More PVL 4597 post-crania

Lecuona et al. 2017 
redescribe the post-crania of the basal archosaur and basal Crocodylomorph (in the large reptile tree = LRT), Gracilisuchus. They used six specimens and recovered them as basal Suchia (= aetosaurs, rauisuchians and crocodylomorphs). The LRT does not recover these three monophyletic clades in one larger monophyletic clade. So the LRT does not support the ‘Suchia’ as a clade.

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

Figure 1. The PVL 4597 specimen attributed to Gracilisuchus by Lecuona et al. 2017, but nesting at the base of the Dinosauria in the LRT. The pelvis of Herrerasaurus is shown on frame 2 of this simple animation. 

Unfortunately
Lecuona et al. excluded from their analysis several taxa that nest close to Gracilisuchus in the large reptile tree. These include Saltopus and Scleromochlus, which nest as sisters to Gracilisuchus in the LRT. Lewisuchus is mentioned in the text and combined as a chimaera with Pseudolagosuchus, but I don’t see the combo in the published trees. Their cladogram includes several suprageneric taxa (always to be avoided) including ‘Pterosauromorpha’ (= pterosaurs + Scleromochlus, not recovered as a clade in the LRT as a clade and how would one score such an internally varied taxon??).

Lecuona et al. nest their purported Gracilisuchus specimens together.
By contrast the LRT nests PVL 4597 at the base of the Dinosauria.

Fortunately 
the authors provide more data on the provisional dinosaur outgroup taxon, PVL 4597, so far based on hind limb traits only (Lecuona and Desojo 2011. The preserved skull in the specimen has not yet been published.

As in the LRT
the authors also find a close relationship between Turfanosuchus and Gracilisuchus. Unlike the LRT, they nest Yonghesuchus between them. The LRT nests it as a sister to Dromicosuchus.

It’s not common for a specimen to be published in bits and pieces
The original pelvis data came out 6 years ago. The new data for PVL 4597 (Fig. 1) still lacks the skull, which will be published in the future. I have written to Dr. Lecuona encouraging an expansion of the taxon list. I also hope the suprageneric taxa will be broken up into lists of genera.

References
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Lecuona A, Desojo JB and Pol D 2017.
New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society zlx011 1–40.

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Pseudhesperosuchus fossil photos

Earlier I used
Greg Paul and José Bonaparte drawings of the basal bipedal croc Pseudhesperosuchus Bonaparted 1969) for data on this taxon. The specimen has some traits that lead toward the secondarily quadrupedal Trialestes. Together they are part of a clade that is closer to basal dinosaurs than traditional taxa paleontologists have been working with.

The drawings were great,
but I wondered what the real material looked like…and more importantly, what was real and what was not.

A recent request to
the curators at Miguel Lillo in Argentina was honored with a set of emailed jpegs from their museum drawers (Fig.1), for which I am very grateful. These were traced in line and color and reassembled with just a few unidentified parts left over (Fig. 2).

Figure 1. GIF movie of the skull of Pseudhesperosuchus showing the original drawing, the fossil and DGS tracings of the bones.

Figure 1. GIF movie of the skull of Pseudhesperosuchus showing the original drawing, the fossil and DGS tracings of the bones.

Pseudhesperosuchus jachaleri (Bonaparte 1969 Norian, Late Triassic ~210mya, ~1 m in length, was derived from a sister to Junggarsuchus and  Lewisuchus and was at the base of a clade that included Trialestes on one branch and the Dinosauria on the other branch.

Figue 1. A new reconstruction of the basal bipedal croc, Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Figue 2. A new reconstruction of the basal bipedal croc, Click to enlarge. Pseudhesperosuchus based on fossil tracings. Some original drawings pepper this image. Note the interclavicle, missing in dinosaurs and the very small ilium, only wide enough for two sacrals. The posterior dorsals are deeper than the anterior ones.

