Dinosaurs Rediscovered, new book by Dr. Michael Benton

FIgure 1. Dinosaurs rediscovered by MJ Benton book cover.

FIgure 1. Dinosaurs rediscovered by MJ Benton book cover.

Dr. Stephen Brusatte wrote
on the cover: “If you want to know how we know what we know about dinosaurs, read this book!”

‘Amazon Customer’ wrote
at the book’s website, “Nice production, but highly biased and speculative.” (more below)

Dr. MJ Benton is professor of vertebrate paleontology and head of the Palaeobiology Research Group at the U of Bristol, England. He has written more than fifty books, including the standard textbooks in palaeontology.

From the intro:
“One by one the speculations about evolution, locomotion, feeding, growth, reproduction, physiology, and, finally, color have fallen to the drive of transformation. A new breed of dinosaur palaeobiologist replace the older ones, and they have applied a hard eye to the old speculations. Smart lateral thinking, new fossils, and new methods of computation have stormed the field.”

Funny though,
Scleromochlus (Fig. 2) is not mentioned. Benton 1999 promoted this genus close to the origin of pterosaurs and in the book he maintains that pterosaurs remain close to the origin of dinosaurs with no further explanation. Evidently Scleromochlus is no longer in favor. Nearly 20 years ago Peters 2000 invalidated the pterosaurs-close-to-dinosaurs = ornithodire hypothesis by testing Benton’s cladogram and three others by simply adding taxa overlooked and poorly scored by Benton and other prior authors. But let’s move on…

Figure 3. According to the AMNH, Scleromochlus is "one of the closest early cousins of pterosaurs." Oddly, they gave it the skull of Longisquama. Note the vestigial hands. These cannot elongate to become wings and pedal digit 5 is a vestige that cannot elongate to match basal pterosaurs.

Figure 2. According to the AMNH, Scleromochlus is “one of the closest early cousins of pterosaurs.” Oddly, they gave it the skull of Longisquama. Note the vestigial hands. These cannot elongate to become wings and pedal digit 5 is a vestige that cannot elongate to match basal pterosaurs.

Chapter 1 — Origin of the Dinosaurs
Even in 2019, Benton writes, “One thing is known for sure: the dinosaurs originated during the Triassic period, between 252 and 201 million years ago. Nearly everything else is uncertain.” This is not exactly a teaser, because it does not jive with what Benton writes earlier (Benton 1999) and later (see below).

Benton reports
that he raised traditional eyebrows back in 1983 when he suggested the old standard model of one group/clade giving way to another should be replaced with a scenario in which new clades only appeared and/or radiated after an extinction event. This view makes great sense and is supported by strong evidence. Ironically, Benton reports, “This new idea of mine was probably quite annoying for the established paleontologists.” Now that he’s older, the tables have turned and it’s Benton’s turn to be annoyed. Philosophically he has taken the place of his 1983 opponent and mentor, Dr. Alan Charig in that Benton now refuses to consider, test or replace invalid scenarios with new ones.

Let’s not forget…
in his unbiased youth, Benton 1985 used an early form of phylogenetic analysis to show that pterosaurs were sister taxa to lepidosaurs, closer to lizards than to dinosaurs by a long shot. Now that this hypothesis has become heterodox, he and others have avoided it ever since by selective deletion of pertinent taxa.

Figure 2. Cladogram from Benton 1985 in which he nests pterosaurs closer to lepidosaurs than to dinosaurs and other archosaurs.

Figure 2. Cladogram from Benton 1985 in which he nests pterosaurs closer to lepidosaurs than to dinosaurs and other archosaurs. Lots of confusion here due to taxon exclusion going back to the advent of Reptilia (= Amniota).

A subchapter follows
on the lepidosaur rhynchosaur, Hyperodapedon (Benton 1983), where Benton first published on taxa he was given to worth with, but made the phylogenetic mistake of lumping rhynchosaurs with archosauromorphs. This was due to taxon exclusion.

The next subchapter, “What was the first dinosaur?”
Benton correctly identifies one of the first dinosaurs as Herrerasaurus. That agrees with the large reptile tree (LRT, 1562 taxa) which uses the last common ancestor method for determining clade member inclusion.

Basal bipedal dinosauriformes, from Lagerpeton through Marasuchus, Lewisuchus, Asilisaurus, Sacisaurus and Silesaurus.

Figure 3. Basal bipedal ‘dinosauriformes’, from Lagerpeton through Marasuchus, Lewisuchus, Asilisaurus, Sacisaurus and Silesaurus, according to Nesbitt (2011). The LRT does not support this listing or sequence.

Then Benton reports on the poposaur
dinosaur-mimic, Silesaurus (Fig. 3), the Early Triassic ichnite Prorotodactylus, and another poposaur dinosaur-mimic, Asilisaurus (Fig. 3). Benton reports, “The discovery of Asilisaurus unequivocally re-dated the origin of dinosaurs back from 230 to 245 million years ago, or older.” There is little to differentiate Asilisaurus from Silesaurus. Both remain poposaurs and dinosaur-mimics, unrelated to the dinosaurs, except through basal bipedal crocodylomorphs, which Benton avoids. So, taxon exclusion strikes Benton, once again.

Quote here, an anonymous, but well-educated, review from Amazon.com:
“Dinosaurs Rediscovered is an engagingly written and highly personalized account of dinosaurs, generally covering the field’s perceived advances from 1980 to the present. The publisher Thames & Hudson did an outstanding job in producing the book, formatting, and in the selection of paper.

