Poposaur palates

The palates of poposaurs are poorly known Some have not been described or reconstructed (Fig.1). Others have been wrongly reconstructed or partially reconstructed (Fig. 4). Here (Fig. 1) are two poposaurs, Effigia and Shuvosaurus next to Daemonosaurus (Sues et al. 2011, also largely guessed at from broken pieces) and Thecodontosaurus, which provides more certitude. Most unfortunately, the palate of Lotosaurus has not been described or illustrated despite the presence of several specimens and museum casts. The little question is: On Daemonosaurus, which way do the ectopterygoids go? Long side against the pterygoid, as in rauisuchids? Or short side, as in Effigia and other dinosaurs?

Figure 1. Poposaur palates (Effigia and Shuvosaurus) along with Daemonoaurus and Thecodontosaurus (= Pantydraco, from Yates 2003)

On rauisuchians, as in ornithosuchians (Fig. 2), the ectopterygoid has a larger contact area with the lateral pterygoid and it produces a small “stem” to contact the jugal (as in Saurosuchus) or the maxilla (as in Riojasuchus). If you flip the ectopterygoid of Daemonosaurus, you get the rauisuchian type of ectopterygoid. Left as is (Fig. 1), however, you get the dinosaurian type,  and that is the preferred reconstruction here based on phylogenetic bracketing.

Figure 2. Click to enlarge. Euparkeriid, ornithosuchian, rauisuchian, aetosaurian, and basal archosaur palates. Here are Euparkeria and Osmolskina, both euparkeriids. Ornithosuchus and Riojasuchus are ornithosuchids. Saurosuchus and Postosuchus are both rauisuchians. Stagonolepis is an aetosaur. Pseudhesperosuchus is close to the basal archosaur pattern with a much smaller ectopterygoid and smaller ectopterygoid/pterygoid contact. The original configuration is shown on the right side. A possible alternative is shown on the left. Not sure how it was preserved. I’d like to know if you have this data. If the left is correct in figure 2 (Pseudohesperosuchus), and Shuvosaurus is also correct in figure 1, these suggest that Daemonosaurus is correctly drawn in figure 1.

Figure 4. Silesaurus palate with missing elements restored on the right. Illustration (without color) from Dzik 2003 who illustrated missing elements on the left.

Silesaurus Palate The missing ectopterygoid and palatine were not illustrated for Silesaurus. Given the palates of related taxa (Fig.1), I have added the missing elements on the right here (Fig. 4) to match them. Thus these restorations are guesses that appear to make sense in context. When better data come along, we’ll make improvements.

This has been a first attempt at reconstructing the palates of several poposaurs at once based on similar morphologies in close kin. The palates should remain somewhat similar. If anyone has good data on the palates of other rauisuchians and basal dinosaurs, please forward them on.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Figure 3 is absent from this post now. Apologies. I had it in my files for several years and thought it had been published by now. It had not. 

 