Much larger and distinct from Lewisuchus,
the skull of Pseudhesperosuchus had a smaller antorbital fenestra, an arched lateral temporal fenestra, a deeper maxilla and a large mandibular fenestra. The seven cervicals were attended by robust ribs.

The scapula and coracoid were each rather slender and elongated. An straight interclavicle was present. The forelimbs were long and slender. The radiale and ulnare were elongated, a croc trait. Only three metacarpals and no digits are known.

The ilium was relatively small, but probably longer than tall and not perforated. The femur remained longer than the tibia. The tarsus, if that astragalus is identified correctly, included a simple hinge ankle joint. Only two conjoined partial metatarsals are known.

There is a small box
full of little sometimes interconnected squares among the Pseudhesperosuchus material (Fig. 2, aqua colored). I’m guessing that those are osteoderms, and if so, were probably located along the back. These would have helped keep that elevated backbone from sagging in this new biped.

The improvements in the Pseudhesperosuchus data
changed a few scores, but did no change the tree topology. The large reptile tree (LRT) can be seen here.

It’s good to see what Pseudhesperosuchyus really looked like,
— or at least get a little closer to that distant ideal. Size-wise and morphologically, this largely complete specimen is closer to the basal dinosaur outgroup than any other currently included in the LRT. And yet it is also distinctly different as it shares several traits with Trialestes unknown in any dinosaur. As a denizen of the Late Triassic, Pseudhesperosuchus represents a radiation that occurred tens of millions of years earlier, probably in the Middle Triassic. None of this clade survived into the Jurassic, as far as we know.

References
Bonaparte JF 1969. Dos nuevos “faunas” de reptiles triásicos de Argentina. Gondwana Stratigraphy. Paris: UNESCO. pp. 283–306.

The forgotten clade: the REAL proximal ancestors to Dinosauria

Ignored by Baron et al. 2017, and everybody else
the Junggarsuchus clade (including Pseudhesperosuchus, Carnufex and Trialestes in order of increasing quadrupedality, Figs. 1–4) nests as the proximal ancestors to Herrerasaurus (Fig. 1) and the rest of the Dinosauria (Fig. 5) in the large reptile tree (LRT). That cladogram tests a wider gamut of taxa in greater detail than any other reptile cladogram ever published, attempting to not overlook anything. The Junggarsuchia is a sister clade to the Crocodylomorpha with both arising from a taxon near Lewisuchus (Fig. 1). Traditional paleontology (see Wikipedia) nests this largely ignored clade with the sphenosuchian crocodylomorphs (Fig. 4)… and for two good reasons!

Figure 1. Members of the Junggarsuchus clade were derived from a sister to the basal crocodylomorph, Lewisuchus and produced one line that includes Pseudhesperosuchus and Trialestes. The other line produced dinosaurs. These taxa are shown to scale. Note the evolution from a bipedal configuration to a quadrupedal stance.

Figure 1. Members of the Junggarsuchus clade were derived from a sister to the basal crocodylomorph, Lewisuchus and produced one line that includes Pseudhesperosuchus and Trialestes. The other line produced dinosaurs. These taxa are shown to scale. Note the evolution from a bipedal configuration to a quadrupedal stance.

One: Paleontologists never seem to include Dinosauria
in their smaller gamut croc analyses because they’re looking at crocs!~. So once again, taxon exclusion is holding some workers back from seeing ‘the big picture’. ReptileEvolution.com and the blog you are currently reading is all about examining ‘the big picture.’

Figure 2. Skulls of the Junggarsuchus clade not to scale. Herrerasaurus is the basalmost dinosaur.

Figure 2. Skulls of the Junggarsuchus clade not to scale. Herrerasaurus is the basalmost dinosaur, closely related to Junggarsuchus.

Two: Junggarsuchians ALSO have elongate proximal wrist bones
Elongate proximal carpals are found in both sphenosuchian crocs and derived members of the Junggarsuchus clade. Paleontolgists wrongly assumed such odd wrist bones were homologous. It’s an easy mistake to make. However, the LRT makes clear that intervening taxa, including Junggarsuchus, do not have elongate wrist bones.

