Haya 2021: still suffering from taxon exclusion

Barta and Norell 2021
give us a detailed look at every bone in the basal ornithischian, Haya griva (Fig. 1). We looked at Haya earlier here and nested it close to Pisanosaurus in the large reptile tree (LRT, 1810+ taxa).

Figure 1. Haya in lateral view.

Figure 1. Haya in lateral view.

For reasons unknown
Barta and Norell did not include Chilesaurus and Daemonosaurus (Fig. 2) in their text or phylogenetic analysis.

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

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

The hypothesis of interrelationships 
that nested Chilesaurus and Daemonosaurus as phytodinosaurs basal to Ornithischia (Fig. 2) has been online since 2011.

Figure 2. Subset of the LRT focusing on the Phytodinosauria with Buriolestes at its base.

Figure 2. Subset of the LRT focusing on the Phytodinosauria with Buriolestes at its base.

No matter how much detail you put into your study of a taxon
it is all for naught if you decide to exclude pertinent taxa. You will not understand the phylogeny of that taxon, how it relates to others. Haya is a basalmost ornithischian in the LRT, an hypothesis of interrelationships not confirmed by Barta and Norell due to taxon exclusion. They had a chance to deliver big news and muffed it.

The Barta and Norell cladogram suffered from massive loss of resolution
at many nodes. Never a good sign. If you can tell two taxa apart generically, as fossils, you should be able to lump and separate them in a cladogram.

Perhaps too many incomplete taxa were tested.
Don’t include incomplete taxa until you have your tree topology all worked out first.


References
Barta DE and Norell MA 2021. The osteology of Haya griva (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia. Bulletin of the American Museum of Natural History 445: 1-111.

 

‘Pennaraptora’ — avoid this junior synonym

A new volume published by the AMNH
(eds. Pittman and Xu 2020), is all about the the putative clade, ‘Pennaraptora’ (Fig. 1). According to the preface, “Pennaraptora comprises birds themselves as well as the pennaceous feathered dromaeosaurids, troodontids, scansoriopterygids, and oviraptorosaurians.”

Here
in the large reptile tree (LRT, 1727+ taxa; subset Fig. 2) scansoriopterygids are birds, not oviraptorosaurian sisters. Oviraptorosaurians are terminal taxa in a larger clade that includes therizinosaurs and the CNJ79 specimen of Compsognathus and that clade is the sister clade of the Compsognathus holotype, struthiomimids and tyrannosaurids (Fig. 2). The last common ancestor of all these clades in the LRT is Aorun zhaoi (Choiniere et al. 2013; IVPP V15709, Late Jurassic 161mya).

So this multipart study on ‘Pennaraptorans’ is off to several bad starts. Neither ‘Aorun‘, nor ‘Tyrannoraptora’ (see below) are mentioned in the text. Several taxa have been omitted from this clade, including the last common ancestor.

Only two generic taxa and “their last common ancestor (LCA)”
should be enough to define a clade. Look what bad things can happen when you use four suprageneric taxa (Fig. 1). Don’t let in generic taxa that do not belong and omit generic taxa that do belong. Even so, and surprisingly, all taxa employed here are clade members. Unfortunately the clades and a few taxa are a little mixed up due to taxon exclusion.

Figure 1. Cladogram of the Pennaraptora from Pittman and Xu eds. 2020. Color overlays added to show clades in the LRT (Fig. 2).

Figure 1. Cladogram of the Pennaraptora from Pittman and Xu eds. 2020. Color overlays added to show clades in the LRT (Fig. 2).

Foth et al. defined Pennaraptora in 2014.
“Pennaraptora is a clade defined as the most recent common ancestor of Oviraptor philoceratops, Deinonychus antirrhopus, and Passer domesticus (the house sparrow), and all descendants thereof,”  Again, this definition only needs the first two taxa. Passer nests within “all descendants thereof”. Even so, this is a definition we can work with (Fig. 2).

