New Farlow et al. (2014) Poposaurus foot paper

Farlow et al. (2014) has a new paper on the foot of the poposaurid, Poposaurus.

Figure 1. Revised skull reconstruction for the PEFO specimen. Here the anterior is considered a premaxilla. Those teeth are shaped like triangles, but they are very deeply rooted and exposed very little, which casts doubts on its hypercarnivory.

Figure 1. Poposaurus in lateral view. This dinosaur like reptile really is a dinosaur with a calcaneal heel.

From their abstract:
“The crocodile-line basal suchian Poposaurus gracilis had body proportions suggesting that it was an erect, bipedal form like many dinosaurs, prompting questions of whether its pedal proportions, and the shape of its footprint, would likewise “mimic” those of bipedal dinosaurs.

Bivariate and multivariate analyses of phalangeal and digital dimensions showed numerous instances of convergence in pedal morphology among disparate archosaurian clades.

Overall, the foot of Poposaurus is indeed more like that of bipedal dinosaurs than other archosaur groups, but is not exactly like the foot of any particular bipedal dinosaur clade.” 

Included is a comparison with other archosaur taxa, (Fig. 1). Note Terrestrisuchus has no calcaneal heel. It develops in the derived Protosuchus and also poposaurid dinosaurs, according to the large reptile tree.

Figure 1. Archosaur feet divided into traditional croc-line and bird-line clades

Figure 1. Archosaur feet divided into traditional croc-line and bird-line clades

These feet can be reordered according to the large reptile tree (Fig. 2). Though many taxa are missing that would fill in morphological gaps, the general trends are more clear here.

Figure 2. Same feet, reordered according to the large reptile tree. Only Terrestrisuchus and Protosuchus are croc-like archosaurs here. Poposaurs are basal dinosaurs.

Figure 2. Same feet, reordered according to the large reptile tree. Only Terrestrisuchus and Protosuchus are croc-like archosaurs here. Poposaurs are basal dinosaurs. Silesaurus converged with theropod dinos, as did Brachylophosaurus. Note the lack of a calcaneal heel on Terrestrisuchus, a basal croc and the development of one on Protosuchus. In similar fashion poposaurid dinosaurs developed a calcaneal heel. 

Farlow et al. noted several instances of convergence (homoplasy). Indeed homoplasy is present here, even in this small sample.

On a separate note, 
Farlow et al. was kind enough to publish a radiograph of an Alligator. I added PILs and they are quite precise in this living reptile.

Figure 3. Radiograph of Alligator foot with PILs (parallel interphalangeal lines) added. Hone and Bennett tried to argue against the presence of PILs but did not have the nerve to show a foot with more than three toes.

Figure 3. Radiograph of Alligator foot with PILs (parallel interphalangeal lines) added. Seems rather clear that such lines representing phalanges working in sets is indeed present here.

Poposaur footprints have not bee found yet. Farlow et al. (2014) reported, “With a digit III length of about 16 cm, Poposaurus gracilis may have been comparable to a small to midrange theropod in overall body size (somewhere between the makers of Anchisauripus sillimani and A. minusculus, in the terminology of Lull [1953]). The dinosaur-like pedal proportions of Poposaurus, and the similarity of its reconstructed footprint to those of some dinosauromorphs, suggest that some grallatorid forms could well have been made by Poposaurus and its close relatives. However, mistaking Poposaurus tracks for dinosaur (particularly theropod) tracks would be less likely to occur if digit I of Poposaurus routinely touched the ground. Furthermore, trackways made by Poposaurus would probably have a shorter stride/footprint length ratio than grallatorid trackways.”

Personal thought
Seems to me that on Poposaurus pedal digit one is going to impress creating a four-toed ichnite.

References
Farlow JO, Schachner ER, Sarrazin JC, Klein H and Currie PJ 2014. Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs. The Anatomical Record. DOI 10.1002/ar.22863

Walking with Dinosaurs – The Movie

Well, it’s getting bad reviews, mostly and only for the sound track. Otherwise it looks spectacular, except for the disfigured pterosaurs. Here’s the poster with editorial comments added, followed by a selection of reviewer comments from rottentomatoes.com

Figure 1. Walking with Dinosaurs poster.

