Feathered T-rex video: Excellent!*

The best video* I’ve seen on feathered dinosaurs.
*But note: their gliding Anchiornis forgot how to flap. Flapping came first. Then flapping with bipedal climbing. Then flapping with flying. Birds don’t come by gliding except to rest while airborne. Same with bats (if any glide ever). Same with pterosaurs. Let’s take gliding out of the equation for the origin of flight. That’s widespread antiquated thinking not supported by evidence. If you glide you do not flap. If you flap, some of your ancestors may learn to glide.

Click here or on the image to play.

Hypsibema missouriensis – a Late Cretaceous Appalachia duckbill dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Hypsibema missouriensis
(Cope 1869; Gilbert and Stewart 1945; Gilbert 1945; Baird and Horner 1979; Darrough et al. 2005; Parris 2006; Campanian, 84-71 mya, Late Cretaceous) is a fairly large hadrosaurid dinosaur discovered in 1942, at what later became known as the Chronister Dinosaur Site near Glen Allen, Missouri. At present this literal pinprick in the map of Missouri is the only site that preserves dinosaur bones.

Figure 2. Where the Hypsibema maxilla chunk came from on the skull of Saurolophus.

Figure 2. Where the Hypsibema maxilla chunk (Figure 3) came from modeled on the skull of Saurolophus.

Small pieces of broken bone and associated caudals and toes
were first discovered when digging a cistern. They had been found about 8 feet (2.4 m) deep imbedded in a black plastic clay. The area is in paleokarst located along downdropped fault grabens over Ordovician carbonates.

Gilmore and Stewart 1945 described a series of Chronister caudal centra (now at the Smithsonian) as sauropod-like, reporting, “The more elongate centra of the Chronister specimen, with the possible exception of Hypsibema crassicauda Cope, and the presence of chevron facets only on the posterior end appear sufficient to show that these vertebral centra do not pertain to a member of the Hadrosauridae.”

First named Neosaurus missouriensis,
the caudals were renamed Parrosaurus missouriensis by Gilmore and Stewart 1945 because “Neosaurus” was preoccupied. The specimen was allied to Hypsibema by Baird and Horner 1979.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Back in the 1980s
I enjoyed going to the Chronister site with other members of the local fossil club, the Eastern Missouri Society for Paleontoogy. I was lucky enough to find both a maxilla fragment (Fig. 3) and a dromaeosaurid tooth. I remember the horse flies were pesky and  one morning, before the other members got there, I was met by a man with a shot gun who relaxed when I identified myself. A friend found a series of hadrosaur toe bones, each about as big as a man’s hand (sans fingers). The bone was so well preserved you could blow air through the porous surfaces.

References
Baird D and Horner JR 1979. Cretaceous dinosaurs of North Carolina. Brimleyana 2: 1-28.
Cope  ED 1869.
Remarks on Eschrichtius polyporusHypsibema crassicaudaHadrosaurus tripos, and Polydectes biturgidus“. Proceedings of the Academy of Natural Sciences of Philadelphia 21:191-192.
Darrough G; Fix M; Parris D and Granstaff B 2005.
 Journal of Vertebrate Paleontology 25 (3): 49A–50A.
Gilmore CW and Stewart DR 1945. A New Sauropod Dinosaur from the Upper Cretaceous of Missouri. Journal of Paleontology (Society for Sedimentary Geology 19(1): 23–29.
Gilmore CW 1945. Parrosaurus, N. Name, Replacing Neosaurus Gilmore, 1945. Journal of Paleontology (Society for Sedimentary Geology 19 (5): 540.
Parris D. 2006. New Information on the Cretaceous of Missouri. online

wiki/Hypsibema_missouriensis
bolinger county museum of natural history
More info and links

They’re out there somewhere!

Back in the ’90s, 
I built several full scale prehistoric reptile models out of wood, wire, foam, glass (eyes) and what have you. Two of them are shown here (Fig. 1).

Figure 1. Baby Camarasaurus and featherless Deinonychus models built by David Peters in the 1990s.

Figure 1. Baby Camarasaurus and featherless Deinonychus models built by David Peters in the 1990s.

At the time, 
like the the extinct Steve Czerkas and the extant Charlie McGrady, I wanted to be build dinosaurs, not just illustrate them in books. At the time, St. Louis did not have a Science Museum and that’s when (so I was told) you are supposed to get in on the ground floor. Also at the time the late sculptor Bob Cassilly was building squids, pterosaurs, sharks and rays for the St. Louis Zoo based on illustrations in my book Giants. (Bob was instrumental in bringing Sharovipteryx, Longisquama and the other Russian dinosaur exhibit to St. Louis.) Alas, that phase fizzled and the writing of papers followed. Early on you’re driven by enthusiasm and reined in by naiveté. In evolutionary terms, it worked out for that time and place.

