusion in the category of ‘what is not said.’

References
Bakker RT 1986. The Dinosaur Heresies.New Theories Unlocking the Mystery of the Dinosuars and Their Extinction. Illustrated. 481 pages. William Morrow & Company.
Baron MG and Barrett PM 2017. A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biology Letters 13, 20170220.
Baron MG, Norman DB and Barrett PM 2017.
A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543: 501–506;  doi:10.1038/nature21700
Baron MG, Norman DB and Barrett PM 2017. Baron et al. reply. Nature 551: doi:10.1038/nature24012
Langer et al. (8 co-authors) 2017. Untangling the dinosaur family tree. Nature 551: doi:10.1038/nature24011
Novas FE et al. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature 522(7556), 331.

Relevant blogposts and theses from Dr. Baron:

https://www.academia.edu/36002282/THE_ORIGIN_AND_EARLY_EVOLUTION_OF_THE_DINOSAURIA

What I think about Ornithischia

Thoughts on Ornithoscelida … over one year on … (part 1)

Thoughts on Ornithoscelida … over one year on … (part 2)

Chilesaurus – what is it?

https://pterosaurheresies.wordpress.com/2017/03/23/new-radical-dinosaur-cladogram-baron-norman-and-barrett-2017

https://pterosaurheresies.wordpress.com/2017/03/24/baron-2017-21-unambiguous-theropodornithischian-synapomorphies-dont-pan-out/

https://pterosaurheresies.wordpress.com/2015/06/25/the-dinosaur-heresies-nytimes-book-review-from-1986/

https://pterosaurheresies.wordpress.com/2017/11/03/dinosaur-family-tree-langer-et-al-responds-to-baron-et-al-2017-in-nature/

https://pterosaurheresies.wordpress.com/2017/08/16/you-heard-it-here-first-chilesaurus-is-a-basal-ornithischian-confirmed/

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You heard it here first: Daemonosaurus is an ornithischian

This one snuck under my radar
until Professor Thom Holtz mentioned it on the Dinosaur Mailing List. Writing about the Baron et al 2017 reply to Langer et al. we looked at earlier, Holtz wrote: “Novel discovery is Daemonosaurus as a basal ornithischian!!” (Fig. 1).

Actually that confirms a hypothesis of relationships
first recovered here back in 2011 when the large reptile tree (LRT, 1120 taxa) nested Daemonosaurus with the Ornithischia. So, the Baron et al. results confirm the earlier Peters 2011 discovery.

Figure 1. Here Daemonosaurus nests with basal ornithischians, not theropods, matching a nesting first recovered here in the LRT in 2011.

Figure 1. In Baron et al. 2017 Daemonosaurus nests with basal ornithischians, not theropods, matching a nesting first recovered here in the LRT in 2011.

As noted earlier, the Baron et al study is lacking a long list of pertinent taxa. Taxon exclusion is often the chief problem in phylogenetic analyses that rely on tradition.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale.

Figure 2. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale. These taxa nest together in the LRT.

Those who dislike the results recovered here
without a PhD and without seeing the specimens firsthand should note the growing list of taxa first recovered in the LRT that years later find confirmation in later studies by other workers.

References
Baron M.G., Barrett P.M. 2017 A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biology Letters 13, 20170220.
Baron MG, Norman DB and Barrett PM 2017.
 xxxx Nature 543501–506;  doi:10.1038/nature21700
Baron MG, Norman DB and Barrett PM 2017. Baron et al. reply. Nature 551: doi:10.1038/nature24012
Langer et al. (8 co-authors) 2017. Untangling the dinosaur family tree. Nature 551: doi:10.1038/nature24011

You heard it here first: Chilesaurus is a basal ornithischian confirmed.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha.

Figure 2. Look familiar? Here are the pelves of Jeholosaurus and Chilesaurus compared. As discussed earlier, this is how the ornithischian pelvis evolved from that of Eoraptor and basal saurorpodomorpha.

A new paper by Baron and Barrett 2017 confirms Chilesaurus (Fig. 1) as a basal member of the Ornithischia, not a bizarre theropod. As long time readers know, this was put online two years ago (other links below) in this blog.

