Leptoceratops repairs an unresolved node

Earlier a skull only taxon, Auroraceratops, nested with a skull-less taxon, Stenopelix in the Ornithischia. Such non-overlapping trait pairings cannot be resolved. Does one nest basal to another? Or vice versa? Do they nest together? The cladogram cannot tell you, so you end up with 3 possible trees. Sometimes that happens.

Figure 1. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT.

Figure 1. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT. Those ribs are oddly straight. Did they produce a horned-lizard like torso (wider than deep)?

What helps is taxon addition.
Here Leptoceratops (Fig. 1), known from complete material (skull + post-crania) is added to the LRT and returns the basal ceratopsian node to resolution.

Leptoceratops gracilis (Brown 1914; Latest Cretaceous; 2m long) is a late surviving member of an early radiation of bipedal ceratopsians that probably browsed while quadrupedal. The ventral maxilla was convex. The skull was narrower than most. The ribs appear to have flared widely, not deeply, creating a horned-lizard-like torso.

References
Brown B 1914. Leptoceratops, a new genus of Ceratopsia from the Edmonton Cretaceous of Alberta. Bulletin of the AMNH 33, article 36.


Dr. David Unwin reports
the untimely death of Dr. Lü Junchang, author and co-author of dozens of publications coming out of China. I met Dr. Lü long ago when he was working in Texas, early in his career and studies. The pterosaur, Beipiaopterus, was the subject of an early paper in 2002. He was kind enough to send PDFs on his work at every request.

Aquilops americanus is not a neoceratopsian

Aquilops americanus was described 
by Farke et al. 2018, “The taxon is interpreted as a basal neoceratopsian closely related to Early Cretaceous Asian taxa, such as Liaoceratops and Auroraceratops.” This may be due to taxon exclusion.

Aquilops is much more primitive
than neoceratopsians, like Chasmosaurus and Triceratops, according to the large reptile tree (LRT, 1304 taxa; subset Fig. 1) which nests Aquilops between Laquintasaura and Hexlinusaurus, both basal to the psittacosaur – ceratopsian split. Both were excluded from the Farke et al. study.

Figure 1. Aquilops nests at the base of psittacosaurs + ceratopsians in the LRT. Pachycephalosaurs, like Stegoceras, are not the sisters to ceratopsians.

Figure 1. Subset of the LRT focusing on the Ornithischia where Aquilops nests at the base of psittacosaurs + ceratopsians in the LRT. Pachycephalosaurs, like Stegoceras, are not the sisters to ceratopsians.

Distinct from Laquintasaura,
Aquilops has an eagle-like hooked rostral bone (Fig. 2) and retains an antorbital fenestra with fossa. It was likely a biped, based on phylogenetic bracketing. Here (Fig. 1) skull only Auroraceratops nests with skull-less Stenopelix at the base of the Neoceratopsia. Liaoceratops nests with Psittacosaurus and Yinlong. We’ll look at them in future posts.

Figure 2. Aquilops skull as restored and as discovered.

Figure 2. Aquilops skull as restored and as discovered. The squamosal has been artificially restored with a parietal shield in the restoration, traits not preserved in the partial material. 

References
Farke AA, Maxwell WD, Cifelli RL and Wedel MJ 2014. A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia. PLoS ONE. 9 (12): e112055. doi:10.1371/journal.pone.0112055

wiki/Aquilops
https://p3d.in/G34T8+welcome
https://samnoblemuseum.ou.edu/collections-and-research/vertebrate-paleontology/discovering-aquilops-americanus/

3D view of Aquilops americanus at Sam Noble Museum website

Figure 1. Tiny Aquilops sits atop the nasal of its descendant, Triceratops, in this Sam Noble Museum photo.

Figure 1. Tiny Aquilops sits atop the nasal of its descendant, Triceratops, in this Sam Noble Museum photo.

The cat-sized early ‘ceratopsian’
Aquilops americanus (Farke et al., 2014; OMNH 34557; Early Cretaceous; skull length 8.4cm) is visible online at the Sam Noble Museum website (links below). The 3D imagery is fascinating to roll, zoom and pitch (some restoration is present).

Figure 2. Digital reconstruction of Aquilops. Click to go to the 3D page.

Figure 2. Digital reconstruction of Aquilops. Click to go to the 3D page.