Figure 1. Walking with Dinosaurs poster. Again, disfigured pterosaurs.

RottenTomatoes.com Reviews:
“The photo-realistic look is striking, but the dialogue is occasionally wince-inducing. Think a sub-par Flintstones episode.”

“The beauty and majesty of the great creatures is marred a bit by too much focus on poop and barf jokes, silly winks at the audience,” and distracting anthropomorphism.”

“If you’re a fan of the 1999 BBC documentary series Walking with Dinosaurs and are hoping for more of the same, get ready for an Apatosaurus-sized level of disappointment from Walking with Dinosaurs 3D.”

“Features animation stunning and accurate enough to make up for its simple story and unnecessary voice-over dialogue.”

“Walking With Dinosaurs: The Movie boasts some impressive special effects but is ultimately let down by a terrible script, a dull story and a poorly conceived American voice dub that is extremely grating.”

YouTube previews London Gala Screening here and here.

Standard trailer here.

Fantastic New Paleoartist: Andrey Atuchin

Once again, I’m going to send you to another website to see the dino-wonders wrought by a new paleoartist: Andrey Atuchin and to read his interview. His talent for light, form and detail are well worth the visit.

Atuchin also has his own website: http://dinoart1.narod.ru

And his own Deviant Art page: http://olorotitan.deviantart.com

Figure 1 Demandasaurus and company by Andrey Atuchin. Click to go to his website.

Figure 1 Demandasaurus and company by Andrey Atuchin. Click to go to his website.

Highest marks for this very talented young artist.

Marasuchus: In or out of the Dinosauria?

Figure 1. Marasuchus lilloensis (above) and Lagosuchus talampayensis (below) compared. The radius and ulna are longer in marasuchus. The hind limbs are more robust in Lagosuchus. The length of the torso in Lagosuchus is based on the insitu placement of the pectoral girdle and forelimb, which may have drifted during taphonomy.

Figure 1. Marasuchus lilloensis (above) and Lagosuchus talampayensis (below) compared from an earlier blog post. Is Marasuchus in or out of the Dinosauria? Either way it was probably close to the origin of dinosaurs. Oddly the scapulocoracoid was quite robust in Marasuchus.

Here’s the problem:
Earlier we looked at the difference between Lagosuchus and Marasuchus, too small dino-like bipeds of the Late Triassic. The Nesbitt (2011) tree nests Marasuchus (Fig. 1) outside the Dinosauria. The large reptile tree nests Marasuchus as a small theropod. Let’s look at both sides of this situation. It appears to come down to micro-traits vs. macro-traits, a theme we’ll return to over the next few blog posts.

According to Nesbitt 2011
The following traits include Marasuchus, Silesauridae and the Dinosauria.

  1. Pubis longer than ischium (also in several post-Euparkeria taxa)
  2. Proximal portion of the pubis articular surfaces with the ilium and the ischium separated by a groove or gap. (also in Postosuchus)
  3. Ischio-pubis contact present and reduced to a thin proximal contact.
  4. Ischium, proximal articular surfaces articular surfaces with the ilium and the pubis continuous but separated by a fossa.
  5. Ischium length markedly longer than the dorsal margin of iliac blade (minus the anterior process). (doesn’t seem to be true in basal dinos)
  6. Anterior trochanter forms a steep margin with the shaft but is completely connected to the shaft.
  7. Anterior trochanter shelf proximal to the fourth trochanter (insertion site for M. iliofemoralis externus) present.
  8. Proximodistally oriented groove on the lateral side of the distal portion of the tibia.
  9. Anterior ascending flange (anterior process) of the astragalus present and less than the height of the dorsoventral height of the posterior side of the astragalus.

The following traits support the Dinosauria, exclusive of Marasuchus.