Unfortunately, the authors don’t have an understanding of the interrelationships of phytodinosaurs, even though they report, For example, Chilesauruspossesses features that appear ‘classically’ theropod-like, sauropodomorph-like and ornithischian-like…” Nor did they mention the sister taxon, Jeholosaurus (Fig. 2).

Remember,
discovery only happens once.
More on this topic later.

This note went out this morning:
Thank you, Matthew,
for the confirmation on Chilesaurus.
In this case, it would have been appropriate to include me as a co-author since I put this online two years ago.

https://pterosaurheresies.wordpress.com/2015/04/28/chilesaurus-new-dinosaur-not-so-enigmatic-after-all/
http://www.reptileevolution.com/reptile-tree.htm
http://www.reptileevolution.com/chilesaurus.htm

References
Baron MG, Barrett PM 2017. A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biol. Lett. 13: 20170220. http://dx.doi.org/10.1098/rsbl.2017.0220 pdf online

Best regards,

Pisanosaurus: dinosaur or silesaurid?

A new paper by Agnolin and Rozadilla 2017
includes new photographs of the holotype that shed new light on Pisanosaurus (Casamiquela 1967, Bonaparte 1976; Late Triassic). This taxon was previously known in the literature chiefly (not exclusively) from drawings. The large reptile tree (LRT, 1043 taxa) nested Pisanosaurus with Haya as a basal ornithischian, confirming prior assessments. Now Agnolin and Rozadilla provide evidence for a Silesaurus affinity among the Poposauridae. Echoing others, they report, “the poor preservation of the specimen is the largest difficulty to overcome when interpreting its morphology. Its phylogenetic position within ornithischians is problematic.”

So, with the new evidence,
let’s test and nest Pisanosaurus 2017! (There are so few traits that can be scored for Pisanosaurus, that the rest of the discussion might seem like I’m pulling a Larry Martin. That happens sometimes, but I’m trying to report results from the LRT.

Before we start…
with present data, shifting Pisanosaurus to Silesaurus in the LRT adds 24 steps. Moreover, Agnolin and Rozadilla did not mention the proximal relatives of Pisanosaurus in the LRT:  Haya, Daemonosaurus, Chilesaurus, Scelidosaurus and Emausaurus. This may be the key to their novel results: taxon exclusion… once again. 

Some general notes to start with:

  1. Silesaurus and other poposaurs have a metatarsus no longer than the longest digit. The same hold true for many basal phytodinosaurs, but Pisanosaurus has a longer metatarsus, like its sister in the LRT, Haya.
  2. The photo of the pelvis does little to clarify any issues. It is a broken up mess (Fig. 2) with, what appear to be smaller pelvis bones (greens)  and several sacral bones (blues) stirred up in a conglomeration. Not much matches the published drawings. And my earlier imagination describing a rotated pubis based on simple published drawings did not pan out.
  3. The anterior dentary appears to be missing a predentary bone, a trait common to the clade Ornithischia, but something like it also appears in Silesaurus.
  4. Pisanoaurus comes from South America, home of most of the other basalmost Triassic phytodinosaurs. Popposaurids, all except Sacisaurus, come from somewhere else on the globe. Haya, the LRT sister to Pisanosaurus, comes from China, but it is Late Cretaceous in age.
  5. Agnolin and Rozadilla consider Silesaurus part of a clade “that is currently recognized as the sister group to Dinosauria.” The LRT recovers Crocodylomorpha closer to Dinosauria and Silesaurus nests within the next proximal outgroup, Poposauridae.
  6. Agnolin and Rozadilla report, “because Pisanosaurus is a unique and very valuable specimen, it is not currently possible to [CT] scan it.”
  7. Authors have not agreed whether the pelvis, represented by fragments of bones and bone impressions in rock. is preserved in medial or lateral view. Agnolin and Rozadilla report, “the sacrum is articulated and preserved in life position with respect to the pelvis.”
Figure 1. The Pisanosaurus pelvis here flipped right to left along with drawings and reconstructions by Agnolín and Rozadilla, plus DGS colors applied to what I can see here. Nothing is clear, but it seems like the pelvic elements are smaller that published and that several sacral vertebrate are sprinkled in this mass. Perhaps a CT scan would be helpful here. Blue = vertebrae. Green = pelvi elements.

