Hone and Holtz review spinosaurids

It’s always good to have a clade reviewed now and then.
Reviews form ready references for those just diving into a subject for the first time, or need to get ‘brushed up’ on all the latest literature. However…

You know you’re in a wee bit of trouble
when authors Dr. David Hone and Dr. Thom Holtz open their abstract with “The spinosaurids represent an enigmatic and highly unusual form of large tetanuren theropods.” In this day and age, after two decades of phylogenetic analysis, there is no longer ANY excuse for labeling ANY taxon or clade enigmatic” or “highly unusual.” Every taxon should be phylogenetically ‘buttoned down’ by now. And this one is, more or less…

Everyone agrees
that spinosaurs nest with megalosaurs… but which ones? This is where avoiding suprageneric taxa pays off. And spinosaurs are not all that weird, especially the early ones. Most of their parts (bones) have readily recognizable counterparts in more typical (non-spinosaurid) theropods.

ALL phylogenetic analyses nest EVERY included taxon.
So, there is always a closest known sister taxon, but you have to do the work and not just repeat old adages or promote old papers…and by all means, avoid suprageneric taxa!

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

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

The authors recover only one suprageneric outgroup taxon
in their tiny six taxon cladogram. Unfortunately, this provides no clue as to the origins of the Spinosauridae other than somewhere within the suprageneric “Megalosauridae”. Hone and Holtz report, “The origins of the Spinosauridae remain somewhat obscure. There is a seemingly undocumented phase of the spinosaurid lineage from 170 until 130 mya.”

Unfortunately,
we’ve seen Dr. Hone punt and sidestep on clade origins before. This habit not only leads to disappointing reading, but feeds into traditional “enigmatic and highly unusual” paradigms that were answered a year ago here (Fig. 1) and should have been answered seven and five years ago by Benson (2010) and by Carrano, Benson & Sampson (2012). Sinocalliopteryx entered the literature in 2007, but was mislabeled a ‘compsognathid.’ There is no longer any value in keeping the sacred vaults of paleontology full of mysteries. To do so runs the risk of permitting amateurs and bloggers to make discoveries that should clearly be in the province of the PhDs. Unless they don’t want to do the work.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017. All clade members are long-snouted theropods.

Here
at the large reptile tree (LRT, 1033 taxa, subset Fig.1) the following taxa nest with Spinosaurus and Suchomimus.

  1. Sinocalliopteryx – 125 mya
  2. Xiongguanlong – 112 mya
  3. Deinocheirus – 70 mya
  4. Proceratosaurus – 165 mya

Obviously all these taxa
had earlier origins and radiations, based on their late appearances in the fossil record and nesting in the cladogram.

Here’s an OPTION for all paleontologists struggling with a phylogenetic enigma:
Just take a look at the LRT, where every taxon is comfortably nested…(even spinosaurs!), request the .nex file, add your taxon to it, review for errors, then report your results. Or keep the results a secret and perform your own analysis while including all pertinent taxa, and then reporting your own results. The days of enigmatic taxa should be over, though I’m sure we’ll keep seeing moderately unusual taxa. The highly unusual ones are getting to be more commonplace and easier to handle given the large gamut already in our vaults. And the biggest benefit: you won’t have bloggers chiding you for taxon exclusion.

References
Benson RBJ 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158:882–935.
Carrano MT, Benson RBJ and Sampson SD 2012: The phylogeny of Tetanurae (Dinosauria: Theropoda), Journal of Systematic Palaeontology, 10:2, 211-300.
Hone DWE and Holtz TR Jr. 2017. A century of spinosaurs — a review and revision of the Spinosauridae with comments on their ecology. Acta Geologica Sinica (English edition) 91(3):1120–1132.

 

 

 

Guaibasaurus: a theropod! (Not a sauropodomorph)

Just look at it!!
With those very short, sharply-clawed forelimbs, how could anyone misidentify Guaibasaurus as ancestral to sauropods? And yet several big-name paleontologists did exactly that, most recently Baron et al. 2017.

Figure 1. Tiny forelimbs with three sharp-clawed fingers indicate that Guaibasaurus is a theropod, not a sauropodomorph. Shown to scale with related theropods Marasuchus and Procompsognathus.