According to Farke et al. 2014:
“The taxon is interpreted as a basal neoceratopsian closely related to Early Cretaceous Asian taxa, such as Liaoceratops and Auroraceratops.” The large reptile tree (LRT, 1302 taxa) does not include these two, but when tested Aquilops nested several nodes apart from the included neoceratopsians, between two bipeds, Laquintasaurus and Hexinlusaurus. These two are not included in Farke et al., but they are basal to psittacosaurs and ceratopsians in the LRT. We’ll look at Aquilops in detail tomorrow and try to iron out the differences.

References
Farke AA, Maxwell WD, Cifelli RL and Wedel MJ 2014. A Ceratopsian Dinosaur from the Lower Cretaceous of Western North America, and the Biogeography of Neoceratopsia. PLoS ONE. 9 (12): e112055. doi:10.1371/journal.pone.0112055

wiki/Aquilops
https://p3d.in/G34T8+welcome
https://samnoblemuseum.ou.edu/collections-and-research/vertebrate-paleontology/discovering-aquilops-americanus/

Laquintasaura: verrrry basal ceratopsian from the Early Jurassic

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 1. Subset of the LRT focusing on the Phytodinosauria. Here Laqunitasaura nests at the base of the Ceratopsia.

I still hold to the hypothesis|
that a phylogenetic analysis that is able to lump and separate taxa is better than one that cannot do this. In the large reptile tree (LRT, 989 taxa), Laquintasaura venezuelae (Barrett et al. 2014; Early Jurassic, 200mya ~1m in overall length; Fig. 2) nests at the base of the ceratopsia (outside of Hexinlusaurus and Yinlong) and not far from the base of the Ornithopoda (outside of Changchunsaurus). It is very plesiomorphic and very early even for an ornithischian, let alone a ceratopsian.

Figure 1. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus).

Figure 2. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus). Compare to premaxillary teeth in figure 3.

Barrett et al. were not so sure where Laquintasaura nested
as they reported, “A strict consensus of these 2160 MPTs places Laquintasaura in an unresolved polytomy with the major ornithischian clades Heterodontosauridae, Neornithischia and Thyreophora along with other early ornithischian taxa, such as Lesothosaurus.”

The Barrett et al. diagnosis reports:
“Laquintasaura can be differentiated from other early ornithischians by the following autapomorphic combination  of dental characters: cheek tooth crowns have isosceles-shaped outlines, which are apicobasally elongate, taper apically, are mesiodistally widest immediately apical to the root/crown junction, possess coarse marginal denticles extending for the full lengths of the crown margins, and possess prominent apicobasally extending striations on their labial and lingual surfaces. Postcranial autapomorphies include: sharply inflected dorsal margin of ischium dorsal to the obturator process; femoral fibula epicondyle medially inset in posterior or ventral views; and astragalus with a deep, broad, ‘U’-shaped notch in anterior surface.”

I had no access to the fossil(s).
And I had to trust the drawing produced by Barrett et al. (Fig. 1) for my data. Contra the Barrett et all. analysis, there was no loss of resolution with Laquintasaura in the LRT.

Figure 2. The skull of Yinlong a basal certatopsian.

Figure 3 The skull of Yinlong a basal certatopsian. Those premaxillary teeth are quite similar to those figure in Barrett et al. for Laquintasaura. Note the dorsal naris, horizontal ventral premaxilla.

References
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR. 2014. A palaeoequatorial ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281:20141147. http://dx.doi.org/10.1098/rspb.2014.1147

Stenopelix reconstructed and nested

Figure 1. Stenopelix in situ with several bones colorized then transferred to figure 2.

Figure 1. Stenopelix in situ with several bones colorized then transferred to figure 2. The ischia appear to be wide, as in birds, but that is due to crushing. In vivo they curved ventrally.

Stenopelix valdensis
(Meyer 1857; Early Cretaceous, Barremian, 125 mya; Germany; Fig. 1) is a small ornithischian dinosaur based on a single partial skeleton preserved in part and counterpart in dorsal view. Stenopelix has been difficult to classify for about 150 years because it lacks a skull. Various authors listed in Wikpedia have weighed in on the nesting of this enigma.