Figure 1. The Pisanosaurus pelvis here flipped right to left along with drawings and reconstructions by Agnolín and Rozadilla, plus DGS colors applied to what I can see here. Other than the sacral vertebrate on top, not much is clear, but it seems like the pelvic elements are smaller that published and that several sacral vertebrate are sprinkled in this mass. Perhaps a CT scan would be helpful here. Blue = vertebrae. Green = pelvi elements.

Agnolin and Rozadilla provided an emended diagnosis.
Pisanosaurus is a basal dinosaurifordiagnosable by the following autapomorphies:

  1. “central teeth bilobate in occlusal view, showing well-developed mesial and distal grooves;
  2. distal end of the tibia anteroposteriorly longer than transversely wide;
  3. bilobate astragalus in distal view;
  4. ascending process of the astragalus being subquadrangular and robust in lateral view;
  5. intense transversal compression of the calcaneum.”
Figure 3. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

Figure 2. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

Other factors of interest:

  1. The number of tooth positions (15) in Pisanosaurus matches both silesaurids and pertinent ornithischians.
  2. “Central teeth are bilobate in occlusal view, and show well-developed mesial and distal grooves, a condition unknown in other herbivorous taxa and a trait that may be an autapomorphy of Pisanosaurus.” Not sure if the teeth in Haya are the same, but they look similar in lateral view (Fig. 2). Neither have denticles. Silesaurid teeth are leaf-shaped.
  3. “the teeth do not form a palisade or continuous masticatory surface as advocated by some authors.” As in Haya.
  4. “Pisanosaurus is similar to saurischians and basal dinosauriforms in having overlapping proximal metatarsals, differing from the non-overlapping condition in ornithischians.” Except Haya.
Figure 1. Haya in lateral view.

Figure 3. Haya in lateral view. Note the dorsal laminae, similar to those in Pisanosaurus.

Agnolin and Rozadilla describe the dorsal vertebrae
as having a strong and complex system of laminae. Haya (Fig. 3).has similar laminae. Poposauridae do not.

Silesaurus

Figure 4 Silesaurus as a biped and occasional quadruped. Note the squareish cervicals, unlike the parallelograms in figure 5.

Agnolin and Rozadilla considered the vertebrae
(Fig. 5) very different from the cervical vertebrae described for basal dinosauriforms and ornithischians. But they did not look at Haya, which has similar cervicals 1 and 2 (Fig. 5). They considered the cervicals ‘indistinguishable from Sacisaurus cervicals, but Langer and Ferigolo 2013, did not refer the cervical to Sacisaurus due to its relatively large size. Concluding Agnolin and Rozadilla considered these verts to be on uncertain position.

Figure 4. Pisanosaurus cervical vertebrae in left lateral view (not right as published) matches cervical vertebrae 1 and 2 in Haya.

Figure 5. Pisanosaurus cervical vertebrae in left lateral view (not right as published) matches cervical vertebrae 1 and 2 in Haya – and does not match the simpler vertebrae in Silesaurus (Fig. 4).

Sacrals are preserved as moulds in Pisanosaurus. 
Various authors have interpreted five, to two sacrals. Agnolin and Rozadilla concurred with Irmis et al. 2007, who found no trace of sacral elements, reporting, “some features previously considered to be impressions of sacral ribs are actually cracks in the matrix, and there is insufficient fidelity to determine whether any of the centra are fused to each other.” 

Figure 6. Pisanosaurus right pes with digit 2 ghosted in and digit 4 rotated into in vivo position. PILS added. Nnte the brevity of the toes compared to the metatarsus, a trait shared with Haya.

Figure 6. Pisanosaurus right pes with digit 2 ghosted in and digit 4 rotated into in vivo position. PILS added. Nnte the brevity of the toes compared to the metatarsus, a trait shared with Haya.

Is the acetabulum open or closed?
Agnolin and Rozadilla ‘suggest’ it is closed, as in poposaurs. If so the closed portion is buried. With available evidence and phylogenetic bracketing, it was probably open. Haya has an acetabulum with a keyhole shape (Fig. 3).