Along with
the baby Camarasaurus and adult Deinonychus, I built a plesiosaur, Tanystropheus, fuzzy Dimorphodon, Pterodactylus and the several pterosaur skeletons seen here. The fleshed out sculptures went to the AMNH in NYC. The baby sauropod went to Martin Lockley in Colorado. The skeletons all went to Mike Triebold. Many artists want to see their art hanging in museums. Well, it happened to me, sort of, with those pterosaur skeletons. They’re out there, all over the world. The AMNH ultimately decided to display only skeletons in their renovated prehistoric displays and sold off what they had purchased.

I have no idea
where the various pieces are now or what shape they are in. But it was fun for awhile and the mailman probably told his kids about the address that had dinosaurs under the carport. Now a longer list of illustrated and animated prehistoric reptiles can be found on the Internet here.

Lagerpeton: not the first of its kind, but the last of its kind

Quick note
I updated the reconstruction and nesting of Colobomycter, which you can see here.

Traditional paleontologists
consider Lagerpeton (Fig. 1, Romer 1971) a basal dinosauromorph, thus the first of its kind (ancestral to dinosaurs).

In contrast
Lagerpeton nests as a terminal taxon in the large reptile tree, leaving no known descendants. Here (Fig. 1) convergent evolution has created a bipedal chanaresuchid, derived from Tropidosuchus that has similar pedal proportions to the second specimen attributed to Tropidosuchus.

Figure 3. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

According to
Wikipedia, seven fossil specimens have so far been attributed to L. chanarensis. They don’t add up to much more than a hind limb and pelvic girdle.

  1. UPLR 06 (holotype) – articulated right hindlimb
  2. PVL 4619 – articulated pelvis with sacrum, partial right and complete left hindlimbs
  3. PVL 4625 – left pelvis with left femur and articulated vertebral column (dorsal, sacral and anterior caudal vertebrae
  4. PVL 5000 – proximal end of left femur
  5. MCZ 4121 – complete left, and partial right, femur.

Brusatte et al.
found Early Triassic footprints they attributed to lagosuchids. In reality the ichnites were closer to Rotodactylus tracks, which match the feet of fenestrasaurs, like Cosesaurus through pterosaurs.

In the large reptile tree
archosauriformes split at their origin, shortly after Youngina (AMNH 5561) and Youngoides (UC 1528) into two clades. The larger specimens start with Proterosuchus and radiate into choristoderes, parasuchians, doswellians and chanaresuchians terminating with Lagerpeton and its sister, Tropidosuchus (Fig. 1). The other branch starts with Euparkeria and extends to crocs, dinos and birds.

So,
Lagerpeton is not a close relative of dinosaurs, but convergent in several regards. The odd feet and pelves give them away as distinctly different from dinosaurs. Even so paleontologists continue clinging to this hypothesis. Better dino ancestors can be found here.

References
Arcucci A 1986. New materials and reinterpretation of Lagerpeton chanarensis Romer (Thecodontia, Lagerpetonidae nov.) from the Middle Triassic of La Rioja, Argentina. Ameghiniana 23(3-4):233-242. online pdf
Brusatte SL, Niedźwiedzki G, Butler RJ 2011. “Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic.”Proceedings of the Royal Society B: Biological Sciences 278 (1708): 1107–1113. doi:10.1098/rspb.2010.1746PMC 3049033PMID 20926435.
Romer AS 1971 The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria, n. 378, p. 1-10.
Sereno PC and Arcucci AB 1993. Dinosaurian precursors from the Middle Triassic of Argentina: Lagerpeton chanarensis. Journal of Vertebrate Paleontology, 13, 385–399.

wiki/Lagerpeton

New insights into the ornithopod manus

Duckbills,
like Edmontosaurus, and their kin are the ornithopod ornithischian dinosaurs, a clade I have been ignoring until now. Wikipedia reports, “[they] started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American landscape.” 

Dryosaurus, Camptosaurus, Iguanodon and Edmontosaurus are genera within this clade and each has an interesting manus (Fig. 1). When one works in phylogenetic analysis it is imperative to compare homologous digits (apples to apples). In ornithopods, those homologies appear to be masked and perhaps misinterpreted by the appearances of new phalanges and the disappearances of old phalanges. Putting them all in one image (Fig.1) clarifies all issues (even without traveling to visit the fossils firsthand!). Hopefully the data are accurate to start with.

