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

 

What traits separate phytodinosaurs from theropods?

Yesterday we looked at the origin of dinosaurs in the context of and contra the recent Baron et al. 2017 paper. Today we’ll look at the basal split between basal phytodinosaurs, like Eodromaeus (Figs. 1, 2), with the closely related basal theropods, like Tawa (Fig. 1).

Figure 1. The theropod Tawa compared to the closely related phytodinosaur, Eodromaeus.

Figure 1. The theropod Tawa compared to the closely related smaller phytodinosaur, Eodromaeus.

Placed side-by-side to scale
Tawa and Eodromaeus are similar overall, though the plant-eaters were initially smaller. The details (below) demonstrate the initial steps toward herbivory that characterize the Phytodinosauria, distinct from the Theropoda and basal Dinosauria from which they evolved (contra Baron et al. 2017).

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow.

Figure 1. Eodromaeus reconstructed. We will look at this taxon in more detail tomorrow.

How do basal phytodinosaurs differ from the basal theropods?
Here’s the LRT list:

  1. lateral rostral shape: convex and smoothly curved (also in ancestral Herrerasaurus and Gracilisuchus);
  2. premaxilla/maxilla angle 25–45º;
  3. naris shape in lateral view almost round (not longer than tall or taller than long);
  4. postfrontal has no contact with the upper temporal fenestra;
  5. opisthotic oriented laterally without posttemporal fenestrae;
  6. palatal teeth (only on basalmost taxa);
  7. maxillary tooth depth ≤ 2x width in lateral view;
  8. last maxillary tooth at mid orbit (also in Herrerasaurus);
  9. olecranon process present (convergent in Buriolestes);
  10. metacarpals 2 and 3 align with m1.1 (except Eodromaeus);
  11. acetabulum laterally oriented (no ventral deflection, as in basal theropods);
  12. femoral head with neck and offset (appears later in theropods);
  13. penultimate manual phalanges not the longest in each series;
  14. loss of pubic boot (likely plesiomorphic because outgroups to Herrerasaurus do not have a pubic boot).

Summary and significance
Compared to the closely related theropod Tawa, the overall similar phytodinosaur Eodromaeus had a taller rounder rostrum, shorter teeth, a higher coronoid process, a longer dorsal region with more robust dorsal vertebrae, reduced gastralia, a more robust pectoral girdle and forelimb with shorter, less raptorial fingers, a deeper pubis and ischium with more robust hind limbs. The shorter teeth and larger belly together with the more robust limbs and back are traits seen in a wide variety of herbivores, even if only transitional at this early stage.

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.

Analyses and random notes on Chilesaurus from the media

Still big news, Chilesaurus was originally considered (Novas et al. 2015) a ‘bizarre’ theropod, but nests at the base of all ornithischians in the large reptile tree.

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

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

Prior hylogenetic analyses
Novas et al. tested Chilesaurus into four different data matrixes with samplings focused on basal dinosauriforms (Nesbitt et al.7), basal sauropodomorphs (Otero & Pol) and basal theropods (Carrano et al.; a modified version of Smith et al.). Some were modified by the addition and removal of characters and taxa. Ultimately, none agreed with one another in the nesting of ChilesaurusThat’s a red flag. 

The results of the four analyses
did agreed in the position of Chilesaurus as a tetanuran theropod (but that’s a very large clade, and done so in the absence of its true sister taxa, see below). According to Novas et al, “Features supporting the theropodan position of Chilesaurus include: pleurocoelous cervical and cranial dorsal vertebrae; hypapophyses on ‘pectoral’ vertebrae; preacetabular wing of ilium dorsoventrally expanded; femoral fourth trochanter semicircular; and tibia distally expanded and with lateral malleolus extending strongly laterally. Tetanuran characteristics present in Chilesaurus are: scapular blade elongate and strap-like; distal carpal semilunate; and manual digit III reduced.”

Novas et al. found this combination of derived Coelurosaurian and Prosauropod-like traits specifically recalls the plant-eating Laurasian therizinosaurs, nevertheless, this set of general characteristics contrasts with the 18 derived features absent in Chilesaurus that are usually recognized as uniting therizinosaurs with derived coelurosaurs.

