SVP 2018: A super-matrix for an invalid ‘Thyreophora’

Raven, Maidment and Barrett 2018 report,
“The individual lineages, Ankylosauria and Stegosauria, have been studied thoroughly, but there has never before been a comprehensive whole-group cladistic analysis of Thyreophora.”

According to Wikipedia:
“Thyreophorans are characterized by the presence of body armor lined up in longitudinal rows along the body. Threophora (Nopsca 1915) has been defined (Sereno 1998) as the group consisting of all species more closely related to Ankylosaurus than to Triceratops. Thyreophoroidea was first named by Nopcsa in 1928 and defined by Sereno in 1986, as “ScelidosaurusAnkylosaurus, their most recent common ancestor and all of its descendants”. Eurypoda was first named by Sereno in 1986 and defined by him in 1998, as “Stegosaurus, Ankylosaurus, their most recent common ancestor and all of their descendants”.

Raven, Maidment and Barrett 2018 report,
“Here, the first species-level phylogenetic super matrix of the whole-group Thyreophora is presented, incorporating all previous known cladistic analyses of ankylosaurs, stegosaurs and basal thyreophorans and including all valid species within Thyreophora, for a total of 89 taxa and 338 characters.

Unfortunately
in the large reptile tree (LRT, 1308 taxa, Fig. 1) the last common ancestor of Ankylosauria and Stegosauria also includes among its descendants: heterodontosaurids, lesothosaurs, duckbills and horned dinosaurs.

So ‘Goodbye, Eurypoda and Thyreophora’
(unless these clades someday become more inclusive by consensus). The super-matrix of Raven, Maidment and Barrett 2018 probably does not include the LRT or the taxonomic tree it finds within the clade Ornithischia. So use their study to learn about the stegosaurs and the ankylosaurs, but not the last common ancestor of stegosaurs and ankylosaurs. That would be a sister to late-surviving Late Cretaceous Haya and/or Late Triassic Pisanosaurus.

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

Figure 1. Subset of the LRT focusing on the Phytodinosauria. Scelidosaurus through Minmi are basal ankylosaurs. Lesothosaurus through Stegosaurus are basal stegosaurs.

References
Raven TJ, Maidment SC and Barrett PM 2018. The first phylogenetic super-matrix of the armored dinosaurs (Ornithischia, Thyreophora). SVP abstracts.

wiki/Thyreophora

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Mirischia: a transitional theropod pelvis

Of the tens of thousands of mistakes I have made
while creating ReptileEvolution.com, the LRT and this blog over the last 7 years, this time I read ‘right’ and I applied ‘left’ to the ilium of Mirischia. Here corrections were made within 24 hours of its original posting. Thanks to MM for reporting the error. Apologies for the error.

Naish, Martill and Frey 2004
bring us an Early Cretaceous Santana Formation theropod pelvis and femur they named Mirischia asymmetrica (Fig. 1; SMNK 2349). They align the specimen with the French compsognathid (CNJ79), which is correct.

A key taxon
The traits visible in the Mirischia pelvis and femur (Fig. 1) are just enough to nest it between the Compsognathus clade (which includes tyrannosaurs, ornithomimosaurs and microraptors) and the Ornitholestes clade (which includes dromaeosaurs, troodontids and birds). And it is transitional in size, too.

Figure 1. The pelvis of Mirischia with color overlays and ilium correctly oriented. Below Mirischia pelvis compared to the CN79 specimen of Compsognathus and Ornitholestes.

Figure 1. The pelvis of Mirischia with color overlays and ilium correctly oriented. Below Mirischia pelvis compared to the CN79 specimen of Compsognathus and Ornitholestes. The yellow ‘bone’ between the pubes of Mirischia is ossified gut contents.

References
Choiniere JN, Clark JM, Forster CA and Xu X 2010. A basal coelurosaur (Dinosauria: Theropoda) from the Late Jurassic (Oxfordian) of the Shishugou Formation in Wucaiwan, People’s Republic of China. Journal of Vertebrate Paleontology. 30 (6): 1773–1796.
Naish D, Martill DM and Frey E 2004. Ecology, systematics and biogeographical relationships of dinosaurs, including a new theropod from the Santana Formation (?Albian, Early Cretaceous) of Brazil. Historical Biology 16(2–4):57–70.