References Bonaparte JF 1969. Dos nuevas “Faunas” de reptiles Triasicos de Argentina: I. Gondwana Symp., IVGS: 283-306.
Borsuk-Bialynicka M and Evans SE 2009. Cranial and mandibular osteology of the Early Triassic archosauriform Osmolskina czatkowicensis from Poland. Palaeontologia Polonica 65, 235–281.
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Chatterjee S 1985. Postosuchus, a new Thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 309 (1139): 395–460. doi:10.1098/rstb.1985.0092.
Chatterjee S 1991. An unusual toothless archosaur from the Triassic of Texas: the world’s oldest ostrich dinosaur? Abstract, Journal of Vertebrate Paleontology, 8(3): 11A.
Chatterjee S 1993. Shuvosaurus, a new theropod: an unusual theropod dinosaur from the Triassic of Texas. National Geographic Research and Exploration 9 (3): 274–285.
Dzik J 2003. A beaked herbivorous archosaur with dinosaur affinities from the early Late Triassic of Poland. Journal of Vertebrate Paleontology 23: 556-574.
Ewer RF 1965. The Anatomy of the Thecodont Reptile Euparkeria capensis Broom Philosophical Transactions of the Royal Society London B 248 379-435. doi: 10.1098/rstb.1965.0003
Rauhut OWM 1997. On the cranial anatomy of Shuvosaurus inexpectatus (Dinosauria: Theropoda). In: Sachs, S., Rauhut, O. W. M. & Weigert, A. (eds) 1. Treffen der deutschsprachigen Palaeoherpetologen, Düsseldorf, 21.-23.02.1997; Extended Abstracts. Terra Nostra 7/97, pp. 17-21.
Long R and Murry P 1995. Late Triassic (Carnian-Norian) Tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4, Pp. 153-163.
Sill WD 1974. The anatomy of Saurosuchus galilei and the relationships of the rauisuchid thecodonts. Bulletin of the Museum of Comparative Zoology 146: 317-362.
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 B, published online
Walker AD 1961. Triassic reptiles from the Elgin area: Stagonolepis, Dasygnathus and their allies. Philosophical Transactions of the Royal Society B 244:103-204.
Walker AD 1964. Triassic reptiles from the Elgin area: Ornithosuchus and the origin of carnosaurs. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 248(744): 53-134.
Yates AM 2003. A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs. Journal of Systematic Palaeontology 1(1):1-42. wiki/Daemonosaurus wiki/Shuvosaurus

An Assault on the Large Reptile Tree (dino section)!

Note added after publication: For those interested the comments section sheds new light. 

Mickey Mortimer, blogger of the Theropod database, put a lot of work into rescoring the dinosaur portion of the large reptile tree. With those changes, here is the recovered tree (taxa abbreviated but those in the know will know).

|–Turfano
`–+–Gracili
`–+–Arizona
`–+–+–Loto
|  `–+–Popo
|     `–+–Effi
|        `–Shuvo
`–+–+–Pseudolago
|  `–Sile
`–+–Mara
`–+–Pisano
`–+–+–Scelido
|  `–+–Heterodonto
|     |–Hexinlu
|     `–+–Agili
|        `–+–Lesotho
|           `–Scutello
`–+–+–Masso
|  `–+–Theco
|     `–Saturn
`–+–Daemono
`–+–+–Panphag
|  `–Pampa
`–+–Herrera
`–+–Trial
|–SMNS
|–Tawa
`–Coelo

You’ll note that Saurischia is recovered with [Sauropodomorpha + Theropoda]. Panphagia + Pampadromaeus nest basal to Theropoda, and the [poposaurids + Arizonasaurus] nest close to the basal archosaur/crocodylomorph, Gracilisuchus. Ornithischians are in the middle.

Figure 1. A segment of the large reptile tree, focused on the Dinosauria.

These are different nestings from the large reptile tree (Fig. 1). Basically the Dinosauria has been flipped top to bottom.

Well, then, let’s test the Mortimer tree
You’ll recall when I removed taxa, clades, or large numbers of clades from the large reptile tree, the rest of the topology did not change. When I tested only skulls or only post-crania, the tree did not change. These are signs of stability and strength.

However,
when I removed the [poposaurs + Arizonasaurus] from the Mortimer tree, the topology reverted to that of the large reptile tree. That’s a big change. And there’s more:

Note
In the Mortimer tree theropods nest as the most derived clade of dinos, preceded by several clades of herbivores in this pattern:

Quoting from my reply to MM: “Turfanosuchus and Gracilisuchus (carnivores) at the base giving rise to Poposaurids (herbivores), then Silesaurids (herbivores), then Marasuchus (carnivore), then Pisanosaurus (herbivore), then a split between Ornithischians (herbivores) and Saurischians led by Sauropodomorphs on one branch (herbivores) and Daemonosaurus (?-vore) at the base of Panphagia + Pampadromaeus (herbivores) and theropods (carnivores). As you can see this is a varied mix of herbies and carnies, which is not the case in the Large Reptile Tree”

In the LRT the theropods nested as basal dinos, giving rise via Panphagia, Pampadromaeus and Daemonosaurus to herbivorous sauropodomorphs, poposaurids and ornithischia. Basically the same tree, just flipped top to bottom.