  1. Exoccipitals do not meet along the midline on the floor of the endocranial cavity. (Also in Crocodylomorpha and Effigia + Shuvosaurus.)
  2. Epipophyses present in postaxial anterior cervical vertebrae.
  3. Apex of deltopectoral crest situated at a point corresponding to more than 30% down the length of the humerus .
  4. Radius shorter than 0.8 of humerus length.
  5. Proximal articular surfaces of the ischium with the ilium and the pubis separated by a large concave surface.
  6. Fourth trochanter a sharp flange.
  7. Fourth trochanter asymmetrical, with distal margin forming a steeper angle to the shaft. 
  8. Cnemial crest arcs anterolaterally.
  9. Distinct proximodistally oriented ridge present on the posterior face of the distal end of the tibia.
  10. Proximal articular facet for fibula of the astragalus occupies less than 0.3 of the transverse width of the element.
  11. Concave articular surface for the fibula of the calcaneum.

The following traits support Marasuchus outside of the Theropoda:

  1. Parabasisphenoid recess absent
  2. Parabasisphenoid ant tympanic recess absent
  3. Epipophyses absent in past axial ant cerv verts
  4. Epipophyses absent in post cerv verts
  5. Cerv verts pneumatic features absent
  6. First primorial sacral art surf circular, not C-shaped in lat view
  7. Forelimb/hindlimb ratio > 0.55 (actually this ratio IS .55. est for manus)
  8. Ischium articular surfaces continuous but separated by fossa
  9. Fourth trochanter mound-like and rounded (looks sharp and described as aliform-wing-shaped)
  10. Femur surface between lat condyle and crista tibiofibularis on distal surface smooth
  11. Tibia prox portion cenemail crest present and straight
  12. DT4 medial side, without a distinct medial process
  13. Astragalus prox art facet for fibula occupies more than .3 transverse width
  14. Astragalus post groove present
  15. Calcaneal tuber present (but Eoraptor also has a slight tuber)
  16. Calc art surf for fibula convex

The following traits support Marasuchus within the Theropoda

  1. Opisthotic ventral ramus covered by lateralmost edge of exoccipital in post view
  2. Acetab antitrochanter present
  3. [not scored by Nesbitt] Gastralia present

The following traits support Marasuchus inside the Dinosauromorpha, but outside of the Dinosauria:

  1. Exoccipital lateral surfaces with clear crest lying ant to both ext foramina
  2. Axis, dorsal margin of the neural spine arcs dorsally
  3. Glenoid posterovent
  4. Prox pubis art surface separated by a groove or gap
  5. Ischio pubis contact present and reduced to a thin prox contact
  6. ischium markedly longer than iliac blade minus ant process
  7. Tibia > femur (not all dinos)
  8. Femur postmed tuber present and small
  9. Femur ant torchanter shelf present
  10. Femur post lat portion ventrally descended
  11. Tibia prox portion cenemail crest present and straight
  12. Tibai lat side of distal portion proxdistal oriented groove
  13. DT 4 width subequal to dt3
  14. DT4 size of art facet for mt 5 less than half of lat surface
  15. Astragalus ant ascending flange present less than height of dorsventral height
  16. Astragalus ant hollow reduced to a foramen or absent
  17. Astragalus antmed corner acute
  18. Compact metatarsus
  19. Longest metatarsal > .5 tibia
  20. Mt 5 phalanges: none (but note more derived taxa have phalanges.)

According to the large reptile tree,
Marasuchus is a derived theropod nesting with Procompsognathus. Moving Marasuchus out of the Dinosauria (outside Herrerasaurus) adds 15 steps.

The following traits support the inclusion of Marasuchus with Procompsognathus in the Theropoda.

  1. Mid-cervicals shorter than mid-dorsal
  2. Chevrons wider proximally
  3. Pedal 2.1 not > p2.2
  4. Pedal digit 4 not narrower than digit 3
  5. Overall size not > 30 cm tall, 60 cm long

The following traits support the inclusion of Marasuchus with Procompsognathus and Segisaurus in the Theropoda.

  1. Dorsal transv proc shorter than centra
  2. Pubis curving ventral
  3. Pedal 1.1 aligns with mt2, mt3

The following traits support the inclusion of Marasuchus within the Theropoda (represented by the addition of Coelophysis and Tawa in the large reptile tree).

