#neornithischians

[misterrogers22]

The latest episode of Dinosaurs Lately - Ep. 6 - Small-bodied Ornithopods is up!

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Dinosaurs Lately - Small-bodied Ornithopods (Fall 2025) | Juras-Sick Park-Cast

Thanks for tuning into the Dinosaurs Lately podcast, the dinosaur podcast that features periodic updates recapping the latest news on the di

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Episode 6 - Small-bodied Ornithopods (Fall 2025)

Thanks for tuning into the  Dinosaurs Lately podcast , the dinosaur podcast that features periodic updates recapping the latest news on the

#dinosaurs #ornithopods #ampelognathus #fona #enigmacursor

[dinosaur-discourse]

Could you please do a breakdown - based on current evidence - of which groups of Archosaurs definitely had feathers, which probably had feathers, which might have had feathers and which definitely didn't have feathers?

Based on current evidence, Ibelieve that all coelurosaurian theropodsand many ornithischians had filamentousbody coverings of one type or another.

The integuments of birds andreptiles contain a substance called beta-keratin,as opposed to the alpha-keratin of mammalian skin.  Beta-keratin is much more rigid thanalpha-keratin, and forms the hard scales of reptiles and the stiff shafts ofbird feathers.  The beta-keratin of mostmodern reptiles is differently structured than that of birds, and is easilydistinguishable on the molecular level; the only exceptions are crocodilians,who possess almost identical beta-keratin structures in their scutes to thosefound in the feathers of birds.  Sincecrocodiles and birds are united under Archosauria, it seems likely thatbeta-keratinous integument of this type is ancestral to archosaurs as a whole.

The archosaurs are divided into twogroups: Pseudosuchia (which includesmodern crocodiles), and Avemetatarsalia(which includes dinosaurs, birds, and pterosaurs).  I believe that the members of Pseudosuchiadeveloped protective crocodilian scutes, while the members of Avemetatarsalia developedmore filamentous body coverings.

Pterosaurs were covered withhairlike structures called “pycnofibres”.  These structures are clearly different fromprimitive feathers, but are composed of the same beta-keratin, creating the possibility that beta-keratinous filamentous coverings were present in the earliestmembers of Avemetatarsalia.  However,since no fossils of early avemetatarsalian body coverings have been preserved,it cannot be certain whether the common ancestor of dinosaurs and pterosaurshad a fuzzy coat, or if the potential for one to grow simply existed.

My personal theory is thatpycnofibres and feathers evolved completely separately, and that earlydinosaurs were scaly, similar to their pseudosuchian relatives.  Mosttheropod dinosaurs did not have feathers; no preserved feathers, orskeletal remains supporting the presence of feathers, have been found for thevast majority of theropods.  Sometheropods have been discovered with skin impressions, revealing scaly,reptilian countenances; one famous example is Carnotaurus, a theropod from the Late Cretaceous.

The only known exceptions are the coelurosaurs, a group of theropods thatoriginated in the Late Jurassic, about 165 million years ago.  Based on current fossil evidence, it’sbelieved that all coelurosaurs were feathered. Coelurosauria encompasses these types of theropods:

Alvarezsaurs

Compsognathids

Dromaeosaurs

Ornithomimosaurs

Oviraptorosaurs

Therizinosaurs

Troodontids

Tyrannosaurids

Primitive and modern birds

The earliest known feathered theropodis from Late Jurassic Germany, about 150 million years ago.  It was named Sciurumimus – “squirrel mimic” – for its fluffyfeathered tail.  While Sciurumimus was a very earlycoelurosaur, it was not the earliest, and so it cannot be definitively saidwhether or not the ancestral coelurosaur was a feathery animal.

Some non-theropod dinosaurs wereknown to have had feathers as well.  Kulindadromeus, the first knownfeathered non-theropod, lived slightly earlier than Sciurumimus – about 165 million years ago.   However,these two emergences of feathers are not related; coelurosaurs were quitedistantly removed from Kulindadromeuson the dinosaur family tree.  Kulindadromeus was a basal member of Neornithischia, the group that includesornithopods (hadrosaurs,iguanodonts, and hypsilophodonts) and marginocephalians(pachycephalosaurs and ceratopsians).  Thefairly distant relation between the neornithischians and the coelurosaurs, aswell as the differences in structure between theropod feathers and Kulindadromeus’s feathers, makes itimpossible for these animals to have directly evolved from a feathered commonancestor.

Tianyulong, an ornithischianfrom China, was also covered in filaments. However, it was not closely related to Kulindadromeus.  Tianyulong belonged to the Heterodontisauridae, a much moreprimitive group of ornithischians.  Thisleads me to believe that filaments were ancestral to the ornithischians as awhole, developing much earlier in that group than in the Theropoda.  However, since fossil evidence of filamentsin ornithischians is scarce, we can only speculate.

The only other ornithischian withpreserved filaments is Psittacosaurus, a preservedceratopsian, which had protective porcupine-like quills on its tail.  Psittacosauruslived at least 25 million years later than either Kulindadromeus or Tianyulong,revealing that many later ornithischians probably kept their filaments as well.

The fossil evidence for filaments inornithischians is scant, but here’s my theories as to which ornithischians hadfilamentous coverings.

Heterodontosaurs

Primitive neornithischians

The vast majority of ornithopods

Pachycephalosaurs

Primitive ceratopsians

Some ornithischians are known tohave been featherless; skin impressions have been discovered from advancedhadrosaurs and ceratopsians, revealing them to be completely scaly.  However, I believe that their more primitiverelatives were almost universally feathered or quilled.  In addition, early thyreophorans (members of the group that includes stegosaurs andankylosaurs) developed scutes instead of filaments, but these scutes probablyoriginated from the same beta-keratinous coverings as the filaments of otherdinosaur types.

Hopefully, we willgain a fuller understanding of the nature and occurrence rates of dinosaurfilaments in the future.  I’ll be excitedto see what the fossil record has to offer, even if it doesn’t support mytheories.