 

The last common ancestor of all dinosaurs in the LRT: ?Buriolestes

Müller et al. 2018
describe a new dinosaur skeleton they attribute to Buriolestes shultzi (Cabreria et al. 2016, ULBRA-PVT280, Figs. 2, 3). In the large reptile tree (LRT, 2015 taxa; subset Fig. 1) the holotype now nests at the base of the Phytodinosauria. The referred specimen is different enough to nest between the herrerasaurs and all other dinosaurs. This, of course, removes herrerasaurs from the definition of the Dinosauria (Passer + Triceratops, their last common ancestor (= CAPPA/UFSM 0035) and all descendants).

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

 

Buriolestes schultzi (Cabreria et al. 2016; Late Triassic, Carnian; 230mya) was originally and later (Müller et al. 2018) considered a carnivorous sauropodomorph, but here two specimens nest as the basalmost dinosaur (CAPPA/UFSM 0035) and the basalmost phytodinosaur (ULBRA-PVT280).

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs.

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs. It should have a distinct name.

All cladograms agree that Buriolestes
is a very basal dinosaur. Taxon exclusion changes the tree topology of competing cladograms. The broad autapomorphic ‘eyebrow’ of the CAPPA specimen indicates it is a derived trait in this Late Triassic representative of an earlier genesis.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

The Müller et al. cladogram
combined both specimens attributed to Buriolestes (never a good idea, but it happens all the time). The Müller et al. cladogram excluded a long list of basal bipedal crocodylomorpha, but did include Lewisuchus. It excluded the archosaur outgroups PVL 4597Turfanosuchus and Decuriasuchus. The Müller et al. cladogram nested Ornithischia basal to Saurischia (= Herrerasauridae + Agnophitys, Eodromaeus, Daemonosaurus + Theropoda + Sauropodomorpha) with Buriolestes nesting between Eoraptor and Panphagia. The CAPPA specimen of Buriolestes is also a sister to the basalmost theropod, Tawa (Fig. 3)… and not far from the other basal archosaur, Junggarsuchus (Fig. 4).

Figure 8. The CAPPA specimen of Buriolestes compared to the more primitive Junggarsuchus, basal to the other branch of archosaurs, the crocs.

Figure 4. The CAPPA specimen of Buriolestes compared to Junggarsuchus, basal to the other branch of archosaurs, the crocs.

References
Cabreira SF et al. (13 co-authors) 2016. A unique Late Triassic dinosauromorph assemblage reveals dinosaur ancestral anatomy and diet. Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040
Müller RT et al. (5 co-authors 2018. Early evolution of sauropodomorphs: anatomy and phylogenetic relationships of a remarkably well-preserved dinosaur from the Upper Triassic of southern Brazil. Zoological Journal of the Linnean Society, zly009 (advance online publication) doi: https://doi.org/10.1093/zoolinnean/zly009

Theropods in the LRT with suggested nomenclature

Figure 1. Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Figure 1. Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently. Names posted here are in use traditionally, but with different definitions in some cases.

Just a moment to update
the theropod subset of the large reptile tree (LRT, 1151 taxa). Given the present taxon list, this is the order they fall into using the generalized characters used throughout the LRT. Validation is required for all such first-time proposals. The names applied here are used in traditional studies, but often not following previous definitions or clade memberships.

The large and small Compsognathus specimens
are closely related, but not congeneric (Fig. 2).

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 2. 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.

Does anyone see
in this list two ‘related’ taxa that do not resemble one another more so than any other taxon? If so, that needs to be noted and repaired.

Go back far enough in dinosaur ancestry and you come to: Heleosaurus

With our never-ending fascination with dinosaurs
it’s interesting to list some of the taxa in their deep, deep!, deep!! ancestry. One such ancestor is Heleosaurus (Fig. 1; Broom 1907; Middle Permian ~270 mya, ~30 cm snout to vent length), the first known basal prodiapsid, the clade the includes diapsids (sans lepidosaurs, which are unrelated but share the same skull topology by convergence).

Figure 1. Heleosaurus is closer to the main lineage of dinosaurs. It retained canine fangs.

Figure 1. Heleosaurus is close to the main lineage of dinosaurs. It retained canine fangs. Note the squamosal distinct from the quadratojugal, as in Nikkasaurus. Also note the continuing lacrimal contact with the naris, as in Protorothyris.