  1. Skull shorter than cervicals (also in Turfanosuchus).
  2. Ant caudal spines shorter than centra.
  3. Caudals 3x longer than tall.
  4. Tibia not shorter than femur
  5. Fibula anterior trochanter low crest
  6. Mt 1 <.5 mt 3
  7. Mt 1 <.5 mt 4
  8. Metatarsals not shorter than half the tibia (also in phytodinosaurs.)
  9. Phalanges pedal digit 5: 0 (also in most crocs)

The following traits support the inclusion of Marasuchus within the Dinosauria.

  1. Interclavicle absent
  2. Forelimb < .55 hindlimb (actually the ratio is right at .55 given the hypothetical size of the manus shown in figure 1).
  3. Ilium anter proces truncated
  4. Acetabulum semiperforate
  5. Femoral head offset and subrectangular
  6. Fourth trochanter sharp
  7. Tibia > 2x ilium length
  8. Advanced mesotarsal ankle
  9. No calcaneal tuber (actually the tuber is vestigial, but poposaurs also have a substantial tuber, a reversal convergent with derived crocs).
  10. Proximal metatarsals 1 and 5 reduced (actually, not so much in Marasuchus, 1 is not reduced in Plateosaurus, 5 is not much reduced in Tawa)
  11. Osteoderms absent

The following traits in the large reptile tree are shared by Marasuchus and other taxa outside the Dinosauria.

  1. Longest metatarsals 3-4

Summary
Even a cursory glance through this list demonstrates the Nesbitt characters are often micro-traits representing characters that must be seen in person and in close-up. These include various bumps and holes in various bones. By contrast the Peters characters are largely macro-traits, visible and able to be measured in published images. That means the sister taxa used by the Peters images are more likely to look alike overall. That also means testing the Nesbitt tree is going to take personal inspection of the specimens. What I don’t understand is why the micro-traits and macro-traits diverge so widely, assuming both were scored correctly.

I wonder if the Nesbitt tree included Segisaurus and Procompsognathus if the tree topology would change? Oddly both have advanced theropod feet with 1 and 5 reduced.

References
Fraser NC, Padian K, Walkden GM and Davis LM 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. Palaeontology. 45(1), 79-95.
Paul GS 1988. Predatory dinosaurs of the world (464). New York: Simon and Schuster.
Romer AS 1971. The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria 378: 1-10.
Romer AS 1972. The Chanares (Argentina) Triassic reptile fauna. XV. Further remains of the thecodonts Lagerpeton and Lagosuchus: Breviora 394: 1-7.
Sereno PC and Arcucci AB 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis gen. nov. Journal of Vertebrate Paleontology, 14: 53-73

wiki/Marasuchus

The Lagerpeton pelvis – what it tells us

Chanaresuchids to scale, including Tropidosuchus and Lagerpeton.

Figure 1. Chanaresuchids to scale, including Tropidosuchus and Lagerpeton.

Lagerpeton (Fig. 1) is widely and erroneously considered a dinosaur ancestor in various phylogenetic analyses (i.e. Nesbitt 2011). We looked at Lagerpeton relations earlier here and here. Today we’ll compare pelves (Fig. 2).

Figure 1. Lagerpeton pelvis  compared to its close kin, Tropidosuchus, Chanaresuchus, Parasuchus and Diangongosuchus, in order of increasing distance. These are all pararchosauriformes, unrelated to dinosaurs and their ancestors -- until you get to the variety that is Youngina

Figure 2. Click to enlarge. Lagerpeton pelvis compared to its close kin, Tropidosuchus, Chanaresuchus, Parasuchus and Diangongosuchus, in order of increasing distance. These are all pararchosauriformes, unrelated to dinosaurs and their ancestors — until you get to  Youngina, their last common ancestor. These pelves are much more alike than Lagerpeton is to any of the dinosaurs and dino ancestors in figure 3. Dorsal view of Lagerpeton based on other views and descriptions. All these pelves are short and broad. Note from Chanaresuchus on the acetabulum is open posteriorly. 

and the more popular candidates, according to Nesbitt 2011.

Figure 2. The pelvis of Marasuchus, Turfanosuchus, Arizonasaurus, Euparkeria, Silesaurus and Dimorphodon. Among these, Dimorphodon is clearly the most different, because it's a lepidosaur in reality.

