Do ceratopsid juveniles (phylogenetically) nest together?

The discovery of a second juvenile ceratopsid
(Currie et al. 2016) raised an interesting point: “In phylogenetic analysis, if all characters are coded as seen, the two juvenile ceratopsids (a partial Triceratops skull and the UALVP 52613 juvenile, Fig. 1) nest together. However, when size or age dependent characters are [not scored], the new juvenile (Chasmosaurus) specimen groups with other adult Chasmosaurus specimens.”

Figure 1. Chasmosaurus juvenile UALVP 52613 specimen.

Figure 1. Chasmosaurus juvenile UALVP 52613 specimen lacking forelimbs due to  taphoniomic loss down a nearby sinkhole.

So, does phylogenetic analysis fail us?
The new UALVP juvenile was recognized/identified as being closer to Chasmosaurus, just as the juvenile Triceratops was recognized as being closer to Triceratops, both on the basis of character traits and prior to analysis. But the Currie et al. unedited analysis takes us in another direction…

From the introduction
“The specimen comprises a nearly complete skeleton lying on its left side, lacking only the front limbs and girdle, which were lost many years ago into a large sinkhole….”

“The juvenile nature of this specimen is based on several lines of reasoning. At approximately 1.5 min total length, it is the smallest articulated ceratopsid skeleton that has ever been recovered. Immature bone textures on cranial bones (Brown et al., 2009), open neurocentral sutures throughout most of the vertebral column, incomplete fusion of sacral vertebrae, lack of fusion between caudal ribs and vertebrae, poorly formed articulations between limb bones, and many other characters confirm that this is an immature ceratopsid….”

“Of all the chasmosaurines from Dinosaur Park, it is most similar to Chasmosaurus belli and C. russelli.”

This interpretation
was made by expert and experienced assessment. The question is, why would the unedited Currie et al. analysis separate the juveniles from the adults and nest the juveniles together? They’re not exactly tadpoles or caterpillars, but they do change somewhat during maturation, following basic archosauromorph (including synapsid/mammal) growth strategies, that lepidosauromorphs (including pterosaurs) are less likely to follow.

When an adult Chasmosaurus
and the juvenile Chasmosaurus are added to the large reptile tree, using a character list NOT specific to ceratoposids, the juveniles nest with their respective adults, not with each other. And this happens despite the very few bones that represent the juvenile Triceratops (posterior face and shield only). Notably there are no other competing ceratopsid candidates in the present taxon list. All data was gleaned from online images. The adult data may be  represented by chimaera mounts and chimaera drawings. If the Currie et al analysis was restricted to just an adult and juvenile Triceratops and just an adult and juvenile Chasmosaurus, would adults nest with juveniles as they do in the large reptile tree? We don’t know because that test was not run.

Here’s how the large reptile tree divides
the Chasmosaurus adult and juvenile from the Triceratops adult and juvenile (posterior skull traits only). Please feel free to provide better data or more precise readings for any of these interpretations. Some were difficult to figure from available sources. At present I do not include traits for parietal fontanelles or horn lengths, which are the easiest two traits that most commonly separate Chasmosaurus from Triceratops and are reflected in their juveniles.