  1. Early pachycephalosaur (Maryanska and Osmólska 1974)
  2. Early ceratopian (Sues and Galton 1982)
  3. Pachycephalosauria (Sereno 2000)
  4. Marginocephalia (Butler and Sullivan 2009)
  5. Ceratopsia and a sister to Yinlong (Butler et al. 2011)
Figure 1. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

Figure 2. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

When Stenopelix was added
to the large reptile tree, it nested between (Yinlong + Psittacosaurus) and the ceratopsians. Note that the psittacosaurs have a long slender publs and straight ischium. Ceratopsians have a reduced pubis and dorsoposteriorly convex ischium, traits shared with Stenopelix. The tail is relatively short with small chevrons, as in ceratopsians. Otherwise this specimen is similar to several ornithischians.

Figure 3. The Phytodinosauria with the addition of Stenopelix basal to the Ceratopsidae.

Figure 3. The Phytodinosauria with the addition of Stenopelix basal to the Ceratopsidae.

The curved ischium and reduced pubis
of ankylosaurs and pachycephalosaurs are convergent with ceratopsian pelves. There is no indication of the ilium turning laterally in Stenopelix, as in ceratopsians. The pedal elements are long as in psittacosaurs. The tibia is shorter than the femur, as in ceratopsians.

A short note on turtle origins:
I wondered if taking out all the extinct turtles from the large reptile tree would change the topology. It did not.

The large reptile tree is now 9 taxa short of 700.
If you want me to add any of your favorites, from the Carboniferous to the present, please offer your suggestion.

References
Butler RJ and Sullivan RM 2009. The phylogenetic position of Stenopelix valdensis from the Lower Cretaceous of Germany and the early fossil record of Pachycephalosauria. Acta Palaeontologica Polonica 54(1):21-34.
Butler RJ, Jin L-Y, Chen J, Godefroit P 2011. The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north-eastern China. Palaeontology 54 (3): 667–683. doi:10.1111/j.1475-4983.2011.01046.x.
Meyer H von 1857. Beiträge zur näheren Kenntis fossiler Reptilien. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie 1857:532–543
Maryańska T and Osmólska H 1974. Pachycephalosauria, a new suborder of ornithischian dinosaurs. Palaeontologia Polonica 30:45-102.
Schmidt H 1969. Stenopelix valdensis H. v. Meyer, der kleine Dinosaurier des norddeutschen Wealden. Palaeontologische Zeitschrift 43(3/4):194-198.
Sereno PC 2000. The fossil record, systematics and evolution of pachy−
cephalosaurs and ceraptosians from Asia. In: M.J. Benton, M.A. Shiskin, D.M. Unwin, and E.N. Kurochkin (eds.), The Age of Dinosaurs in Russia and Mongolia, 480–516. Cambridge University Press, Cambridge.
Sues H-D and Galton PM 1982. The systematic position of Stenopelix valdensis Reptilia: Ornithischia) from the Wealden of north-western Germany. Palaeontographica Abteilung A 178(4-6): 183-190.

wiki/Stenopelix

 

Inside Psittacosaurus

Figure 1. Psittacosaurus wood and wire model by yours truly, several years back.

Figure 1. Psittacosaurus wood and wire model by yours truly, several years back, now sitting on a kitchen shelf with other hand made and ITC plastic dino models.

Psittacosaurus is a bipedal/quadrupedal ceratopsid sister to Yinlong, recently added to the large reptile tree (now at 689 taxa). Scoring involved a good look at the skull. Note a recent interpretation (You et al. 2008) deletes the vomer, palatine and ectopterygoid (Fig. 2).

Figure 2. Psittacosaurus major skull from You et al. colorized here withe the addition of the vomer, palatine and ectopterygoid. The great height of the rostrum permits a great height to the internal nares and lingual side of the maxilla. Note, the postfrontals, that are fused to the postorbitals in many sister taxa, do not appear to be completely fused together here. 

Figure 2. Psittacosaurus major skull from You et al. colorized here withe the addition of the vomer, palatine and ectopterygoid. The great height of the rostrum permits a great height to the internal nares and lingual side of the maxilla. Note, the postfrontals, that are fused to the postorbitals in many sister taxa, do not appear to be completely fused together here.