Figure 3. The pelvis of Marasuchus, Turfanosuchus, Arizonasaurus, Euparkeria, Silesaurus and Dimorphodon. Among these, Dimorphodon is clearly the most different, because it’s a lepidosaur in reality. Among the rest the posterior acetabulum is always closed. 

Comparisons and Trees
Nesbitt nested Lagerpeton between pterosaurs (like Dimorphodon, Fig. 3) and Marasuchus, but their pelves do not share more traits than the pararachosaurs shown in figure 2. Not sure why recent analyses don’t see this, other than the fact that they fail to include younginids and choristoderes, taxa that nest at the base of the pararchosauriformes in the large reptile tree. And they typically include pterosaurs, which may act like wild cards or jokers in the deck.

References
Arcucci A 1986 New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf
Bonaparte JF 1994. Dinosaurios de America del Sur. Impreso en Artes Gráficas Sagitario. Buenes Aires. 174pp. ISBN: 9504368581
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, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218.
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.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton

Basal Dinos: Fusion of the Postfrontal and Postorbital Documented

Dinosaurs and higher crocs share the trait of a fused postorbital (PO) and postfrontal (POF). Almost universally the postfrontal portion is ignored. T fused bone is simply called the postorbital. But the postfrontal is not absent. The postfrontal doesn’t shrink into nothingness. It fuses to the postorbital, so it’s still there!

Basal archosauriformes, basal crocodylomorphs, like Gracilisuchus, and basal dinosauromorphs, like Turfanosuchus, do not fuse these two bones. But most crocs and most dinos do fuse these bones.

So, the next step up the dino phylogenetic line might show some vestige of the suture, as it appears to do in Herrerasaurus (Figs. 1, 2) and Pampadromaeus (Fig. 3) for which photos are known. Only drawings are published of the pertinent basal crocs, like Terrestrisuchus.

Figure 1. Herrerasaurus has a fused postfrontal/postorbital. Their parts are colorized here.

Figure 1. Herrerasaurus has a fused postfrontal/postorbital. Here both sides are shown as if they were both left sides. The postfrontal and postorbital portions are colorized here. Image courtesy of digimorph.org.

And here (Fig. 2) they are without the color overlay.

Figure 2. Herrerasaurus postfrontal/postorbital. Can you see the incomplete fusion?

Figure 2. Herrerasaurus postfrontal/postorbital. Can you see the incomplete fusion?

Figure 3. Postorbital/postfrontal of Pampadromaeus. More fusion here as these two bones remain together after disarticulation.

Figure 3. Postorbital/postfrontal of Pampadromaeus. More fusion here as these two bones remain together after disarticulation. And here also you can see how sutures can be easily misinterpreted as bone cracks and vice versa.

If we look closely and ignore the cracks (they are very confusing here), we can just make out the former outlines of the postfrontal / postorbital suture. Those become less visible on more derived dinos.

The same situation appears in Pampadromaeus, a primitive phytodinosaur. Eoraptor is too broken up in that area to observe sutures.

So, no big discoveries here other than to maybe call the bone what it truly is, the fused postfrontal / postorbital.

References
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.

wiki/Herrerasaurus
wiki/Sanjuansaurus

Eoraptor Re-Reconstruction

Earlier we took note of the new nesting ofEoraptor as a basal sauropodomorph in Sereno (2013), matching its nesting in the large reptile tree.

The basal phytodinosaur, Eoraptor (Figs. 1, 2), has recently been described and illustrated (Sereno et al. 2013) in its entirety.

Figure 1. Eoraptor as illustrated by Carol Abraczinskas for Sereno et al. 2013.

Figure 1. Eoraptor as illustrated by Carol Abraczinskas for Sereno et al. 2013.

The Abraczinkas illustration (Fig. 1) portrays Eoraptor as a basic theropod, despite its nesting as a basal sauropomorph. I get the impression that the torso was done essentially freehand, especially with regard to the ribs. Fingers 4 and 5 are missing in the fossil because the matrix ends there. Descendant taxa (according to the large reptile tree), like Anchisaurus, Brachiosaurus and Iguanodon have fingers 4 and 5, so Eoraptor probably had them too. They are shown in figure 2 in pink.