Not sure yet what ordering, scoring, what-have-you turned the Mortimer tree upside-down, but having theropods as derived and widely separating Gracilisuchus from Herrerasaurus raises red flags. It just ain’t right. Isn’t it more tenable that certain theropods gave rise to herbivores, first with saurischian pelves and later with ornithischian pelves?

The unstable topology is also bothersome. Removing taxa should not upset the topology. Hopefully we’ll come to a resolution on this. The devil is probably in the details many or all of which can be seen here at M. Mortimer’s blog post.

Arizonasaurus does not belong here. It nests with rauisuchians and shares few to  no synapomorphic traits with Gracilisuchus, a basal crocodylomorph.

I appreciate the work by MM and, perhaps, some of the rescoring is justified. I don’t know. In any case, the results do not appear to be tenable.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Eosinopteryx – part 1 – Feathers, but no flapping

Eosinopteryx brevipenna (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation) is represented by a new complete skeleton. It was a feathered theropod dinosaur about 30 cm long. The forelimb feathers were quite long (Fig. 1), but the tail feathers were not.

Paravian? or Preavian?
We’ve been looking for a feathered theropod without elongated coracoids to precede Archaeopteryx. We also need this taxon to be not pre-oviraptorid or pre-alvarezsaurid. The authors argue, with a very extensive phylogenetic analysis, that this is a troodontid resembling Anchiornis, with less extensive feathers on the hind limbs and tail. Anchiornis greatly resembled Archaeopteryx and is, therefore, closely related. Of that, there is no doubt.

Why There is Doubt
I have not created a competing analysis. Checking out Greg Paul’s figure of Anchiornis (Paul 2010), I note his Anchiornis has the short torso and elongated coracoid also seen in Archaeopteryx, troodontids and deinonychosaurs.

Figure 1. Click to enlarge. Eosinopteryx reconstructed in lateral view. Soft tissue impressions preserved on the fossil are represented here in gray. Note the small size of the coracoid (yellow) and its curved lower rim, which indicates this specimen was a pre-flapping dinosaur. Pedal digit 2 was not modified as a “killing” claw. Elements figured with DGS.

What sets Eosinopteryx apart from these?
A short coracoid with a broad curved ventral rim - Therefore Eosinopteryx did not flap and was not descended from flappers. We haven’t seen a terrestrial descendant of Archaeopteryx yet without elongated coracoids. For more on this, compare Huaxiagnathus (with its short coracoid) to Velociraptor, (with its long, tall coracoid). Otherwise these two greatly resemble one another, with the former lacking sternal plates, a retroverted pubis and caudal rods. These traits are also lacking in Eosinopteryx.

A relatively smaller skull – Much smaller than in Anchiornis.

A relatively longer torso – Much longer than in Anchiornis.

A relatively shorter pubis – Much shorter than in Anchiornis.

All these traits are primitive for theropods.

Unfortunately, 
Huaxiagnathus was not included in the analysis of Godefroit et al. (2013). Neither were oviraptorids or alvarezsaurids. Eosinopteryx needs to be compared to these missing basal taxa along with the other taxa they previously tested. Once that’s done, let’s see if the topology of the tree doesn’t shift Eosinopteryx down below (more primitive than) Archaeopteryx. 

Addendum: The analysis of Godefroit et al. (2013) was based on and provided only a segment of an earlier analysis that DID include these more primitive taxa. Thus my doubt is reduced somewhat as all pertinent taxa were included.  Even so, I wonder why these two “sisters” don’t look more alike.

If anyone has details on why Godefroit et al. 2013 said the “bone structure would have limited its ability to flap its wings,” I’d like to see it.

