Unusual Dinosaurs: What Their Fossils Actually Show

“Unusual” is a description of our expectations, not a scientific category. A dinosaur may seem strange because its closest living relatives have a very different body plan, or because only a fragment of its skeleton is known. Fossils can establish the shape of a claw, spine or skull; they seldom preserve the behaviour that made that feature useful.

Long claws do not reveal a single job

Therizinosaurus carried enormous curved claws on its hands. The best-known unguals are close to a metre long along their outer curve, but they are not complete measures of the living keratin sheaths. The animal’s relatives and other bones show that the claws belonged to a large theropod, not a turtle or an isolated marine reptile as early interpretations once suggested.

Pulling vegetation closer, defence and display have all been proposed as functions. Mechanical tests of the claws found that their narrow, elongated form was poorly suited to forceful digging or slashing. That result narrows the possibilities; it does not prove one exclusive use. The Therizinosaurus profile separates the preserved claw shape from the uncertain soft-tissue edge and from claims about feeding behaviour.

Deinocheirus was more than a pair of arms

For decades, Deinocheirus was famous for two giant forelimbs discovered in Mongolia. Later skeletons revealed a broad, toothless snout, a deep body, tall vertebral spines and unusually broad feet. The new material changed the reconstruction because the original arms alone could not show how the rest of the animal was proportioned.

One specimen preserved many gastroliths and fish remains near the abdominal region. They support a varied diet, although stomach contents from one individual cannot establish a fixed menu for the species. The raised back is directly supported by the vertebrae; a continuous fleshy hump drawn over them is a reconstruction. See the Deinocheirus evidence guide for the distinction between the two.

A membrane unlike a bird or pterosaur wing

The small Jurassic theropod Yi qi is known from a flattened skeleton preserving a long rod-like bone near the wrist and traces interpreted as a wing membrane. The combination is unlike the feathered wings of birds and the elongated finger-supported wings of pterosaurs. Its single known specimen gives an unusually direct glimpse of the animal’s integument, but it does not preserve a complete three-dimensional wing.

Whether Yi qi could glide, flap or mainly use the membrane in another way remains debated. A membrane impression and supporting bone document anatomy; they do not provide a measured flight performance. The fossils also do not show that every close relative had the same wing.

Spines and crests have limits too

High neural spines in Deinocheirus, the paired neck spines of Bajadasaurus and the horn-like projections of Carnotaurus are bony structures. They can be measured and compared. Their coverings, colour and exact outline in life are less certain unless skin or other soft tissues are preserved alongside them.

A conspicuous structure may have affected display, recognition, defence or heat exchange, but its mere size does not identify which role mattered most. Several functions could also have operated together. A responsible reconstruction states what the bone itself establishes and marks the rest as a testable interpretation.

Why unusual fossils matter

Rare body plans expand the range of forms that evolution can produce. They also expose the limits of reconstructing a whole animal from one bone or one unusual silhouette. New specimens can overturn an old picture, as happened when the rest of Deinocheirus was found. A vivid anatomical feature is a starting point for investigation, not proof of a dramatic behaviour.