Figure 1. Tiny forelimbs with three sharp-clawed fingers indicate that Guaibasaurus is a theropod, not a sauropodomorph. Shown to scale with related theropods Marasuchus and Procompsognathus. The posture of this skeleton is similar to the resting position of birds, which are also theropods.

Guaibasaurus candelariensis (Bonaparte et al., 1999, 2007; UFRGS PV0725T; Late Triassic) is known from an articulated skeleton lacking a neck and skull. Originally considered a basal theropod, later studies allied it with basal sauropodomorphs. Here this specimen nests as a basal theropod in a rarely studied clade. In the large reptile tree (LRT, 1018 taxa) Guaibasaurus nests between Segisaurus and Marasuchus + Procompsognathus (Fig. 1).

Wikipedia reports:
José Bonaparte and colleagues, in their 1999 description of the genus, found it to be possible basal theropod and placed it in its own family, Guaibasauridae. Bonaparte and colleagues (2007) found another early Brazilian dinosaur Saturnalia to be very similar to it, and placed the two in the Guaibasauridae which was found to be a primitive saurischian group. Bonaparte found that these forms may have been primitive sauropodomorphs, or an assemblage of forms close to the common ancestor of the sauropodomorphs and theropods. Overall, Bonaparte found that both Saturnalia and Guaibasaurus were more theropod-like than prosauropod-like. However, all more recent cladistic analyses found the members of Guaibasauridae to be very basal sauropodomorphs, except Guaibasaurus itself which was found to be a basal theropod or alternatively a basal sauropodomorph.”

On a similar note, Ezcura 2010 report, 
“A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus.” See Figure 2. We need to realize there are some phytodinosaurs, like Eoraptor, Eodromaeus, Panphagia and Pampadromaeus, that are outside of the Sauropodomorpha and outside the Ornithischia. The greater paleo community has not recognized this yet.

Figure 2. Taxa variously considered members of the Guaibasauridae. Here the top few nest with or closer to Sauropodomorpha. The bottom taxa nest with theropods in the LRT.

Figure 2. Taxa variously considered members of the Guaibasauridae. Here the top few nest with or closer to Sauropodomorpha. The bottom taxa nest with theropods in the LRT. Note the small size of Marasuchus, Agnophitys and Procompsognathus. Evidently phylogenetic miniaturization was taking place here, but in this case we know of no ancestors. Maybe someday we will..

I realize the authors
of the Guaibasaurus Wiki article can’t take a stand nor do they choose to test the hypotheses of PhDs, but I can and do here. Science is all about testing observations, comparisons and analyses. When Baron et al. nested Guaibasaurus with the sauropodomorphs, and Eoraptor + Eodromaeus with theropods, and avoided including a long list of taxa from the only other archosaur clade, Crocodylomorpha. and avoided including a long list of taxa from the outgroup to the Archosauria, the Poposaurs, then their results have to be considered suspect at least and bogus at worst. Headline grabbing is fun and lucrative for paleontologists, but not always good for paleontology. So many mistakes have been chronicled that it’s getting to the point that discoveries need to be put on simmer and only lauded when other studies validate them. On the same note, referees are not being tough enough on manuscripts.

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature  543:501–506.
Bonaparte JF;Ferigolo J and Ribeiro AM 1999. 
A new early Late Triassic saurischian dinosaur from Rio Grande do Sol state, Brazil. Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs. 15: 89–109.
Bonaparte JF, Brea G, Schultz CL and Martinelli AG 2007. A new specimen of Guaibasaurus candelariensis (basal Saurischia) from the Late Triassic Caturrita Formation of southern Brazil. Historical Biology, 19(1): 73-82.

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.

Let’s talk about the pygostyle in birds

…because Wang and O’Connor 2017 just wrote a paper on pygostyle evolution.

From their abstract: “The transformation from a long reptilian tail to a shortened tail ending in a pygostyle and accompanied by aerodynamic fanning rectrices is one of the most remarkable adaptations of early avian evolution. All birds with a pygostyle form a monophyletic clade, the Pygostylia (Chiappe, 2002), which excludes only the long bony-tailed birds, Archaeopteryx and the Jeholornithiformes (Jeholornis and kin).”