Interesting that this birdy topic just came up a few days ago with Mahakala. Reminds me to be careful what I wish for.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié FO and Claeys P. 2013. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4: 1394. doi:10.1038/ncomms2389
Paul GS 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press 320 pp.

wiki/Eosinopteryx

Sereno on Stage: Must See YouTube Video

Sorry for the short post today.

Dr. Paul Sereno discusses paleontology and extreme dinosaurs for National Geographic. Click to see video.

Dr. Paul Sereno discusses Nigersaurus and other Sahara “Extreme Dinosaurs” in this engrossing, extremely well done 45 minute video. See it here. Great details and he’s a great speaker.

Dr. Sereno discusses paleontology here.

The Peabody Torosaurus by Mike Anderson, sculptor

The video “Creating the Peabody Torosaurus” is a fascinating and educational documentary of the sculpting of the museum’s entry piece. Sculptor Mike Anderson went to high school with me. Small world. Neither of us showed any interest in sculpture or dinosaurs back then. Click to visit the Peabody website.

The 30-minute video “Creating the Peabody’s Torosaurus“ is featured today chiefly because the sculptor, Mike Anderson, is an old high school chum (1972, Parkway Central High, Chesterfield, MO, a suburb of St. Louis), and also because this is a great piece of scientific artwork.

This video has been around for several years and I’m overdue in giving it the credit it deserves. Jacques Gauthier narrates.

Sculptors and dino-lovers alike will enjoy and learn from this fascinating a well-produced video of a carefully crafted dinosaur. From bones to clay to wax and finally in bronze, this remarkable marriage of science and art will become a welcome addition to any collection.

At the 20th reunion (twenty years ago) Mike showed me photos of his Lucy, the australopithecine. So he knows his stuff. Experts have called on him for some pretty monumental work.

You will be wowed. I was too.

The Origin of Dinosaurs Goes Way, Way Back

Dinosaurs: A Concise Natural History by Fastovsky and Weishampel 2012

Hot on the heels of the rediscovery of Nyasasaurus (did it have heels?), a new book by Fastovsky and Weishampel (2012) Dinosaurs: A Concise Natural History (2nd Ed) discusses the origin of dinosaurs and many other dino topics. That publication inspired this post.

Earlier we looked at various competing hypotheses for the origin of the dinosaurs, closer to their departure from other reptiles, and why pterosaurs and phytosaurs have no business in the lineage of dinosaurs. Earlier we also looked at the base of the Archosauria and the Origin of the Dinosauria. Here we’re going to take this story way, way back and cover more bases.

We’re going to take dinosaur origins back to Ichthyostega, an early tetrapod. Why? Because we can! We have the only large reptile tree that documents every evolutionary step it took to create dinosaurs from their ancestral pollywogs in the Devonian. And we’ll met several dozen very interesting taxa along the way. For more details I encourage you to click on the links that interest you. There are more details and images there. And please remember, these are NOT the direct ancestors, but the closest reps we have to that unbroken string of unknown parents, grandparents, great grandparents, etc. etc.

Icthythostega (still pretty fishy), Pederpes (down to only five toes), Proterogyrinus (nostrils move to the snout tip), Eldeceeon (long toes), Seymouria (more terrestrial but convergently off to the side), Utegenia (more aquatic and off to the froggy side), Silvanerpeton (closer to Eldeceeon, with larger eyes, longer fifth toe) and Gephyrostegus (ankle includes fused elements creating an astragalus, a premaxilla/maxilla notch is present, more gracile limbs and a trend toward a much smaller size, which makes amniotic eggs possible) brings us to the base of the Reptilia.

Cephalerpeton (lose of palatal fangs, fusion of the intertemporal, straight posterior squamosal and longer, more gracile limbs) nests at the base of the otherwise diphyletic Reptilia.

