Dinosaur crests: what their shapes can tell us

Dinosaur crests were not one anatomical feature with one shared job. Some were hollow extensions of the skull; others were solid bony projections or ornamented surfaces. A crest can help identify a species and may have affected how an animal looked or sounded, but its shape alone does not prove a display, weapon or cooling function.

It is also useful to keep terms distinct. The horns and frill of a ceratopsian, the dome of a pachycephalosaur and the sail along a dinosaur’s back are not all cranial crests. They differ in position, construction and likely mechanical properties. Grouping every dramatic outline under one label hides the anatomy that makes each case worth testing.

Different crests, different evidence

The long crest of Parasaurolophus is formed from bones around an extended nasal passage. Its internal anatomy has been studied with CT data and acoustic modelling. Those analyses make resonance and sound production testable ideas, because the airways have measurable shapes. A model can estimate possible frequencies under stated assumptions; it cannot record the call of a living dinosaur.

Lambeosaurine hadrosaurs such as Lambeosaurus, Corythosaurus and Hypacrosaurus had other hollow crest forms. Their shapes and internal passages differ, so the Parasaurolophus result cannot simply be transferred to every crested hadrosaur. The fossils support anatomical diversity first; any shared role must be argued separately.

Dilophosaurus, Monolophosaurus, Cryolophosaurus and some early tyrannosauroids carried solid cranial crests. Their bony ridges may have changed the animal’s outline, but they do not preserve soft tissues or a precise display pattern. The number and shape of crests vary across species and are useful characters in anatomical comparisons.

Display is plausible, but details remain open

A conspicuous structure can make an animal more visible to members of its own species. That makes visual display a reasonable hypothesis for some crests. Yet fossil bone does not show whether a crest was brightly coloured, how it moved, what signal it conveyed or whether the signal differed between sexes. A dramatic modern illustration often supplies those details from artistic choice.

Growth series can help establish whether a crest changed as an animal matured. Researchers compare specimens of different sizes and inspect bone texture and proportions. But age, species differences, distortion and incomplete skulls complicate the comparison. A larger crest in one fossil cannot by itself identify a male, a breeding season or dominance behaviour.

What crests were not

A horn projects from the skull and may have a core covered in keratin during life; a bony frill is a broad extension at the back of the skull. Pachycephalosaur domes are thickened cranial roofs. A neural-spine sail, such as the structure along the back of Spinosaurus, is not on the head. Each structure calls for its own mechanical and evolutionary explanation.

Fighting and temperature control have been proposed for various ornaments, but the shape must be capable of performing the suggested task. Thin, fragile crests are poor candidates for direct impact unless bone strength and injury evidence support that use. Likewise, a crest’s surface area alone does not establish meaningful heat exchange. These ideas can be tested, but should not be presented as established behaviour.

Why a crest can help identify a species

The outline and internal anatomy of a skull ornament can be diagnostic when compared with other bones. A crest that begins at a different point, curves in another direction or contains a distinct airway pattern may separate closely related taxa. Researchers still test whether the difference is due to species, age or distortion. Compression can flatten a hollow structure, and missing parts can make an incomplete crest appear unlike a complete one.

Several ornamented lineages evolved in different periods and regions. Their structures are not all homologous simply because they rise above the skull. A shared function such as visual display can evolve independently, while the underlying bones retain evidence of separate ancestry. Classification uses the full character set rather than treating every crest as one inherited feature.

Parasaurolophus and the hollow nasal passage

The long crest of Parasaurolophus is often pictured as a trumpet, but that shorthand goes beyond the fossil. The nasal passage loops through the crest and connects back toward the airway. Researchers measured its geometry and used acoustic models to explore possible resonance. The results make sound modification physically plausible; they do not establish a particular call, volume or social message.

Other lambeosaurines had different hollow shapes. The helmet-like crest of Corythosaurus and the distinctive outline of Lambeosaurus contain their own passage arrangements. Differences among them suggest that the crests could create different acoustic or visual signals, but a proposed signal must be tested against anatomy rather than assigned from the outline alone.

Solid crests in theropods

Dilophosaurus had a pair of thin bony crests, while Monolophosaurus carried a single ridge. Cryolophosaurus had a crosswise crest above the skull, and the early tyrannosauroid Guanlong had a tall, delicate cranial ornament. These solid structures lacked the extended nasal tubes of lambeosaurines, so the same acoustic explanation cannot be assumed.

Their thin construction has been used to argue against repeated forceful impacts. A crest might still have been shown during display or helped an animal recognise members of its species. These proposals remain cautious because the fossils do not preserve a display sequence, colour or the behaviour of a living group.

Age, sex and function are separate questions

Some crest forms change substantially during growth. A juvenile may have a small or differently proportioned structure, and adult skulls can look distinctive only after the crest expands. This can help explain why earlier classifications sometimes separated specimens that later appear to represent growth stages of one lineage. It also means that age needs to be considered before a crest difference is treated as a species boundary.

Sexual display is possible, but a single large crest cannot identify sex. Researchers would need multiple mature individuals showing repeated, consistent differences and evidence that age or species does not explain them. A crest may have signalled maturity to both sexes or served recognition within a species. Fossils alone rarely reveal which audience mattered most.

Colour and temperature control remain uncertain

No ordinary fossilised crest preserves a reliable full colour pattern. Some chemical residues may survive in exceptional deposits, but they require careful interpretation and cannot be assumed from a painted reconstruction. Colour shown in popular art is therefore an artistic choice unless a specific specimen provides stronger evidence.

A cooling function has also been proposed for some ornaments. To support it, researchers would need to show that blood flow, surface area and heat exchange fit the anatomy. A tall structure does not automatically act as a radiator, and the soft tissues needed to test that model are usually absent. Display and recognition are often more conservative hypotheses, but even those remain functions inferred from form.

What the fossil does not preserve

Bone can show where a crest attached and how its cavities connected, but usually not its living surface. A keratin sheath could extend beyond the bony margin, as it does in some living animals, yet the amount and shape of that covering may remain unknown. Soft tissues could also alter airflow through an internal passage, which affects acoustic models.

An adult skull does not tell whether the crest changed colour during courtship, whether it was used in a threat display or how often it was shown. Fossils may make one explanation more plausible than another, but a vivid reconstruction should not present added behaviour as an observation.

Reading a reconstruction responsibly

Fossil bone can establish the crest’s outline, attachment and sometimes internal cavities. It cannot normally preserve the skin, keratin, blood supply or pigment that covered the living structure. Soft tissue impressions and related species can narrow some possibilities, but uncertainty remains.

The most defensible reconstruction shows what the skull supports and marks added details as interpretive. A hollow crest may have altered sound; a prominent solid crest may have been visible to other animals. Neither proposition tells us exactly how the dinosaur behaved. The evidence becomes clearer when every proposed function is tied to a specific anatomy rather than inferred from appearance alone. The Parasaurolophus profile looks at one crest in detail, while the dinosaur anatomy guide explains how skull structures are compared.