Furthermore, under constrained suboptimal topologies, 11 additional steps are necessary to force the position of Chilesaurus as a therizinosaur. This set of anatomical distinctions implies a phylogenetic position for Chilesaurus outside Therizinosauria, Maniraptora and Coelurosauria.

Ornithischians were considered:
Novas et al. report, “Apart from typically saurischian and theropodan characters, Chilesaurus also shows several potential apomorphies of ornithischians or subclades thereof. Unfortunately, very few basal ornithischians are currently known from good materials. The data matrix of Nesbitt et al. 2009 includes Scutellosaurus, Lesothosaurus, Eocursor, Heterodontosaurus and Pisanosaurus, and thus provides as good a taxon. This matrix discards that Chilesaurus is an ornithischian.”

As noted above,
none of the Novas analyses included the basal ornithischians, Daemonosaurus and Jeholosaurus. By excluding these taxa Novas et al. were comparing apples to oranges, something that happens far too often in paleontology as noted tar too many times in this blog.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Figure 1. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Quotes from the PR machine:
I thought it interesting to run through some quotes from the various online news stories carried today on this new find. When you read this, keep the new phylogenetic nesting in mind and it will clarify the mysteries raised.

NBC News: “Scientists have unearthed fossils of a strange dinosaur in southern Chile that boasts such an unusual combination of traits that they are comparing it to a platypus, that oddball egg-laying, duckbilled mammal from Australia…  it ate only plants with a beak and leaf-shaped teeth, scientists said on Monday. …Its skull and neck resembled those of primitive long-necked dinosaurs, and its vertebrae those of primitive meat-eating theropods. It had robust arms, but just two blunt fingers on each hand. It was bipedal, but its wide, four-toed feet were unlike the slender, three-toed feet of most theropods. And it had a bird-like pelvis.”

“Chilesaurus constitutes one of the most bizarre dinosaurs ever found,” said paleontologist Fernando Novas. “No other dinosaurs exhibit such a combination or mixture of features.”

America Aljazeera: “Four nearly complete skeletons and dozens of bones from other individuals were found, making Chilesaurus one of the best-understood Jurassic Southern Hemisphere dinosaurs. It belongs to a previously unknown dinosaur lineage,” University of Birmingham paleontologist Martín Ezcurra said.

Brian Switek writing for Smithsonian: “In the place where Diego discovered it, there are more bones of Chilesaurus than any other creature. This is odd. In most environments of about the same age, the most common dinosaurs are beaky little herbivores that belonged to a very different lineage of dinosaurs called ornithischians. Here, for some reason, a theropod came to dominate instead.

“This is a really unusual beastie, a bit of a dinosaur Frankenstein,” says paleontologist Lindsay Zanno of the North Carolina Museum of Natural Sciences.

Reuters: “It belongs to a previously unknown dinosaur lineage,” University of Birmingham paleontologist Martín Ezcurra said. “Convergent evolution’ is a process in which two unrelated species or groups acquire similar characteristics from living in similar environments or having a similar behavior,” like the wings of a bat and a bird, Ezcurra added. “In the case of ‘mosaic convergent evolution,’ different parts of the body resemble those of other unrelated species, such as in the case of the platypus and Chilesaurus.”

Sydney Morning Herald: “Chilesaurus can be considered a ‘platypus’ dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution,” study author Martín Ezcurra of the University of Birmingham said in a statement. “In this process, a region or regions of an organism resemble others of unrelated species because of a similar mode of life and evolutionary pressures. Chilesaurus provides a good example of how evolution works in deep time and it is one of the most interesting cases of convergent evolution documented in the history of life”

EurkaAlert (the Global Source for Scientific News): “Chilesaurus represents one of the most extreme cases of mosaic convergent evolution recorded in the history of life. For example, the teeth of Chilesaurus are very similar to those of primitive long-neck dinosaurs because they were selected over millions of years as a result of a similar diet between these two lineages of dinosaurs.” 

Novas et al. writing in Nature: “Early theropod evolution is currently interpreted as the diversification of various carnivorous and cursorial taxa, whereas the acquisition of herbivorism, together with the secondary loss of cursorial adaptations, occurred much later among advanced coelurosaurian theropods12. A new, bizarre herbivorous basal tetanuran from the Upper Jurassic of Chile challenges this conception.”

