Pachycephalosaurus: Are Stygimoloch and Dracorex Valid?

[@FactorTrace]

Correction 1:32: the specimen YPM VP 335 wasn't re-described 1 year after being misinterpreted in 1892, but 91 years later with the description of Stygimoloch in 1983. Among the three, Pachycephalosaurus was the first one described in 1931, then Stygimoloch in 1983, and lastly Dracorex in 2006. Worth mentioning: In 2021, in the establishment of a new Pachycephalosaurid genus Sinocephale, the researchers treated Stygimoloch as a separate taxon in their phylogenetic analysis. There is a slight difference in stratigraphic data between the Stygimoloch and the Pachycephalosaurus specimens. However, some paleontologists, including the writer of the Sinocephale paper, David Evans, have said on Twitter that Stygimoloch most likely is a young Pachycephalosaurus, but of a different species, called "Pachycephalosaurus spinifer". (Has yet to be formally described)

[@safyra6691]

I find it far more interesting knowing all 3 of these are the growth stages of a single animal genus rather than their own genera. Suddenly everything we knew about Dracorex and Stygimoloch gets added to the bundle of strange and fascinating that is Pachycephalosaurus

[@FactorTrace]

Yeah, and it also gives us an insight as to how this dinosaur grew. Truly fascinating!

[@jamessparkman6604]

I think they’re all separate species to say that they are the same as lie

[@jamessparkman6604]

@Mr. Hazama (Yuki Terumi) Could you expressed that Jack Horner hop out tell him if you do not treat those separate species as they are he will go extinct

[@jamessparkman6604]

@@FactorTrace I think this is a pack of lies. I just wish that paleontologists with stop jumping to conclusions already.

[@Bagelgeuse]

​@@jamessparkman6604They aren't jumping to conclusions though. It's still an ongoing debate.

[@lifdohop]

Such high quality content. It is criminal how there aren't more subscribers. Hope this channel will grow.

[@20footAmethystinePython]

Me too

[@İzmir_city_state_republic]

Lack of english skills but got the spirit

[@romantito8892]

Another factor to stir things up in this debate is the recent hypothesis that's been circulating among the paleo-media that instead of being different ontogenetic stages of P. wyomingensis, Stygimoloch and Dracorex would actually be different growth stages of a different Pachycephalosaurus species ('P. spinifer'), since both didn't seem to overlap with P. wyomingensis (with it being limited to lower layers of the lancian stage and the other two in the upper layers) and the whole debacle of losing bone core as the animal ages. This might suggest a case of anagenesis similar to what we see with T.horridus and T.prorsus, with P.wyomingensis possessing lumpier horns and 'P.spinifer' spikier ones (Perhaps with UCMP 556078 being an in-between?). But keep in mind that since this concept has not yet been published or deeply explored, the fact that the stratigraphy of the Pachycephalosaurus genus as a whole is poorly analyzed and the obvious lack of described remains of an adult 'Stygimoloch' or 'P.spinifer' (Although there is an unpublished specimen that could be a possible candidate) makes this whole idea more of an food for thought rather than absolute truth, but nonetheless, it's fun to take it into consideration, specially regarding the huge individual variation within Marginocephalia. Btw, I just found out about this channel and immediately after finishing this video I went straight to binge-watch the rest of the content that you had put together. Really, really well made stuff 😁. (Edit): And right after I finish writing this comment I see that you already covered this topic in the pinned comments lol

[@firegator6853]

yea i heard about this too mostly from the saurian game community where im a part off i saw a remodel concept flying buy that uses the pachycephalosaurus spinifer as remodel because its the one that is found in the place of hell creek where the game focuses interesting theory and makes quite sense i believe i also noticed at 4:07 that one of the two dracorex specimens lacks the big horns, if this is not due to them being broken during preservation and its really complete maybe the upper specimen could be the young of P. Wyomingensis and the lower one the young of P. Spinifer i hope we find more material in the future about this

[@FactorTrace]

Yeah, thank you for your addition! My pinned comment certainly doesn't cover as much information as yours. It'd be lovely to get a formal description of P. spinifer and a new phylogenetic analysis, hopefully sometime soon in the future. Also, thanks for checking my other videos! Highly appreciated.