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

In the LRT ‘Pennaraptora’
is almost a junior synonym of Compsognathidae (Cope 1871; Fig. 2) because two specimens of Compsognathus are basalmost taxa. However, Aorun is the last common ancestor taxon. It was originally considered the oldest known coelurosaurian theropod and a juvenile.

Figure 3. Aorun compared to several other theropods to scale.

Figure 3. Aorun compared to several other theropods to scale.

Figure 4. Aorun skull in situ and slightly restored. This is the basalmost tyrannoraptor.

Figure 4. Aorun skull in situ and slightly restored. This is the basalmost tyrannoraptor in the LRT.

According to Wikipedia, Aorun is now considered a member of
the Tyrannoraptora (Sereno 1999) defined as, “Tyrannosaurus, Passer their last common ancestor [Aorun] and all of its descendants.” So Pennaraptora (2014) is a junior synonym of Tyrannoraptora (1999). The two define the same clade in the LRT and share a last common ancestor.

Coelurosauria (von Huene 1914 is defined as theropods closer to birds than to carnosaurs. In the LRT Tyrannoraptora is also a junior synonym for Coelurosauria.


References
Bidar AL, Demay L and Thomel G 1972b. Compsognathus corallestris,
une nouvelle espèce de dinosaurien théropode du Portlandien de Canjuers (Sud-Est de la France). Annales du Muséum d’Histoire Naturelle de Nice 1:9-40.
Choiniere JN, Clark JM, Forster CM, Norella MA, Eberth DA, Erickson GM, Chu H and Xu X 2013. A juvenile specimen of a new coelurosaur (Dinosauria: Theropoda) from the Middle–Late Jurassic Shishugou Formation of Xinjiang, People’s Republic of China. Journal of Systematic Palaeontology. online. doi:10.1080/14772019.2013.781067
Cope ED 1871. On the homologies of some of the cranial bones of the Reptilia, and on the systematic arrangement of the class. Proceedings of the American Association for the Advancement of Science 19:194-247
Foth C, Tischlinger H and Rauhut OWM 2014. New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature. 511 (7507): 79–82.
Huene F v 1914. Über de Zweistämmigkeit der Dinosaurier, mit Beiträgen zer Kenntnis einiger Schädel. Sep.-Abd. Neuen Jahrb. für Mineralogie Beil.-Bd.37:577–589. Pls. vii-xii.
Ostrom JH 1978. The osteology of Compsognathus longipes. Zitteliana 4: 73–118.
Peyer K 2006. A reconsideration of Compsognathus from the upper Tithonian of Canjuers, southeastern France, Journal of Vertebrate Paleontology, 26:4, 879-896.
Pittman M and Xu X eds. 2020.
Pennaraptoran theropod dinosaurs. Past progress and new Frontiers. Bulletin of the American Museum of Natural History 440; 353pp. 58 figures, 46 tables.
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.

wiki/Compsognathus
wiki/Tyrannoraptora
wiki/Aorun
wiki/Pennaraptora

Restoring and re-nesting Murusraptor

Traditional megaraptorans,
like Megaraptor namunhuaiquii (Novas 1998, Fig. 1) and Murusraptor barrosaensis (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; MCF-PVPH-411; Fig. 1), are currently only known from bits and pieces. Perhaps for these reasons Wikipedia reports, “the clade Megaraptora (Benson, Carrano and Brusatte 2010 ) has controversial relations to other theropods.”

According to Wikipedia
“Murusraptor is a megaraptoran, one of a group of large predatory dinosaurs whose exact classification remains disputed. Once believed to be dromaeosaurids, they have since been classified as either allosauroid carnosaurs or as tyrannosauroid coelurosaurs. While the discovery of Murusraptor does not clarify as of yet the placement of this group of theropods, the specimen does add further clarity to some aspects of megaraptoran anatomy and potentially, eventual classification of the Megaraptora within the theropod evolutionary tree.”

