Spinosaurus thermoregulation

Spinosaurus has been recently revised from a long-legged terrestrial big brother to Baryonyx, to a short-legged aquatic giant that probably found it difficult to walk bipedally (Ibrahim et al. 2014; Fig. 1). As the only quadrupedal theropod, Spinosaurus needs to be considered in terms of its environment.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish. Click to enlarge. Spinosaurus may have been so large because its prey was so large. As the only aquatic dinosaur, Spinosaurus may have developed a sail to help regulate body temperature while staying submerged except to lay eggs. It may have never needed to stand bipedally, like its theropod sisters.

As the only aquatic dinosaur (until Hesperornis, ducks and penguins came along), Spinosaurus was unlike its closest sisters in several regards. It was larger. It had shorter hind limbs. And it had that famous sail back. If we put Spinosaurus into it proper environment, shallow waters, then the reason for the sail, the great size and the short hind limbs becomes readily apparent.

Sail for thermoregulation
Most dinosaurs did not live in water. Those that do (like aquatic birds) are covered with insulating feathers that keep them warm. Spinosaurus likely did not have feathers, or enough feathers to keep it warm, but it did have that sail. Exposed above the surface to the warmer air, the sail could have helped Spinosaurus maintain a higher body temperature in cooler waters. Overheating was unlikely surrounded by water. Other theropods with longer dorsal spines, like Acrocanthosaurus, show no aquatic adaptations.

Short legs for walking underwater
The hind limbs on Spinosaurus are so short relative to the body that it is difficult to see how it could have walked bipedally like other theropod dinosaurs. Those heavily clawed arms appear to be ill-suited to support the great weight of its forequarters. In an aquatic environment, however, that great weight essentially disappears. Spinosaurus could have walked along the muddy/sandy bottom. It is not known if the hind feet were webbed, but they look like they were best articulated when they were spread (Fig. 2).

Figure 2. The foot of Spinosaurus with PILs and possible webbing. The joints of the foot on the right appear to be better aligned.

Figure 2. The foot of Spinosaurus in ventral view with PILs and possible webbing. The joints of the foot on the right appear to be better aligned.That’s the vestige of digit 5 below metatarsal 4.

Spinosaurus likely preferred water of a certain depth. Deep enough to cover everything but the sail (floating enough to keep weight off its feet), yet just deep enough to touch the bottom with its clawed feet. After all, Spinosaurus did not have flippers or fins. That’s not to say it didn’t swim in deeper waters, or visit shallower waters. After all, it had to lay eggs on land, but it is likely to have been awkward when not supported by water.

Great size
At the same time and in the same waters as Spinosaurus several different types of giant fish co-existed. Many, no doubt, were on Spinosaurus’ menu. Younger spinosaurs would have eaten younger, smaller fish. The snout of Spinosaurus has many small pits. These are thought to have housed pressure sensors to detect prey in murky waters, as in living crocs.

Spinosaurus has been well studied
and there is little else I can add to the data and hypotheses available online here, here and here. The Spinosaurus in Jurassic Park 3 represents the old long-legged, terrestrial version, so best to forget images of Spino attacking T-rex on land. There is great artwork of the new Spinosaurus here, here, here and here.

And I just ran across this beauty.

References
Ibrahim N, Sereno PC, Dal Sasso C, Maganuco S, Fabbri M, Martill DM, Zouhri S, Myhrvold N, Iurino DA 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science. doi:10.1126/science.1258750.

At Jurassic World size matters (and so do feathers)

Everyone it seems
is excited by the prospect of a new Jurassic Park 4/Jurassic World movie coming this summer, June 12. While most will be wowed by the special effects (yours truly among them), there will be a few who will roll their eyes so far back inside their skull that they will actually see their brain.

Two issues to the forefront: size and feathers (Figs. 1-5).

Figure 1. Click to enlarge. The giant sea monster (not sure if this is a pliosaur or a mosasaur) is feeding on a great white shark.  Actual size comparisons below.