Key thought from their abstract: “There further exist distinct differences in pygostyle morphology between Sapeornithiformes, Confuciusornithiformes, Enantiornithes, and Ornithuromorpha.”

Figure 1. Flawed theropod cladogram according to Wang and O'Connor 2017 based on Brusatte 2014.

Figure 1. Flawed theropod cladogram according to Wang and O’Connor 2017 based on Brusatte 2014. This cladogram suffers from taxon exclusion and so tells us little about pygostyle evolution.  Only one clade here has a pygostyle. See figure 2 for more data.

Wikipedia reports, “The pygosylians fall into two distinct groups with regard to the pygostyle. The Ornithothoraces have a ploughshare-shaped pygostyle, while the more primitive members had longer, rod-shaped pygostyles. The earliest known member of the group is the enantiornithine species Protopteryx fengningensis, from the Sichakou Member of the Huajiying Formationof China, which dates to around 131 Ma ago,”

Figure 2. Subset of the LRT focusing on derived theropods. Those with a pygostyle are colored.

Figure 2. Subset of the LRT focusing on derived theropods. Those with a pygostyle are colored. Among birds, gray taxa have a distal fusion, as do other very derived non-bird taxa, some of which are not included here. Wnag and O’Connor apparently did not test several Solnhofen birds and so did not understand the basal division of bird clades that occurred  among the ‘Solnhofen birds’  shown here.

 

Wang and O’Connor correctly note
that some derived therizinosaurs and ovitrapotorsaurs have distal caudal vertebrae that are fused after a long string of unfused verts. Not correctly they consider this the first of many evolutionary steps toward the completely fused pygostyle of extant birds. A subset of the large reptile tree (LRT, figure 2) documents three origins for the pygostyle in Avialan taxa and a few other aborted attempts in other clades.

If only Wang and O’Connor
had used a half-dozen Solnhofen birds (they can’t ALL be Archaeopteryx) in their study they would have found the multiple convergent evolution of the pygostyle in basal Aves. Once again, taxon exclusion is keeping the blinders on paleontologists.

Wang and O’Connor do not recover
Sapeornis as a basal Ornithourmorph. The write: “Despite published diversity, the Sapeornithiformes is considered a monospecific clade with all taxa referable to Sapeornis chaoyangensis.

Wang and O’Connor were very interested in
Caudipteryx, traditionally considered a basal member of the Oviraptorosauria. It now nests with Limusaurus, or closer yet, the ‘juvenile’ Limusaurus, a sister to the oviraptorid, Khaan. It lacks a pygostyle, but has a fan of tail feathers.

Wang and O’Connor conclude “Fusion or partial fusion of the terminal caudal vertebrae in maniraptorans is observed in the Therizinosauroidea, Oviraptorosauria and potentially also the Scansoriopterygidae. However, morphological differences between these phylogenetically separated taxa indicate these co-ossified structures cannot be considered equivalent to the avian pygostyle. Outside the Ornithuromorpha, no group preserves evidence of a tail complex.”

Scatter diagrams of pygostyle traits provided by Wang and O’Connor
(their figure 7) also show four clades of rarely and then barely overlapping data. The vast majority is non-overlapping data as the pygostyle really did evolve several times within Aves.

Notably the bird mimics
Microraptor and Sinornithosaurus, both closer to T-rex and Orinitholestes than to birds, have no trace of a pygostyle.

References
Chiappe LM 2002. Basal bird phylogeny: problems and solutions. In: Chiappe L M, Witmer L eds. Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press. 448–472.
Wang W and O’Connor JK 2017. Morphological coevolution of the pygostyle and tail feathers in Early Cretaceous birds. Vertebrata PalAsiatica 2017:10: 55:3: 1-26.

wiki/Pygostylia

Sciurumimus: a feathered sister to Ornitholestes and Microraptor

This specimen is old news for many.
It came to my attention in a YouTube video lecture you can see here.

Figure 1. Sciurumimus in situ. Most of the skeleton as buried below the bedding plane.

Figure 1. Sciurumimus in situ. Only some off the tail filaments are colored here. Most of the skeleton as buried below the bedding plane. It would be interesting to dig out the remaining matrix behind the hands and legs with the understanding that sister taxon Microraptor has long feathers there. Total length ~ 60cm.