Figure 2. Eoraptor based on tracing illustrations in Sereno et al. 2013, including the in situ composite image.

Figure 2. Eoraptor based on tracing illustrations in Sereno et al. 2013, including the in situ composite image. Here the ribs are shorter, fingers 4 and 5 are restored, the dorsal series is less arched, the dorsal ribs are shorter, the pelvis tilts further foreword and rides lower, the crus appears more robust and neural spines are more individualized and not generalized. Ribs are not shown from posterior cervicals. I’m struck by how robust the forelimbs are.

Several other differences in the new reconstruction more accurately reflect the in situ fossil, from which it was traced. The back was straighter without the shoulder hump found in figure 1. Other slight changes are listed in the figure two caption. Even so, this early biped appears to have had a carnivorous dentition that perhaps tasted plants occasionally.

Looks like a carnivore, except…
Sereno et al. (2013) report, “The first dentary tooth in Eoraptor, in addition, is retracted from the anterior end of the dentary, which is marked by a pair of conspicuous neurovascular foramina—features that characterize plant-eating basal sauropodomorphs. These features and the short length of the lower jaws suggest that there may have been a small keratinous beak at the anterior end of the lower jaws in Eoraptor and Panphagia. We have yet to discover a carnivorous dinosaur—or for that matter a carnivorous extant lizard—that has retained teeth for predation and that has inset these teeth from the anterior end of the lower or upper jaws (Sereno, 2012). This favors Eoraptor as a herbivore.”

Manual digits 4 and 5
In Eoraptor, Herrerasaurus and other basal dinos metacarpals 4 and 5 are tiny, almost vestigial (Fig. 2) yet in their descendant, Brachiosaurus, all five metacarpals are subequal. This is odd. Fingers and metacarpals usually disappear after they become vestiges, but not this time. Evidently metacarpals 3 and 5 re-elongated to support the weight when sauropod ancestors became quadrupedal.

Figure 3. Plateosaurus hand. Note metacarpal 4 is longer than in Eoraptor, but metacarpal 5 is not.

Figure 3. Plateosaurus hand. Note metacarpal 4 is longer than in Eoraptor, but metacarpal 5 is not.

In the prosauropod, Plateosaurus (Fig. 3), the hand is quite similar to that of Eoraptor. Metacarpal 4 is  about 3/4 the size of metacarpal 3 and three phalanges are present. Metacarpal 5 remains a vestige with a single phalanx. In the basal sauropod, Shunosaurus the lateral metacarpals are more nearly alike.  Somewhere between these two taxa, we find the origin of sauropods with longer lateral digits.

Wikipedia reports, 
“Evidence against sauropod ancestry within Prosauropoda comes from the fact that prosauropods had a smaller outer toe on their hind feet than the sauropods. Many maintain that it is easier for digits to be reduced or lost during evolution than the reverse, however there is no evidence for this. The lengthening, or gaining of extra digits is common in marine reptiles, and within the theropods digit lengthening occurred at least once. Therefore, using this as evidence against ancestral prosauropods is questionable.”

References
Sereno PC, Martînez RN and Alcober OA 2013. Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). Society of Vertebrate Paleontology Memoir 12, 32 (Supp. to #6):83-179.

Eoraptor Confirmed as Basal Phytodinosaur

Figure 2. Eoraptor based on tracing illustrations in Sereno et al. 2013, including the in situ composite image.

Figure 1. Eoraptor based on tracing illustrations in Sereno et al. 2013, including the in situ composite image.