Among taxa that preserve the manus,
(Fig. 3) it is Junggarsuchus that nests closest to Herrerasaurus and the Dinosauria.

Figure 3. Hands of Lewisuchus, Herrerasaurus, Junggarsuchus, Pseudhesperosuchus and Trialestes. The proximal carpals (radiale and ulnare) were elongate by convergence with a line of crocodylomorphs. This has confused paleontologists and mentally removed them from possible ancestry to the Dinosauria. Note the very short proximal carpals in Junggarsuchus.

Figure 3. Hands of Lewisuchus, Herrerasaurus, Junggarsuchus, Pseudhesperosuchus and Trialestes. The proximal carpals (radiale and ulnare) were elongate by convergence with a line of crocodylomorphs. This has confused paleontologists and mentally removed them from possible ancestry to the Dinosauria. Note the very short proximal carpals in Junggarsuchus.

Like the basal members of the Crocodylomorpha
the Junggarsuchus clade (the Prodinosauria here) transition from bipedal basal members to quadrupedal derived members, with the longest forelimbs belonging to the most derived member, Trialestes (Fig. 3). Distinct from the others and contra the original interpretation, I think Trialestes may have had a larger ulnare than radiale, to match its larger ulna.

Figure 4. Crocodylomorph manus and carpus samples including Terrestrisuchus, Erpetosuchus, Hesperosuchus and Dibothrosuchus along with Scleromochlus documenting the elongate radiale and ulnare on derived taxa. Ticinosuchus is the closest example of an ancestral/plesiomorphic manus in the LRT.

Figure 4. Crocodylomorph manus and carpus samples including Terrestrisuchus, Erpetosuchus, Hesperosuchus and Dibothrosuchus along with Scleromochlus documenting the elongate radiale and ulnare on derived taxa. Ticinosuchus is the closest example of an ancestral/plesiomorphic manus in the LRT.

Let’s not forget
PVL 4597 (Fig. 6) which was mistakenly considered a specimen of Gracilisuchus by (Lecuona and Desojo 2011), but under phylogenetic analysis in the LRT, still nests as the proximal outgroup to Herrerasaurus. It is tiny specimen, supporting the hypothesis of phylogenetic miniaturization at clade origin. And it retains a small proximally oriented calcaneal tuber, as found in other Junggarsuchians.

Figure 1. Subset of the LRT focusing on the Archosauria (Crocodylomorpha + Dinosauria and kin). Gray areas document specimens with elongate proximal carpals (radiale and ulnare).

Figure 5. Subset of the LRT focusing on the Archosauria (Crocodylomorpha + Dinosauria and kin). Gray areas document specimens with elongate proximal carpals (radiale and ulnare).

We looked at
phylogenetic miniaturization at the origin of several pterosaur clades. Well, it happens here too, at the base of the Dinosauria (Fig. 1) with PVL 4597 (Fig. 6), easily overlooked, easily mistaken for something else.

One should not ‘choose’ outgroup taxa
based on paradigm, tradition, guessing, convenience or opinion. Rather outgroup taxa should ‘choose themselves’ based on rigorous testing of a large gamut of outgroup candidates in phylogenetic analysis. To minimize selection bias, the LRT provides 858 outgroup taxa the opportunity to nest close to dinosaurs.

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 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.

