Diplodocus joins the LRT

There are several ways to measure the tallest dinosaur.
One way is to let the long sauropods, like Diplodocus carnegii (Fig. 1; Marsh 1878; Late Jurassic; 25-32 m long), stand on their hind limbs, like their prosaurod ancestors, balanced by a very long narrow whiplash tail of up to 80 vertebrae. While the neck could not be elevated much beyond horizontal (relative to the dorsal vertebrae), by standing on its hind limbs the torso + neck could be elevated.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors.

Figure 1. Diplodocus standing in a typical feeding posture, as in its prosauropod ancestors. Diplodocus could potentially increase its feeding height up to about 11m

Wikipedia reports,
“No skull has ever been found that can be confidently said to belong to Diplodocus, though skulls of other diplodocids closely related to Diplodocus are well known.”

Figure 2. Diplodocus skull animation. Note the short chin and voluminous throat.

Figure 2. Diplodocus skull (USNM 2672, CM 11161) animation. Note the short chin and voluminous throat.

The peg-like teeth of Diplodocus
were smaller and fewer than in other sauropods. And the skull was smaller with nares placed higher on the skull. Evidently diplodocids could only handle smaller needles and leaves from conifer trees matching their height. Wikipedia reports, “Unilateral branch stripping is the most likely feeding behavior of Diplodocus.”

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

We know of junior diplodocids
(Fig. 5), half the skull length but with relatively larger eyes. Cute!

Figure 5. A small Diplodocus skull to scale with an adult one.

Figure 5. A small Diplodocus skull to scale with an adult one.

References
Marsh OC 1878. Principal characters of American Jurassic dinosaurs. Part I. American Journal of Science. 3: 411–416.

 

At last! Some sauropods enter the LRT.

Overlooked no longer: the clade Sauropoda.
Learning about clade members now for the first time. Three have been added to the large reptile tree (LRT, 1291 taxa): Diplodocus, Camarasaurus and Brachiosaurus (Figs. 1, 4).

Figure 1. Several sauropod skulls to scale with DGS colors on the bones. Here are Shunosaurus, Camarasaurus, Brachiosaurus and Diplodocus.

Figure 1. Several sauropod skulls to scale with DGS colors on the bones. Here are Shunosaurus, Camarasaurus, Brachiosaurus and Diplodocus.

Note:
the antorbital fossa is absent in derived taxa.

Figure 2. Family of Brachiosaurus illustration from A Dinosaur Year 1989.

Figure 2. Family of Brachiosaurus illustration from A Dinosaur Year 1989 (flipped left to right). The original illustration hangs on the wall behind my computer monitor.

Note 2:
The palate of sauropods shows an increasing space allotted to the internal nares. That makes sense given the increased volumes of air passing in and out of the nares of these increasingly gigantic dinosaurs — a volume that has to be several times the volume of the dead air in that long sauropod throat.

Figure 3. Sauropodiform and sauropod palates, Yizhousaurus, Diplodocus, Camarasaurus and Brachiosaurus. The choanae (internal nares) get bigger in sauropods.

Figure 3. Sauropodiform and sauropod palates, Yizhousaurus, Diplodocus, Camarasaurus and Brachiosaurus. The choanae (internal nares) get bigger in derived sauropods.

Other sauropod traits:

  1. Fingers reduced to single phalanx stubs below semi-tubular metatarsals. Only digit 1 retains an ungual and tracks show it was retroverted, dorsal side down, saving the point, oriented medially to posteriorly (Fig. 4).
  2. External nares dorsal with fragile to absent premaxillary ascending process (Fig. 1).
Figure 5. Reconstructions of manus and pes of Camarasaurus SMA0002 from Tschopp et al.

Figure 4. Reconstructions of manus and pes of Camarasaurus SMA0002 from Tschopp et al. 2015.

The LRT
divided dinosaurs into theropods and phytodinosaurs in 2011. Sauropodomorpha is a phytodinosaur clade, the sister clade of the clade Ornithischia (Fig. 5). Currently 5 taxa within the Phytodinosauria precede this split.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

Figure 4. Subset of the LRT focusing on the Phytodinosauria. Three sauropods are added here.

More
on each of these sauropods will come shortly.

References
Tschopp E, Wings O, Frauenfelder T, and Brinkmann W 2015. Articulated bone sets of manus and pedes of Camarasaurus (Sauropoda, Dinosauria). Palaeontologia Electronica 18.2.44A: 1-65.