Abstract - We (Sereno et al. 2013) describe the basal sauropodomorph Eoraptor lunensis, based on the nearly complete holotypic skeleton and referred specimens, all of which were discovered in the Cancha de Bochas Member of the Ischigualasto Formation in northwestern Argentina. The lightly built skull has a slightly enlarged external naris and a spacious antorbital fossa with a prominent, everted dorsal margin and internal wall lacking any pneumatic extensions into surrounding bones. The tall quadrate is lapped along its anterior margin by the long, slender ventral process of the squamosal, and the lower jaw has a mid-mandibular joint between a tongue-shaped splenial process and a trough in the angular. All but the posterior-most maxillary and dentary crowns have a basal constriction, and the marginal denticles are larger and oriented more vertically than in typical theropod serrations. Rows of rudimentary palatal teeth are present on the pterygoid. Vertebral centra are hollow, although not demonstrably pneumatized,and all long bones have hollow shafts. The radius and ulna are more robust, the manus proportionately shorter, and the manual unguals less recurved than in the contemporaneous basal theropod Eodromaeus murphi. An outstanding feature of the manus of Eoraptor is the twisted shaft of the first phalanx of the pollex, which deflects medially the tip of the ungual as in basal sauropodomorphs. The long bones of the hind limb have more robust shafts than those of Eodromaeus, although in both genera the tibia remains slightly longer than the femur.

From the text - Eoraptor lunensis was placed by Sereno et al. (1993) and Sereno (1999) as the basal member of Theropoda on the basis of phylogenetic analyses that identified synapomorphies uniting Eoraptor with Herrerasaurus and other theropods.

An opposing camp emerged with the view that Eoraptor was a more basal saurischian, outside both Theropoda and Sauropodomorpha (Langer, 2004; Mart´ınez and Alcober, 2009; Brusatte et al., 2010; Langer et al., 2010).

We now regard Eoraptor as a basal sauropodomorph (Mart´ınez et al., 2011), and there are important events that led us to this new understanding. It was not until excellent remains of this dinosaur were discovered in 1996 and prepared several years later that its distinction from Eoraptor was revealed (Mart´ınez et al., 2011).

Secondly, two key discoveries came to light while working on the holotypic skeleton of Eoraptor for this monograph. We discovered that, prior to its final fossilization, slight disarticulation of digit I in the well-preserved right manus of Eoraptor (Fig. 69) had obscured a remarkable derived feature known only among large bodied basal sauropodomorph dinosaurs (Sereno, 2007b)—the medial rotation in the shaft of proximal phalanx of manual digit I that directs the tip of the ungual inward (Fig. 73D). 

We also realized that the lower jaws of Eoraptor seemed slightly short relative to the upper jaws (Figs. 16, 17) and that the anterior end of the dentaries also had vascular openings (Fig. 23) similar to those of many larger-bodied basal sauropodomorphs thought to have a small keratinous lower bill (Sereno, 2007b; Mart´ınez, 2009). By preparing between the premaxillary teeth, we were able to verify evidence from the computed tomography (CT) data that the first dentary tooth in Eoraptor, as in Panphagia (Mart´ınez and Alcober, 2009), is inset a short distance from the anterior end of the dentary.

Thirdly, the discovery of Panphagia in Ischigualasto (Martínez and Alcober, 2009) and Saturnalia in southeastern Brazil (Langer et al., 1999, 2007; Langer, 2003) highlighted postcranial features in the girdles and hind limb shared with later sauropodomorphs.

The striking similarities between Eoraptor and Panphagia and Saturnalia became apparent. 

More recently, the discovery in southeastern Brazil of wellpreserved cranial remains of Pampadromaeus (Cabreira et al., 2011) has extended the striking similarities between Eoraptor and Brazilian genera to include the skull.

We reconsider the relationships of Eoraptor and other basal dinosaurs elsewhere (Sereno and Martínez, in review). Evidence is mounting that Eoraptor and several other taxa from the Ischigualasto and Santa Maria formations (Panphagia, SaturnaliaPampadromaeus) are basal sauropodomorphs.

Based only on Sereno et al. 1993 data and whatever was online at the time
Now that several traits in Eoraptor are now published, the large reptile tree (and its limited number of characters, will be updated soon) also nested Eoraptor with Pampadromaeus and these two with Panphagia in a clade basal to the Phytodinosauria (= Sacisaurus and the poposaurs + Sauropodomorpha + Ornithischia).

This order is confirmed by Martínez et al. (2013) which found, “The analysis positions Panphagia as the basal-most sauropodomorph, followed by Eoraptor, Pampadromaeus, and a clade that includes Chromogisaurus and Saturnalia.”

So, another confirmation for a much maligned study. Nice.

