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

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

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

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

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

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

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

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

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

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

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

Best regards,

Pisanosaurus: dinosaur or silesaurid?

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

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

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

Some general notes to start with:

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

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

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

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

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

Other factors of interest:

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

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

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

Silesaurus

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

wiki/Sacisaurus
wiki/Pisanosaurus
wiki/Haya

 

New phylogeny of Stegosauria

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

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

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

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

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

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

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

Laquintasaura: verrrry basal ceratopsian from the Early Jurassic

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

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

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

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

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

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

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

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

Figure 2. The skull of Yinlong a basal certatopsian.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

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.

Hypsibema missouriensis – a Late Cretaceous Appalachia duckbill dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Hypsibema missouriensis
(Cope 1869; Gilbert and Stewart 1945; Gilbert 1945; Baird and Horner 1979; Darrough et al. 2005; Parris 2006; Campanian, 84-71 mya, Late Cretaceous) is a fairly large hadrosaurid dinosaur discovered in 1942, at what later became known as the Chronister Dinosaur Site near Glen Allen, Missouri. At present this literal pinprick in the map of Missouri is the only site that preserves dinosaur bones.

Figure 2. Where the Hypsibema maxilla chunk came from on the skull of Saurolophus.

Figure 2. Where the Hypsibema maxilla chunk (Figure 3) came from modeled on the skull of Saurolophus.

Small pieces of broken bone and associated caudals and toes
were first discovered when digging a cistern. They had been found about 8 feet (2.4 m) deep imbedded in a black plastic clay. The area is in paleokarst located along downdropped fault grabens over Ordovician carbonates.

Gilmore and Stewart 1945 described a series of Chronister caudal centra (now at the Smithsonian) as sauropod-like, reporting, “The more elongate centra of the Chronister specimen, with the possible exception of Hypsibema crassicauda Cope, and the presence of chevron facets only on the posterior end appear sufficient to show that these vertebral centra do not pertain to a member of the Hadrosauridae.”

First named Neosaurus missouriensis,
the caudals were renamed Parrosaurus missouriensis by Gilmore and Stewart 1945 because “Neosaurus” was preoccupied. The specimen was allied to Hypsibema by Baird and Horner 1979.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Back in the 1980s
I enjoyed going to the Chronister site with other members of the local fossil club, the Eastern Missouri Society for Paleontoogy. I was lucky enough to find both a maxilla fragment (Fig. 3) and a dromaeosaurid tooth. I remember the horse flies were pesky and  one morning, before the other members got there, I was met by a man with a shot gun who relaxed when I identified myself. A friend found a series of hadrosaur toe bones, each about as big as a man’s hand (sans fingers). The bone was so well preserved you could blow air through the porous surfaces.

References
Baird D and Horner JR 1979. Cretaceous dinosaurs of North Carolina. Brimleyana 2: 1-28.
Cope  ED 1869.
Remarks on Eschrichtius polyporusHypsibema crassicaudaHadrosaurus tripos, and Polydectes biturgidus“. Proceedings of the Academy of Natural Sciences of Philadelphia 21:191-192.
Darrough G; Fix M; Parris D and Granstaff B 2005.
 Journal of Vertebrate Paleontology 25 (3): 49A–50A.
Gilmore CW and Stewart DR 1945. A New Sauropod Dinosaur from the Upper Cretaceous of Missouri. Journal of Paleontology (Society for Sedimentary Geology 19(1): 23–29.
Gilmore CW 1945. Parrosaurus, N. Name, Replacing Neosaurus Gilmore, 1945. Journal of Paleontology (Society for Sedimentary Geology 19 (5): 540.
Parris D. 2006. New Information on the Cretaceous of Missouri. online

wiki/Hypsibema_missouriensis
bolinger county museum of natural history
More info and links