This all started with a phylogenetic analysis
that appeared to indicate that Edmontosaurus had a manual digit 1 with an extra digit that made it look like manual digit 2. Comparisons to other ornithopods ensued. A quick look through the Internet brought B. Switek’s article (see below) to the fore.

Figure 1. Ornithopod manus. Here the hands of Dryosaurus, Camptosaurus, Iguanodon and Edmontosaurus are compared. Note the turquoise metatarsal homologies and the digit identification based on that.

Figure 1. Ornithopod manus. Here the hands of Dryosaurus, Camptosaurus, Iguanodon and Edmontosaurus are compared. Note the turquoise metatarsal homologies and the digit identifications based on that.

Science writer Brian Switek 
writing for Smithsonian.com reports,

  1. “…the great herbivore Iguanodon had prominent thumb spikes.
  2. “The peculiar false thumb of Iguanodon was originally thought to set into the dinosaur’s nose.”
  3. “But why should Iguanodon have a hand spike? “
  4. “Though my own suggestion is not any better than those I have been disappointed by, I wonder if the Iguanodon spike is a Mesozoic equivalent of another false thumb seen among animals today—the enlarged wrist bones of red and giant pandas…  the Iguanodon spike was rigid.” Unfortunately that’s as far as journalist Switek has allowed himself to go, rather than proposing the homologies and comparisons demonstrated here.

Giving credit where credit is due,
Switek may be the first to suggest the spike was not a digit. I don’t know and was not able to find out the history of the spike. Given the text from his blogpost, you can see Switek’s choice of words actually evolves from “thumb spikes” to “false thumb” to “hand spike” to “enlarged wrist bone”. Like Brian, I also lack a PhD, but that doesn’t stop us from making contributions. If I’m duplicating earlier academic efforts, please let me know so credit can be given.

Here we’ll show
that the spike is indeed a wrist element… that digit 1 in Iguanodon and related taxa have one more phalanx, making it look like digit 2.

We’ll start with
the right manus of Dryosaurus, a basal ornithopod (at least in the large reptile tree it is, where only one other ornithopod, Edmontosaurus, is currently represented). During the course of this, I want you to focus on the the homologies of metatarsals 2 and 3 (colored in turquoise). These, I think, will guide us to correct interpretations of the other elements of the various ornithopod manus.

Now back to the manus of Dryosaurus:

  1. Data comes form loose bones in a photo formed in the shape of a hand, not an in-situ articulated hand. Thus I do not know the identification or placement of the carpals
  2. Five metatarsals are present.
  3. Mt3 is the longest. Slightly shorter is mt2.
  4. Phalangeal formula is 2-3-4-3-2, but digit 1 does not appear to be tipped with a sharp ungual. Is it missing? If so, that adds a phalanx to the formula 3-3-4-3-2.
  5. Digit 3 is the longest. Slightly shorter is digit 2.
  6. Unguals are lost in digits 4 and 5.

The manus of Camptosaurus

  1. Is reduced (stumpy) by comparison to Dryosaurus
  2. Mt 1 is a disk. M1.1 is a disk
  3. M3.2 appears to fuse with m3.3
  4. m4.3 and m5.2 are lost
  5. The new phalangeal formula is 2-3-3-2-1

The manus of Iguanodon

  1. is more robust and highly modified by comparison to Dryosaurus
  2. Two wrist elements fill the wrist. Two others extend medially.
  3. Digit 1 is longer and now sports an ungual
  4. Ungual 1 is not sharp
  5. Ungual 2 is a round hoof
  6. Ungual 3 (m3.4) is lost along with m3.3
  7. Mt4 is shorter. Two tiny phalanges are added.
  8. Digit 5 is absent.
  9. The new phalangeal formula is 3-3-2-4-0

The manus of Edmontosaurus 

  1. is long and gracile by comparison to Dryosaurus.
  2. Again, digit 1 has 3 phalanges, matching digits 2–4.
  3. Digit 4 is a vestige
  4. Mt 5 is again absent
  5. As in Iguanodon, ungual 1 is not sharp and ungual 2 is a hoof
  6. The new phalangeal formula is 3-3-3-3-0.

Always interesting to 
uncover little paradigm busters like these. Now back to phylogenetic analysis…

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