References
Martínez RN, Apaldetti C and Abelin D 2013. 
Basal sauropodomorphs from the Ischigualasto Formation. Basal sauropodomorphs and the vertebrate fossil record of the Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina. Journal of Vertebrate Paleontology Memoir 12:51-69.
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). Journal of Vertebrate Paleontology Memoir 12:83-179.

Procompsognathus – What does it look like?

The small Late Triassic archosaur Procompsognathus (~60 cm length, von Huene 1921, Fig. 1) was earlier and convincingly revealed to be a chimaera by Sereno and Wild (1992). The croc skull (Figs. 2,3) did not belong to the dino post-crania. Unfortunately no reconstruction was provided. Here (Fig. 1) is a Procompsognathus reconstruction , along with Segisaurus (~1 m length, Camp 1933) an early Jurassic dinosaur, to which it was allied.

Figure 1. Procompsognathus (below) along with Segisaurus (not to scale). We don't have the actual skull of Procompsognathus, but it was likely small, but taller than wide.

Figure 1. Procompsognathus (below) along with Segisaurus (not to scale). We don’t have the actual skull of Procompsognathus, but it was likely small, but taller than wide.

Procompsognathus post-crania
The post-cranial portion of the specimen (SMNS 12591) was considered close to Segisaurus (Fig. 1) and here nests close to it, but closer to the tiny Middle Triassic theropod, Marasuchus.  Pedal digit 1 rides a little higher on the metatarsus in Procompsognathus and Marasuchus among only a few distinguishing traits.

Distinct from Segisaurus, Procompsognathus has longer, more robust hind limbs and essentially vestigial forelimbs. It is also half as large with a much longer pubis, longer cervicals with smaller cervical ribs, a higher metatarsal 1 and shorter, more robust phalanges on pedal digit 4, which also has a very long ungual.

Figure 2. SMNS 12591a, a basal croc skull close to the ancestry of dinosaurs.

Figure 2. SMNS 12591a, a basal croc skull close to the ancestry of dinosaurs. The premaxilla is unknown and has been restored here. The palatine appears in the antorbital fenestra.

SMNS 12591a – the croc skull
A basal croc, the SMNS 12951a skull, is twice as wide as tall. The quadrate leans anteriorly. Phylogenetically the skull nests in the large reptile tree at the base of the Gracilisuchus + Scleromochlus clade and next to the Terrestrisuchus + Saltoposuchus clade. So there is a good chance that the SMNS 12951a skull was attached to gracile bipedal crocodylomorph post-crania, along the morphological lines of Procompsognathus, and not too far from the base of the Archosauria.

Figure 3. The SMNS 12591a skull reconstructed. It is twice as wide as tall, a croc feature.

Figure 3. The SMNS 12591a skull reconstructed. It is twice as wide as tall, a croc feature.

Sereno and Wild (1992) described postfrontals (blue in Fig. 2), but strangely did not illustrate them (Fig. 3). Gracilisuchus and Scleromochlus also retain postfrontals but most other crocs do not. What appears to be a post dividing the antorbital fenestra in situ is actually the displaced palatine, as described by Sereno and Wild (1992).

References
Camp C 1936. A new type of small bipedal dinosaur from the Navajo sandstone of Arizona. Univ. Calif. Publ., Bull. Dept. Geol. Sci., 24: 39-56.
Huene F von 1921.
Neue Pseudosuchier under Coelurosaurier aus dem württembergischen Keuper. Acata Zoologica 2:329-403.
Sereno P and Wild R 1992. Procompsognathus: theropod, “thecodont” or both? Journal of Vertebrate Paleontology 12(4): 435-458.

Tribute to Doug Henderson, Paleoartist

Perhaps no other paleoartist cares more about the environment of his subjects than does Doug Henderson. Sometimes it is hard to find the animals in the layout filled with rotting logs and misty swamps. Henderson paints with light and so takes his creations beyond mere graphics and elevates it to art. Now there is a YouTube video tribute that is linked here. I enjoy all of Henderson’s artwork. He never fails to amaze.

Click to view YouTube video of Doug Henderson paleo artwork.

Click to view YouTube video of Doug Henderson paleo artwork.