“The author notes that the field transformed from 1984 onwards by cladistic methods, and the resulting phylogenetic trees or cladograms have thus become the “basis” for evaluating evolutionary models and all things dinosaurian, including anatomical reconstructions, physiology, behaviour, etc. The work described is rather restricted, with most emphasis given to the University of Bristol’s vertebrate palaeontologists, often ignoring important discoveries from other groups, and regrettably ignoring most conflicting evidence. The most egregious is the complete omission of any discussion of the persisting problem of dinosaur/avian digital homology.

“Benton begins with the discovery (in his laboratory) of microsomes known as melanosomes from SEMs of fibers from the back of the small theropod Sinosauropteryx, that were described as “proto-feathers” back in 1998. However, there was never any evidence that the fibers had any feather affinity, and many who studied the specimens found an external coating of small tubercular scales above the layer of fibers —- since prepared away and lost! It is clear, however, that the fibers called proto-feathers or “dino-fuzz” were beneath the skin and therefore not feathers. Too, as South African palaeontologist Lingham-Soliar showed in several important papers (not cited) the structures called melanosomes cannot be interpreted from the scanning electron micrograph (p. 8) as being within the fibers. Speculation!

“Plate V shows a fuzzy Sinosauropteryx with a ring tail like that of a civit or ring-tailed cat!! Then there is an outlandish image of a reconstruction of the Jurassic urvogel Anchiornis (incorrectly called a troodontid, see Pei ref below), as a terrestrial animal; but the feathers emanating from the legs and feet would have been a hindrance in ground locomotion. New fossil images (Pei et al., 2017 AMNH Bull 411, 66 pp) show claws consistent with tree-trunk climbing, similar to those of other urvogels. Plate VI shows photos of a “dinosaur tail” in amber, but there is NO evidence it is from a dinosaur and is most likely an enantiornithine bird.

“The section on dinosaur evolution is straight forward, but laden with speculation, and given the massive convergence among various archosaur lineages during the Triassic it is difficult to have full faith in the interpretations; and authors from Cambridge and the British Museum have questioned the time-honored phylogeny (pp. 82-84).

“Most of the remainder of the book is a romp through the various dinosaurian groups, with comments on everything from brains and internal organs to behaviour. Archaeopteryx is depicted as an earth-bound runner (p. 112), with open wings (like no living avian cursor – e.g. capercallie, chicken, etc.), despite the fact that Manchester’s Derek Yalden showed conclusively that the urvogel’s claws were those of a trunk-climber, quite similar in structure to those of woodpeckers and climbing mammals.

“Benton notes (122) without reservation that Sinosauropteryx “was the first dinosaur to have its feather colour determined”—-and on page 123 he shows a feathered Caudipteryx with avian wing feathers and notes “it is clearly a theropod and not a bird” in contrast to numerous papers arguing that it is a secondarily flightless bird. If not, flight feathers, a perfection of aerodynamic engineering, would have to evolve in a non-flight context, a real stretch of biological thought!

“In chapter 5 “Jurassic Park” he seems ambivalent about reconstructing dinosaurs from ancient DNA, although most would agree that it is impossible. Certainly Mary Schweitzer’s supposed discovery of T. rex blood vessels and proteins has been firmly refuted. He comments on small genome size in birds and dinosaurs, but the studies conflated the two groups, and small genome size is to be found in flying animals: bats, pterosaurs and birds. Growth studies on dinosaurs are discussed but much of that has recently been brought into question. Allosaurus (188) and Tyrannosaurus, with no evidence, are shown with a feathered coat! Diplodocus (210) is shown with neck high in the air, a posture disputed by computer-generated imaging. Benton appears to favor the model of flight origin of Dial and Heers, but such a model requires a fully developed flight apparatus, and both putative dinosaurian ancestors of birds, urvogels, and even archosaurian antecedents, all lacked the pectoral architecture to enact this model. It just will not work. Much speculation!

“Finally, although there is no citation in the text, the monolithic bibliographic listing in the section on ‘Further Reading’ is alarming; it appears highly selected to bolster the Bristolian view of dinosaurs, while ignoring any contrary views, many of which are supported by solid scientific data. Most disturbingly, the discoveries by Chinese palaeontologists, especially those at Beijing’s Institute of Paleontology and Paleoanthropology, which in reality propelled the recent revolution in our knowledge of dinosaur/bird evolution is largely ignored.”

Conclusion:
Dr. Benton’s new book gave us old, misguided and too often invalid information. In 2019 we know better how taxa are related to one another and Benton should have known better, too. Taxon exclusion (= phylogenetic context) seems to be his number one problem because his descriptions and illustrations of specimens are typically excellent. After messing up on his first paper (removing rhynchosaurs from rhynchocephalians), Benton’s reputation and output continue to be tarnished with his latest book and many of his recent papers all due to taxon exclusion. On the other hand, and in the present climate, Dr. Benton understands there is no consequence for ignoring new hypotheses. If only he could recall what it was like for him back in 1983, trying to promote his own new scenario to the establishment.

Those paleo professionals who wrote glowing reports
for this book should also have known better, but allegiance can sometimes trump good science. Author and paleontologist, Stephen Brusatte (quoted above) was a student at Bristol, where Benton teaches.

A wide gamut phylogenetic analysis based on specimens
is a necessary ingredient before, during and after any specimen description. It remains the one and only way to minimize taxon exclusion.