[@FactorTrace]

@@firegator6853 What a sharp eye! Those two same specimens can be more clearly seen at 3:37 I wish I could've provided some information about the different horn shapes, I couldn't find any info online. In the referenced paper [11] it was said "The holotype of Tylosteus ornatus, a small squamosal with broken spike- like nodes and low bulbous nodes, is not referable to Pachycephalosaurus wyomingensis, but rather is consistent with the ornamentation of Dracorex hogwartsia" is the only info have, it is inferred that the specimen had nodes instead of spikes.

[@alexandracorrea803]

I do find it od that spike grow before shrinking, so many stygi is its own species with P. Spinifer?

[@c4c4cr0773]

You have no idea how much I enjoyed your video! The sequence with all the skulls showing the growth is so much satisfying that I had to watch it 3 times before continuing the video.

[@FactorTrace]

Thanks! It took me a lot of time just to make that short sequence, glad to know that it doesn't go unappreciated!

[@nixogen7810]

Another **amazing** video! You have some of the most fantastic content on KZbin; most million-subscriber channels pale compared to your quality. This level of quality cannot go unappreciated!

[@FactorTrace]

Wow, thank you! This means a lot to me!

[@Shellvine-draws]

Stage one: DRAGON KING Stage two: DEMON FROM THE RIVER STYX Stage three: hard headed lizard

[@parkerredeker5216]

The king of dinosaur videos is back. Great video!

[@FactorTrace]

Wow, thanks for the grand title 😁

[@La_Évoluons]

Aint no way, even dinosaurs have receading hairlines

[@lebruv915]

Very high quality video! You deserve more recognition!

[@FactorTrace]

I appreciate that, thanks!

[@groque1654]

Beautiful didn't expect another paleo video so this was a surprise

[@dylangeltzeiler946]

Pachycephalosaurus, Stygimoloch & Dracorex are one of my favorite Pachycephalosaurs in North America.

[@CHANN3L_NAME]

One?

[@kirill7129]

About Homalocephale. While it was thought to be a juvenile synonym to Prenocephale, the latest scientific papers reaffirmed that Homalocephale is its own genus.

[@parkerredeker5216]

Congratulations! This video finally got you to 1,000 subscribers!

[@FactorTrace]

Yes! Thank you, I'm truly amazed!

[@VeryFunStudio]

Love the info about Pachycephalosaurus! Thanks for sharing the detail.

[@redpower6956]

Amazing video, please keep making these videos, you have my full support!

[@FactorTrace]

Thank you! Will do!

[@redonkled]

always love seeing your uploads. amazing work as always

[@FactorTrace]

Thank you! I really appreciate your support!

[@Fed.E]

Excellent as always! I wonder what's the topic of your next video

[@FactorTrace]

Thank you! I'm planning to continue on the Holocene Extinction series, the thylacine next. But I'm also thinking about making another dinosaur video, haven't looked into the research yet so I don't know if I can develop the topic into a video.

[@samuraispartan7000]

“Demon of the River Styx” and “Dragon king” huh? These paleontologists have got to stop with these edge lord names.

[@FactorTrace]

Haha I know right? Have you heard about the recently described Charcarodontosaurid named "Meraxes gigas"? Literally named after a dragon from the George R.R. Martin fantasy novel series, A Song of Ice and Fire. Dinos are getting more and more flamboyant names.

[@samuraispartan7000]

@@FactorTrace Not dinosaurs, but I would say that pterosaurs probably have the edgiest names in all of paleontology. Thanatosdrakon (death dragon) Cryodrakon (frozen dragon) and Ferrodraco (iron dragon) are just a few examples. The pterosaur family Azhdarchidae is named after the Persian name for dragon. Though the naming conventions are a bit childish, I will concede that 10 to 20 foot tall flying reptiles are more deserving of the dragon-based names than Dracorex. In my opinion, the worst offenders are the pop-culture names. Dracorex is doubly bad because not only does it have a needlessly edgy name, but it has a meaningless pop-culture reference thrown in for good measure.