  1. skull table: C: depressed terrace, medial and lateral crests; T: convex
  2. snout in dorsal view: C: not constricted; T: constricted
  3. orbit positon: C: postorbital > preorbital; T: subequal
  4. lateral rostral shape: C: convex, smooth curve; T: double convex
  5. nasals/frontals: C: nasals >; T: subequal
  6. antorbital fenestra: C: absent; T: without mx fossa
  7. orbit/upper temporal fenestra: C: orbit not > T: orbit >
  8. orbit position/skull: C: anterior half of skull; T: not
  9. orbit shape: C: round to square: T: taller than wide
  10. upper temporal fenestrae: C: not closed or slit-like; T: closed or slit-like
  11. frontal shape: C: not wider posteriorly; T: wider posteriorly
  12. frontal shape 2: C: without posterior processes; T: with posterior processes
  13. posterior rim of parietal: C: transverse; T: anteriorly oriented or curved.
  14. parietal skull table: C: forms a sagittal crest: T: broad
  15. squamosal descent: C: mid level; T: ventral skull (ventral maxilla)
  16. skull roof fusion: C: parietal fusion only; T: frontal fusion and parietal fusion
  17. jaw joint orientation: C: descends from ventral mx; T: in line with ventral mx, after jugal arch.
  18. last maxillary tooth: C: posterior orbit; T: mid orbit
  19. mandible ventrally: C: 2-tier convex; T: straight
  20. 2nd sacral rib: C: not: T: double wide laterally
  21. manus/pes: C: subequal: T: manus smaller
  22. ilium: C: posterior process >; T: not
  23. metatarsal 1:4 ratio: C: 1 not > than half: 4 T: 1> half of 4
  24. metatarsals 2-4: C: < than half the tibia; T: not
  25. pedal 3.1 vs p2.1: C: not > T: 3.1>
  26. metatarsals 2 and 3: C: aligns with mt1; T: aligns with pedal 1.1
  27. pedal 4 length: C: subequal to mt 4; T: > mt4
  28. pedal digit 3 vs 4: C: 4 narrower than 3; T: 4 is not narrower

Shifting the juvenile Triceratops
to the juvenile Chasmosaurus adds 12 steps. Doing the opposite adds 21 steps. Bootstrap scores are over 99-100 for the three nodes represented by the four taxa. I have not reviewed the scores or data in the Currie et al study, which obviously adds more ceratopsid traits.

Added < 24 hours after original publication Below is a new reconstruction of the Triceratops juvenile based on text measurements and an adult skull compared to the original reconstruction that does not appear to have correctly scaled the mandible to the skull elements.

Figure 4. A new reconstruction of the Triceratops juvenile with the mandible and squamosal scaled to text measurements and shaped to adult elements compared to the original (Goodwin et al.) reconstruction which appears to have shortened the mandible.

Figure 4. A new reconstruction of the Triceratops juvenile with the mandible and squamosal scaled to text measurements and shaped to adult elements compared to the original (Goodwin et al.) reconstruction which appears to have shortened the mandible.

_______________________

Short notes for readers and critics
“Criticism of a writer is absolutely inevitable.” — Malcolm Gladwell.
Gladwell is one of the most respected and best-selling authors in current decades. Nevertheless, this interview on YouTube quotes several critics, many with scathing barbs. So, this give and take between writers and their critics is universal and ‘inevitable.’

On the other hand,
in Science, one either can or cannot duplicate experiments and observations. It should be cut and dried, but with errors and egos on both sides, it rarely is. Even so, most people think it is better to try/experiment with/refute alternate hypotheses. Aaaaaat least that’s the editorial policy at ReptileEvolution.com where occasional lack of talent and insight is sometimes overcome by tenacity, huge blocks of data and the ability to update online blunders.

References
Currie PJ,  Holmes RB, Ryan MJ and Coy C. 2016. A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1048348.

 

 

Nesting Triceratops and its juvenile

Updated May 26 with suggestions from C. Collinson on skull sutures.

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).

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
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

 

 

 

The large French Compsognathus specimen

Updated May 23, 2016 with a new mandible. M. Mortimer pointed out correctly that I had traced two coincident mandibles as one. 

The less well-known
French specimen of Compsognathus corallestris (Bidar et al. 1972b; Peyer 2006; CNJ79) is a bit larger with a different morphology (Fig. 1) than the coeval smaller Bavarian Solnhofen specimen, Compsognathus longipes (Fig. 1 right). Dr. Peyer considers these two Late Jurassic theropods conspecific and representative of ontogenic rather than phylogenetic variation.

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 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.