Sauropods as neotenous prosauropods

In the course of dinosaur evolution
sauropods reverted to quadrupedal locomotion, a trait found in embryo prosauropods, like Massospondylus, Fig. 1), but not in adult prosauropods or their dinosaurian ancestors.

FIgure 1. Massospondylus embryo in situ and reconstructed.

FIgure 1. Massospondylus embryo in situ and reconstructed.

This topic came to mind after seeing the new paper
on the Early Jurassic basal saurpodiform, Yizhousaurus (Zhang et al. 2018, which appears to remain bipedal as an adult; Fig. 2).

Notably, and despite it’s bipedal appearance,
in the large reptile tree (LRT, 1286 taxa), Yizhousaurus nests with the embryo Massospondylus (Fig. 1), not the adult (Fig. 4). Hence the title of this blogpost.

Figure 1. Yizhousaurus is an early Jurassic basal sauropod.

Figure 2. Yizhousaurus the early Jurassic basal sauropod that currently nests with the embryo Massospondylus.

Yes, the skeleton of Yizhousaurus
has much longer hind limbs than front limbs, which shows that the transition to a quadrupedal locomotion was gradual in adults, but the skull has several sauropod traits and the manual digit 1 ungual is no longer a big hook, but a stub, like the other manual unguals.

Figure 2. Skull of Yizhousaurus in several views.

Figure 3. Skull of Yizhousaurus in several views.

Sauropods like Yizhousaurus had their genesis
in the Early Jurassic and their greatest radiation in the Late Jurassic. Some clades extended to the Late Cretaceous.

FIgure 4. Massospondylus adult in situ.

FIgure 4. Massospondylus adult in situ.

Did sauropods have several or a single origin?
I have no idea, but the idea is already floating around out there.

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Carrano MT 2005.The evolution of sauropod locomotion: morphological diversity of a secondarily quadrupedal radiation.” in The Sauropods: Evolution and Paleobiology, edited by Curry Rogers, K. A. and Wilson, J. A., 229–251. University of California Press.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp.
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus PDF. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.
Zhang Q-N, You H-K, Wang T and Chatterjee S 2018. A new sauropodiform dinosaur with a ‘sauropodan’ skull from the Lower Jurassic Lufeng Formation of Yunnan Province, China. Nature.com/scientificreports 8:13464 | DOI:10.1038/s41598-018-31874-9

wiki/Massospondylus
wiki/Yizhousaurus

Massospondylus embryo joins the LRT

…and guess where it nests?

Figure 1. Massospondylus embryo from Reisz et al. 2010.

Figure 1. Massospondylus embryo from Reisz et al. 2010.

This should be easy:
The embryo nests with the adult Massospondylus in the large reptile tree (LRT, 1212 taxa), despite the many proportional and a few osteological changes that attend ontogeny in this basal sauropodomorpth from the Early Jurassic.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale. Note the bipedal pose based on hind and fore limb disparity… distinct from the quadrupedal embryo.

These embryos are the oldest known
dinosaur embryos and apparently they were just days from hatching.

Massospondylus kaalae was a short-snouted basal sauropodomorph from the Early Jurassic closely related to Efraasia and SaturnaliaMassospondylus had a short round snout and long blunt fangs. Another species, Massospondylus carinatus, had a relatively longer skull as an adult.

The embryo Massospondylus
includes a taller antorbital fenestra, a premaxilla lacking a posterior narial process, a naris closer to the jaw line, a straight (not descending) jaw joint, a smaller coronoid process, a lack of teeth, relatively shorter neck, larger fore limbs, a shorter ventral pelvis, distally broader chevrons and smaller feet.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx. The predator babies were larger than the bite-sized and more numerous prey babies. 

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. “Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.

wiki/Massospondylus

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

 

New radical dinosaur cladogram: Baron, Norman and Barrett 2017

Baron, Norman and Barrett 2017
have just allied Ornithischia with Theropoda to the exclusion of Sauropodomorpha. That radical hypothesis was not recovered by the large reptile tree (LRT, 980 taxa) nor any other study in the long history of dinosaurs. Despite the large size of their study, it was not large enough. And so taxon exclusion bites another group of well-meaning paleontologists who used traditional small inclusion sets.

From the Baron et al. abstract:
“For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.”