Westlothiana (a little too long waisted, but no tabular horns, mandible reduced to three major bones in lateral view, the premaxilla did not descend), nests at the base of the new Archosauromorpha, followed by Paleothyris (now that’s more like it, short-waisted, athletic, enlarged canines, longer rostrum, high coronoid process, ossified scapulocoracoid, more gracile limbs and toes), Brouffia (minor improvements), Coelostegus (maxilla deeper, supratemporals angled down, vertebrae taller), Hylonomus (jugal invades the squamosal, gastralia present), Protorothyris (larger skull and deeper canine) and Aerosaurus (reduced squamosal, first appearance of the lateral temporal fenestra, but getting too robust in the postcrania) take us to the base of the Synapsida.

Heleosaurus (not so robust, smaller skull, longer neck, pelvis larger than scapulocoracoids, longer limbs, reduced to absent posterior ribs), Milleropsis (finally a tail is preserved and it is whip-like, metacarpal 3 is longer than 4, possible biped), Eudibamus (longer neck, upper temporal fenestra gives us a diapsid configuration, definite biped with another attenuated tail, but the toes were way too asymmetrical), Spinoaequalis (taller tail spines link this taxon to water, ulna and radius are longer and straighter, the tibia and fibula have less interossial space) and Petrolacosaurus (shorter rostrum, larger orbit, longer neck, whip-like tail, tibia and fibula bowed apart) take us past the base of the Diapsida.

Acerosodontosaurus (a little too robust, with smaller cervicals and with forelimbs too long and robust,) and Adelosaurus (smaller and more gracile with shorter fingers and toes) lead toward the Enaoliosauria, a large clade of aquatic and marine reptiles.

Tangasaurus (neck getting way too long, but limbs large and subequal) nests at the base of the Tangasauria (the more terrestrial lineage) followed by Thadeosaurus (gracile palatal elements, sterna appear for a short time), Orovenator (large naris, descending premaxilla, gracile posterior skull elements, skull taller than wide, rostrum concave dorsally) and Youngina (BPI3859) (taller lateral temporal fenestra, maxilla taller, pubis and ischium separate elements) take us to the base of the Protorosauria, which diverge at this point.

Youngina (AMNH5661) (skull a little too flat and wide, heading toward pararchosauriformes) and Youngoides (UC1528)  (smaller temporal fenestra, frontals without posterior process, pineal foramen tiny, quadrate leans anteriorly, possible antorbital fenestra) take us to the base of the Archosauriformes.

Now we come to more familiar territory, the base of the Euarchosauriformes, with Proterosuchus (first verified appearance of the antorbital fenestra, drooping premaxilla, mandibular fenestra, more robust taller cervicals, lower limb elements not bowed), Fugusuchus (larger more robust skull, fewer larger teeth), Garjainia (convex maxilla, naris rises on nose tip, shorter tail, deeper chest, deeper pelvis directed ventrally, more upright limbs), Euparkeria (smaller, more gracile, longer tail, higher naris, hooked fifth metatarsal), Ornithosuchus (a side branch experimenting with both convergent bipedality (deeper pelvis) and a deeper, narrower skull) and Vjushkovia (not so derived, taking its time evolving evidently, but with a high naris and pedal digit 3 longer than 4) take us to the base of the Rausuchia and a fish-eating side branch that includes the long-necked Yarasuchus and Ticinosuchus, which had lost its premaxillary teeth.

Now we hit the base of the Archosauria represented by Decuriasuchus (super slender forelimbs and pectoral girdle), Turfanosuchus (looks like a reptilian horse with a smaller skull, longer neck and a high carriage) and Gracilisuchus (at the base of the crocodylomorpha). Some early members were bipeds.

Figure 1. Lewisuchus, a tiny predecessor to crocs and dinos (including birds).

Lewisuchus is known from too few pieces, but might be just what we’re looking for in a basalmost dino. It likely had much longer hind limbs than forelimbs, considering the general proportions that are known. And it was much smaller than its closest kin. Such traits could lead toward crocs or dinos, but at this point the back of the skull suggests this taxon leads to a third bipedal lineage without many descendants.