Sciurumimus albersdoerferi (Rauhut et al. 2012; Late Jurassic, 150 mya; Bürgermeister Müller Museum Solnhofen (BMMS) BK 11) is traditionally considered a basal coelurosaurian theropod, but was originally considered a basal megalosaur. Here it nests with Ornitholestes, close to Microraptor, also a Late Jurassic taxon. Microraptor is an Early Cretaceous taxon.

This specimen
(Fig. 1) has filament-like tail feathers growing in a pattern like squirrel tail hair over the proximal tail as in several ornithischians. There is a small egg-like shape between the ischia. Not sure what it is, but if you’re smiling right now, you’re guessing that this specimen is not a post-hatchling juvenile.

Figure 2. Skull of Sciurumimus with bones colorized.

Figure 2. Skull of Sciurumimus with bones colorized.

It would be interesting
to dig out the remaining matrix behind the hands and legs with the understanding that sister taxon Microraptor has long feathers there.

Figure 3. Sciurumimus manus and pes using DGS to find the best elements from both extremities and reassemble them. Note the shift of pedal digit 2 to metatarsal 3 in situ, repaired in vivo.

Figure 3. Sciurumimus manus and pes using DGS to find the best elements from both extremities and reassemble them. Note the shift of pedal digit 2 to metatarsal 3 in situ, repaired in vivo.

Surprisingly
pedal digit 2 has taphonomically drifted to metatarsal 3. Pedal digits 1 and 5, if present, are string-like and spindly vestiges.

Size vs. Juvenile status
Sciurumimus is correctly sized as a basal coelurosaurian, but tiny compared to megalosaurids. Rauhut et al. considered their specimen a megalosaur “probably early-post-hatchling” with teeth that are “markedly similar to that of basal coelurosaurian theropods.”. They nested Sciurumimus between spinosaurs and Megalosaurus and kin.

So why did Rauhut et al. consider their find a megalosaur? And a juvenile?

From the Rauhut et al. diagnosis: 
Megalosauroid theropod with the following apomorphic characters:

  1. axial neural spine symmetrically “hatchet-shaped” in lateral view;
  2. posterior dorsal neural spines with rectangular edge anteriorly and lobe-shaped dorsal expansion posteriorly;
  3. anterior margin of ilium with semioval anterior process in its dorsal half.

Unfortunately these traits also describe
Compsognathus and Ornitholestes, among other coelurosaurs. So, in theitr discussion Rauhut et al. list other synapomorphies of megalosaurids present in Sciurumimus.

  1. An elongate anterior process of the maxillary body
  2. a medially closed maxillary fenestra
  3. a very slender anterior process of the lacrimal
  4. a lateral blade of the lacrimal that does not overhang antorbital fenestra’
  5. the presence of a deep fossa ventral to the basioccipital condyle
  6. a splenial foramen that opens anteroventrally
  7. a slightly dorsally expanded anterior end of the dentary
  8. a pronounced ventral keel in the anterior dorsal vertebrae
  9. the absence of a posteroventral process of the coracoid,
  10.  and an enlarged manual ungual I.

Note:
The LRT recovers a different theropod tree topology and nests Sciurumimus apart from megalosaurs by using different character traits and by interpreting Sciurumimus differently. This was done without referring to more recent papers, like Godefroit et al. 2013, or having the specimen to study firsthand. According to Wikpedia, Godefroit et al. nested Sciurumimus with the much larger Sinraptor, among taxa tested here, and far from Ornitholestes. So now we have three competing theropod tree topologies. At least now Sciurumimus actually looks like a transition between Ornitholestes and/or Compsoognathus and micorraptors.

Juvenile traits present in Sciurumimus, according to Rauhut et al. include:

  1. the body proportions, with a very large skull and rather short hindlimbs
  2. lack of fusion in the skeleton (unfused neurocentral sutures in all of the vertebral column
  3. unfused sacral vertebrae
  4. lack of fusion between elements of the braincase
  5. a coarsely striated bone-surface texture in all skeletal elements
  6. and a very regular pattern of tooth development in the maxilla, possibly indicating that no teeth had been replaced.
FIgure 6. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor.