[@samuraispartan7000]

@@FactorTrace Meraxes is a weird choice. Was Balerion already taken? Did Drogon sound too similar to dragon?

[@FactorTrace]

@@samuraispartan7000 Oh, about pterosaurs, there is one named Ikrandraco avatar. Understandably it has a crest in it's lower jaw somewhat similar to the flying creature "Ikran" from the film Avatar, but the species name is what bothers me, why avatar? Isn't the genus "Ikran"-draco enough of a reference already? It is clearly done for the clout. To be honest tho, I like unique dinosaur names I prefer the ones not ending in the word "saurus". And Draco for pterosaurs is cool for me. It's the unnecessarily pop-culture names that get to me sometimes, I agree with you about Dracorex hogwartsia. And I have no idea why they choose Meraxes instead of the more well-known dragons 😆

[@The_PokeSaurus]

I don't see how they're edgy.

[@juliancaraveo5700]

So does this mean Jurassic World should have put the Stygimoloch as a juvenile Pachycephalosaurus.

[@FactorTrace]

Ideally yeah, but the movie franchise has little to no care about scientific accuracy, so it is not likely they'll do it.

[@juliancaraveo5700]

@@FactorTrace They could do a slight change since they never said / mentioned the name Stygimoloch in the films. But then again I could be wrong.

[@yoboibeerus1387]

Awesome, another video!

[@FactorTrace]

Thanks, more to come!

[@perumafioso517]

pls continue doing this

[@BrotherVerseProductions]

Dracorex being a juvenile sure both lived in the eraly maastrictian but only Stigymolock saw the KT extinction

[@arishok89]

Dracorex being a Pachycephalosaurus is so cool. I hated that name, it's nice it doesn't "exist" anymore.

[@Ons_TV]

I love your voice, a very documentary approved voice

[@discobolos4227]

♥

[@RampagingGuanlong]

Awesome video!

[@FactorTrace]

Glad you enjoyed it

[@Eshkanama]

People are always so quick to name a new species instead of doing the work first. This newer generation is giving them the silliest names too, naming them after Harry Potter characters, like come on man haha. Great video my friend, keep them coming.

[@Pickle_Style-22]

So your saying that they found all the stages of life for this Dinosaur and many more!? That’s so cool!

[@SmashBrosAssemble]

Dracorex is a juvenile Pachycephalosaurus. Stygimoloch is it’s own genus.

[@discobolos4227]

Why?

[@eliforeal5261]

I had no idea so much speculation went into depicting Stygimoloch! I thought we had more complete remains from that animal, very interesting

[@Salmon_Lamb0]

Always grew up believing they were different, and just for that I refuse to believe they’re the same…

[@munchrai6396]

Dang, losing awesome horns for a thicker head is definitely a tradeoff I wouldn't do. Its honestly a crazy transformation for any Vertebrate head design to redistribute so much of its head design over its lifespan

[@marcopohl4875]

What I would like to see someone adress is how Dracorex lost its horns as it grew up, I can't think of any other animal where a body part shrinks with age.

[@Ozraptor4]

Spiny tortoise (Heosemys spinosa) and Ocean sunfish (Mola mola) have large spines as small juveniles which are resorbed during growth into smooth adults.

[@darkar932]

I don’t know nothing about dinosaur but this vidéo cool af, Like

[@JoseR1207]

Bye buen Dracorex and Stygimoloch, hello Young Pachycephalosaurus.