 

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543:501–506.
Bonaparte JF 1969. 
Dos nuevos “faunas” de reptiles triásicos de Argentina. Gondwana Stratigraphy. Paris: UNESCO. pp. 283–306.
Butler RJ. et al. 2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evol. Biol. 14, 128.
Clark JM et al. 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20 (4): 683–704.
doi:10.1671/0272-4634(2000)020[0683:ANSOHA]2.0.CO;2.
Clark JM, Xu X, Forster CA and Wang Y 2004. A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodilian skull. Nature 430:1021-1024.
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum(Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Nesbitt SJ 2011. The early evolution of archosaurs: relationship and the origin ofmajor clades. Bull. Amer. Mus. Nat. Hist. 352, 1–292.
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.
Zanno LE, Drymala S, Nesbitt SJ and Schneider VP 2015. Early Crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports 5:9276 DOI: 10.1038/srep09276.

wiki/Pseudhesperosuchus
wiki/Junggarsuchus
wiki/Carnufex
wiki/Herrerasaurus
wiki/Sanjuansaurus

 

Teleocrater: a sister to Yarasuchus, not the earliest bird-line archosaur.

Unfortunately
another paper that was improperly vetted (refereed). I heard about this one on NPR when co-author Richard Butler was interviewed by the BBC.

Nesbitt et al. 2017
report: The relationship between dinosaurs and other reptiles is well established (1–4,) but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies.”

We’re in trouble from the opening salvo.
The large reptile tree (LRT) does not recover the same tree topology as these authors hypothesize (Fig. 1). And the sequence of dinosaurian features is not obscured in the LRT. There are plenty of fossils with transitional morphologies. Unfortunately, these authors either chose to ignore them or scored them haphazardly. Based on the theory that evolution happens with small changes the Nesbitt et al. tree topology (Fig. 1) is completely bonkers, adding unrelated taxa while excluding pertinent sisters to Teleocrater (here labeled under its new clade, Aphanosauria).

Figure 1. Aphanosauria according to Nesbitt et al. 2017. Two of these clades are unrelated to archosaurs. Marasuchus IS a dinosaur. Silesaurus is a poposaur more distantly related to dinos than crocs.

Figure 1. Aphanosauria according to Nesbitt et al. 2017. Two of these clades are unrelated to archosaurs. Marasuchus IS a dinosaur. Silesaurus is a poposaur more distantly related to dinos than crocs. Where are the crocs?

Nesbitt et al. report:
“H
ere we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch.” There is no such thing as an avian stem lineage. Avemetarsalia includes pterosaurs and dinosaurs, so it is a junior synonym for Reptilia in the LRT. The closest ancestors to dinosaurs were bipedal basal crocodylomorphs in the LRT. I don’t see them in figure 1. 
Teleocrater holotype.
NHMUK (N
atural History Museum, London, UK) PV 
R6795, a disassociated skeleton of one individual, including: cervical, trunk, and caudal vertebrae, partial pectoral and pelvic girdles, partial forelimb and hind limbs. 
Referred material.
Elements f
ound near the holotype, but from other 
individuals, which represent most of the skeleton and that are derived from a paucispecific bone bed containing at least three individuals.
Figure 2. The chimaera created by several specimens attributed to Telocrater. Even if all these piece do fit together like Nesbitt et al. indicate, Telocrater is closer to Yarasuchus and Ticinosuchus than it is to the last common ancestor of Archosauria.

Figure 2. The chimaera created by several specimens attributed to Teleocrater. Even if all these piece do fit together like Nesbitt et al. indicate, Teleocrater is closer to Yarasuchus and Ticinosuchus than it is to the last common ancestor of Archosauria. See figure 3.

The specimens that produced this reconstruction (Fig. 2)
are all associated. So there is great confidence that all of the bones are conspecific. The problem, once again, is taxon exclusion, and maybe a large dose of bad scoring (see below)

Figure 3. Telocrater to scale compared with likely sister taxa among the Ticinosuchidae in the LRT. Note the resemblance of the Telocerater maxilla to that of these sister taxa.

Figure 3. Teleocrater to scale compared with likely sister taxa among the Ticinosuchidae in the LRT. Note the resemblance of the Teleocerater maxilla to that of these sister taxa.

Oddly
the authors report that “Osteoderms are not preserved and were probably absent.” And yet their reconstruction (Fig. 2) has osteoderms in the black outline. What bias is present here?