As a reminder, the fully resolved cladogram
at ReptileEvolution.com/reptile-tree.htm finds Herrerasaurus as a basal dinosaur arising from the Pseudhesperosuchus clade. Tawa (Fig. 1) and Buriolestes lead the way toward Theropoda. Barberenasuchus and Eodromaeus are basal to Phytodinosauria, which includes Sauropodomorpha + Ornithischia. So the Nature piece is totally different due to taxon exclusion and improper taxon inclusion.

Earlier heretical dinosaur origins were presented here with images and complete resolution with high Bootstrap scores at every or virtually every node.

Problems with the Baron et al. report

  1. Lack of resolution: Over dozens of nodes, only 5 bootstrap scores were over 50 (the minimum score that PAUP shows as fully resolved).
  2. Lack of correct proximal outgroup taxa (taxon exclusion) and they chose several wrong outgroup taxa (see below) because they had no large gamut analysis that established the correct outgroup taxon out of a larger gamut of choices
  3. Lack of several basal dinosaur taxa. (again, taxon exclusion, see below)
  4. Improper taxon inclusion: poposaurs, pterosaurs and lagerpetons are not related to dinos or their closest kin
  5. Lacking reconstructions for all pertinent basal/transitinal taxa so we can see their data at a glance, see if a gradual accumulation of traits can be observed and not have to slog through all the scores
Figure 1. Unrelated archosaurs. Silesaurus is a poposaur. Eoraptor is a phytodinosaur (note the big belly). And Tawa is a lean theropod.

Figure 1. Unrelated archosaurs mentioned in this blog. Silesaurus is a poposaur. Eoraptor is a phytodinosaur (note the big belly). And Tawa is a lean theropod.

LRT differences with the Baron et. al results

  1. Carnivorous Staurikosaurus, Herrerasaurus, Chindesaurus and Sanjuansaurus nest at the base of the herbivorous Sauropodomorpha.
  2. Herbivorous Eoraptor nests at the base of the Theropod with Tawa.
  3. Poorly known Saltopus sometimes nests as the last common ancestor of Dinosauria.
  4. Six taxa nest basal to dinosaurs in SupFig1 including the poposaur Silesaurus and kin. Silesaurus has ornithischian and theropod traits and so appears to make an ideal outgroup taxon,  but nests with neither clade when more taxa are included. This is the key problem with the study: pertinent taxon exclusion. 
  5. The lack of Gracilisuchus and other bipedal basal crocs that nest basal to dinos in the LRT certainly skewed results.

In an effort to understand Baron et al. I duplicated their outgroup taxon list
but retained all the LRT dinosaurs to see what would happen. The SupFigs are available free online at Nature.com

  1. SupFig 1: When Euparkeria is the outgroup and Postosuchus is included: 3 trees result and (theropods Herrerasaurus + Tawa + Buriolestes) + (poposaurs Sacisaurus + Silesaurus) nest as the base of the Phytodinosauria, while bipedal croc Saltopus nests at the base of the Theropoda.
  2. SupFig 2: When the lepidosaur pterosaur Dimorphodon is the outgroup and Euparkeria + Postosuchus are excluded: 12 trees and basal scansoriopterygid birds (come to think of it, they DO look like Dimorphodon!) nest as basal dinosaurs, then the bird cladogram gets reversed such that basal becomes derived, but Phytodinosauria is retained.
  3. SupFig. 3: when Silesaurus is the outgroup: 12 trees and Phytodinosauria is retained in the LRT
  4. SupFig. 4: when no characters were treated as ordered. Neither does the  LRT order any characters, so this test was moot.

Dr. Kevin Padian said, 
“‘original and provocative reassessment of dinosaur origins and relationships”. And because Baron and his colleagues used well-accepted methods, he notes, the results can’t simply be dismissed as a different opinion or as mere speculation. “This will send people back to the drawing board,” he added in an interview.”

“There have been a lot of studies on the phylogenetic relationships, the family tree of the dinosaurs, but they’ve mostly been on individual dinosaurian groups. They haven’t really examined the entire dinosaur tree in such depth. And so this analysis had the advantage of using a different and larger set of critters than most previous trees. They’ve analyzed the characters used by others before and then also adding their own characteristics and getting their selves quite different configurations, radically different in fact.

The LRT has had, for several years, an even larger set of taxa, so large that any bias in selecting an outgroup taxon list has been minimized. Unfortunately, Baron et al. were biased and used traditional outgroup taxa that skewed their results.