The tibia, tarsus and metatarsus
in Pisanosaurus the cnemial crest does not peak at the knee, but somewhat lower. Haya is similar. The fibula diameter is 70% that of the tibia, as in Scelidosaurus. The fibula for Haya is unknown. Anolín and Rozadilla identified a calcaneal tuber. That is odd because it is so small that it does not extend as far as the fibula does. in Haya the calcaneum extends slightly beyond the astragalus. The astragalus of Pisanosaurus is longer than wide (when the medial condyle is included), which is distinctly different from Haya and other sister taxa and different from Silesaurus.

Figure 8. Calcaneum of Pisanosaurus. You can see why some authors saw a tuber while others did not.

Figure 8. Calcaneum of Pisanosaurus. You can imagine why some authors saw a tuber while others did not.

A flawed phylogenetic analysis
Other than excluding several taxa that nest close to Pisanosaurus in the LRT, Agnolin and Rozadilla employed the invalid Nesbitt (2011) database, also suffering greatly from taxon exclusion. It does not nest sauropodomorphs with ornithischians as phytodinosaurs, but nests sauropodomorphs, like Pampadromaeus, with Tawa and other theropods. In their first analysis, 20 trees resulted with Pisanosaurus nested as an unresolved polytomy of several dinos and non-dinos. After excluding wild card taxa, 82 trees resulted with Pisanosaurus within the Silesauridae. Bremer support is low in their analysis, but Bootstrap support is high in the LRT.

Discussion
Agnolín and Rozadilla discuss several traits of Pisanosaurus (typically related to herbivory) and their appearances elsewhere within the Archosauria. They find no epipophyses in the cervicals, but Haya lacks these, as well on the pertinent first two verts. Agnolín and Rozadilla note “The vertebral centra are very elongate and transversely compressed, differing from the short and stout dorsal vertebrae of known ornithischians, including heterodontosaurids.” They do not realize the close relationship of Pisanosaurus to sauropodomorphs like Saturnalia and the basalmost ornithischian, Chilesaurus, both with elongate dorsals. Agnolín and Rozadilla made a “tentative reconstruction” of the pelvis (Fig. 1), but it bear little to no resemblance to the in situ fossil. In every comparison made, Agnolín and Rozadilla delete or ignore Haya and related taxa and thus recover semi-blind results.

Today and in the future
we can’t keep going back to the same short lists of taxa for our inclusion sets. We know of so many more now that need to be included in phylogenetic analyses. The LRT can be your guide.

References
Agnolín FL and Rozadilla S 2017. Phylogenetic reassessment of Pisanosaurus mertii Casamiquela, 1967, a basal dinosauriform from the Late Triassic of Argentina. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2017.1352623
Ferigolo and Langer 2006. A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone. Historical Biology, 2006; 1–11, iFirst article
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History, 352, 1–292.

wiki/Sacisaurus
wiki/Pisanosaurus
wiki/Haya

 

New phylogeny of Stegosauria

A few problems here.
Raven and Maidment 2017 have produced a phylogeny of the clade Stegosauria (Fig. 1). Unfortunately it splits stegosaur proximal outgroups (in the large reptile tree (LRT, subset in Fig. 2) from stegosaurs. It splits stem or basal ankylosaurs from derived ankylosaurs. And it supports a clade, the Thyreophora, that was found to be paraphyletic in the LRT. Finally, it nests Laquintasaurus with Scutellosaurus, contra the LRT.

Figure 1. Phylogeny of Stegosauria according to Ravena and Maidment 2017. Yellow/green taxa are stegosaurs and their ancestors in the LRT. Gray taxa are nodosaurs and ankylosaurs. Blue taxon is a basal ceratopsian. Magenta taxon is lost. The LRT nests stegosaurs apart from ankylosaurs, thus the Thyreophora is paraphyletic and invalid.

Figure 1. Phylogeny of Stegosauria according to Ravena and Maidment 2017. Yellow/green taxa are stegosaurs and their ancestors in the LRT. Gray taxa are nodosaurs and ankylosaurs. Blue taxon is a basal ceratopsian. Magenta taxon is lost. The LRT nests stegosaurs apart from ankylosaurs, thus the Thyreophora is paraphyletic and invalid.

Raven and Maidment appear to have chosen outgroups
for Stegosauria instead of letting a larger gamut analysis choose them. So, once again, taxon exclusion lessens the effectiveness of and confidence in a hypothesis.

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 2. Subset of the LRT: Phytodinosauria with a focus on Stegosauria (yellow green).