FIgure 4. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor. Sciurumimus is about the size of Microraptor at 60 cm in length.

Figure 6. Subset of the LRT that includes Sciurumimus and kin.

Figure 5 Subset of the LRT that includes Sciurumimus and kin.

Note:
The Solnhofen formation, from which Sciurumimus was recovered, has no large megalosaurid theropods. But it does have small coelurosaurian theropods, like Compsognathus, which nests as a more primitive relative one node away in the LRT (Fig. 5).

As readers may recall
the LRT finds several clades of birds, near-birds and bird mimics, including a basal radiation of several clades of post-Archaeopteryx birds that became extinct by the end of the Cretaceous. Furthermore, as readers may recall, small theropods appear at the base of many theropod clades, including those that create giants. So, there may not have been a gradual size decrease leading to birds, throughout the Theropoda, just including the Troodontidae (which includes extant birds).

References
Rauhut OWM, Foth C, Tischlinger H and Norell MA 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences. 109 (29): 11746–11751.

Godefroit P, Cau A, Hu D-Y, Escuillié F, Wu, W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature498 (7454): 359–362.

Baby Limusaurus had teeth!

This is pretty remarkable.
Wang et al. 2016 reported on a growth series for Limusaurus (Xu et al. 2009; Jurassic, Oxfordian; 1.7m in est. length; IVPP V 15923; Figs. 1-5,) “the only known reptile to lose its teeth and form a beak after birth.”  

You might remember
Limusaurus became famous earlier for its tiny forelimbs complete with a digit 0 medial to digit 1, that made theropod workers go bonkers because they assumed the digits present were 1-4, not 0-3.

Figure 2. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Figure 1. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Wang et al. report,
“The available data are important for understanding the evolution of the avian beak.” Except… Limusaurus is not close to the avian line of ancestry anyway you look at it. The LRT nests Limusaurus, with or without teeth, with Khaan, a toothless, beaked oviraptorid. Wang et al. nest Limusaurus with Elaphrosaurus (Fig. 3) even though Khaan is part of their taxon list. So something is not scored right. Not sure about the discrepancy, but some of that could be due to the misidentification of manual digits 0-3.

Figure 3. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Figure 2. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Wang et al. report,
“The ontogenetically variable features (e.g. teeth/no teeth, etc.) have little effect on its phylogenetic position.” The LRT agrees. Wang et al. report that no matter which ontogenetic stage is tested for Limusaurus, it always nests with or near the ceratosaur, Elaphrosaurus (Fig. 3).The LRT disagrees.  In other words, with or without teeth, the topology does not change. In the LRT  toothed juvenile Limusaurus also nested with Khaan. Toothed Juravenator and Sinosauropteryx nest as sisters to that clade. The large Compsognathus specimen CNJ79 (Fig. 6) was a basal taxon. All of these sisters are closer to Limusaurus in size and morphology than is Elaphrosauru (Fig. 3).

Figure 3. Elaphrosaurus is known from a partial skeleton lacking a skull.

Figure 3. Elaphrosaurus is known from a partial skeleton lacking a skull. Adult Limusaurus added to scale. Wang et al. consider these two to be sister taxa among basal theropods, which is not confirmed by the LRT.

The ontogenetic series of Limusaurus
is shown in figure 4. Not all the specimens are complete. None are shown to scale. All are portrayed as tiny rough tracings. I think this lack of detail is one shortcoming of the paper.

Figure 4. Specimens attributed to Limusaurus, not to scale.

Figure 4. Specimens attributed to Limusaurus, not to scale, from Wang et al. 2016.

Wang et al. also provided
reconstructions of a juvenile and adult Limusaurus (Fig. 5). Unfortunately, Wang et al. filled in all the missing bones and gave both reconstructions something of a generic theropod character, lacking some of the traits unique to this genus.

Limusaurus reconstructions from Wang et al. 2016, to scale and not to scale.

Figure 5. Limusaurus reconstructions from Wang et al. 2016, to scale and not to scale. The angle of the pubis is difficult to determine.

That Limusaurus juveniles had teeth
and adults did not, tells us less about the avian line and more about the oviraptorid line of theropod dinosaurs.