Trialestes (had croc-like elongated carpals, a tridactyl pes, pelvis perforated, femoral head inturned, vertebral centra with excavated lateral surfaces, longer radius than humerus, but late Triassic) and probably Nyasasaurus (large deltopectoral crest and Early Middle Triassic) nest at the base of the Dinosauria, specifically the Theropoda. Panphagia and Pampadromaeus nest at the base of the Phytodinosauria (sauropodomorphs + the other herby dinos, enlargement of premaxillary teeth, longer neck). Pisanosaurus (shorter neck, blunter teeth) nests at the base of the Poposauridae (traditionally considered dinosaur-like rauisuchians due to the extended calcaneum, but here nesting with dinos). Massospondylus (more cervicals, shorter forelimb, two lateral fingers vestigial) nests at the base of the Sauropodomorpha. Daemonosaurus (reduced antorbital fenestra, longer premaxillary fangs, postnarial process of premaxilla longer, shorter jaw) nests at the base of the Ornithischia.

Figure 2. The heretical model of dinosaur origins (Peters 2007).

YouTube has a short video on the Origin of Dinosaurs that pretty much follows the traditional route.

Please remember that, despite tradition and textbooks, the Phytosauria, Proterochampsia and Pterosauria have nothing to do with dinosaur origins. The Proterochampsia include Dromomeron and Lagerpeton, as close relatives to Tropidosuchus, another convergent biped. A large reptile tree demonstrates this. And this experiment can be repeated if anyone cares to add a taxa or two.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Various other online refs
Discovery News
Wiki-Dinosaur
Science News

Nyasasaurus: World’s Oldest Dinosaur?

At 243 million years old (Late Anisian, Early Middle Triassic), Nyasasaurus parringtoni, was yesterday promoted as a possible world’s oldest dinosaur. Found in the 1930s, described in the 1950s, it was recently redescribed from a museum shelf by Nesbitt et al. (2012) as the oldest known member of, or the sister-taxon to, the Dinosauria.

According to Wiki, dinosaur traits in Nyasasaurus include the long deltopectoral crest with a deflected top on the humerus,  elongated cervicals with hollowed-out lateral portions; and, perhaps, the possession of three sacral vertebrae instead of two. 

The large reptile tree includes Lotosaurus among the Dinosauria at 240 million years ago, so not as old. An ancestral taxon, Vjushkovia, was a contemporary. Euparkeria was older at 247 million years ago, along with some – but not all – of the more primitive known taxa. Even Proterosuchus at the base of the Archosauriformes goes back only to 250 million years ago. That’s a lot of variation in a very short amount of time.

So, there was lots of evolution somewhere, or everywhere, in the Early Triassic! The Dinosauria likely originated in Tanzania or elsewhere thousands to millions of years earlier than Nyasasaurus today represented by a single partial fossil -probably- from among the millions of Nyasasaurus living back then.

I won’t be able to provide a cladistic analysis with so few bones known, but having three sacrals points to something other than dinosaurs since Herrerasaurus and basal phytodinos like Pampadromaeus have only two. The long neck could be dinosaurian. It would also be worthwhile to compare that humerus to Decuriasuchus, a basal archosaur from 240 mya, closer to basal Rauisuchia and basal crocs.

Nyasasaurus is certainly a key taxon at the cusp of several important clades. Let’s hope more material comes out soon.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Charig AJ 1956. New Triassic archosaurs from Tanganyika, including Mandasuchus and Teleocrater. Dissertation, Cambridge University.
Nesbitt SJ, Barrett PM, Werning S, Sidor CA and Charig AJ 2012. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters. online

Nyasasaurus Wiki

Lambeosaurus crest reinterpretation

So, while looking through old JVPs I ran across this oddity. Perhaps it has already been discussed elsewhere. Any dino-guys out there, feel free to chirp in.