References
Raven TJ and Maidment SCR 2017. A new phylogeny of Stegosauria (Dinosauria, Ornithischia). Palaeontology 2017:1–8.
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR (2014) A palaeoequatorial Ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281(1791): 20141147. http://dx.doi.org/10.1098/rspb.2014.1147

Laquintasaura: verrrry basal ceratopsian from the Early Jurassic

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 1. Subset of the LRT focusing on the Phytodinosauria. Here Laqunitasaura nests at the base of the Ceratopsia.

I still hold to the hypothesis|
that a phylogenetic analysis that is able to lump and separate taxa is better than one that cannot do this. In the large reptile tree (LRT, 989 taxa), Laquintasaura venezuelae (Barrett et al. 2014; Early Jurassic, 200mya ~1m in overall length; Fig. 2) nests at the base of the ceratopsia (outside of Hexinlusaurus and Yinlong) and not far from the base of the Ornithopoda (outside of Changchunsaurus). It is very plesiomorphic and very early even for an ornithischian, let alone a ceratopsian.

Figure 1. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus).

Figure 2. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus). Compare to premaxillary teeth in figure 3.

Barrett et al. were not so sure where Laquintasaura nested
as they reported, “A strict consensus of these 2160 MPTs places Laquintasaura in an unresolved polytomy with the major ornithischian clades Heterodontosauridae, Neornithischia and Thyreophora along with other early ornithischian taxa, such as Lesothosaurus.”

The Barrett et al. diagnosis reports:
“Laquintasaura can be differentiated from other early ornithischians by the following autapomorphic combination  of dental characters: cheek tooth crowns have isosceles-shaped outlines, which are apicobasally elongate, taper apically, are mesiodistally widest immediately apical to the root/crown junction, possess coarse marginal denticles extending for the full lengths of the crown margins, and possess prominent apicobasally extending striations on their labial and lingual surfaces. Postcranial autapomorphies include: sharply inflected dorsal margin of ischium dorsal to the obturator process; femoral fibula epicondyle medially inset in posterior or ventral views; and astragalus with a deep, broad, ‘U’-shaped notch in anterior surface.”

I had no access to the fossil(s).
And I had to trust the drawing produced by Barrett et al. (Fig. 1) for my data. Contra the Barrett et all. analysis, there was no loss of resolution with Laquintasaura in the LRT.

Figure 2. The skull of Yinlong a basal certatopsian.

Figure 3 The skull of Yinlong a basal certatopsian. Those premaxillary teeth are quite similar to those figure in Barrett et al. for Laquintasaura. Note the dorsal naris, horizontal ventral premaxilla.

References
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR. 2014. A palaeoequatorial ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281:20141147. http://dx.doi.org/10.1098/rspb.2014.1147

Baron 2017: 21 ‘unambiguous’ theropod/ornithischian synapomorphies don’t pan out

Yesterday we looked at Baron et al. 2017, who proposed uniting Ornithischia with Theropoda to the exclusion of Sauropodomorpha + Herrerasaurus and kin (Fig. 1), among several other relationships not recovered by the large reptile tree (LRT, 980 taxa). They did so by excluding dinosaur outgroup taxa recovered by the LRT, like Gracilisuchus and Pseudhesperosuchus, while including inappropriate outgroup taxa, like pterosaurs, Lagerpeton and kin, and poposaurs, like Silesaurus. In paleontology this is known as ‘cherry-picking’ and yesterday’s post showed how cherry-picking outgroup taxa, like the pterosaur Dimorphodon, can lead to having scansoriopterygid basal birds recovered as basal dinosaurs. Baron et al. did this by focusing on, and mis-scoring minute traits, not readily visible from an arm’s length of viewing. See below.

By contrast,
the LRT provides a very long list of candidate outgroup taxa going back to Devonian tetrapods and lets the computer decide the topology of the reptile family tree including the Dinosauria. It thereby minimizes a priori bias and subjective or traditional opinion in taxon selection. The LRT also employs more readily observable traits and few to no minutia. The LRT is fully resolved with high Bootstap scores, in contrast to the Baron et al. trees.

Today we’ll dive deeper into Baron et al. 2017
They start with a false premise by supporting the clade ‘Ornithodira‘, which is a junior synonym for Reptilia, since it includes pterosaurs. In the LRT pterosaurs share a last common ancestor with dinosaurs in the Devonian amniote Tulerpeton, the last (and only) known common ancestor of all reptiles.