But first
I want to discuss a derived Heleosaurus cousin, Nikkasaurus (Ivahnenko 2000; Fig. 2), also one of the most basal prodiapsids.

It is only by coincidence
that Ivahnenko labeled Nikkasaurus one of his ‘Dinomorpha,’ a clade name ignored by other authors. Wikipedia considers Nikkasaurus one of the Therapsida and possibly a relic of a more ancient stage of therapsid development. Like Heleosaurus, Nikkasaurus had a single synapsid-like lateral temporal fenestra. Only their nesting outside of that clade and basal to the clade Diapsida in the LRT tell us what they really are. Most of the time, as you know, we can tell what a taxon is simply by looking at it. In this case, as in only a few others, we cannot do so readily.

Figure 1. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Figure 2. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Nikkasaurus tatarinovi (Ivahnenko 2000) Middle Permian was a tiny basal prodiapsid with a large orbit. It retained a large quadratojugal. The fossil is missing the squamosal. Others mistakenly considered the quadratojugal the squamosal, as in therapsids. That’s an easy mistake to make. Compare this bone to the QJ in Heleosaurus (Fig. 1), another prodiapsid. Nikkasaurus has small sharp teeth and no canine fang. Nikkasaurus is a sister to Mycterosaurus. They both share a large orbit and fairly long snout. What appears to be a retroarticular process may be something else awaiting inspection in the actual fossil. Based on all other data points, I don’t trust that post-dentary data. It doesn’t match the in situ figure.

Distinct from other prodiapsids,
the Nikkasaurus, Mycerosaurus and Mesenosaurus maxilla extended dorsally, overlapping the lacrimal and contacting the nasal, as it does in Dimetrodon and basal therapsids like Hipposaurus and Stenocybus. This trait tends to be homoplastic / convergent in all derived taxa, but the timing differs in separate clades.

Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.

Figure 2. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it. Note the posterior mandible mismatch in the purported retroarticular process. I suspect the process is not there.

And finally we come back to Heleosaurus.
Slightly closer to the lineage of dinosaurs is the slightly more basal prodiapsid, Heleosaurus (Fig. 2), which retained canine fangs, had a more typical posterior mandible and retained a lacrimal / naris contact. This naris trait was retained by Petrolacosaurus, Eudibamus, Spinoaequalis and other basal diapsids (archosauromorpha with both upper and lateral temporal fenestra ). The maxilla did not rise again to cut off lacrimal contact with the naris in the ancestry of dinosaurs until the small Youngina specimens huddled together, SAM K 7710 and every more derived taxon thereafter, up to and including dinos.

References
Broom R 1907. On some new fossil reptiles from the Karroo beds of Victoria West, South Africa. Transactions of the South African Philosophical Society 18:31–42.
Ivahnenko MF 2000. 
Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013

Nesting Triceratops and its juvenile

Updated May 26 with suggestions from C. Collinson on skull sutures.
Updated again with a new reconstruction of the missing juvenile Triceratops face. 

No surprises here. 

Figure 1. Triceratops mount from an auction house. Pectoral girdle repaired. Skull colorized. Dorsal view comes from another specimen - always a dangerous proposition.

Figure 1. Triceratops mount from an auction house. Pectoral girdle repaired. Skull colorized. Dorsal view comes from another specimen – always a dangerous proposition.

Triceratops (Fig. 1, Marsh 1889) and its juvenile (Fig. 2) nest together with Yinlong downsi (Xu et al. 2006) Late Jurassic ~150 mya, ~1.2 m in length; Fig. 3) a primitive bipedal hornless pro-ceratopsian ornithischian, dinosaur, archosaur, archosauriform, archosauromorph, reptile. The large reptile tree is now up to 678 taxa.

Figure 2. Juvenile Triceratops compared to subadult Triceratops (in shadow).

Figure 2. Juvenile Triceratops compared to subadult Triceratops (in shadow).

A YouTube video, Dinosaurs Decoded, shows Mark Goodwin reassembling the juvenile Triceratops skull. Click here to watch.