Definition
Megaraptora (Benson et al 2010) “The most inclusive clade comprising Megaraptor namunhuaiquii, but not Chilantaisaurus tashuikouensis.” 

Wikipedia reports,
“Megaraptorans were most diverse in the early Late Cretaceous of South America, particularly Patagonia. However, they had a widespread distribution. Fukuiraptor, the most basal (“primitive”) known member of the group, lived in Japan. Megaraptoran material is also common in Australia, and the largest known predatory dinosaur from the continent, Australovenator, was a megaraptoran.” 

Taxa traditionally included within Megaraptora:

  1. Megaraptor (known from a long maxilla and forelimb, Figs. 1, 2)
  2. Fukuiraptor (known from jaw fragments, coracoids, humeri, femur, acetabulum, two vertebrae
  3. Australovenator (known from a dentary, a few dorsal ribs, distal forelimbs and nearly complete hind limbs)
  4. Murusraptor (known from several skull elements and other bones Figs. 1, 2)

Of these, only two, Megaraptor and Murusraptor, are tested in the LRT.

Other megaraptoran traits according to Wikipedia

  1. “Their forelimbs were large and strongly built,
  2. The ulna bone had a unique shape (except Fukuiraptor).
  3. The first two fingers were elongated, with massive curved claws ,
  4. The third finger was small. 
  5. Megaraptoran skull material is very incomplete, but a juvenile Megaraptor described in 2014 preserved a portion of the snout, which was long and slender. 
  6. Leg bones referred to megaraptorans were also quite slender and similar to those of coelurosaurs adapted for running. 
  7. Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The vertebrae, ribs, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in taxa such as Neovenator
  8. Other characteristic features include opisthocoelous neck vertebrae
  9. and compsognathid-like teeth.” 

Several of the above traits
are shared with other taxa. The LRT employes a suite of 231 shared, unique and often convergent traits to lump, split and ultimately nest all taxa. Surprisingly, even the poorly preserved, disarticulated and incomplete Megaraptor and Murusraptor found secure nodes.

Araciaga, Rolando, Novas and Agnolin 2019
bring us ‘new evidence about the phylogenetic relationships of Megaraptora.’ They report, “The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”

From their abstract:
“Murusraptor is particularly similar to juvenile specimens of tyrannosaurids; both share: 1) lacrimal with a long anterior prosess; 2) corneal process and; 3) lateral pneumatic fenestra; 4) square and dorsoventrally low frontals; 5) parietals with well-developed sagittal and nuchal crests, among other features. The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”

“Murusraptor is unique in having several diagnostic features that include anterodorsal process of lacrimal longer than height of preorbital process, and a thick, shelf-like thickening on the lateral surface of surangular ventral to the groove between the anterior surangular foramen and the insert for the uppermost intramandibular process of the dentary.

“Other characteristic features of Murusraptor barrosaensis n.gen. et n. sp. include a large mandibular fenestra, distal ends of caudal neural spines laterally thickened into lateral knob-like processes, short ischia distally flattened and slightly expanded  dorsoventrally. Murusraptor belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor.”

A little backstory with links for more details:
Aerostean is a giant (9m) Late Cretaceous theropod with no skull material known. Orkorpator is a large (6m) Latest Cretaceous theropod includes only a post-orbital and quadratojugal for skull material and bits and pieces otherwise.

Figure 1. Murusraptor compared with related taxa to scale.

Figure 1. Murusraptor compared with related taxa to scale. Ghosted rostrum of Guanlong added to missing rostrum of Mururaptor.

Phylogenetic analysis
In the large reptile tree (LRT, 1415 taxa; Fig. 4) Megaraptor (Fig. 1) nests with the basal theropod, Sinocalliopteryx. Murusraptor (Fig. 1) nests between long-snouted Dilong and the long-snouted Guanlong / Spinosaurus clade.