From the Peyer abstract:
“The absence of an external mandibular fenestra, dorsally fan-shaped dorsal neural spines with hook-shaped ligament attachments, and a  very short McI and a PhI-1, which is stouter than the radius distinguish compsognathids from other coelurosaurs. Anatomical and morphological characters of the Bavarian specimen of Compsognathus are nearly identical to those of the French specimen. The differences are related to ontogenetic or within-species variation or are caused by preservational factors. Therefore this study proposes that C. corallestris is a subjective junior synonym of Compsognathus longipes from Bavaria.”

You’ll note that “compsognathids” sensu Peyer are scattered throughout this large reptile tree subset of the Theropoda (Fig. 2). Sinocalliopteryx and Juravenator are widely considered compsognathids, yet both nest far from one another here.

I tested the ontogenetic hypothesis of Peyer
in the large reptile tree. Indeed, the two Compsognathus specimens do nest next to one another, but at the bases of two different clades.

The smaller Compsognathus specimen
nested with Struthiomimus, Ornitholestes, Microraptor and T-rex, among others.

The large Compsognathus specimen
nested with the oviraptorid, Khaan, Limusaurus, therizinosaurs, Sinosauropteryx and others. More derived clades include Eotyrannosaurus and other paravians such as dromareosaurids, troodontids and birds.

Figure 2. Compsognathus corrallensis nests close to the holotype smaller specimen, but at the base of the next clade, which includes oviraptors, therizinosaurs, Juravenator and Sinosauropteryx.

Figure 2. Compsognathus corrallensis nests close to the holotype smaller specimen, but at the base of the next clade, which includes oviraptors, therizinosaurs, Juravenator and Sinosauropteryx. That means it is not the adult version of the smaller specimen.

The new reconstruction
of the large Compsognathus skull is relatively shorter. Both the premaxilla and the dentary tip are oriented slightly down. The bones of the mandible slid apart during taphonomy. Put them back together to match the skull length and you might get a mandibular fenestra, as also seen in the smaller Compsognathus. The new skull reconstruction (Fig. 1) was created using DGS, not freehand as in the Peyer reconstruction.

Figure 3. DGS tracing of large French Compsognathus skull. These parts were used to make the reconstruction in figure 1. Only the left side and top elements were colorized.

Figure 3. DGS tracing of large French Compsognathus skull. These parts were used to make the reconstruction in figure 1. Only the left side and top elements were colorized.

Current traditional compsognathids include the following taxa

  1. Compsognathus
  2. Sinocalliopteryx
  3. Juravenator (some say yes, others say no)
  4. Sinornithosaurus
  5. Huaxiagnathus

In the large reptile tree the clade that includes Compsognathus now include the following taxa

  1. Compsognathus
  2. all ornithomimids, including Struthiomimus

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.
Ostrom JH 1978. T
he 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,
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.

wiki/Compsognathus

Nasal crests on theropods… insight from Sinosaurus

The latest addition 
to the large reptile tree is the crested theropod, Sinosaurus (Young 1948, Hu 1993; Figs. 1,2, Early Jurassic). So far (provisionally), It nests basal to the Allosaurus + Yutyrannus clade and is a sister to the Proceratosaurus+ Spinosaurus clade that also gave rise Deinocheirus (Fig. 1).

Figure 1. Here's where the crested theropod, Sinosaurusn nests in this subset of the large reptile tree.

Figure 1. Here’s where the crested theropod, Sinosaurusn nests in this subset of the large reptile tree. Note that other crested theropods, like Dilong and Gaunlong nest nearby. Proceratosaurus might have had a crest, larger than the tiny remnant that was preserved.

 

Figure 2. Sinosaurus cast with premaxilla in yellow.

Figure 2. Sinosaurus cast with premaxilla in yellow.

Two nasal crests
top the rostrum in Sinosaurus, but they are very close together. Because Sinosaurus does not nest with Dilophosaurus, and crestless taxa separate them, those two taxa developed similar crests by convergence.