Figure 2b. Original figure from Goodwin et al. of juvenile Triceratops, but mandible and squamosal scale bars don't match. Then compared to an adult. Then reconstructed based on new mandible/squamosal proportions based on text measurements. Evidently the juvenile Trike had a longer rostrum than Goodwin thought.

Figure 2b. Original figure from Goodwin et al. of juvenile Triceratops, but mandible and squamosal scale bars don’t match. Then compared to an adult. Then reconstructed based on new mandible/squamosal proportions based on text measurements. Evidently the juvenile Trike had a longer rostrum than Goodwin thought.

Liike all ornithischians, 
ceratopsians fuse the postfrontal to the frontal. However, in Yinlong, cracks (sutures?) appear where the postfrontal would have appeared and where the orbital horns ultimately appeared. So are the postorbital horns actually derived from postfrontal buds? We won’t know until we can determine a suture from a crack in the ontogenetically youngest and phylogenetically most primiitive specimens. It is also possible that, like the nasal horn, the orbital horns arose from novel ossificatiions that ultimately fused to the underlying bone.

Figure 3. Yinlong skull showing possible postfrontal in the position of the future orbit horns.

Figure 3. Yinlong skull showing possible postfrontal in the position of the future orbit horns.

Another juvenile nests with its adult counterpart!
Several workers and readers have pointed to studies (sorry, I don’t have the reference here) in which juveniles did NOT nest with adults in morphological analysis. Notably these samples  (as I recall…) came from taxa that metamorphosed during ontogeny, like caterpillars > butterflies and tadpoles > frogs.

In another argument, perhaps reflecting a majority view, a peerJ reviewer expressed concern/fear/trepidation that: – “Finally, I don’t know that a phylogenetic analysis including juvenile specimens alongside adult specimens is going to give you a particularly trustworthy result.“ citing no references, but noting that juvenile hadrosaurs have distinct characters in the skull from adults, which we all know.

Such arguments have been raised whenever I suggested workers include tiny Solnhofen pterosaurs in phylogenetic analyses, especially so since we KNOW that hatchling pterosaurs were virtual copies of adults. Not so with dinosaurs in which the rostrum is shorter and the orbits are larger than in adults. Even with that handicap, the differences, at least in this one case, were not enough to separate adult from juvenile Triceratops, given the present taxon list, which, frankly has no other ceratopsians.

References

Goodwin MB, Clemens WA, Horner JR and Padian K 2006. The smallest known Triceratops skull: new observations on ceratopsid cranial anatomy and ontogeny. Journal of Vertebrate Paleontology 26(1): 103-112.Lambe LM 1902. New genera and species from the Belly River Series (mid-Cretaceous), Geological Survey of Canada Contributions to Canadian Palaeontology 3(2):25-81
Marsh OC 1898. New species of Ceratopsia. Am J Sci, series 4 6: 92.
Xu X, Forster CA, Clark J M and Mo J 2006. A basal ceratopsian with transitional features from the Late Jurassic of northwestern China. Proceedings of the Royal Society B: Biological Sciences. First Cite Early Online Publishing. online pdf

 

wiki/Yinlong 
wiki/Triceratops

 

 

 

Tyrannosaurus ancestors to scale

Ornitholestes now nests nearby.
The CNJ7 specimen of Compsognathus (Fig. 0) is closer to the base of the Tyrannosaurus clade.

Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

At odds with other published trees
the large reptile tree finds the following taxa in the clade of, and ancestral to, Tyrannosaurus, everyone’s favorite dinosaur.

Figure 1. The following taxa nest in the clade of Tyrannosaurus at present: Gorgosaurus, Alioramus, Zhenyuanlong, Tinayuraptor and Ornitholestes.

Figure 1. The following taxa nest in the clade of Tyrannosaurus at present: Gorgosaurus, Alioramus, Zhenyuanlong, Tinayuraptor and Ornitholestes. Click to enlarge. There appears to be a linkage from Zhenyuanlong to T-rex in the shape of the orbit and relatively short rostrum.

Seems pretty obvious.
even when you look at that very distinctive hourglass-shaped quadratojugal. Not sure why others have missed this.

We looked at traditional contenders,
now almost all nesting with similarly long-snouted spinosaurs here and here. None have a similar QJ.

And, as we learned earlier…
Ornitholestes nests basal to the very bird-like Microraptor and Sinornithosaurus.