References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Benton MJ 2019. Dinosaurs rediscovered. Thames & Hudson.
Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RMH and Tsuji LMA 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464 (7285): 95–98. doi:10.1038/nature08718. PMID 20203608.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

Three basic mistakes in a new dino origin paper

Marsola and Langer 2019
are trying their best to rely on traits to define dinosaurs and their outgroups. This is always a mistake. The last common ancestor method is the only one that works. Otherwise you risk ‘Pulling a Larry Martin‘.

Marsola and Langer 2019
also rely on previously published cladograms without testing which one, if any, is the best. This is also always a mistake. It’s not that difficult to find fault with cladograms like these… or to build your own. After all, they are scientists. That is their job. Don’t blindly accept the work of others. Test it.

Marsola and Langer 2019
also exclude taxa that, if added, would radically change these cladograms. Taxon exclusion is also always a mistake. It’s not that difficult to add taxa. I do it every week.

Figure 1. Three cladograms from Marsola and Langer 2019, essentially copied from other sources and more or less trusted despite their differences.

Figure 1. Three cladograms from Marsola and Langer 2019, essentially copied from other sources and more or less trusted despite their differences.

Why waste the readers’ time with invalid cladograms?
The large reptile tree (LRT, 1530 taxa) has been online for several years. The taxa therein (from fish to birds) can be used along with any character list in your collection.

In the meantime,
we looked at dinosaur origins years ago here along with an illustration of the pertinent taxa below (Fig. 2).

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

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

Why do paleontologists not test new hypotheses?
Good question. Is it because they are employed as teachers who run the risk of informing their students that assigned textbooks are out-of-date in small or large part? Is it because they want to be the ones to announce a paradigm shift from their own studies? Is it because they risk the ire of colleagues who are also teachers with their own textbooks? Is it really, when you get down to it, all about money? Reputation? Sticking one’s head in the sand (= maintaining an invalid status quo) is always a mistake.


References
Marsola JC de A and  Langer MC 2019. Dinosaur Origins. Reference Module in Earth Systems and Environmental Sciences 2019
doi: https://doi.org/10.1016/B978-0-12-409548-9.11846-9

SVP 2018: The clade ‘Ornithoscelida’ tested

Mortimer et al. 2018
reevaluate taxa and scores for the proposed clade ‘Ornithoscelida’ (Baron, Norman and Barrett 2017) and find it less parsimonious than alternatives. The authors, “find hundreds of questionable scores, many characters are correlated with each other, score for multiple variables at once, or are formed in such a way that potential homology is masked.” 

After repairing scores,
the authors report, “none of these experiments supported Ornithoscelida over Saurischia.” Their results show:”that phylogenetic analysis of morphological data is highly vulnerable to typographic errors and other accidental, unsystematic misscores in data matrices; both quantity and quality of scores are important.”

We looked at
the Ornithoscelida hypothesis earlier here, here, here, and here. It is not supported by the large reptile tree (LRT, 1313 taxa, subset Fig. 1), which supports the hypothesis of a Theropoda-Phytodinosauria dichotomy splitting Dinosauria after the Herrerasaurus clade.

Importantly
the outgroup taxa to the Dinosauria must be recovered correctly. At present few to no other studies have included a robust selection of bipedal crocodylomorphs, which nest as the sister group to the Dinosauria in the LRT. Together only Dinosauria and Crocodylomorpha make up the Archosauria in the LRT.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria.

Scoring errors
are found in all (yes, all) phylogenetic analyses, including the LRT. One way to ‘eyeball’ whether an analysis is close to recovering actual evolutionary events is to look at every node for a gradual accumulation of derived traits. Key to this ideal is the inclusion of a sufficient number of relevant taxa. The LRT provides a good guide for taxon selection. As it grows larger it becomes a self-healing cladogram where imprecisely nested taxa reveal themselves. Some scores, when corrected, cement relationships. Other scores crack them apart.

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543:501–506.
Mortimer M, Gardner N, Marjanovic D and Dececchi A 2018. Ornithoscelida, phytodinosauria, saurischia: stesting the effects of miss cores in matrices on basal dinosaur phylogeny. SVP abstracts.

SVP 2018: More complete post-crania for Dromomeron

Smith, Irmis, Nesbitt and Turner 2018 report
on new Dromomeron material from the Petrified Forest, Late Triassic, Chinle Formation. Previously Dromomeron was known from a femur similar to that of Lagerpeton, a traditional dinosaur ancestor that nests with the chanaresuchid, Tropidosuchus in the large reptile tree (LRT, 1308 taxa; Fig. 1; Novas and Agnolin 2016).

Smith, et al., write:
“Discovery of the non-dinosauriform dinosauromorph Dromomeron romeri from the HQ established that early dinosauromorphs were contemporaries with dinosaurs for a substantial part of the Late Triassic, refuting hypotheses of rapid transition to dinosaur dominated faunas. This discovery was based on hindlimb elements, which diagnosed
Dromomeron as a member of Lagerpetidae, the sister group to all other dinosauromorphs.
Despite a flurry of new discoveries, the anatomy of lagerpetids remains poorly known. We
describe new specimens of Dromomeron romeri, including an articulated post-cranium,
further revealing lagerpetid anatomy.”

Importantly the foot of Dromomeron is different than that of Lagerpeton.
“An articulated metatarsus is short relative to the tibia, in contrast to the elongate metatarsus of Lagerpeton chanarensis and most dinosauromorphs. MTIII is the longest, with sub equal MTIV/MTII, and MTI 50% the length of MTII. This configuration differs starkly from the highly modified metatarsus of Lagerpeton.” 