Not so oddly
those two crests on Sinosaurus are barely a crest width apart from one another. Moreover, those those two crests include a healthy portion of premaxillae — and that’s unexpected because in most dinosaurs the ascending process of the premaxilla generally does not extend beyond the naris. But it does in this clade, as we saw earlier with Deinocheirus.

Figure 3. Sinosaurus skull model along with tracing and line art from Hu 1993 then stretched to fit the model.

Figure 3. Sinosaurus skull model along with tracing and line art from Hu 1993 then stretched to fit the model. Note the extent of the premaxilla. Hu considered this another Dilophosaurus, but other workers corrected that hypothesis.

 

That sent me back looking at other clade members. 
And I found premaxillae extending beyond the naris in basal clade members. The derived forms have their own story to tell with the fused nasal boss overlying whatever premaxillary ascending process might have remained below it.

Figure 3. Yutyrannus with revised premaxilla extending beyond the naris.

Figure 3. Yutyrannus with revised premaxilla extending beyond the naris. Sinovenator and Majungasaurus both overlap the ascending process of the premaxilla with the nasal boss, so it appears much shorter. 

Is the crest of Ceratosaurus 
an emerging ascending process of the premaxilla? We’d have to look at the fossil itself, but this colorized version of an old illustration is a tantalizing clue to that possibility. In Allosaurus (Fig. 4) and Acrocanthosaurus the ascending process of the premaxilla is reduced to a slender rod that looks like a medial ridge of the nasal. I think this has been overlooked by prior workers.

Figure 4. Ceratosaurus with extended premaxilla. It is the horn sticking up between the nasals.

Figure 4. Ceratosaurus with extended premaxilla. It is the horn sticking up between the nasals.

What we’re seeing here is 
the counterintutiive phenomenon that crests came first in this clade, with convergent reduction, or coverup. in derived larger taxa.

Figure 5. Allosaurus skull with bones colorized. Note the extent of the premaxillary ascending processes over the nasals.

Figure 5. Allosaurus skull with bones colorized. Note the extent of the premaxillary ascending processes over the nasals.

With present taxa as data
the twin, barely separated crests of Sinosaurus apparently evolved from the similar morphology in its sister, Proceratosaurus, (Figs. 6, 7).

Figure 6. Proceratorsaurus skull with premaxilla (yellow) and nasal (pink) demonstrating how twin nasal crests could have originated with the loss of the premaxillary ascending process.

Figure 6. Proceratorsaurus skull with premaxilla (yellow) and nasal (pink) demonstrating how twin nasal crests could have originated with the reduction of the premaxillary ascending process.

A closeup in anterior view
of Proceratosaurus (Fig. 7) shows the early stages of splitting of the premaxilla and nasals to form two crests.

FIgure 7. Proceratorsaurus premaxilla. Note the tentative split at the top.

FIgure 7. Proceratorsaurus premaxilla. Note the tentative split at the top of the premaxilla. 

References
Hu S-J 1993. Short Report on the Occurrence of Dilophosaurus from Jinning County, Yunnan Province. Vertebrata PalAsiatica 31(1):65-79. Translated by Will Downs 1998.
Young CC 1948. On two new saurischians from Lufeng, Yunnan. Bulletin of the Geological Society of China (Acta Geologica Sinca) 28 (1–2): 75–90. doi:10.1111/j.1755-6724.1948.mp281-2007.x.

Those Dilophosaurus crests…

Revised February 15, 2016 with the deletion of the putative sister taxa, Megapnosaurus, which did not nest with Dilophosaurus when finally put to the test in the large reptile tree today. 

Sometimes it is easy to see the sutures on a skull. 
Sometimes, not so easy. That’s the case with Dilophosaurus (Welles 19454) an early theropod dinosaur with a partial skull that is cracked in so many places, the skull sutures that create the crest are camouflaged. So some alternates are proposed here (Fig. 1) without seeing the original paper, unfortunately.

Figure 1. Dilophosaurus skull with alternates for the maxilla (green), nasal (pink), premaxilla (gold) and lacrimal (tan) colorized. I have not yet seen the paper, so I don't know where Welles identified sutures.