Baron et al. report, “A formal hypothesis proposing dinosaur monophyly was proposed in 1974, and consolidated in the 1980s. As a direct result of these and other analyses, Ornithischia and Saurischia came to be regarded as monophyletic sister-taxa: this hypothesis of relationships has been universally accepted ever since.” Not in the LRT, which recovered evidence in 2011 to support a clade Phytodinosauria, uniting Sauropodomorpha with Ornithischia + several basal phytodinosaur genera.

Baron et al. report, “No studies on early dinosaur relationships have included an adequate sample of early ornithischians and the majority of studies have also excluded pivotal taxa from other major dinosaur and dinosauromorph (near dinosaur) lineages.” The LRT did so include more than an adequate sample of all pertinent taxa.

Baron et al. report, “In order to examine the possible effects of these biases on our understanding of dinosaur evolution, we carried out a phylogenetic analysis of basal Dinosauria and Dinosauromorpha and compiled, to our knowledge, the largest and most comprehensive dataset of these taxa to date.” No, the LRT is larger and more comprehensive. It is under the authority of the LRT that mistakes can be revealed in the Baron et al. study.

Baron et al. report,Although this study has drawn upon numerous previous studies, no prior assumptions were made about correlated patterns of character evolution or dinosaur interrelationships.” Not true. Their exclusion of appropriate and inclusion of inappropriate taxa demonstrates their assumptions. By this statement they appear to have fooled themselves as well, based on the taxon list of the the LRT.

Baron et al. report, “We analysed a wide range of dinosaurs and dinosauromorphs, including representatives of all known dinosauromorph clades.” Not true. They did not include dinosaur outgroup taxa recovered by the LRT (Fig. 2).

Figure 1. According to Baron et al. 2017 these taxa are related in this fashion.

Figure 1. According to Baron et al. 2017 these taxa are related in this fashion. The LRT does not recover these relationships.

Here is the ‘meat’ of todays post:
Baron et al. report, “The formation of the clade Ornithoscelida [Ornithischia + Theropoda] is strongly supported by 21 unambiguous synapomorphies including: [comments follow]

  1. an anterior premaxillary foramen located on the inside of the narial fossa [present in basal sauropodomorphs Leyesaurus and Pampadromaeus.]
  2. a sharp longitudinal ridge on the lateral surface of the maxilla [present in basal sauropodomorph Pantydraco.]
  3. a jugal that is excluded from the margin of the antorbital fenestra by the lacrimal–maxilla bone contact (this appears convergently in some ‘massospondylids’) [not excluded in Tawa or Coelophysis.]
  4. an anteroventrally oriented quadrate [seemingly all dinosaurs have this sort of quadrate orientation]
  5. short and deep (length of more than twice the dorsoventral height) par occipital processes [apparently a mistake because the figure 2 caption text lists, “elongate par occipital processes.”]
  6. a post-temporal foramen that is entirely enclosed within the par occipital process [I cannot check this minutia with available data]
  7. a supraoccipital that is taller than it is wide [I cannot check this minutia with available data]
  8. a well-developed ventral recess on the parabasisphenoid [I cannot check this minutia with available data]
  9. a surangular foramen positioned posterolaterally on the surangular [I cannot check this minutia with available data]
  10. an entirely posteriorly oriented retroarticularprocess, which lacks any substantial distal upturn [present in basal sauropodomorph Pantydraco.]
  11. at least one dorsosacral vertebra anterior to the primordial pair [I cannot check this with available data]
  12. neural spines of proximal caudals that occupy less than half the length of the neural arches (which are also present in some sauropodomorphs, but absent in Herrerasauridae, Guaibasaurus, and nearly all sauropodomorphs as or more derived than Plateosaurus [it doesn’t matter about derived taxa, we’re looking only at basal taxa, this is a variable trait not present on Scuttelosaurus, but present on Efraasia]
  13.  scapula blade more than three times the distal width (also found in Guaibasaurus) [also found in Herrerasaurus and Sajjuansaurus]
  14. humeral shaft that has an extensively expanded ventral portion of the proximal end, creating a distinct bowing (convergently acquired in plateosaurids and more derived sauropodomorphs) [sounds like a deltopectoral crest, If so, this is universal among Dinosauria]
  15. absence of a medioventral acetabular flange (which was also lost in plateosaurids and more derived sauropodomorphs) [unable to check this minutia with available data]
  16. a straight femur, without a sigmoidal profile (which was also acquired by more derived sauropodomorphs, but absent in basal forms such as Saturnalia and Pampadromaeus, and is also absent in Herrerasauridae) [also absent in Eoraptor, present in Pantydraco]
  17. a well-developed anterior trochanter that is broad and at least partly separated from the shaft of the femur [absent in Eodromaeus and otherwise difficult to check with available data]
  18. a strongly reduced fibular facet on the astragalus [unable to check this minutia with available data]
  19. a transversely compressed calcaneum with reduced posterior projection and medial process [unable to check this minutia with available data]
  20. a first metatarsal that does not reach the ankle joint, but that is instead attached ventrally to the shaft of metatarsal II [not in Tawa, Scelidosaurus or Haya]
  21. fusion of the distal tarsals to the proximal ends of the metatarsals.[not in Tawa, Scelidosaurus or Haya]