Interesting that these authors seem to have ignored
the abstract from two years ago by Novas and Agnolin 2016, who also found Lagerpeton nested as a derived proterochampsid, confirming of an earlier blogpost here in 2011. No other proterochampsid has a longer metatarsal 3 than 4.

Archosauriform taxa with metatarsal 3 the longest:

  1. Basal Dinosauria
  2. Gracilisuchus (and no other crocs, which might mean Romer made a mistake)
  3. Most erythrosuchids through poposaurs (many derived exceptions)
  4. Champsosaurus

So maybe Dromomeron is a dinosaur. Not a lagerpetid.
That seems to be the most likely solution at this stage. No one wants to ‘Pull a Larry Martin’ and make a decision based on one or a few traits. Let’s see what a suite of traits gets us.

Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

Figure 5. Tropidosuchus in its two variants. In the holotype (above) the humerus is more robust and pedal digit 4 is gracile, as in Chanaresuchus (Fig. 3). In the referred specimen of Tropidosuchus (below) the humerus is smaller and pedal digit 4 is longer than 3, as in Lagerpeton. The rise to a bipedal configuration appears to coincide with the change in pedal proportions.

References
Smith N, Irmis R, Nesbitt SJ and Turner AH 2018. New material of Dromomeron romeri (Archosauria, Dinosauromorpha) from the Upper Triassic Chinle Formatin of New Mexico provides insight into the evolutionary morphology of early dinosauromorphs. SVP abstracts.
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

https://pterosaurheresies.wordpress.com/2016/11/13/you-heard-it-here-first-lagerpeton-is-not-a-dinosauromorph/

Fact checking dino books

As stated from the beginning
of this blog, I am more interested in clade origins and relationships than any other paleo topic (like diet or asteroid impact). So the following review of recent and important dino books will focus on what they say about the origin of dinos: i.e. what happens when taxon exclusion meets the LRT.

Figure 1. Dinosaurs a Concise Natural History by Weishampel and Fastovsky, editions 1, 2 and 3.

Figure 1. Dinosaurs a Concise Natural History by Weishampel and Fastovsky, editions 1, 2 and 3.

Dinosaurs: a concise natural history (Weishampel and Fastovsky 2009)
This book defines the living reptiles as: turtles + diapsids (including living birds)

That is outdated
according to the large reptile tree (LRT, 1240 taxa) where mammals are also reptiles, and diapsids are not monophyletic. According to the LRT reptiles can be defined as any archosauromorph (e.g. Eldeceeon, mammals, ichthyosaurs, archosaurs), plus any lepidosauromorph (e.g. Urumqia, captorhinids, turtles, lepidosaurs), their last common ancestor (e.g. the amphibian-like reptiles Silvanerpeton, Gephyrostegus) and all descendants.

In the W+F book there are two main clades of Diapsids: Lepidosauromorpha and Archosauromorpha.

This is outdated.
See above.

In the W+F book there are five main clades of Archosauromorpha: Rhynchosauria, Prolacertiformes, Crurotarsi (including Crocodylia), Pterosauria, Dinosauria.

This is outdated.
Their way-too-simplified-cladogram is what makes paleontology and evolution look bad due to taxon exclusion. No taxa display a gradual accumulation of traits in the W+F cladogram. You can’t have super specialized rhynchosaurs at the base of any large clade. They are terminal taxa arising from sphenodontids in the LRT. Pterosaurs share nothing in common with their purported W+F sisters, crocs and dinos. Pterosaurs actually arise from fenestrasaur, tritosaur lepidosaurs. Another terminal taxon, Tanystropheus, the poster-child for prolacertiforms is not related to Prolacerta in the LRT, but arises from Huehuecuetzpalli, Macrocnemus and Langobardisaurus, among others, not far from pterosaurs. Derived taxa in this clade share a nearly identical foot morphology.

The W+F book presents two hypotheses of dinosaur origins:

  1. pterosaurs + Lagosuchus + dinosaurs (Gauthier and Padian) = Ornithodira.
  2. Lagosuchus, Lagerpeton, Pseudolagoschus, Marasuchus (Sereno) = dinosaur precursors. Pterosaurs are more distantly related.

These two hypotheses are both outdated
Pterosaurs are lepidosaurs, unrelated to dinosaurs. Lagerpeton is a sister to the chanaresuchid, Tropidosuchus. Marasuchus is a theropod, not a dinosaur outgroup. In the LRT bipedal crocs are the proximal outgroups to dinosaurs.

________________________________________

Figure 2. Rise and fall of the dinosaurs by Brusatte 2018.

Figure 2. Rise and fall of the dinosaurs by Brusatte 2018.

The rise and fall of the Dinosaurs. Brusatte 2018. Don’t confuse this 2018 book with ‘The rise and fall of the dinosaur’ (singular, not plural) by Wallace 1987.

Unfortunately
Brusatte clings to his wrong-from-the-start hypothesis (Brusatte et al. 2011) that the first dinosaurs are represented by Prorotodactylus (Fig. 3) footprints in the Early Triassic (251 mya). Prorotodactylus tracks were actually made by tritosaur lepidosaurs, like Macrocnemus, with a small, symmetrical, 5-fingered manus and an asymmetric pes with a short digit 5.