[I have to confess, I threw this one together rapidly and I made a mistake. Andrew Farke and Jaime Headden steered me in a better direction. Even so, there's still something  to say here. After further examination, I learned something. And no, I did not misinterpret a tracing earlier. There was no tracing. I was working solely on the tracing by Evans and Reisz (2007.]

Evans and Reisz (2007) took a look at the skull of Lambeosaurus magnicristatus (Fig. 1) and identified the bones and plaster that make up the crest. They put the nasal above and behind the orbit in a narrow strip. That struck me as odd. Odd things make for interesting posts.

Figure 1. From Evans and Reisz (2007) in which the skull of Lambeosaurus has really morphed beyond the primitive patterns such that the lateral and ascending processes of the premaxilla were greatly enlarged to form the anterior rim of a large crest. The gray areas represent plaster. That adds a problem in that the boundaries of the various bones that make up the crest become even more difficult to ascertain.

The pattern of the bones in the Lambeosaurus crest might be more like this:

Figure 2. Lambeosaurus magnicristatus skull bones colorized. Darker areas are plaster. Orange is support metal. Note the larger extent of the nasal as part of the crest than figured by Evans and Reisz (2007). This pattern of a larger nasal is more like that of Corythosaurus than the other species of Lambeosaurus. This also replicates the triple strip premaxilla shared with Corythosaurus.

The strongest lines in the Lambeosaurus crest might define bone sutures. Or they might represent cracks. Or they might represent bone surface irregularities. I went with sutures. I might be wrong.

The image below of Corythosaurus, Hypacrosaurus and another species of Lambeosaurus (Fig. 3) helps set the possibilities of the extent of the premaxilla and nasal – along with the minor contribution by the prefrontal in the first two taxa.

Figure 3. Lambeosaur ontogeny with bones colorized. Nasal in blue. Premaxilla in yellow. Image from Brink et al. 2011.

Overall the broad crest of L. magnicristatus (Figs. 1, 2) appears closer in morphology to that of Corythosaurus (Fig. 3). The premaxilla appears to have three ascending processes in both taxa. The crest is expanded to a larger extent than in the other two. There appears to be a contribution from the prefrontal that Lambeosaurus lambei (Fig. 3) crest does not have.

Here again, I’m stepping out of my comfort zone, but I’m avoiding the temptation of calling the nasal narrow just because L. lambei has a narrow nasal. They are all closely related taxa. I’m probably missing some of the fine points that differentiate them.

Again, sorry for the earlier mistake. It did lead to some interesting study.

We’ll take a look at bones that make up crests soon, as I see similarities here to the pterosaur Tupuxuara (by convergence, of course).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References 
Brink KS, Zelenitsky DK, Evans DC, Therrien F and Horner JR 2011. A sub-adult skull of Hypacrosaurus stebingeri (Ornithischia: Lambeosaurinae): Anatomy and comparison. Historical Biology 23(1):63-72.
Evans DC and Reisz RR 2007. Anatomy and relationships of Lambeosaurus magnicristatus, a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, Alberta. Journal of Vertebrate Paleontology 27 (2): 373–393.

Stenocybus and Daemonosaurus Convergence

Figure 1. Daemonosaurus and Stenocybus, two big-toothed, earlier adopters of an herbivorous diet? At least they both nest at the bases of two herbivorous clades. The morphology similarities are readily visible.

Dinosaurs produced several herbivorous clades, but the big one is the Phytodinosauria, which includes sauropodomorphs, poposaurids and the ornithischians. At its base is Daemonosaurus (Fig. 1).

Therapsids produced several herbivorous clades, but one of the first was the Anomodontia (dicynodonts and dromosaurs). At its base is Stenocybus (Fig. 1).

Despite their phylogenetic differences, Damonosaurus and Stenocybus (known only from skulls so far) share several character traits (Fig. 1).