Figure 1. Click to enlarge. The Jurassic Park 4 giant sea monster (not sure if this is a pliosaur or a mosasaur) is feeding on a great white shark. Actual size comparisons below, from Giants and A Gallery of Dinosaurs by yours truly, 1986, 1989. Even the largest prehistoric sea monsters could not swallow an average great white shark whole. If the great white in JW is a typical 15 foot length, the skull of the monster is 2x or 30 feet in length. Based on the skull/neck ratio of the monster it appears to be a mosasaur possibly 250 feet long.

Bigger is better.
And let’s face it, we go to the movies to be thrilled. We go to the library to learn something. Here (Fig. 1) The JW sea monster (pliosaur? or mosasaur?) is a wee bit too large for our great white shark former supervillain, now relegated to being a prehistoric dog biscuit or sardine. Based on the skull/neck ratio of the monster it appears to be a mosasaur possibly 250 feet long.

Figure 2. Jurassic Park 4 giant Apatosaurus/Diplodocus-like sauropod. Inset, Diplodocus to scale.

Figure 2. Jurassic Park 4 giant Apatosaurus/Diplodocus-like sauropod. Inset, Diplodocus to scale.

Sauropods (Fig. 2), the largest of all land animals, are made twice their original size in Jurassic World.

Figure 3. Jurrasic Park 4 giant Stegosaurus (above, highlighted by Photoshop) and to scale with President Obama (below).

Figure 3. Jurrasic Park 4 giant Stegosaurus (above, highlighted by Photoshop) and to scale with President Obama (below).

Jurassic World Stegosaurus (Fig. 3) might be on the large side as well.

Figure 4. Here they got the scale right, but not the scales. Jurassic Park 4 scaly velociraptors (presumeably Deinonychus, above) and below feathered Deinonychyus (below) from A Gallery of Dinosaurs by David Peters, from 1989.  JP4 is at least 24 years behind in its depiction because I saw feathered 'raptors' in various books a few years before that.

Figure 4. Here they got the scale right, but not the scales. Jurassic Park 4 scaly velociraptors (presumeably Deinonychus, above) and (below) feathered Deinonychyus from A Gallery of Dinosaurs by yours truly from 1989. That means JP4 is at least 24 years behind in its depiction because I saw feathered ‘raptors’ in various books a few years before that.

The movie villains are here turned heroes as the scaly 2015 velociraptors are trained by the dude in the Paul Sereno vest (Fig. 4). Below a 1989 feathered Deinonychus. So the scale is right. The scales are wrong…

And finally, 
Look, out of the sky! It’s a bird! It’s a plane! No its a flock of pterosaurs (Fig. 5). At first they seem like Dimorphodon. And hey, look! They have a narrow chord wing membrane attached to the front of the femur. But wait! The shadow is gigantic and has no tail. Then the lightweight pterosaur grabs a much more massive primate on holiday and without even an umphhh takes its prey aloft using its feet, like an eagle does with a salmon. Let me say that again, “with a salmon.” Then the metacarpals are revealed to be elongate. Perhaps not as exciting as all that, a few to scale images of pterosaurs are also shown below.

Figure 5. Jurassic Park 4's giant Dimorphodon(?) (probably weighing 36 lbs) picking up a tourist (probably weighing 120 pounds) in a tribute to Raquel Welch and Faye Wray who were taken aloft by Pteranodon.  Below the rather feeble feet of several Pteranodon specimens, none of which had trenchant claws and mighty toe tendon anchors. These feet, some flat-footed others not, were made for walking. The foot of Dimorphodon with trenchant claws, but look how small it is to scale! Below that the even more feeble feet of the ornithocheirid Anhanguera.

Figure 5. Jurassic Park 4’s giant Dimorphodon(?) (probably weighing 36 lbs) picking up a tourist (probably weighing 120 pounds) in a tribute to Raquel Welch and Faye Wray who were taken aloft by Pteranodon. Below the rather feeble feet of several Pteranodon specimens, none of which had trenchant claws and mighty toe tendon anchors. These feet, some flat-footed others not, were made for walking. The foot of Dimorphodon with trenchant claws, but look how small it is to scale! Below that the even more feeble feet of the ornithocheirid Anhanguera.

To read Giants and A Gallery of Dinosaurs free online, click here.

Click here to see the Jurassic Park 4 trailer on YouTube.
Click here to see the Jurassic Park 4 SuperBowl trailer on YouTube.
See you at Jurassic World this summer!