Unfortunately
Brusatte’s mistake comes from a misunderstanding of reptile relationships, probably because he was schooled using the Weishampel and Fastovsky books (see above). Brusatte was familiar with the invalid Lagerpeton hypothesis of dinosaur origins because he was an undergrad student of Paul Sereno (see above). Thus Brusatte was ready to accept the asymmetric pedal track of  Prorotodactylus track as homologous with that of Lagerpeton. Brusatte was also a student of Mike Benton. You might remember, Benton infamously promoted the bipedal croc with tiny hands and no pedal digit 5, Scleromochlus, as a pterosaur sister. Later Benton joined with his other student, David Hone (Hone and Benton 2007, 2008) in deciding to include, then exclude Peters 2000 data on fenestrasaurs. In so doing Hone gained his PhD and pterosaur origins were taken back to the dark ages. We talked about professor/student influences earlier here. In my youth I was influenced by books and professors, so I know how readily that can happen. If the influence is valid, that’s fine. If not, that’s a problem.

Porotodactylus pes

Figure 2. Porotodactylus pes and manus ichnites. Latest Early Triassic.

The actual last common ancestor of all dinos (and all crocs, too) in the LRT is the Túcuman specimen wrongly attributed to Gracilisuchus, PVL 4597 (Lecuona and Desojo 2011; Fig. 4) which has been known for 7 years.

It’s unfortunately ironic
that as much as Dr. Brusatte loves tyrannosaurs, as co-author (Lü and Brusatte 2015) he also misidentified Zhenyuanlong as a dromaeosaurid, not a tyrannosaur ancestor, as we looked at earlier here. He also listed a number of unrelated taxa, like Dilong, as tyrannosaur ancestors in an earlier magazine article discussed here. So his track record regarding dino systematics is not validated in the LRT.

Figure 6. The closest known taxa to the Dinosauria, PVL 4597, is a tiny taxon (phylogenetic miniaturization) with erect hind limbs, a large and deep pelvis and a tiny calcaneal tuber.

Figure 4. The closest known taxon to the Dinosauria in the LRT, PVL 4597 (Lecuona and Desojo 2011, Ladinian (Late Miiddle Triassic). It is a tiny taxon (phylogenetic miniaturization) with erect hind limbs, a large and deep pelvis and a tiny calcaneal tuber.

Finally,
let’s remember that paleontology works at a snail’s pace. We’ve know that birds are dinosaurs since TH Huxley looked at Archaeopteryx in the 1860s, but workers were not keen to accept that. Then Ostrom 1969 echoed Huxley’s hypothesis with new discoveries of Deinonychus. Still to little to no progress in the paleo community.

According to
the Hartford Courant (2000), “In 1973, Ostrom broke from the scientific mainstream by reviving a Victorian-era hypothesis (see above) that his colleagues considered far-fetched: Birds, he said, evolved from dinosaurs. And he spent the rest of his career trying to prove it.” With the announcement of the first dinosaurs with feathers from China, Ostrom (then age 73) was in no mood to celebrate. He is quoted as saying, ““I’ve been saying the same damn thing since 1973, `I said, `Look at Archaeopteryx!’” Ostrom was the first scientist to collect physical evidence for the theory. Ostrom provoked a debate that raged for decades. “At first they said, `Oh John, you’re crazy,”’ Ostrom said in 1999.”

It wasn’t until dozens of Chinese specimens
appeared with feathers that paleontologists finally got out of their academic chairs and said in essence, ‘well, we better change our mind about feathers and dinosaurs, or else.’ The scaly theropods in the Jurassic Park/Jurassic World movies reflect that slow-to-accept mentality.

The Dinosaur Heresies book by Dr. Robert Bakker.

The Dinosaur Heresies book by Dr. Robert Bakker 1986.

Books should not just echo false tripes
and recirculate untenable cladograms. Books should break old paradigms and advance new and valid ideas. Case in point: The Dinosaur Heresies by Bakker 1986.

References
Bakker RT 1986. The dinosaur heresies. New theories unlocking the mystery of the dinosaurs and their extinction. Citadel Press.
Brusatte S, Niedźwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Brusatte S 2015. Rise of the Tyrannosaurs. Scientific American 312:34-41. doi:10.1038/scientificamerican0515-34
Brusatte S 2018. The rise and fall of the dinosaurs. Harper Academic. author interview
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. 
Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Lü J and Brusatte SL 2015. 
A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution. Scientific Reports 5, 11775; doi: 10.1038/srep11775.
Ostrom JH 1969. “Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana”Peabody Museum of Natural History Bulletin. 30:1–165.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Wallace J 1987. The rise and fall of the dinosaur. Gallery Books
Weishampel DE and Fastovsky DB 2009: Dinosaurs: a concise natural history. 3 editions. Cambridge University Press. pdf

wiki/Zhenyuanlong

https://pterosaurheresies.wordpress.com/2016/03/16/sometimes-it-takes-the-paleo-crowd-an-epoch-to-accept-new-data/

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/

The last common ancestor of all dinosaurs in the LRT: ?Buriolestes

Müller et al. 2018
describe a new dinosaur skeleton they attribute to Buriolestes shultzi (Cabreria et al. 2016, ULBRA-PVT280, Figs. 2, 3). In the large reptile tree (LRT, 2015 taxa; subset Fig. 1) the holotype now nests at the base of the Phytodinosauria. The referred specimen is different enough to nest between the herrerasaurs and all other dinosaurs. This, of course, removes herrerasaurs from the definition of the Dinosauria (Passer + Triceratops, their last common ancestor (= CAPPA/UFSM 0035) and all descendants).