As noted
earlier, Chilesaurus is not bizarre, convergent or enigmatic in the large reptile tree. Rather it nests at the base of the Ornithischia, close to the base of the Sauropodomorpha, together nesting near the base of the Phytodinosauria and derived from Eoraptor, Pampadromaeus and kin.

Together with Jeholosaurus, Chilesaurus provides a rare glimpse into the genesis of the ornithischian beak and pelvis, something paleontologists have been looking for for decades. This long-sought relationship was completely overlooked by the original authors. AND this is one of the holy grails of paleontology… sadly passed by due to taxon exclusion.

Gotta work on that…

Theropod database
See M.Mortimer’s take on Chilesaurus here. Mortimer found a raft of miscodings in the original paper by Novas et al.

References
Novas FE, Salgado, Suárez LM, Agnolín FL, Ezcurra MND, Chimento NSR.,de la Cruz R, Isasi MP, Vargas AO, Rubilar-Rogers D. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature. doi:10.1038/nature14307

Chilesaurus, new dinosaur: not so ‘enigmatic’ after all…

Chilesaurus diegosuarezi (Novas et al. 2015; Late Jurassic, 150 mya, Fig. 1) is the current media darling. Described as an ‘enigmatic’ and ‘bizarre’ theropod, Chilesaurus was nested  with Velociraptor, Tawa and kin, and Elaphrosaurus using various prior cladograms in the supplementary data. So that’s an issue (no internal agreement).

Several articulated specimens are known at distinct ontogenetic stages.

Unfortunately taxon exclusion raises its ugly head again…
The large reptile tree nests Chilesaurus outside of the Theropoda, near the base of the Phytodinosauria, at the base of the Ornithischia and at the base of the clade that also includes Daemonosaurus and Jeholosaurus (Fig. 1), two taxa that were unfortunately ignored by the Novas et al. study. Hate to see that happen yet again.

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

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

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..

Folks,
Chilesaurus is not bizarre.

It is simply a descendant from an unknown Late Triassic transitional taxon at the base of the Ornithischia, a hypothesis overlooked by Novas et al. Chilesaurus is not a theropod, but a phytodinosaur (Fig. 3). The fact that fossils of Chilesaurus were found much later than the original split is not a cause for concern. That happens all the time.

Pelvis  changes
Along with Jeholosaurus, Chilesaurus demonstrates the changes that were happening to the dinosaurian pelvis at the genesis of the ornithischian pelvis. As a plant eater, Chilesaurus and kin were expanding their gut volume to digest less digestible plant matter.

Manus and tooth changes
The hands of Chilesaurus are not as primitive and plesiomorphic as might be hoped, but then Chilesaurus is a descendent of that Late Triassic transitional taxon, appearing tens of millions of years after the split. Things evolve! While the teeth remain large and robust, Chilesaurus had flat teeth, rather than the pointed ones of its Triassic sister, Daemonosaurus or its Cretaceous sister, Jeholosaurus.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Figure 3. Cladogram of basal dinosaurs. Note that Chilesaurus nests near the base of the Phytodinosauria and at the base of the Ornithischia, both far from the Theropoda.

Clues
to the largely missing post-crania of Daemonosaurus are provided by its sister Chilesaurus.

Now let’s talk about the PR barrage
This is where the science reporters separate themselves from the scientists. All those who reported without testing the results of Novas et al. … you may have to do some backtracking.

Theropod database
See M.Mortimer’s take on Chilesaurus here. Mortimer found a raft of miscodings in the original paper by Novas et al.

References
Novas FE, Salgado, Suárez LM, Agnolín FL, Ezcurra MND, Chimento NSR.,de la Cruz R, Isasi MP, Vargas AO, Rubilar-Rogers D. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature. doi:10.1038/nature14307

Daemonosaurus cervicals and the recurring problem of taxon exclusion

Updated March 9, 2015 with the note that Sues et al. did not use suprageneric data,as reported earlier.. The supplemental data shows that several ornithischians were employed. I spent the day yesterday making the SuppData computer friendly and am today reviewing the scorings. I see several typos and reinterpretations. A later post will present both nexus files. 

