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)

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

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analyzed and the obvious lack of described remains of an adult 'Stygimoloch' or 'P.spinifer' (Although there is an unpublished specimen that could be a possible candidate) makes this whole idea more of an food for thought rather than absolute truth, but nonetheless, it's fun to take it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

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

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

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.

The king of dinosaur videos is back. Great video!

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

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.

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

Very high quality video! You deserve more recognition!

always love seeing your uploads. amazing work as always

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

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

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

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

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

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

Love your videos. So harmonic.

pls continue doing this

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

Awesome, another video!

Awesome video!

I love your voice, a very documentary approved voice

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

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

Nice vid 👍🏼

thank you!:)

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

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.

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

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

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

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

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

Good

Bye buen Dracorex and Stygimoloch, hello Young Pachycephalosaurus.

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

Try making a video about extinct desert species.

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?

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

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.

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.

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

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.

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

Correct pachycephalosaurus is only one

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.

It’s Like A Pokèmon!

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

I don't personally believe this theory.

Praise the LORD for creating so many beautiful bipedal dinosaurs!

stygimoloch is its own species and nanotryannus never existed.

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.

Jack Horner was right about this

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

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

Yeah, Jack Horner killed many egos. 😁

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.