Pachycephalosaurus: Are Stygimoloch and Dracorex Valid?

In 2009, Pachycephalosaurus, Stygimoloch, and Dracorex, three unique dome-headed dinosaurs, were determined to be the same species.
Dinosaurs ontogeny has caused confusion in the description of multiple dinosaur taxa, but none comes close to the case of Pachycephalosaurus. It arguably underwent the most remarkable growth curve amongst all other dinosaurs. Their crowns seemingly morph into different shapes throughout their lifetime and have fooled paleontologists who've split them into 3 distinct genera and in total of 5 different species.

References:

Credits:
1. Images:
• Architecture bones building city from Pexels
• Close up photo of fossils Photo by Alejandro Quintanar from Pexels
• Topographic map New York

#pachycephalosaurus #stygimoloch #dracorex #dinosaur

[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)

[La_Évoluons]

Aint no way, even dinosaurs have receading hairlines

[safyra]

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

[cccr]

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.

[lifdohop]

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

[romantito]

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

[nixogen]

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

[parkerredeker]

The king of dinosaur videos is back. Great video!

[dylangeltzeiler]

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

[groque]

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

[kirill]

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

[lebruv]

Very high quality video! You deserve more recognition!

[VeryFunStudio]

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

[Shellvine-draws]

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

[redpower]

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

[saturnine.]

Wow this is a criminally underrated channel.

[AuraLeafstorm]

Based on the morphological differences in the skulls, my layman's hypothesis is that the Dracorex Hogwartsia is indeed just a juvenile Stygimoloch Spinifer, although I also believe the Stygimoloch Spinifer to be its own distinct species within the Pachycephalosaurid genus, rather than being a growth stage of the Pachycephalosaurus Wyomingensis. I don't claim to know for certain, of course. Hopefully we get a more definitive answer someday!

[parkerredeker]

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

[redonkled]

always love seeing your uploads. amazing work as always

[Fed.E]

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