Earlier we looked at the palate and occiput of Daemonosaurus Today we’ll reexamine the cervicals and update some notes.

Little noticed and poorly preserved,
the cervicals of the basal phytodinosaur, Daemonosaurus (Sues et al. 2011, CM 76821, Carnegie Museum of Natural History, Late Triassic) appear curiously small and elongated relatively to the tall, narrow skull (Fig. 1).

Figure 1. Daemonosaurus cervicals traced from in situ fossils and compared to sister taxa, Eoraptor, Leyesaurus, Heterodontosaurus and Pisanosaurus. Among these taxa, Daemonosaurus has the largest skull and most gracile cervicals. Click to enlarge.

Figure 1. Daemonosaurus cervicals traced from in situ fossils and compared to sister taxa, Eoraptor, Leyesaurus, Heterodontosaurus and Pisanosaurus. Among these taxa, Daemonosaurus has the largest skull and most gracile cervicals. Daemonosaurus likely had four more cervicals than preserved.

If the cervicals have been correctly traced
then, compared to sister taxa, Daemonosaurus has the largest skull relative to the most gracile cervicals. And there were likely four and a half more cervicals that were not preserved.

The cervicals are long, like those of basal sauropodomorphs, but the skull is tall, short and narrow, like those of basal ornithischians, like Heterodontosaurus. Overall the imagined body of Daemonosaurus was larger than all sister taxa except Leyesaurus, which had a longer neck. Note the similarities of Daemonosaurus to Pisanosaurus, which had much shorter cervicals, but was more closely related to other ornithischians, and to Dryosaurus, which also had shorter cervicals and no premaxillary teeth, but otherwise rather similar in morphology.

Here’s where Sues et al. 2011 differ from the large reptile tree
Sues et al. 2011 found Ornithischia and Sauropodomorpha branched off prior to Herrerasaurus. In  the large reptile tree they both branched off close to Eoraptor (which confirms sauropodomorph affinities according to Sereno et al. 2013) and Daemonosaurus is a basal ornithischian. Using the Sues et al. taxa (Fig. 2 and deleting all sauropodomorphs and ornithischians) the large reptile tree recovers the same tree topology. Different than I thought when this blogpost was first published, Sues et al. 2014 used genus-based taxa. A review of their work is in progress, but since they used Nesbitt 2011 for their database, I found several problems and strange-bedfellows earlier.

Figure 4. Daemonosaurus tree from Sues et al. 2014. Their one mistake was assuming sauropods and ornithischians branched off prior to Herrerasaurus. The large reptile tree has these clades branching off after Eoraptor. Delete those suprageneric clades and the tree recovered here matches the large reptile tree with similar deletions.

Figure 2. Daemonosaurus tree from Sues et al. 2014. Their one mistake was assuming sauropods and ornithischians branched off prior to Herrerasaurus. The large reptile tree has these clades branching off after Eoraptor. Delete those suprageneric clades and the tree recovered here matches the large reptile tree with similar deletions.

Daemonosaurus diagnosis (with my additions in color).
“Distinguished by the following unique combination of characters: skull proportionately deep and narrow (like Jeholosaurus, Heterodontosaurus = J, H), with short antorbital region (like J, H); premaxillary and anterior maxillary teeth much enlarged relative to more posterior maxillary teeth (like J, H)prefrontal large and occupies about 50 per cent of the dorsal margin of the orbit (like J, H); ventral process of lacrimal with slender posterior projection extending along anterodorsal margin of jugal (cannot confirm, this may be part of the jugal); dorsoventrally deep jugal with prominent lateral ridge (like H); postorbital with anterolateral overhang over orbit (like J, H); first two dentary teeth large and procumbent (like J, H); alveolar margin of dentary downturned at symphysis (like J, H); and third cervical vertebra with deep, rimmed, ovoid pleurocoel on the anterolateral surfaces of both centrum and neural arch (hard to see). Possible autapomorphies of Daemonosaurus include long posterior process of premaxilla that almost contacts anterior process of lacrimal (like J, H); and antorbital fenestra nearly the same size as external naris (like J, H);.”