Figure 1. Dilophosaurus skull with alternates for the maxilla (green), nasal (pink), premaxilla (gold) and lacrimal (tan) colorized. I have not yet seen the paper, so I don’t know where
Welles identified sutures.

 

If anyone has more valid details on this problem
please send them here.

References
Welles SP 1954. New Jurassic dinosaur from the Kayenta formation of Arizona”. Bulletin of the Geological Society of America 65 (6): 591–598. doi:10.1130/0016-7606(1954)65[591:NJDFTK]2.0.CO;2.

The Theropoda: just a few (albeit heretical) changes to traditional trees

Adding taxa
is a method I have supported in order to discover taxonomic relationships among reptiles. The large reptile tree (theropod subset in Fig. 1) has now passed 650 taxa. The theropod subset has been considered at odds with traditional trees. But when you really look at it, maybe, not so much.

Figure 1. Theropod subset of the large reptile tree. Unresolved clades are resolved in heuristic analyses. Here traditional clades are named. A few taxa nest somewhere other than their traditional nestings here. Click to slightly enlarge.

Figure 1. Theropod subset of the large reptile tree. Unresolved clades are resolved in heuristic analyses. Those are due to incomplete skeletons. Here traditional clades are named. A few taxa nest somewhere other than their traditional nestings here. Click to slightly enlarge.

I added four more theropods
to the large reptile tree and applied traditional names to various clades (Fig. 1). Those additions and all scoring corrections did not change the overall tree topology.

Tradition is upheld overall here
as the major clades: 1. Neotheropoda; 2. Avetheropoda/Averostra; 3; Tetanurae; 4. Maniraptora; 5. Paraves; 6. Deinonychosauria/Eumaniraptora; 7. Troodontidae; and 8. Birds/Aves appear in their traditional order and with most of their traditional taxa.

Heresy is introduced here

  1. A clade between Tawa and Coelophysis includes Marasuchus, Segisaurus and Procompsognathus, taxa too often omitted from traditional theropod trees.
  2. Several former compsognathids, including Juravenator, Sinosauropteryx, now nest as derived maniraptors close to Limusaurus + Khaan and another former compsognathid, Sinocalliopteryx, now nests with spinosaurs.
  3. Several former tyrannosauroids, including Proceratorsaurus, Dilong, Guanlong and Xiongguanlong now nest with spinosaurs.
  4. A former ornithomimid, Deinocheirus, now nests with spinosaurs.
  5. Several former dromaeosaurs, including Microraptor, Sinornithosaurus, Zhenyuanlong and Tianyuraptor now nest with tyrannosauroids.
  6. A former bird/dromaeosaur, Rahonavis now nests with basal therizinosaurs.
  7. A former ceratosaur, Limusaurus, now nests with oviraptors.
  8. Eotyrannus and Tanycolagreus nest together as basal Paraves.

The following taxa do not belong in theropod studies
because they are basal phytodinosaurs.

  1. Eodromaeus
  2. Eoraptor
  3. Daemonosaurus
  4. Chilesaurus

The problem for traditional theropod workers is
the above heretical sisters really do look like sisters, both overall and in detail. With 651 nesting opportunities, this is where they found maximum parsimony (the fewest changes to their morphology).

These nestings look like heresies, but they follow prior work

  1. Ornithomimosaurs and maniraptors were both derived from Compsognathidae (Compsognathus) according to Lee et al. 2014.
  2. A series of small troodontids give rise to birds according to Godefroit et al. 2013.
  3. Dilophosaurus nests with Coelophysis according to Sues et al., 2011.
  4. Others I missed? It’s better for everyone when I’m not the first to notice taxonomic similarities.

Added taxa
have, so far, only supported earlier clades from earlier large reptile tree topologies. There have been score changes, but that’s standard operating procedure when adding taxa. It goes to show that a pretty good tree CAN have scoring mistakes. The best tree, of course, has no mistakes.