Among these are: 1. short, convex rostrum; 2. large round orbit about a quarter the length of the skull; 3. Elongated, rake-like teeth; 4. Ventrally convex maxilla; 5. Canine tooth; 6. Reduced mandibular fenestra; 7. Reduced quadratojugal; 8. Small coronoid process; 9. Elongated anterior dentary teeth; 10. Little to no retroarticular process. 11. Jaw joint descends below tooth row. Perhaps you’ll see others.

These traits can be labeled superficial or convergent due to their phylogenetic differences. The relatives of Daemonosaurus were dinosaur-ish bipeds. The relatives of Stenocybus were pelycosaur-ish quadrupeds. Even so, at these taxa we see two transitions from carnivory to herbivory.

So What Do We See and What Does It Mean?
Taken alone, neither Daemonosaurus nor Stenocybus would strike anyone as a plant-eater, and perhaps they weren’t — but their descendants were.

The rake-like teeth would have been suitable for pulling leaves off of stems. Together with this, as in all therapsids and sphenacodonts the jaw joint was lowered in Stenocybus. Similarly, compared to Pampadromaeus the jaw joint was lower in Daemonosaurus. This arrangement helps retain jaw joint articulation with muscles pulling the jaw back in opposition to forces pulling the jaw out while feeding.

Compared to ancestors, Pampadromaeus and Ophiacodon, both Daemonosaurus and Stenocybus, respectively, had a shorter rostrum. A longer rostrum makes it a little easier to grab prey. Plants don’t run and fight.

The mandibular fenestra was smaller than in ancestors. Not sure what this means other than reinforcing the mandible structure. I have no idea what the palate of Daemonosaurus looks like, so no comparisons can be made there.

Anyway, It thought the similarities were curious.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Cheng Z and Li J 1997. A new genus of primitive dinocephalian – the third report on Late Permian Dashankou lower tetrapod fauna. Vertebrata PalAsiatica 35 (1): 35-43. [in Chinese with English summary]
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia), Journal of Systematic Palaeontology, 9: 2, 261 — 304, First published on: 13 December 2010 (iFirst)
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 B, published online 

wiki/Daemonosaurus
wiki/Stenocybus

Maybe Asilisaurus had shorter arms

Figure 1. Asilisaurus. Above: as reconstructed by Nesbitt et al. (2010). Below: With shorter arms, more in accord with the thickness of the bones. The related Lotosaurus was a quadruped and had much more robust forelimbs. Other sister taxa had relatively short arms.

How Long Were the Arms of Asilisaurus?
Asilisaurus (Nesbitt et al. 2010) is a basal dinosaur with incomplete forelimbs. It was originally reconstructed with long forelimbs in a quadrupedal configuration (Fig. 1). The question is: were the arms reconstructed too long? The humerus includes both ends but has a broken middle. The ulna/radius does not include the proximal ends.

Asilisaurus is the oldest known reptile in the dinosaur lineage, according to Nesbitt et al. (2010) and Wikipedia, but the large reptile tree finds Lotosaurus* is also a dinosaur that is just as old. Both lived during the Anisian period of the Middle Triassic (245-237 mya). Asilisaurus is a sister to Silesaurus in alll studies.

Considering only the Nesbitt drawings (my only data), it appears that the fore limbs may have been drawn too long in order to force a quadrupedal configuration. Why not let the bone diameters help determine their lengths? Moreover, sister taxa, like Pisanosaurus and Poposaurus, had short forelimbs. Silesaurus may have been bipedal. Lotosaurus was a sister taxon with robust forelimbs and a quadrupedal configuration. If Asilisaurus were indeed quadrupedal more robust forelimbs might be expected following these patterns. Even Pisanosaurus has more robust forelimbs.

*Nesbitt (2007) suggested Lotosaurus was a poposaurid, more closely related to Shuvosaurus, not to Xilosuchus, but in the same large clade of rauisuchians. The large reptile tree nested poposaurids within the Dinosauria, but Xilosuchus and Arizonasaurus, the other two finbacks, with the rauisuchids.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RMH and Tsuji LMA 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464 (7285): 95–98. doi:10.1038/nature08718. PMID 20203608.