Oddly
the authors report, Our phylogenetic analyses recovered Teleocrater in a clade containing Yarasuchus, Dongusuchus and Spondylosoma.” And yet they did not include Yarasuchus in their phylogenetic figure (Fig. 1). The latter two are know from scraps. Yarasuchus (Fig. 3) is much more complete. 

Problems with the Nesbitt et al. 2017 cladogram

  1. The outgroup for Prolacerta + Archosauriformes (Proterosuchus) is the unrelated lepidosaur, Mesosuchus.
  2. The unrelated thalattosaur, Vancleavea, nests between Erythrosuchus and the unrelated chanaresuchid, Tropidosuchus. None of these taxa even look alike!
  3. The Yarasuchus clade, and before it the Parasuchus clade gives rise to the pterosaurs DimorphodonEudimorphodon and another chanaresuchid, Lagerpeton, both purportedly in the lineage of dinosaurs. These are all actors pretending to be relatives. How is this possible that Nesbitt et al, and the referees and editors at Nature are not raising objections to this? This is total madness at the highest levels.

Need I go on???
Why is Teleocrater big news? Because the authors positioned it as an ancestor to dinosaurs. It may be, but it is buried deep, deep, deep in the lineage. Why was the relationship with Yarasuchus buried? You know why… it’s not as ‘sexy’ to the press.

Nesbitt et al. report,Aphanosauria…is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia.” Surprised to see they didn’t say, ‘pterosaurs and Tyrannosaurus rex.’ 

Folks, it’s all showmanship.
I’m sure the authors have all toasted their new paper in Nature by now. I hate seeing the subject of evolution twisted, torn and laid bare like this.

The real importance of Teleocrater
is its basal position in a clade I earlier called Ticinosuchidae, arising from basal rauisuchians, like Vjushkovia, giving rise to a wide variety of taxa like Aetosaurus and Arizonasaurus) while also giving rise to Decuriasuchus, which gave rise to poposaurs, like Turfanosuchus, and archosaurs, thus ultimately including dinosaurs.

References
Nesbitt SJ et al. (10 co-authors) 2017. The earliest bird-line archosaurs and the assemblof the dinosaur body plan. Nature doi:10.1038/nature22037. (online pdf)

1. Benton, M. J. & Clark, J. M. in The Phylogeny and Classification of the Tetrapods.
Volume 1: Amphibians, Reptiles, Birds. Systematics Association Special Volume
35A (ed. Benton, M. J.) 295–338 (Clarendon, 1988).
2. Gauthier, J. Saurischian monophyly and the origin of birds. Mem. Calif. Acad.
Sci. 8, 1–55 (1986).
3. Sereno, P. C. Basal archosaurs: phylogenetic relationships and functional
implications. Soc. Vertebr. Paleontol. Mem. 2, 1–53 (1991).
4. Sereno, P. C. The evolution of dinosaurs. Science 284, 2137–2147 (1999).

The cervical/dorsal transition in Herrerasaurus

Figure 1. Lewisuchus cervical/dorsal transition at top photo and the same for Herrerasaurus drawings, including a foreword shift of the pectoral girdle in a 2-frame GIF movie. The cervical ribs are imagined.

Figure 1. Lewisuchus cervical/dorsal transition at top photo and the same for Herrerasaurus drawings, including a foreword shift of the pectoral girdle in a 2-frame GIF movie. The cervical ribs are imagined in the drawing. See text for details. Drawings from Novas and Sereno 1994.

In their report on the basal dinosaur Herrerasaurus,
Sereno and Novas 1993 reported, “The cervical column (Fig. 1) was preserved in articulation with the skull. The anterior cervical vertebrae are better preserved than the posterior cervical vertebrae, and nearly all the ribs are lacking.”

“Because the cervical-dorsal transition in vertebrae or ribs is not preserved, we regard the first ten presacral vertebrae as cervical vertebrae, based on the condition in other basal dinosaurians.”

