Everything was NOT fine...

Haolong dongi

Haolong by Connor Ashbridge. Most depictions of Haolong online have it positively covered in spike, when the paper describe these structures as microscopic.

So I finally read the paper on Haolong dongi, the spiky dinosaur sensation awashing over the internet. This dinosaur is noted as having small sized (as in, millimeter long) spikes that alledgedly are neither feathers nor scales, representing an entirely novel integumentary structure.

But are they really?

This is the passage from the study cited:

“With their cylindrical shape, their hollow structure, their pluristratified and cornified epidermis, and their central pulp showing a decreasing density from their tip to their base, it could be tempting to consider those spikes in Haolong as protofeathers. Indeed, they are reminiscent of the first stage in the long prevailing hypothesis for feather evolution. However, more recent hypotheses suggest that the first stage of feather evolution was not a hollow structure but a simple monofilament stuffed with melanosomes and assimilated to a single barb. Those simple monofilaments usually form a dense ‘protoplumage’, widespread among non-avian theropod dinosaurs but also described in the heterodontid Tianyulong, in the basal neornithischian Kulindadromeus and in pterosaurs. Those simple protofeathers likely appeared in the avemetatarsalian ancestor of pterosaurs and dinosaurs, at a time of major innovations such as endothermy and higher metabolic rates, brain enlargement, and the development of an erect stance. Therefore, the hollow spikes in Haolong likely do not represent an early stage in feather evolution. They cannot be considered as elongated scales either, because scaly spines present in extant squamates and in Kulindadromeus arise from a more enlarged base. Tubular structures, as observed in Haolong, are rarer in non-avian dinosaurs: elongated broad filamentous feathers, associated with the mandible, skull, neck, trunk and tail in the therizinosaur Beipiaosaurus and in a larger tyrannosauroid were tentatively identified as stiff large tubes with an elliptical cross-section. The long bristle-like structures on the proximal part of tail of Psittacosaurus were also interpreted as cylindrical and seemingly tubular epidermal structures; so we support the hypothesis that those bristles in Psittacosaurus are not directly related to feather evolution either.”

I find their reasoning for them not being proto-feathers to not be very sound. They argue a non-relation due to being sparser and differing from the ancestral monofillament… but what if they simply evolved from such a state? After all, porcupine quills, which the media does compare them to, evolved from mono-fillament mmmalian hair.

Novel structures are not entirely new in dinosaurs. The horn of the horned screamer is apparently not related to feathers at all. But I find it hard to believe that hadrosauromorphs replaced feathers with entirely novel structures instead of modifying already existing fillaments.

Haolong dongi is also noted to have scutate scales on its tail. These are noted as similar to those of Kulindadromeus, and in turn also to the scutate scales in bird feet, which are known to be repressed feathers. Seeing as basal ornithsichians like Tianyulong had elongated tail spikes, it seems clear these are feather derivatives as well.

Sketch_ Harmful Haolong. Pencils, 2026.

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