Figure 1. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

Figure 6. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

References
Wang S, Stiegler J, Amiot R, Xu W, Du G-H, Clark JM, Xu X 2016. Extreme ontogenetic changes in a ceratosaurian theropod. Currently Biology 27:1-5 plus SupData.

Paravian phylogeny revisited – SVP abstracts 2016

Pei et al. 2016
reveal the origin of birds in a new phylogenetic analysis. Some aspects confirm earlier recoveries in the large reptile tree (LRT) made about a year ago. Not sure about other aspects given the brevity of the abstract and lack of cladogram imagery.

From the Pei et al. 2016 abstract
“Paraves are theropod dinosaurs comprising of living and fossil birds and their closest fossil relatives, the dromaeosaurid and troodontid dinosaurs. Traditionally, birds have been recovered as the sister group to Deinonychosauria, the clade made up of the two
subclades Dromaeosauridae and Troodontidae. However, spectacular Late Jurassic paravian fossils discovered from northeastern China – including Anchiornis and Xiaotingiapreserve anatomy that seemingly challenges the status quo. (1) To resolve this debate we performed an up-to-date phylogenetic analysis for paravians using the latest Theropod Working Group (TWiG) coelurosaur data matrix which we supplemented with new data from recently described Mesozoic paravians from Asia and North America (e.g., Zhenyuanlong and Acheroraptor). This includes data from the unnamed dromaeosaurid IVPP V22530 and Luanchuanraptor, which are included in a phylogenetic analysis for the first time. We also incorporate new data from iconic paravians such as Archaeopteryx and Velociraptor based on firsthand study. (2) The analysis adopted the maximum parsimony criterion and was performed in the phylogenetic software TNT. Our preliminary results support the monophyly of each of the traditionally recognized paravian clades. (3) The Late Jurassic paravians from northeastern China (e.g., Anchiornis and Xiaotingia) are recovered as avialans rather than deinonychosaurians, at a position more basal than Archaeopteryx and other derived avialans (4). The traditional sister group status of Troodontidae and Dromaeosauridae is reaffirmed (5) and is supported by a laterally exposed splenial and a characteristic raptorial pedal digit II. Recently reported Early Cretaceous dromaeosaurids from northern and northeastern China, including Zhenyuanlong, Changyuraptor and IVPP V22530, are closely related to other microraptorines as expected. (6) Luanchuanraptor, a dromaeosaurid from the Late Cretaceous of central China is recovered as a more advanced eudromaeosaurian. By tracing character evolution on the current tree topology we report on the latest insights into the adaptive radiation amongst early paravians, including the origin of flight and changes in body size and diet. (7)

Notes

  1. In the LRT Xiaotinigia and Anchiornis have nested as derived troodontids, basal to birds since their insertion into the LRT more than 3 years ago. So that’s confirmation that troodontids are basal to Archaeopteryx and other birds with Xiaotinigia and Anchiornis as proximal outgroup taxa.
  2. But did they include five or more Archaeopteryx specimens, as in the LRT? They don’t say so…
  3. In the LRT there is a clade that includes Velociraptor, but the Troodontidae does not produce a clade that does not include birds. Rather birds are derived troodontids in a monophyletic clade.
  4. If avialans are usually defined as all theropod dinosaurs more closely related to modern birds (Aves) than to deinonychosaurs, all troodontids are avialans in the LRT. Since Troodontidae was named by Gilmore in 1924, the term Avialae (Gauthier 1986) is a junior synonym.
  5. Troodontidae and Dromaeosauridae are also sisters in the LRT.
  6. This confirms the topology recovered in the LRT from about a year ago. Microraptorines, like Microraptor and basal tyrannosauroids like Zhenyuanlong are not related to troodontids or birds, but to tyrannosaurs and compsognathids.
  7. I’d like to see their tree whenever it is published to compare the two.
Figure 7. Bird cladogram with the latest additions. Here the referred specimen of Yanornis nests with enantiornithes while Archaeovolans nests within the Scansoriopterygidae, not with Yanornis.

Figure 1. Bird cladogram from several months ago. Here Avialae is a junior synonym for Troodontidae.

References
Pei R, Pittman M, Norell M and Xu X 2016. A review of par avian phylogeny with new data. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.