One problem comes from
the hypothesis of relationships published by Coria and Currie 2016 that nests long-snouted Xiongguanlong, Dilong, Proceratosaurus and Guanlong with robust-snouted Tyrannosaurus, rather than with long-snouted spinosaurs. Even so, Coria and Currie 
nest Murusraptor with Megaraptor. The closest theropod also tested in the LRT is the finback allosaurAcrocanthosaurus. So, the Coria and Currie cladogram is different in most respects from the LRT. Coria and Currie also nest the giant horned theropod, Ceratosaurus, as a basalmost/outgroup taxon. In the LRT (Fig. 4) Ceratosaurus has no descendants.

Figure 2. Megaraptor, Murusraptor and Sinocalliopteryx. See figure 1 for revised restoration of Murusraptor. Not to scale.

Figure 2. Megaraptor, Murusraptor and Sinocalliopteryx. See figure 1 for revised restoration of Murusraptor. Not to scale. The Rolando et al. restoration draws more on Megaraptor and Dilong.

In counterpoint to Coria and Currie 2016,
Novas et al. 2016 reported, “megaraptorids retained several of the manual features present in basal tetanurans, such as Allosaurus. In this regard, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus).” 

In the LRT,
(Fig. 4) Guanlong is closer to Allosaurus than to Tyrannosaurus.

Figure 4. Megaraptor also preserves a complete and distinct manus, here compared to Sinocalliopteryx, which also has a digit 4, and Suchomimus has a robust ungual 1.

Figure 3. Megaraptor also preserves a complete and distinct manus, here compared to Sinocalliopteryx, which also has a digit 4, and Suchomimus has a robust ungual 1. According to the LRT, Suchomimus is not related to Megaraptor, but is shown here to demonstrate the convergence.

According to the writers of Wikipedia,
the large compsognathid, Sinocallioteryx (Figs. 1-3) is not related to megaraptorids, despite the many similarities in the skull. Curiously, other long-snouted theropods with massive curved claws on their forelimbs, like Suchomimus (Fig. 3), are also not traditionally considered related to megaraptorids. I wish they were. Everyone wishes they were. However, I have to report results, no matter how controversial, as I have for the last eight years. That way, if I made mistakes, someone will tell me. If someone has forgotten certain taxa, perhaps next time they will add them.

Figure 4. Subset of the LRT focusing on basal theropods. Megaraptor and Murusraptor are highlighted.

Figure 4. Subset of the LRT focusing on basal theropods. Megaraptor and Murusraptor are highlighted.

In conclusion
Murusraptor barrosaensis
  (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; Late Cretaceous) was originally considered a sister to Megaraptor and close to tyrannosaurs. Here (Fig. 4) Murusraptor nests between Dilong and Guanlong closer to spinosaurs. Megaraptor nests with Sinocalliopteryx, a basal theropod, not close to Murusraptor. Wherever other traditional megaraptorans (see list above) nest has not yet been tested in the LRT. We looked at the relationship of long-snouted theropods with spinosaurs, rather than tyrannosaurs earlier here.


References
Rolando AMA, Novas FE and Agnolin FL 2019. A reanalysis of Murusraptor barrosaensis Coria & Currie (2016) affords new evidence about the phylogenetical relationships of Megaraptora. Cretaceous Research. https://doi.org/10.1016/j.cretres.2019.02.021
Benson RBJ, Carrano MT and Brusatte SL 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic.
Naturwissenschaften 97(1): 71–78.
Coria RA and Currie PJ 2016. A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLoS ONE 11(7): e0157973. doi:10.1371/journal.pone.0157973
Novas FE 1998. Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia. Journal of Vertebrate Paleontology. 18: 4–9. doi:10.1080/02724634.1998.10011030
Novas FE, Rolando AMA and Agnolín FL 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria. 74: 49–61.
Porfiri JD, Novas FE, Calvo JO.; Agnolín FL.; Ezcurra MD and Cerda IA. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research. 51: 35–55.

wiki/Megaraptor
wiki/Murusraptor
wiki/Megaraptora

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

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

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.