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

 

Buriolestes schultzi (Cabreria et al. 2016; Late Triassic, Carnian; 230mya) was originally and later (Müller et al. 2018) considered a carnivorous sauropodomorph, but here two specimens nest as the basalmost dinosaur (CAPPA/UFSM 0035) and the basalmost phytodinosaur (ULBRA-PVT280).

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs.

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs. It should have a distinct name.

All cladograms agree that Buriolestes
is a very basal dinosaur. Taxon exclusion changes the tree topology of competing cladograms. The broad autapomorphic ‘eyebrow’ of the CAPPA specimen indicates it is a derived trait in this Late Triassic representative of an earlier genesis.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

The Müller et al. cladogram
combined both specimens attributed to Buriolestes (never a good idea, but it happens all the time). The Müller et al. cladogram excluded a long list of basal bipedal crocodylomorpha, but did include Lewisuchus. It excluded the archosaur outgroups PVL 4597Turfanosuchus and Decuriasuchus. The Müller et al. cladogram nested Ornithischia basal to Saurischia (= Herrerasauridae + Agnophitys, Eodromaeus, Daemonosaurus + Theropoda + Sauropodomorpha) with Buriolestes nesting between Eoraptor and Panphagia. The CAPPA specimen of Buriolestes is also a sister to the basalmost theropod, Tawa (Fig. 3)… and not far from the other basal archosaur, Junggarsuchus (Fig. 4).

Figure 8. The CAPPA specimen of Buriolestes compared to the more primitive Junggarsuchus, basal to the other branch of archosaurs, the crocs.

Figure 4. The CAPPA specimen of Buriolestes compared to Junggarsuchus, basal to the other branch of archosaurs, the crocs.

References
Cabreira SF et al. (13 co-authors) 2016. A unique Late Triassic dinosauromorph assemblage reveals dinosaur ancestral anatomy and diet. Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040
Müller RT et al. (5 co-authors 2018. Early evolution of sauropodomorphs: anatomy and phylogenetic relationships of a remarkably well-preserved dinosaur from the Upper Triassic of southern Brazil. Zoological Journal of the Linnean Society, zly009 (advance online publication) doi: https://doi.org/10.1093/zoolinnean/zly009

The assembly of the avian body plan (Cau 2018) pt. 1 of 3

Dr. Andrea Cau 2018 summarizes traditional knowledge
on the origin of birds breaking the process into three stages:

  1. Huxleyian stage: Early Triassic to Middle Jurassic the earliest ancestors of birds acquired postcranial pneumatisation, an obligate bipedal and digitigrade posture, the tridactyl hand and feather-like integument
  2. Ostromian stage: Middle to Late Jurassic is characterised by a higher evolutionary rate, the loss of hypercarnivory, the enlargement of the braincase, the dramatic reduction of the caudofemoral module, and the development of true pennaceous feathers.
  3. Marshian stage: Cretaceous. The transition to powered fl ight with the re-organisation of both forelimb and tail as fl ight-adapted organs and the full
    acquisition of the modern bauplan

This is a pretty good plan overall.
Unfortunately Dr. Cau uses an antiquated cladogram (Fig. 1) riddled with taxon exclusion (especially among the outgroups), so the details tend to get a little messed up. Let’s review the pluses and minuses.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

The Cau cladogram and LRT
both feature many of the same basal theropods at the beginning, birds at derived nodes and a variety of carnivores in between, with dromaeosaurs then troodontids leading to birds.

Dr. Cau opens his paper
with several paragraphs devoted to nomenclature. He finds the term ‘non-avian’ particularly irksome. Cau employed 132 taxa and 1781 (1431 informative) characters. He reports that he decided not to include pterosaurs as outgroup taxa. That shows wisdom.

Unfortunately
Cau was not wise to largely ignore basal bipedal crocodylomorphs, including such favorites as Scleromochlus and Gracilisuchus. Thankfully Lewisuchus made his list.

So Cau starts off with four very distant outgroup taxa (Euparkeria, Teleocrator, Dormomeron and Lagerpeton), and that is never good (relevant taxon exclusion, again). It also shows a lack of understanding that could have been had with a quick glance at the large reptile tree (LRT, 1213 taxa). That’s what it’s there for.

Cau 2018 Results
3072 shortest trees (vs. LRT has one, fully resolved tree, last time I tested the whole tree).

Here are Cau’s nodes:

  1. Teleocrater + Dinosauromorpha: Unfortunately this clade does not include the Crocodylomorpha, so it is invalid. ‘Dinosauromorpha’, at best, is a junior synonym of Archosauria in the LRT.
  2. Dinosaurormorpha: (Lagerpetids + Dinosauriformes). Unfortunately this clade does not include the Crocodylomorpha, so it is invalid. When more taxa are added, lagerpetids nest with Tropidosuchus among the chanaresuchidae. Thus,  ‘Dinosauriformes’, at best, is a junior synonym of Archosauria in the LRT.
  3. Dinosauriformes: (Marasuchus + Dracohors). More taxa move Lewisuchus into the Crocodylomorpha, Silesaurus into the Poposauria and Pisanosaurus deep into the Phytodinosauria.
  4. Dracohors: (includes Megalosaurus, but not Marasuchus). More taxa (e.g. Segisaurus, Procompsognathus) move Marasuchus into the Theropoda and other taxa as listed above in the LRT.
  5. Dinosauria: (Eodromaeus, Herrerasauridae, Sauropodomorpha and Ornithoscelida). This is too many taxa and shows a lack of understanding. No basal dichotomy can be made. The LRT defines Dinosauria as Theropoda + Phytodinosauria, their last common ancestor (Herrerasaurus) and all descendants.
  6. Ornithoscelida: (Ornithischia + Theropoda) Adding more taxa will split up and invalidate this clade, based on LRT results.
  7. Theropoda: (Coelophysoidea + Averostra) In the LRT several theropods are listed as outgroups in the Cau analysis and it includes the phytodinosaur, Chilesaurus. (Daemonosaurus is curiously absent from this paper). Almost toothless Limusaurus should nest with oviraptorids. Elaphrosaurus has not been tested in the LRT. The basalmost coelophysoid (with feathers!), Sinocalliopteryx, nests as a derived compsognathid in the Cau taxon list.
  8. Averostra: (Ceratosauria + Tetaneurae) The LRT recovers a clade of large carnivores between Sinocalliopteryx and Compsognathus. This clade includes ProceratosaurusDeinocheirus, Xiongguanlong, Suchomimus and Spinosaurus, taxa not employed by Cau. These taxa attract Guanlong and Dilong to this basal feathered clade, away from tyrannosaurs. Otherwise, the LRT and Cau both place the same long list of medium to large basal theropods in clades at the base of this clade/grade.
Figure 1. Cladogram subset of the LRT focusing on Theropoda.

Figure 2. Cladogram subset of the LRT focusing on Theropoda.

More tomorrow.

References
Cau A 2018. The assembly of the avian body plan: a 160-million-year long process. Invited Paper, Bollettino della Societa Paleontologica Italiana 57(1):1–25.

 

Redefining what makes a dinosaur

Ran across this online article (citation below)
summarized: “The once-lengthy list of “definitely a dinosaur” features had already been dwindling over the past few decades thanks to new discoveries of close dino relatives such as Teleocrater. With an April 2017 report of Teleocrater’s skull depression (SN Online: 4/17/17), yet another feature was knocked off the list.”

Evidently the only trait that is still on the list is a perforated acetabulum.

My résponse:
long time readers will recognize this answer:

The dear departed Dr. Larry Martin used to play this game. He’d say ‘tell me a character you think defines a clade and I’ll give you an exception.’ In dinosaur pelves, ankylosaurs are the exception that do not have a perforated acetabulum. The lesson: You can’t define a clade by a single or a dozen character traits. 

You can define a clade using a cladogram. A cladogram uses hundreds of traits to recover relationships including “the last common ancestors and all of its descendants.” On that basis Dinosauria include Herrerasaurus at the base and the first dichotomy splits Theropoda from Phytodinosauria. The proximal outgroup is the Crocodylomorpha, basal members of which were small and bipedal, like early dinosaurs. That means Archosauria includes only dinos and crocs. Teleocrater is in the lineage of stem Archosauria. Unfortunately, prior workers excluded many relevant taxa, which is why they did not recover these relationships. Cladogram, links and more data here: 
The last few items on the dinosaur list:
  1. Until Teleocrater came along, only dinosaurs were known to have a deep depression at the top of the skull, an attachment site for some jaw muscles probably related to bite strength.
  2.  Dinosaurs and some other dinosauromorphs such as Silesaurus opolensis have an enlarged crest on the upper arm bone where muscles attached
  3. Along with dinosaurs, dinosauromorphs S. opolensis and Asilisaurus kongwe may have had epipophyses, bony projections at the back of the neck vertebrae.
  4. An extra (fourth) muscle attachment site, called a trochanter, at the point on the femur that meets the hip is also found in dinosauromorph Marasuchus lilloensis.

Sources: S.J. Nesbitt et al/Nature 2017; S.L. Brusatte et al/Earth-Science Reviews 2010

Taxon exclusion. Phylogenetic analysis. Yada-yada. 

References
https://www.sciencenews.org/article/new-fossils-are-redefining-what-makes-dinosaur

Nesbitt et al. 2017 The earliest bird-line archosaurs and the assemblof the dinosaur body plan. Nature (Teleocrater paper).

Dinosaur family tree: Langer et al. responds to Baron et al. 2017 in Nature

Earlier
Baron et al. revised the dinosaur family tree by uniting Ornithischia with Theropoda to the exclusion of Herrerasaurus + Sauropodomorpha. Then Baron and Barrett 2017 moved Chilesaurus (Fig. 1) from Theropoda to Ornithischia, confirming the earlier hypothesis advanced here in 2015, but in the context of uniting Ornithischia with Sauropodomorpha (= Phytodinosauria) to the exclusion of Herrerasaurus + Theropoda.

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

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

Today
Langer et al. 2017 argue, “we evaluate and reanalyse the morphological dataset underpinning the proposal by Baron et al.5 and provide quantitative biogeographic analyses, which challenge the key results of their study by recovering a classical monophyletic Saurischia and a Gondwanan origin for dinosaurs. Our international consortium of early dinosaur evolution specialists has come together to critically assess the Baron et al.5 dataset.”