 

Stephen Czerkas

Paleoartist and writer Stephen Czerkas died this week.
I respected his artwork (Fig. 1). He was 63 years old.

Stephen Czerkas paleoartist with his most famous creation, before and after feathers.

Figure 1. Stephen Czerkas paleoartist with his most famous creation, Deinonychus, before and after feathers.

I only met Stephen Czerkas once, 
but saw his famous Deinonychus everywhere. He and his wife Sylvia were at or near the center of dinosaur reconstruction several decades ago when I was just a pup. They published several books. Opened a museum. Introduced the world to sauropod spines and made some bad decisions.

Stephen Czerkas was a serious worker, intent on ‘getting things right.’ To that end he added feathers to his Deinonychus (Fig. 1).

Sorry to see him go. He influenced us all.

Learn more here from Bill Stout’s homage to Stephen Czerkas.

 

Daemonosaurus, the Phytodinosauria and the Persistence of the Postfrontal

Earlier
we nested the Triassic saber-tooth, Daemonosaurus, at the base of the Ornithischia and near the base of the Phytodinosauria. The addition of the sauropodomorph, Leyesaurus (Apaldetti et al. 2014, Triassic/Jurassic boundary) to the large reptile tree supports that nesting with a very similar skull (Fig.1).

Figure 1. Click to enlarge. Sisters to Daemonosaurus, including Leyesaurus and Jeholosaurus. The postfrontal (in light red) is not fused in most of these taxa (Heterodontosaurus is the exception), contra current dinosaur paradigms. Note the resemblance of Daemonosaurus to the basal sauropodomorph, Leyesaurus. The increase in tooth size in Daemonosaurus was not derived from theropods, but was a unique character trait, shared, more or less with its sister, Jeholosaurus and to a lesser extent in Heterodontosaurus.

Figure 1. Click to enlarge. Sisters to Daemonosaurus, including Leyesaurus and Jeholosaurus. The postfrontal (in light red) is not fused in most of these taxa (Heterodontosaurus is the exception), contra current dinosaur paradigms. Note the resemblance of Daemonosaurus to the basal sauropodomorph, Leyesaurus. The increase in tooth size in Daemonosaurus was not derived from theropods, but was a unique character trait, shared, more or less with its sister, Jeholosaurus and to a lesser extent in Heterodontosaurus.

Along the way
it appeared that the postfrontal was retained in basal dinosaur taxa and outgroups, contra traditional dinosaur thinking.

Leyesaurus and Daemonosaurus
share greatly elongate cervicals and other traits (Fig. 1). Daemonosaurus was not included in the original analysis, but then Leyesaurus did not nest as a basal sauropodomorph as it does here. Leyesaurus has quite a wide skull, distinct from most basal dinosaurs. It nests with Massospondylus, which earlier we noted looked a lot like Daemonosaurus.

References
Apaldetti C, Marinez RN, Alcober OA and Pol D 2014. A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina. PLoS ONE 6(11): e26964. doi:10.1371/journal.pone.0026964

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The Origin of Dinosaurs – Updated Again

Earlier we looked at the origin of dinosaurs here, here and here.

Today we’ll take the linear approach, documenting the origin of dinosaurs with to scale images (Fig. 1), constant length specimens (Fig. 2) and skull-only specimens (Fig. 3).

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

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

Traditional workers (Irmis et al. 2007, Nesbitt 2011, Brusatte et al. 2010) add pterosaurs and Lagerpeton to the lineage of dinosaurs, but they are not related, according to the large reptile tree (at last updated!).

Derived from a sister to Vjushkovia, Decuriasuchus nests outside the Rauisuchia, but has many traits found in that clade. Notably it retained a simple axle acetabular joint, while rauisuchians overlapped the top of the femur with the ilium.

Figure 2. The origin of dinosaurs using constant length specimens. Here Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes and Herrerasaurus not to scale.

Figure 2. The origin of dinosaurs using constant length specimens. Here Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes and Herrerasaurus not to scale.