Note
several of these ‘traits’ are minutia. The LRT uses larger traits that one can see and measure from a greater viewing distance or with published figures.

According to Baron et al.
other shared features uniting Ornithischia with Theropoda included: [comments again follow]

  1. a diastema between the premaxillary and maxillary tooth rows of at least one tooth crown’s length [not in Eodromaeus, Emausaurus]
  2. an extended contact between the quadratojugal and the squamosal bones [not in a wide variety of ornithischians]
  3. an anterior tympanic recess (convergently acquired in Plateosaurus) [unable to check this minutia with available data]
  4. a fibular crest on the lateral side of the proximal portion of the tibia (described as present in Eoraptor, although we could not confirm its presence, which is also absent in Tawa [unable to check this minutia with available data]
  5. an oblique articular end of the tibia in which the outer malleolus extends further distally than the inner malleolus (although this appears to be absent in Pisanosaurus [unable to check this minutia with available data]
  6. fusion of the sacral neural spines [unable to check this minutia with available data, often hidden by the pelves]
  7. presence of an antitrochanter on the ilium [unable to check this minutia with available data]
  8. reduction of the distal end of the fibula [not in Buriolestes, Tawa, Scelidosaurus]
  9. fusion of the tibia, fibula and proximal tarsals into a tibiotarsus [not in BuriolestesTawaScelidosaurus]
  10. fusion of the metatarsals [not in BuriolestesTawaScelidosaurus]

Apparently Baron et al. were not
thorough enough in these assessments and again depended for the most part, on minute traits rather than large, readily observable ones, Apparently referees were likewise not thorough enough on their vetting of this manuscript. I imagine because it is difficult to do when all the data is not gathered into a single readily reference resource, like RepitleEvolution.com. The present vetting took only a few hours.

According to Baron et al. 
“20 additional steps would be needed to recover Saurischia as previously defined.” But that’s a false goal according to the LRT results that do not recover a clade Saurischia. And with such bad scoring (see above) this goal turns out to be a misstep, not a step.

Baron et al. report,
“in our hypothesis a fully carnivorous feeding strategy is not recovered as the plesiomorphic condition for Dinosauria and we are forced to interpret some of the anatomical similarities between herrerasaurids and theropods as convergences.” In the LRT, herrerasaurids are basal to all remaining dinosaurs, yet have certain autapomorphies that indicate an older, more plesiomorphic last common ancestor of all dinosaurs is awaiting discovery.

Baron et al. report, 
“Dinosauria is recovered in a polytomy with Silesauridae and the enigmatic Late Triassic British taxon Saltopus elginensis.” In the LRT, both of those outgroups are surrounded by other taxa that separate them from Dinosauria.

Figure 1. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale according to the LRT.  Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Herrerasaurus, Tawa and Eoraptor.

Several years ago
the above (Fig. 2) was published online. It remains the best graphic portrayal of basal Dinosauria and their outgroups to date, based on a much larger number of outgroup taxa than has ever been published before. Unfortunately, the Baron et al. team did not take advantage of this readily available and thoroughly verified hypothesis.

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature  543:501–506.