The Langer team recovered a traditional Saurischia/Ornithischia tree, but noted it would take only 2-3 additional steps to enforce a Sauorpodomorpha/ Ornithoscelida split, as recovered by the Baron team – this after changing 2,500 scorings (10% of the dataset). The Langer team also confirmed the origin of dinos in southern Pangaea and left with three conclusions (my comments follow):

  1. There is currently great uncertainty about early dinosaur relationships and the basic structure of the dinosaur family tree. Not in the large reptile tree (LRT, 1119 taxa)/
  2. Dataset construction is key. No, taxon inclusion is the key. Neither the Baron team nor the Langer team included the correct outgroup taxa nor a long list of basal dinosaur taxa (see below) that direct the tree topology toward the phytodinosaur clade.
  3. It is important to use appropriate computational analytical tools before making macro-evolutionary claims. No, taxon exclusion will lead to wrong results. Trait selection matters, but not as much. Scoring correctly matters, but not as much. Employing decades old software does not matter because the math and statistics are the same. Remember, only a poor workman blames his tools so don’t  blame the “computational analytical tools” for poor macro-evolutionary claims.

Bottom line:
The Langer team used the same incomplete taxon list as the Baron et al. team did. So they were looking for their ‘keys’ beneath the bright lamp, while the keys were lost in the dark alley they ignored.

This happens so often.

And
Baron et al. 2017 reply. “This  extensive re-scoring results in recovery of the ‘traditional’ topology, although with less resolution and very weak support; their result is statistically indistinguishable from the possibility that our topology provides a better explanation of the data. This weak support, despite these extensive changes, suggests that the ‘traditional’ tree struggles to account for many character distributions.”

And they disagree with many of the re-scorings. Their re-scoring of just Pisanosaurus reproduced the clade Ornithoscelida in their revised tree.

Both presented trees were poorly resolved.
The LRT is fully resolved. Baron et al. defended the possibility of a Northern origin for dinosaurs. That big ‘maybe’ does not follow the data in the LRT.

On a similar, but side note
Biology Letters was kind enough to publish my reply to the Baron and Barret 2017 paper on Chilesaurus, but much of it has bearing for today’s discussion. Here is that letter in its entirety:

Baron and Bennett [1] nest Chilesaurus [2] as the sister group to Ornithischia, rather than a tetaneuran theropod as previously proposed [2]. Unfortunately, the Baron and Bennett [1] taxon list, like the Novas et al. [2] taxon list before it, did not include many of the taxa essential to resolve this issue.

A larger study of over 1060 taxa [3] includes more taxa essential to resolve this issue. The matrix was created using MacClade [4]. Analyses were run in PAUP 4.0b10 [5] using a heuristic search and a Bootstrap/Jackknife search for 100 random addition replicates. Scores are indicated on the webpage.

On that cladogram Chilesaurus (Late Jurassic) nests as a basal ornithischian in a clade that also includes Daemonosaurus (Late Triassic) and Jeholosaurus (Early Cretaceous). The latter two taxa were not included in Baron and Bennett [1]. This clade of three taxa nested as a sister to the Sauropodomorpha with Leyesaurus at its base. The analysis recovered the clade Phytodinosauria as the sister taxa to the Theropoda. Herrerasaurus was the outgroup to these two clades as basalmost member of the Dinosauria. Basal phytodinosaurs not nesting within Sauropodomorpha + Ornithischia include Barberenasuchus, Eodromaeus, Eoraptor and Pampadromaeus.

On that cladogram Silesaurus nests within a clade Poposauridae outside the Archosauria. The clade Archosauria includes only the Crocodylomorpha + the Dinosauria. Lagerpeton nests with Tropidosuchus and other proterochampsids. The pterosaur, Dimorphodon, nests with lepidosaurs like Huehuecuetzpalli, Macrocnemus and Cosesaurus (the last of which had an antorbital fenestra by convergence [6, 7]). None of these are archosauriformes nor prolacertiformes [contra 7]. The following pertinent taxa were not included in Baron and Bennett [1]: Daemonosaurus, Jeholosaurus, Haya, Barberenasuchus, Buriolestes, Segisaurus, Procompsognathus, PVL 4597, Junggarsuchus, Pseudhesperosuchus, Carnufex, Trialestes, Gracilisuchus, Scleromochlus, Decuriasuchus, Turfanosuchus, Poposaurus, Lotosaurus, Shuvosaurus, Effigia and Tropidosuchus.

Chilesaurus was first nested as a basal ornithischian in April 2015 [8] in an earlier version of the above analysis, then with fewer taxa. With the addition of more pertinent taxa the position of Chilesaurus is indeed well resolved contra the previous e-letter [9].

1. Baron MG and Barrett PM 2017. A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biology Letters 13, 20170220.
2. Novas FE et al. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature 522(7556), 331.
3. http://www.ReptileEvolution.com/reptile-tree.htm .nex file link on that webpage
4. Maddison DR., & Maddison WP 2001 MacClade 4.08: Analysis of Phylogeny and Character Evolution. Version 4.03. Sinauer Associates.
5. Swofford D 2002 PAUP 4.0 b10: Phylogenetic analysis using parsimony. Sinauer Associates.
6. Ellenberger P. and de Villalta JF 1974. Sur la presence d’un ancêtre probable des oiseaux dans le Muschelkalk supérieure de Catalogne (Espagne). Note preliminaire. Acta Geologica Hispanica 9, 162-168.
7. Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
8.https://pterosaurheresies.wordpress.com/2015/04/28/chilesaurus-new-dinos…
9. King B 2017. Chilesaurus is not a basal ornithischian. http://rsbl.royalsocietypublishing.org/content/13/8/20170220.e-letters

References
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