[@TheMightyN]

Even though evidence suggests these three genera are synonymous to otherwise indicate Dracorex lacked the cranial scaring found in Pachycephalosaurus provides less reason to consider its own genus? Why would Paleontologists want to make those assumptions without putting effort to locate more specimens like Dracorex to confirm otherwise? As of currently this situation is still disputable and the leading cases aren't telling the full story of Pachycephalosaur brooding behavior and lack thereof. Plus we have one or more Flat-Head representative in the form earlier species like Homalocephale.

[@FactorTrace]

Admittedly, combining three different genera into one is rather extreme, but the evidence is adequate to justify it. Why would the lack of cranial scarring not support the argument? Since the current generally accepted theory for the function of the dome is for intraspecific combat, not to defend themselves from predators. It makes sense that young, sexually immature individuals that don't engage in head butting behavior do not obtain wounds.

[@monkeyguy80]

Nice vid 👍🏼

[@FactorTrace]

Thanks!

[@daffierpython7755]

I like to think theyre all different animals but filled slightly different niches. While all would be omnivores, dracorex would use its flatter, more spikey head to gore prey and be primarily carnivorous but would occasionally eat plants, Pachycephalosaurus would bemore herbivorous and stygimoloch would be inbetween

[@jaydeflayme2890]

Wait so if Stygimoloch was named first, doesn't that mean if they prove the juvenile theory that they would have to rename Pachycephalosaurus into Stygimoloch?

[@Denasor1holande]

صاحب الصوت هولندي 🦕

[@hosseinmafi-ps4jy]

thank you!:)

[@leilaclarridge5807]

My personal theory as to why Pachycephalosaurus starts off with longer and sharper horns but loses them as its dome grows is that they probably start breeding fairly early in life, but compete for mates in different ways at different points in life to avoid competing with individuals of other age brackets. Younger individuals probably poked and prodded at each other with their horns while older individuals fought more head on.

[@iamarizonaball2642]

Try making a video about extinct desert species.

[@kekprod_]

you should put your videos on reddit or somewhere to try get some traction

[@alexevon6794]

Hey in 2013 they actually found they skulls with marks from butting

[@CoreyStudios2000]

Personally, I think Dracorex is a growth stage of Stygimoloch whereas the latter is a separate species from Pachycephalosaurus.

[@FactorTrace]

Actually, another commonly suggested argument based on stratigraphic data is that Dracorex is the juvenile form of Pachycephalosaurus, and Stygimoloch is possibly a young form of a different Pachycephalosaurus species.

[@CoreyStudios2000]

@@FactorTrace We may not know for sure, but I bet Stygimoloch is a different species from Pachycephalosaurus and the remains we have are merely a juvenile member of that genus. We could find remains of a larger adult of the Stygimoloch genus. Perhaps it could be bigger than Pachycephalosaurus. I don't know.

[@jamessparkman6604]

@@FactorTrace Well I say that’s a big fat lie Jack Horner is a complete moron to think that all the species are just growth stages of one another

[@dagoodboy6424]

I once read that stygy is a subspecies of pachy so technically that would make it kinda valid?

[@discobolos4227]

Nah!

[@VaderReviews]

I wonder if the non-domed Pachycephalosaurs are just the female of the species. It would make sense that the males could have the dome for combat and display, while the females would've really need one. Like how Bucks have antlers, and Does don't.

[@Sudha.]

Good

[@bspiekerman]

I don't think this debate is as settled as it appears. One thing about Dracorex that isn't often mentioned is that the cervical vertebrae of the holotype was highly ossified, suggesting that the animal was nearly fully grown and not a juvenile. It also has one more squamosal spike than Stygimoloch (4 vs the latter's 3), though this could easily amount to individual variation. Also, Homalocephale was reaffirmed to be separate from Prenocephale and not a juvenile of the latter as was previously proposed, so flat-headed species may have been distinct from the domed species. Lastly, Peter Larson has a fully-grown Stygimoloch skull which has a full dome and long spikes (not reduced as proposed by Horner et al). He's only posted about it on Twitter once and it still hasn't been described, but it does nonetheless seem to indicate that Stygimoloch was real.