The ceratopsian palate
rises, with essentially vertical maxillary walls lining the central choanae. This obviates the need for the vomers, palatine and ectopterygoid, which become incorporated with the maxilla. Evidently You et al. thought they were gone. I see vestiges here, at least on one side, and note them above.

The ceratopsian ancestral taxon
is currently Hexinlusaurus, a gracile, long-necked, small headed ornithischian close to Dryosaurus. Unfortunately, the premaxilla and naris are missing in the Hexinlusaurus holotype.

The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs.

Figure 3. The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs. Currently this taxon is the outgroup to the Ceratopsia, but no pachycephalosaurs are currently included. 

References
Osborn HF 1923. Two Lower Cretaceous dinosaurs from Mongolia. American Museum Novitates 95: 1–10.
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
You H−L, Tanou K and Dodson P 2008. New data on cranial anatomy of the ceratopsian dinosaur Psittacosaurus major. Acta Palaeontologica Polonica 53 (2): 183–196.

wiki/Yinlong 

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.

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

_______________________

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.
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

 

 

 

Hexinlusaurus, Yinlong and Stenopelix

Earlier we looked at the skull of the basal ornithischian, Hexinlusaurus. Today we’ll look at the post-crania. A reconstruction (Fig. 1) was created by simply putting the original drawings (He and Cai 1983) together to the same scale.

The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs.

Figure 1. The post-crania of Hexinlusaurus reveals it to be a small-skull taxon with long running legs. A likely biped, the long neck permitted the skull to reach the substrate for water while maintaining a bipedal configuration, but just as easily the forelimbs could have steadied this dinosaur. The wide caudal transverse processes are also found in pachycephalosaurs.

Hexinlusaurus multidens ZDM T6001 (He and Cai 1983, Barrett, Butler and Knoll 2005) middle Jurassic is a long-legged ornithischian with a rather long neck and small skull. Ironically, this is hardly what one would expect at the base of the short-necked, large skull ceratopsians like Yinlong (Figs. 2,3), yet that is where the large reptile tree (dinosaur focus) nests these two. Hexinlusaurus is primitive enough to also be basal to pachycephalosaurs, the thick-headed dinosaurs, long known to share a common ancestor with ceratopsians, and to Ornithopoda, the iguanadontid and duckbill dinosaurs represented here by Dryosaurus.

Figure 2. The skull of Yinlong a basal certatopsian. The marked concavity in the postorbital of Hexinlusaurus is accented in Yinlong.

Figure 2. The skull of Yinlong a basal certatopsian. The marked concavity in the postorbital of Hexinlusaurus is accented in Yinlong.

The marked concavity noted in the postorbital of Hexinlusaurus is accented in Yinlong. The temporal region in Yinlong is larger and longer, probably to house larger jaw muscles working on tougher plant materials. We can suppose that Hexinlusaurus had large premaxillary fangs due to phylogenetic bracketing.

Figure 3. Yinlong overall. This basal ceratopsian had a larger skull, shorter neck and shorter tail than Hexinlusaurus, its phylogenetic predecessor.

Figure 3. Yinlong overall. This basal ceratopsian had a larger skull, shorter neck and shorter tail than Hexinlusaurus, its phylogenetic predecessor. The marked concavity in the postorbital of Hexinlusaurus is accented in Yinlong.

The Stenopelix connection
A skull-less fossil sharing several traits with Yinlong was described by Meyer (1857) and named Stenopelix (Fig. 4). Yes, they do look quite similar, don’t they?

Figur 4. Known since 1857, Stenopelix appears to be a sister to Yinlong. Ischia are color coded here.

Figur 4. Known since 1857, Stenopelix (Meyer 1857) appears to be a sister to Yinlong. Ischia are color coded here. Click to enlarge.

References
Barrett PM, Butler RJ and Knoll F 2005. Small-bodied ornithischian dinosaurs from the Middle Jurassic of Sichuan, China. Journal of Vertebrate Paleontology 25: 823-834.
He X-L and Cai K-J 1983. A new species of Yandusaurus (hypsilophodont dinosaur) from the Middle Jurassic of Dashanpu, Zigong, Sichuan. Journal of Chengdu College of Geology, Supplement 1:5-14.
Meyer H von 1857. Beiträge zur näheren Kenntis fossiler Reptilien. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie 1857: 532–543.
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