It’s too bad
these authors missed this big, I mean really big discovery (the basalmost ornithischian!) due to their use of supragreneric taxa, false assumptions and taxon exclusion. It is also puzzling that no one since 2011 has raised their hand about these issues, except yours truly. Come on people, now that we know the problem, let’s fix this!

So, these questions pop up:
did the Ornithischia inherit short cervicals directly from a sister to Eoraptor? Or did basal phytodinosaurs enjoy a brief fling with elongate cervicals, as in the intervening sauropodomorphs — AND as demonstrated by Daemonosaurus? Or did Daemonosaurus independently elongate its cervicals?

That’s the frustration, joy and mystery of incomplete fossils.

PS Good news! Just heard Hans Sues and Sterling Nesbitt are working on a detailed description of Daemonosaurus.

References

Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Sereno PC, Martínez RN and Alcober OA 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology Memoir 12:83-179.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. 
A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online

The palate and occiput of Daemonosaurus

Daemonosaurus, a basal phytodinosaur, was published in two lateral views, left and right with bones partly disarticulated (Fig. 1). Not readily apparent, some palatal and occipital bones are also visible. I ignored those earlier, but add them here (Fig. 2). This is made doubly difficult because sister taxa palate data is scarce.

Figure 1. Daemonosaurus with bones colored here. The right side of the skull is flipped. Color shapes correspond to color shapes in figure 2. Click to enlarge.

Figure 1. Daemonosaurus with bones colored here. The right side of the skull is flipped. Color shapes correspond to color shapes in figure 2. Click to enlarge. Note the rotation of the T-shaped quadratojugal. If you see any errors here, please advise with data.

Using DGS
the colors traced here (Fig. 1) are restored to their in vivo places (Fig. 2). Notably this is quite a tall and narrow skull, as in Heterodontosaurus.  Note the relatively short mandible (overbite) — unless you add a mandible tip. Luckily such a tip is apparent just beyond that anterovental break in the matrix in the upper image of figure 1 (Fig. 3). Without some sort of addition, the mandible is way too short relative to the rostrum.

Figure 2 Daemonosaurus skull in 4 views. The new reconstruction is narrower than previously with a new descending pterygoid flange and very few other refinements. The jaw is shorter. The dentary fang(s) appear to slip into that pmx/mx notch as in Heterodontosaurus. A small comb-like dentary tip appears to be a precursor for the predentary found in ornithischians. If this is an artifact, please provide data. Gray areas are unknown.

Figure 2 Daemonosaurus skull in 4 views. The new reconstruction is narrower than previously with a new descending pterygoid flange and very few other refinements. The jaw is shorter. The dentary fang(s) appear to slip into that pmx/mx notch as in Heterodontosaurus. A small comb-like dentary tip appears to be a precursor for the predentary found in ornithischians. If this is an artifact, please provide data. Gray areas are unknown.

The proto-predentary
of Daemonosaurus is here (Fig. 3). It extends the mandibles to their proper length (Fig. 2). As a phytodinosaur, Daemonosaurus might have used its long premaxillary teeth to comb vegetation to remove the greenery while leaving the stems.

Several basal sauropodomorphs also had an overbite. So an overbite is not an autapomorphy at this node. Even with the addition of a predentary, Daemonosaurus also had a short mandible (Fig. 2).

The proto-predentary extends the mandibles to their proper length.

Figure 3. The proto-predentary extends the mandibles to their proper length. Several basal sauropodomorphs also have an overbite. So an overbite is not an autapomorphy at this node.

Figure 4. Overall the skull of Dryosaurus is similar to that of Daemonosaurus, but has no premaxillary teeth, has a distinct predentary, and develops a palpebral.

Figure 4. Overall the skull of Dryosaurus is similar to that of Daemonosaurus, but has no premaxillary teeth, has a distinct predentary, and develops a palpebral.

It’s worth taking a look at another, more distant sister, Dryosaurus (Fig. 4), another phytodinosaur that provides clues to the architecture of the palate of Daemonosaurus. Perhaps Dryosaurus gives us further clues to the unknown post-crania of Daemonosaurus.

References
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online