Dr. Hans-DieterSues reported,
“For one thing, palaeontologists’ analyses of relations among species are keenly sensitive to which species are considered, as well as which and how many anatomical features are included, he says.”

True.
Many more outgroup taxa would have minimized the inherent bias clearly present in Baron et al. When Silesaurus is your outgroup, herbivores will nest with carnivores. When you start your study with a goal in mind (read and listen to Baron’s comments) that’s never good. When you exclude taxa that have been shown to be pertinent to your study, that’s never good.

That’s what ReptileEvolution.com is here for (on the worldwide web). Free. Testable. And with a demonstrable gradual accumulation of traits along with minimal bias due to its large gamut.

I was surprised to see Nature print this
because they have not published relationship hypotheses in favor of  new specimens of note. Co-author Dr. David Norman has published for several decades and has a great reputation.

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

Scale models from the vault

You can also title this post: Toys for Christmas.

Yesterday I presented
several full scale models of prehistoric reptiles. Today, some scale models are presented.

Figure 1. Camarasaurus adult scale model.

Figure 1. Camarasaurus adult scale model.

Camarasaurus (Fig. 1) is a Late Jurassic sauropod.

Figure 2. Mosasaurus scale model.

Figure 2. Mosasaurus? scale model.

Mosasaurus, or is this Tylosaurus (Fig. 2)? I can’t remember. The belly is sitting on a ‘rock’.

Figure 3. Kronosaurus scale model.

Figure 3. Kronosaurus scale model.

Kronosaurus (Fig. 3) is here based on the Yale skeleton, which was revised here with a bigger belly among other traits.

Figure 4. Styracosaurus and Albertasaurus to scale.

Figure 4. Styracosaurus and Albertasaurus to scale.

Styracosaurus (Fig. 4) is a ceratopsian, derived from Yinlong. Albertasaurus is a theropod, close to Tyrannosaurus.

Figure 5. Tapinocephalus scale model.

Figure 5. Tapinocephalus scale model.

Tapinocephalus (Fig. 5) is an herbivorous tapinocephalid, close to Moschops.

Figure 6. Anteosaurus scale model.

Figure 6. Anteosaurus scale model.

Anteosaurus (Fig. 6) is an anteosaur known from the skull only, close to Titanophoneus, which here provides the body proportions.

These were produced 
back in my heyday, as models for paintings in books, and just to see how they would turn out. Most are made of Sculpey over a wire frame. After baking the soft clay turns into a hard plastic. So far these all remain on my shelves.

 

 

 

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.

Hexinlusaurus – A Small Heterodontosaur

This is a revision of an earlier blog on the same taxon.

A Basal Ornithischian of Uncertain Affinities
Hexinlusaurus multidens ZDM T6001 (He and Cai 1983, Barrett, Butler and Knoll 2005) middle Jurassic, was originally considered a basal ornithischian of uncertain affinities. Unfortunately the predentary area (anterior mandible) was not preserved, but the pelvis was standard for ornithischians with a completely retroverted pubis. A palpebral bone (“eyebrow” bone) was also present, as in other ornithischians.

Nesting in the Large Reptile Study
This blog originally found Hexinlusaurus to be  nested between the Sauropodomorpha and the Ornithischia, apparently linking these two clades of the Phytodinosauria. However, I noted then that with that pelvis morphology, Hexinlusaurus was 100% ornithischian.

Here, with further study, Hexinlusaurus nests with Heterodontosaurus (Fig. 1). The missing anterior likely included some fangs. The Middle Jurassic age of Hexinlusaurus compares to the Early Jurassic age of Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus.

Hexinlusaurus compared to its closest relative, Heterodontosaurus. Is the size related to ontogeny or phylogeny? I don’t know.

A Single Autapomorphy
Barrett, Butler and Knoll (2005) described Hexinlusaurus with a single autapomorphy, a laterally concave postorbital. It appears that Heterodontosaurus has a similar postorbital depression.

Generally I Avoid the Dinosauria
There are very few dinosaurs in the present study, only basal taxa. The family tree of the Dinosauria is relatively uncontroversial and is better covered in detail elsewhere (and references therein).

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
Barrett PM, Butler RJ and Knoll F 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. Journal of Vertebrate Paleontology 25:823-834.
He X-L and Cai K-J 1983.
A new species of Yandusaurus (hypsilophodont dinosaur) from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Journal of Chengdu College of Geology, Supplement 1:5-14.

wiki/Hexinlusaurus