[@daxbashir6232]

💚 💚 💚

[@tyrannotherium7873]

Correct pachycephalosaurus is only one

[@Red-EyedWanderer]

I love the production quality in your videos but I will never trust a thing Jack Horner says

[@discobolos4227]

🙂

[@aliciabarnum7400]

I don't personally believe this theory.

[@niranjansrinivasan4042]

Jack Horner was right about this

[@FactorTrace]

Yeah, for this one it turns out he was right!

[@niranjansrinivasan4042]

@@FactorTrace also it was him who made Spinosaurus kill T rex and ended JP series lol.

[@charlesmartin1121]

Buckle-up buttercup. You may soon be proven wrong. New fossil material is shortly going to be published.

[@ProfezorSnayp]

Is that supposed to be bad? Science always advances and corrects itself, BUTTERCUP.

[@charlesmartin1121]

@@ProfezorSnayp Ok BUBBLES.

[@jesusmejia79]

stygimoloch is its own species and nanotryannus never existed.

[@danielmalinen6337]

Depicting juvenile and sub-adult Pachycephalosaurus with long neck horns and spikes is probably inaccurate, and in fact the neck bumbs of "Dragorex" and "Stygimoloch" have been more smaller, smoother and rounder just like the the neck bumbs of adult specimen.

[@METATRONS_CUBE]

Yeah, Jack Horner killed many egos. 😁

[@cheslxy]

Jack Horner asked where’s the baby dinosaurs. This should’ve been more studied cause there’s RARELY studies of baby dinosaurs 🦕

[@quranicbard7881]

Dracorex and Stygimoloch were two seperate dinosaurs, not growth stages of Pachycephalosaurus. I disagree with you and anyone who thinks this.

[@s_meekerorum]

it makes so much sense though

[@paleoph6168]

"And I refuse to elaborate" - Quranic Bird

[@The_PokeSaurus]

I don't agree. I have talked to paleontologists about this and they do not think Stygimoloch and Dracorex are juveniles of Pachycephalosaurus, the main thing they pointed out is that both Stygimoloch and Dracorex have longer horns on the back of the head, no animal loses horns as they age.

[@FactorTrace]

Currently, the general consensus in the paleontology community is that the three are synonymous, it is backed up by quite convincing evidence of cranial plasticity, the horns were reabsorbed into the animal's skull, as presented in the referenced papers (linked in the description). Other possible hypothesis, although hasn't been published, is that the Stygimoloch specimen might belong to a different Pachycephalosaurus species, informally known as P. spinifer.

[@The_PokeSaurus]

@@FactorTrace Out of honesty, I don't find that convincing. What animal that lives today reabsorbs horns as it ages?

[@paleoph6168]

@@The_PokeSaurus is that the only reason that's holding you back, especially when compared to the other evidence as stated in the video? Also what are the names of these paleontologists you asked?

[@The_PokeSaurus]

@@paleoph6168 One of the paleontologists was Robert T. Baker himself. Also, the stated evidence just proved that the animals in question were not as old as the Pachycephalosaurus found. It does a very poor job proving they're the same animal.

[@FactorTrace]

@@The_PokeSaurus Bones although appear to be static, is actually a very reactive organ, the entire human skeleton is constantly being reabsorbed and redeployed, completely turning over every about 7 or 10 years. There are 2 types of bone managing cells called osteoblast and osteoclast, the former builds and latter dissolves, Osteoporosis in humans happens because of the imbalance in activities of the two cell types causing more bone loss than growth. The question of bones being re-modelled into different shapes throughout ontogeny lies within the genetic code of the organism, not the physical structure of bones itself. The different stratigraphy from the Stygi specimens has been addressed by multiple renowned paleontologists (amongst them include Mark Witton, Thomas Holtz, David Evans and Gregory S. Paul) as a sign of different species within the generic name of Pachycephalosaurus. Stygimoloch is still considered to be the juvenile form.

[@PlushCar]

I would love it if Dracorex hogwartsia didn't exist.