Bipedal locomotion
was an early innovation, even if only occasionally in long-necked Turfanosuchus, which gave rise to poposaurs, and wide-skulled Gracilisuchus, which gave rise to basal bipedal crocs.  Miniaturization occurred at the base of the Archosauria and the base of the Dinosauria.

Figure 2. Origin of dinosaurs documented by skulls shown at constant length in evolutionary order. Shown here are Decuriasuchus, Turfanosuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Eoraptor and Tawa, not to scale.

Figure 2. Origin of dinosaurs documented by skulls shown at constant length in evolutionary order. Shown here are Decuriasuchus, Turfanosuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Eoraptor and Tawa, not to scale. Despite the evolutionary progress of the skulls, each one also represents a distinct branch not on the single lineage of dinosaurs, a lineage that will never be found precisely, but only estimated using sister taxa shown here and those yet to be discovered.

Figure 5. Family tree of the Archosauria and basal Dinosauria. Bootstrap scores are shown.

Figure 5. Family tree of the Archosauria and basal Dinosauria. Bootstrap scores are shown.

 

 

 

Relative to basal crocs,
basal dinos had a taller, narrower skull first seen in tiny Lewisuchus and Pseudhesperosuchus, which further developed a very tall postorbital.

Most basal dinosaurs, like Tawa (a basal theropod) and Eoraptor (a basal phytodinosaur) had a gracile premaxilla, but Herrerasaurus had a robust premaxilla with overlapping nasals to reinforce its rostrum.

Family Tree
The tree at left represents the latest thinking with Lewisuchus at the base of the previously unrecognized proto-dinosaurs. If dinosaurs are defined as birds + Triceratops, then the grade Lewisuchus to Herrerasaurus are not dinos in this tree even though they are  on the same lineage.

I hesitate to use the term Dinosauromorpha because it was defined by Sereno 1991 as: “the last common ancestor of Lagerpeton chanarensisMarasuchus lilloensisPseudolagosuchus major and the Dinosauria (including Aves) and all its descendants.” Unfortunately that definition is redundant with the Archosauriformes as it includes Proterosuchus. You can see where Lagerpeton nests here

References
Bittencourt JS, Arcucci AB, Maricano CA and Langer MC 2014. Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina) its inclusivity, and relationships amongst early dinosauromorphs. Journal of Systematic Palaeontology. Published online: 31 Mar 201. DOI:10.1080/14772019.2013.878758
Bonaparte JF 1969. Dos nuevos “faunas” de reptiles triásicos de Argentina. Gondwana Stratigraphy. Paris: UNESCO. pp. 283–306.
Bonaparte JF 1982. Classification of the Thecodontia. Geobios Mem. Spec. 6, 99-112
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.
Clark JM et al. 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20 (4): 683–704.
Clark JM, Xu X, Forster CA and Wang Y 2004. A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodilian skull. Nature 430:1021-1024.
Clark JM, Sues H-D and Berman DS 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20(4):683-704.
França MAG, Ferigolo J and Langer MC 2011. Associated skeletons of a new middle Triassic “Rauisuchia” from Brazil. Naturwissenschaften.
DOI 10.1007/s00114-011-0782-3
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
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.
Nesbitt SJ. et al. 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464(7285):95-8
Nesbitt SJ, Smith ND, Irmis RB, Turner AH,Downs A and Norell, MA 2009. A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs”, Science 326 (5959):1530–1533.
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. Journal of Vertebrate Paleontology 13(3):287-308.
Reig, OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna; XIV, Lewisuchusadmixtus, gen. et sp. nov., a further thecodont from the Chañares beds. Breviora 390:1-13
Sereno PC, Forster CA, Rogers RR and Moneta AM 1993. Primitive dinosaur skeleton form Argentina and the early evolution of the Dinosauria. Nature 361, 64-66.
Sereno PC, Martínez RN and Alcober OA 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina. Journal of Vertebrate Paleontology Memoir 12: 83-179 DOI:10.1080/02724634.2013.820113
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.
Wu X-C and Russell AP 2001. Redescription of Turfanosuchus dabanenesis (Archosauriformes) and new information on its phylogenetic relationships. Journal of Vertebrate Paleontology 21(1):40-50. Online pdf.
Young CC 1973. [On a new pseudosuchian from Turfan, Sinking (Xinjiang).] Memoirs of the Institute of Vertebrate Paleontology and Paleoanthropology of the Academia Sinica, Series B 10:15-37.

wiki/Decuriasuchus
wiki/Lewisuchus
wiki/Gracilisuchus
wiki/Trialestes
wiki/Pseudhesperosuchus
wiki/Eoraptor
wiki/Tawa
wiki/Herrerasaurus
wiki/Sanjuansaurus

 

Eoraptor, Panphagia and Pampadromaeus: how closely are they related?