It is so good to have photo references
to look over when trying to decide what an unidentified or misidentified crumb of bone might represent. I can’t imagine having to buy a ticket to go revisit a fossil every time I needed to see it again. The logistics would prove nightmarish. (You have to realize that NO ONE does this). Remember, no one is an expert on a fossil the moment they first see it. Spending time with data makes you an expert on it. How much of an expert do you need your experts to be?

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.
Godefroit P, Cau A, Hu D-Y, Escuillié, Wu, W-H and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498 (7454): 359–362.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B 278 (1723): 3459–3464

Proceratosaurus: another theropod leaves the tyrannosauroids for the spinosauroids

This blogpost
continues a series of prior blogposts featuring the tested removal of taxa traditionally considered to be in the ancestry of Tyrannosaurus. Find those posts here, here, here and here. There were also a few blogposts that added non-traditional taxa to the lineage of tyrannosaurs. Find those here, here and here.

Figure 1. Only the lower 7/8 of the skull of Proceratosaurus is known. Here the skull in siitu, A tracing modified from Tracy Ford. And another tracing by Rauhut et al. 2010 with anterior and occipital views.

Figure 1. Only the lower 7/8 of the skull of Proceratosaurus is known. Here the skull in siitu, A tracing modified from Tracy Ford. And another tracing by Rauhut et al. 2010 with anterior and occipital views. Note the entire skull is concave ventrally, but the maxilla and jugal are both straight.

Proceratosaurus bradleyi
(Middle Jurassic, Bathonian, England, NHM R 4860, Fig. 1) was originally considered another Megalosaurus (Woodward 1910), then identified as a unique taxon, a likely ancestor of a another much larger and more robust horned theropod, Ceratosaurus (von Huene 1926). Those reports were made back in the day when there were very few theropods to compare with one another.

In more recent times,
Proceratosaurus was phylogenetically nested (according to Wikipedia, Angela Milner and the BBC, Rauhut et al. (2010), Loewen et al. (2013) and Brusatte et al. (2015)) as the earliest member of the tyrannosaur lineage (Figs. 2-4).

Figure 3. Theropods from Rauhut et al. 2010. Here Proceratosaurus, Dilong and Guanlong nest with tyrannosaurs.

Figure 2. Theropods from Rauhut et al. 2010. Here Proceratosaurus, Dilong and Guanlong nest with tyrannosaurs, but key taxa are missing.

The question is why do their trees and the large reptile tree differ?
The answer could be (once again) due to taxon exclusion and tradition. The shift in nestings could be due to the lack of more attractive sister taxa in traditional tyrannosaur studies. The large reptile tree includes those more attractive sister taxa. But that is not the complete answer in every case.

Figure 4. Tyrannosaurs from Brusatte et al. 2013. Some taxa nest elsewhere in the large reptile tree. Others are missing from this tree.

Figure 3. Tyrannosaurs from Brusatte et al. 2013. Some taxa nest elsewhere in the large reptile tree. Others are missing from this tree. Click to enlarge.

Could it be scoring?
I have not checked the scores and matrices in other studies. I do know that the sisters in the large reptile tree do share long lists of character traits, but D-shaped premaxillary teeth (often touted as a key trait restricted to tyrannosaurs) are not among the traits listed there. Did Spinosaurus and Suchomimus also have D-shaped premaxillary teeth? I don’t know. If not, could that trait be in their relatively short-snouted ancestors by convergence? At this point the answer is, apparently so.

Rauhut (2010 reported, “As close relationships of Proceratosaurus with several of the clades included in this analysis (coelophysoids, spinosauroids, and maniraptorans) have never been proposed previously, these clades were collapsed [individually] into [a] single operational taxonomic unit[s] (OTU[s]).” 