Despite their assessment, 
Novas and Sereno appear to have reconstructed Herrerasaurus with no more than six or possibly seven cervicals (Fig. 1, original).  With phylogenetic scoring at issue, a deeper look was warranted.

Novas and Sereno 1993 considered Herrerasaurus
a member of the ‘Ornithodira’ thus related to pterosaurs and Lagerpeton. That hypothesis is not supported by the present study.

By contrast,
in the large reptile tree (LRT) Herrerasaurus arises from another list of taxa, including Junggarsuchus, Pseudhesperosuchus, LewisuchusTurfanosuchus and further distantly Decuriasuchus. Bittencourt et al. 2014 identify seven cervicals in Lewisuchus (Fig. 1) with the eighth having ribs descending into the torso. Seven is a number common to crocodylomorpha* and Lewisuchus nests at its base. Turfanosuchus and Decuriasuchus each have eight cervicals, a plesiomorphic number going back at least to basal archosauriformes, like Proterosuchus and to basal diapsids, like Petrolacosaurus.

Based on available data,
Herrerasaurus had but seven cervicals as a basal dinosaur. Based on data from Tawa, Marasuchus, Eodromaeus and Eoraptor, all slightly more derived basal dinosaurs had 9 or 10.

* Among Crocodylomorpha, Scleromochlus has six cervicals, Gracilisuchus, Litargoschus and Terrerstrisuchus have eight, as do modern crocs and their relatives by convergence. Intervening taxa often have seven.

References
Bittencourt JS, Arcucci AB, Maricano CA and Langer MC 2014. Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina) its inclusivity, and relationships amongst early dinosauromorphs. Journal of Systematic Palaeontology. Published online: 31 Mar 201. DOI:10.1080/14772019.2013.878758
Nesbitt SJ. et al. 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464(7285):95-8
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna; XIV, Lewisuchusadmixtus, gen. et sp. nov., a further thecodont from the Chañares beds. Breviora 390:1-13
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.

wiki/Lewisuchus
wiki/Herrerasaurus

 

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.

 

 

New radical dinosaur cladogram: Baron, Norman and Barrett 2017

Baron, Norman and Barrett 2017
have just allied Ornithischia with Theropoda to the exclusion of Sauropodomorpha. That radical hypothesis was not recovered by the large reptile tree (LRT, 980 taxa) nor any other study in the long history of dinosaurs. Despite the large size of their study, it was not large enough. And so taxon exclusion bites another group of well-meaning paleontologists who used traditional small inclusion sets.

From the Baron et al. abstract:
“For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.”

As a reminder, the fully resolved cladogram
at ReptileEvolution.com/reptile-tree.htm finds Herrerasaurus as a basal dinosaur arising from the Pseudhesperosuchus clade. Tawa (Fig. 1) and Buriolestes lead the way toward Theropoda. Barberenasuchus and Eodromaeus are basal to Phytodinosauria, which includes Sauropodomorpha + Ornithischia. So the Nature piece is totally different due to taxon exclusion and improper taxon inclusion.

Earlier heretical dinosaur origins were presented here with images and complete resolution with high Bootstrap scores at every or virtually every node.

Problems with the Baron et al. report

  1. Lack of resolution: Over dozens of nodes, only 5 bootstrap scores were over 50 (the minimum score that PAUP shows as fully resolved).
  2. Lack of correct proximal outgroup taxa (taxon exclusion) and they chose several wrong outgroup taxa (see below) because they had no large gamut analysis that established the correct outgroup taxon out of a larger gamut of choices
  3. Lack of several basal dinosaur taxa. (again, taxon exclusion, see below)
  4. Improper taxon inclusion: poposaurs, pterosaurs and lagerpetons are not related to dinos or their closest kin
  5. Lacking reconstructions for all pertinent basal/transitinal taxa so we can see their data at a glance, see if a gradual accumulation of traits can be observed and not have to slog through all the scores
Figure 1. Unrelated archosaurs. Silesaurus is a poposaur. Eoraptor is a phytodinosaur (note the big belly). And Tawa is a lean theropod.