Lumping and splitting
is something paleontologists do with the various specimens they find as they assign them names and nodes in the family tree of life. Jack Horner recently made news for lumping several pachycephalosaur genera together as distinct ontogenetic growth stages of the same genus and species. He did the same with Triceratops, which changed its appearance rather drastically while reaching maturity.

Today
let’s look at three closely related specimens, Panphagia protos Martinez and Alcobar (2009) , Eoraptor lunensis (Sereno et al. 1993, 2014) and Pampadromaeus barberenai (Cabriera et al. 2011, Fig. 1). These three nest between basalmost theropods and basalmost phytodinosaurs (sauropodomorphs + ornithischians) in the large reptile tree. Others consider them basal or stem sauropodomorphs, but only because basal ornithischians are not included in their analyses.

Figure 1. Eoraptor, Pampadromaeus and Panphagia. Three coeval South American dinosaurs between Theropoda and Phytodinosauria. Are they congeneric?

Figure 1. Eoraptor, Pampadromaeus and Panphagia. Three coeval South American dinosaurs between Theropoda and Phytodinosauria. Are they congeneric? Or are they distinct enough to be considered separate genera? To my eye, they appear to be morphs of a single genus.

The number of bones preserved
with each specimen varies, so all the bones cannot be compared with one another. What is preserved, however, appears to be more closely matched than many other specimens sharing the same generic name, like Pteranodon and Rhamphorhynchus. (Evidently dino-workers are splitters and ptero-workers are lumpers as, until recently, they preferred not to provide new names for distinct specimens, some of which were improperly considered juveniles of distinctly different larger specimens).

These three proto-phytodinosaurs (Fig. 1) are obviously similar.  Sereno, et al. (2014) often refers to “the closely related Pampadromaeus and Panphagia” when writing about Eoraptor.

What are the differences? 

Using the 228 characters of the large reptile tree is not enough to split and lump these three specimens. Only these three traits split them and cause loss of resolution.

  1. The anterior nasal is wider in Panphagia.
  2. The mandible tip does not descend in Pampadromaeus.
  3. The tibia is shorter than 2x the ilium length in Pampadromaeus

More resolution might come from adding taxa and more complete taxa, unless these three are indeed congeneric. Almost certainly there are obscure, but important differences not covered by the list of 228 rather obvious traits.

Enter Martinez et al. (2012).
Their strict consensus tree (51 taxa, 378 characters) was also unable to resolve relationships among these three and several other taxa. Their reduced consensus tree (eliminating poor specimens) nested them in ascending order: Phanphagia > Eoraptor > Pampadromaeus separated by single decay indices.

The position of Panphagia as basal to other sauropodomorphs is supported by nine unambiguous synapomorphies:

  1. pterygoid wing of the quadrate extending for more than 70% of the total quadrate length;
  2. presence of postparietal fenestra between supra occipital and parietals;
  3. supraoccipital wider than high;
  4. coarse serrations of the teeth angled upwards at 45◦;
  5. absence of a  postzygodiapophyseal lamina in cervical vertebrae 4–8;
  6. weakly developed laminae in the neural arches of cervical vertebrae 4–8;
  7. minimum width of the scapula less than 20% of its length;
  8. posterior end of the fibular condyle of the tibia anterior to the posterior margin of proximal articular surface;
  9. and strongly laterally curved iliac blade in dorsal view.

The more derived position of Eoraptor is supported by three unambiguous  synapomorphies:

  1. subtriangular cross-section of the ischial midshaft;
  2. supraacetabular crest of the ilium contacting the distal end of pubic peduncle;
  3. and sub triangular distal end of the ischium.