Xiongguanlong: not a tyrannosauroid

A few years ago
Li, et al. 2010 described a new theropod dinosaur, Xiongguanlong (Fig. 1), as “a longirostrine tyrannosauroid from the Early Cretaceous of China” which they nested between Eotyrannus + Dilong and Tyrannosaurus + other Late Cretaceous tyrannosaurs.

Figure x. The skull of Xiongguanlong is long and low, like that of spinosaurs and kin, not like that of tyrannosaurs and kin.

Figure 1. The skull of Xiongguanlong is long and low, like that of spinosaurs and kin, not like that of tyrannosaurs and kin.

Unfortunately,
the large reptile tree nests Xiongguanlong along with other longistrine theropods, like Murusraptor (Fig. 2), Sinocalliopteryx and the spinosaurs. I have not yet encountered any valid longirostrine tyrannosauroids. Dilong and Guanlong also nest close to these long-rostrum theropods. They were removed from the tyrannosauroids earlier here and here. Eotyrannus was likewise removed from the tyranosauroids here, and nested with Tanycologreus close to the base of the dromaeosaur/troodontid + bird split.

Li et al. report
“Xiongguanlong marks the earliest phylogenetic and temporal appearance of several tyrannosaurid hallmarks such as a sharp parietal sagittal crest, a quadratojugal with a dramatically flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and a flaring axial neural spine surmounted by distinct processes at its corners.”

“Remarkably, Xiongguanlong has dorsally smooth nasals. Unlike the conical tooth crowns of taxa such as Tyrannosaurus, Xiongguanlong has mediolaterally compressed tooth crowns. The cervical vertebrae display only a single pair of pneumatic foramina, and the dorsal centra are not pneumatic in contrast to Albertosaurus and more derived tyrannosaurids. Xiongguanlong is remarkable in having a shallow and narrow snout forming more than two thirds of skull length…most tyrannosaur ids have short deep snouts mechanically optimized for powerful biting.”

Figure 1. Murusraptor compared with related taxa to scale.

Figure 1. Murusraptor compared with related taxa to scale.

No blame here. 
Li et al could have extended their comparative search to Sinocalliopteryx, which was published in 2007. The LRT looks at a wide gamut of taxa.


References
Li D, Norell MA, Gao K-Q, Smith ND and Makovicky PJ 2010. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proceedings of the Royal Society B 277:183-190.

Deinocheirus: a giant ornithomimosaur

Updated January 28, 2020
with a new comparison to the ornithomimosaur, Gallimiumus, distinct from Struthiomimus.

Following a long list of blog posts
that reported an inability of the large reptile tree, to nest various theropods in their traditional nodes, today Deinocheirus (Fig. 1) nests with ornithomimosaurs, like Gallimimus,  despite not having a pinched mt3 and having a pedal digit 1.

Figure 1. The skull of Deinocheirus. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures? That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Figure 1. The skull of Deinocheirus. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures? That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Previous studies
assumed that Deinocheirus was an ornithomimosaur, because it had very similar manus and forelimb proportions. When the skull was discovered, it was likewise toothless.

Figure 2. Deinocheirus specimens and a composite illustration.

Figure 2. Deinocheirus specimens and a composite illustration.

Deinocheirus mirificus (Osmólska & Roniewicz, 1970, Latest Cretaceous, 70 mya 11m) was originally and later considered a giant and basal ornithomimosaur. The large reptile tree nests Deinocheirus with Gallimimus.


References
Lee YN, Barsbold R, Currie PJ, Kobayashi Y, Lee HJ, Godefroit P, Escuillié F and Chinzorig T 2014. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature 515 (7526): 257–260.
Osmólska H and Roniewicz E 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica. 21:5-19.

wiki/Deinocheirus