Figure 1. Unrelated archosaurs mentioned in this blog. Silesaurus is a poposaur. Eoraptor is a phytodinosaur (note the big belly). And Tawa is a lean theropod.

LRT differences with the Baron et. al results

  1. Carnivorous Staurikosaurus, Herrerasaurus, Chindesaurus and Sanjuansaurus nest at the base of the herbivorous Sauropodomorpha.
  2. Herbivorous Eoraptor nests at the base of the Theropod with Tawa.
  3. Poorly known Saltopus sometimes nests as the last common ancestor of Dinosauria.
  4. Six taxa nest basal to dinosaurs in SupFig1 including the poposaur Silesaurus and kin. Silesaurus has ornithischian and theropod traits and so appears to make an ideal outgroup taxon,  but nests with neither clade when more taxa are included. This is the key problem with the study: pertinent taxon exclusion. 
  5. The lack of Gracilisuchus and other bipedal basal crocs that nest basal to dinos in the LRT certainly skewed results.

In an effort to understand Baron et al. I duplicated their outgroup taxon list
but retained all the LRT dinosaurs to see what would happen. The SupFigs are available free online at Nature.com

  1. SupFig 1: When Euparkeria is the outgroup and Postosuchus is included: 3 trees result and (theropods Herrerasaurus + Tawa + Buriolestes) + (poposaurs Sacisaurus + Silesaurus) nest as the base of the Phytodinosauria, while bipedal croc Saltopus nests at the base of the Theropoda.
  2. SupFig 2: When the lepidosaur pterosaur Dimorphodon is the outgroup and Euparkeria + Postosuchus are excluded: 12 trees and basal scansoriopterygid birds (come to think of it, they DO look like Dimorphodon!) nest as basal dinosaurs, then the bird cladogram gets reversed such that basal becomes derived, but Phytodinosauria is retained.
  3. SupFig. 3: when Silesaurus is the outgroup: 12 trees and Phytodinosauria is retained in the LRT
  4. SupFig. 4: when no characters were treated as ordered. Neither does the  LRT order any characters, so this test was moot.

Dr. Kevin Padian said, 
“‘original and provocative reassessment of dinosaur origins and relationships”. And because Baron and his colleagues used well-accepted methods, he notes, the results can’t simply be dismissed as a different opinion or as mere speculation. “This will send people back to the drawing board,” he added in an interview.”

“There have been a lot of studies on the phylogenetic relationships, the family tree of the dinosaurs, but they’ve mostly been on individual dinosaurian groups. They haven’t really examined the entire dinosaur tree in such depth. And so this analysis had the advantage of using a different and larger set of critters than most previous trees. They’ve analyzed the characters used by others before and then also adding their own characteristics and getting their selves quite different configurations, radically different in fact.

The LRT has had, for several years, an even larger set of taxa, so large that any bias in selecting an outgroup taxon list has been minimized. Unfortunately, Baron et al. were biased and used traditional outgroup taxa that skewed their results.

Dr. Hans-DieterSues reported,
“For one thing, palaeontologists’ analyses of relations among species are keenly sensitive to which species are considered, as well as which and how many anatomical features are included, he says.”

True.
Many more outgroup taxa would have minimized the inherent bias clearly present in Baron et al. When Silesaurus is your outgroup, herbivores will nest with carnivores. When you start your study with a goal in mind (read and listen to Baron’s comments) that’s never good. When you exclude taxa that have been shown to be pertinent to your study, that’s never good.

That’s what ReptileEvolution.com is here for (on the worldwide web). Free. Testable. And with a demonstrable gradual accumulation of traits along with minimal bias due to its large gamut.

I was surprised to see Nature print this
because they have not published relationship hypotheses in favor of  new specimens of note. Co-author Dr. David Norman has published for several decades and has a great reputation.

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