Pampadromaeus and more derived sauropodomorphs share four unambiguous synapomorphies:

  1. squamosal bordering the laterotemporal fenestra for more than 50% of its depth (62:0)
  2. length of the base of proximal caudal neural spines greater than half the length of the neural arch;
  3. transverse width of the distal humerus greater than 33 of its length;
  4. and length of the pubic peduncle of the ilium greater than twice the anteroposterior width of its distal end.

So the question remains,
are these several distinctions sufficient to split these three specimens? Are they indeed distinct genera? Or are they all three species of Eoraptor?  (Eoraptor is the earliest of these three to be named.)

References
Cabreira SF, Schultz CL, Bittencourt JS, Soares MB, Fortier DC, Silva LR and Langer MC 2011. New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil. Naturwissenschaften (advance online publication) DOI: 10.1007/s00114-011-0858-0
Martínez RN and Alcober OA 2009. A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha (pdf). PLoS ONE 4 (2): 1–12. doi:10.1371/journal.pone.0004397. PMC 2635939. PMID 19209223. online article
Martínez RN , Apaldeti C and Abelin  D 2012. Basal sauropodomorphs from the Ischigualasto Format ion, Journal of Vertebrate Paleontology, 32:sup1, 51-69.
Sereno PC, Forster CA, Rogers RR and Moneta AM 1993. Primitive dinosaur skeleton form Argentina and the early evolution of the Dinosauria. Nature 361, 64-66.
Sereno PC, Martínez RN and Alcober OA 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina. Journal of Vertebrate Paleontology Memoir 12: 83-179 DOI:10.1080/02724634.2013.820113

wiki/Eoraptor
wiki/Panphagia
wiki/Pampadromaeus

Daemonosaurus has two sister taxa: Haya and Jeholosaurus

Updated February 28, 2015 with a new skull for Daemonosaurus.

Earlier we talked about the Late Triassic saber-toothed dinosaur, Daemonosaurus (Sues et al. 2011, Fig. 1, CM 76821) originally considered a weird basal theropod between Eoraptor and Tawa. That’s due to taxon exclusion. The real sisters of Daemonosaurus were not tested. The authors also mistakenly nested Eoraptor within the Theropoda when it is actually an outgroup, a phytodinosaur closer to Sauropodomorpha, which were only included as a suprageneric taxon, along with Ornithischia. Unfortunately that’s the same suprageneric/taxon exclusion/inclusion problem that happens so often it’s not funny anymore.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale nest as sister taxa. And it’s easy to see why. Somewhere in this clade lies the origin of the predentary bone and the retroverted pubis. Long premaxillary teeth and a short rostrum are key traits. Note the infilling of the mandibular fenestra.

Solution: add taxa and avoid suprageneric taxa
In the large reptile tree Daemonosaurus did not nest with theropods, but at the base of the Ornithischia between basal phytodinosaurs like Eoraptor and the basal ornithischian, Pisanosaurus. It’s been three years since that post.

Today Jeholosaurus (Han et al 2012) and Haya (Figs. 1,2), two widely acknowledged basal ornithischians, nest with Daemonosaurus. One look at the three of them together pretty much sums up the rest of this post. Note their chronology. This is a basal clade that lasted through all three periods of the Mesozoic.

That they nest together tells me the post-crania of Daemonosaurus likely had at least a proto-ornithischian pelvis and supports my earlier observation of a proto-predentary.

Figure 1. Haya skull and post-crania.

Figure 1. Haya skull and post-crania. At present this specimen gives us the best approximation of the post-crania of Daemonosaurus, although the neck vertebrate were longer. Note the stub of a fifth toe on the pes.

Fossils of Coelophysis were present on the same block that contained the skull of Daemonosaurus, Wonder if there was a predator/prey relationship? Skull lengths were similar. Overall size was likely similar too.

References
Han F-L, Barrett PM, Butler RJ and Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China. Journal of Vertebrate Paleontology 32:1370-1395.
Makovicky PJ, Kilbourne BM, Sadleir RW and Norell MA 2011. A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology 31: 626–640.
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 
Xu, Wang and You, 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4)318-325.

wiki/Daemonosaurus
wiki/Haya
wiki/Jeholosaurus