That’s a problem
as the large reptile tree found Proceratosaurus to nest closest to basalmost spinosauroids (former tyrannosauroids). Now do you see why it is SO important NOT to employ suprageneric taxa — ever! It is possible that Rauhut et al. (and those that followed) created their own problems by creating suprageneric taxa where they should not have done so. In Science you have to be open to any and all answers, without bias or a priori assumptions wherever practicable and possible. That’s why it is so convenient to start with the large gamut of possibilities provided by the large reptile tree (now 647 taxa and growing).

Figure 5. Theropods from Loewen et al. with pertinent taxa highlighted.

Figure 4. Theropods from Loewen et al. with pertinent taxa highlighted.

Proceratosaurus was added
to the large reptile tree (subset in Fig. 5) and it did not nest with tyrannosaurs, but with smaller Early Cretaceous taxa that traditionally nest with tyrannosaurs, but now nest with spinosaurs. Everyone agrees that Proceratosaurus nests with Guanlong and Dilong. Everyone else agrees that these three nested with tyrannosaurs (Figs. 2-4). So, I am the only unorthodox heretic at present.

Figure 2. The Dinosauria subset of the large reptile tree as of February 5, 2016. Here Proceratosaurus nests with several former long-snouted tyrannosaurs now closer to spinosaurs and allosaurs.

Figure 5. The Dinosauria subset of the large reptile tree as of February 5, 2016. Here Proceratosaurus nests with several former long-snouted tyrannosaurs now closer to spinosaurs and allosaurs.

The large reptile tree
provides ancestral taxa that share more traits (see below) with Late Cretaceous tyrannosaurs than the traditional putative Jurassic and Early Cretaceous candidates provided by the authors listed in the references. I promote these recovered candidates so they will be tested by others, as I have tested their candidate taxa.

Without a doubt,
the Late Cretaceous tyrannosaurs are all monophyletic. The question is, which taxa phylogenetically preceded them in the Early Cretaceous and Jurassic? Note that none of the taxon lists in any of the studies totally match one another. On the other hand, all of the studies are in general agreement. However, the recovered topologies don’t exactly match one another. And so the game is afoot.

Getting back to Proceratosaurus
Take a look at its sister on the allosaur branch in the large reptile tree: it’s Ceratosaurus. So maybe von Huene (1926) was on to something… or he was lucky.

Basic traits that Proceratosaurus, Guanlong and Dilong
share with Sinocalliopteryx, Deinocheirus and the spinosaurs.

  1. Long, low rostrum
  2. Sometimes smaller premaxillary teeth vs. maxillary teeth
  3. Tall orbit
  4. Premaxillary postero-lateral processes that may be present due only to the down tip of the naris.
  5. Ventral border of elongate naris formed by premaxilla + nasal
  6. Long, strongly recurved maxillary teeth
  7. Majority coverage of the quadrate by the squamosal and quadratojugal.
  8. Often, but not always, a nasal median crest.
  9. Often, but not always, a descending posterior skull relative to the maxilla

Given that
Sinocalliopteryx and Dilong had primitive feathers, all (except perhaps the giants) probably shared that rarely preserved trait. Given that the above nine traits are all skull traits, it is likely that this clade was trending toward a specific feeding niche, in this case, an aquatic one.

Someday this will all come together. 

References
Brusatte SL and Carr TD 2016. The phylogeny and evolutionary history of tyrannosauroid dinosaurs. Nature, Scientifice Reports 6 (8 pages), 20252; doi: 10.1038/srep20252.
Loewen MA, Irmis RB, Sertich JJW, Currie PJ, Sampson SD 2013. Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. PLoS ONE 8(11): e79420. doi:10.1371/journal.pone.0079420
Rauhut OWM, Milner AC and Moore-Fay S 2010. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, published online before print November 2009. doi:10.1111/j.1096-3642.2009.00591
von Huene F 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Geologie und Palaeontologie (Serie 1), 4: 1–361.
Woodward AS 1910. On a Skull of Megalosaurus from the Great Oolite of Minchinhampton (Gloucestershire). Quarterly Journal of the Geological Society 66: 111–115.