Could dinosaurs swim?

Yes, at least some non-avian dinosaurs could swim. The strongest direct evidence is not a streamlined skeleton but repeated sets of toe scratches left on lake or river beds while water supported the animal's body. Jurassic and Cretaceous examples occur on several continents. They record an action: a dinosaur crossed water by paddling and intermittently touched the bottom.

A short crossing is not the same as an aquatic way of life. A dinosaur could wade, float, paddle across a channel, feed habitually at the water's edge or evolve anatomy suited to sustained swimming. Each claim needs a different combination of tracks, bones, chemistry, gut contents and geological context. Most dinosaurs remained terrestrial, while the degree of aquatic specialisation in Spinosaurus and a few small maniraptorans is still debated.

Swimming, wading and living in water are different claims

An animal is wading while its feet contact the bottom and carry most of its weight. Swimming begins when buoyancy supports the trunk and the limbs or tail generate useful thrust. A shallow channel can produce a transition between the two: the swimmer paddles, touches down for a step, becomes buoyant again and continues.

A semiaquatic lifestyle means more than an accidental river crossing. Water must repeatedly provide food, shelter or a route of movement, and the behaviour should leave a cluster of compatible signs. A fully aquatic animal spends nearly its whole life in water and is substantially restricted on land. No non-avian dinosaur is yet a secure equivalent of an ichthyosaur or whale.

Toe scratches provide the most direct evidence

Bone reveals the structure available for movement, but a track surface can preserve the movement itself. In 2007 researchers described twelve successive groups of S-shaped furrows from Early Cretaceous lake deposits in La Rioja, Spain. Each group contained traces of two or three theropod toes, yet complete footprints were absent. The reconstructed margin reached water deep enough to buoy the animal. Its hind limbs paddled while the claws only brushed the soft bottom.

Comparable alternating marks occur in the Early Cretaceous Feitianshan Formation of Sichuan, China. They were assigned to the trace form Characichnos and interpreted as a theropod crossing sufficiently deep water. A trace name describes the furrow pattern, not the trackmaker's biological genus. Toe tips cannot identify a particular dinosaur.

An unusually large sample was reported in 2025 from Carreras Pampa in Bolivia. Researchers counted 1,378 swimming traces organised into 280 trackways. The longest could be followed for 130.2 metres. Ordinary three-toed prints, tail traces and bird tracks occur nearby. Repeated left-right alternation makes cracks, currents or drifting branches implausible explanations for the complete pattern.

How a swimming trace differs from a damaged footprint

One long groove proves very little. It might come from a branch, current drag, a claw moving through sticky mud or erosion of an ordinary print. A persuasive swimming trackway combines several features. Furrow groups recur at similar intervals, alternate across a centre line and contain two or three narrow digit marks without the broad pads of a weight-bearing foot.

The central toe often cuts the longest and deepest furrow. Side toes may leave shorter marks, ends may curve inward and a small ridge of displaced sediment can build behind a stroke. Investigators also compare the direction of travel with ripple marks, palaeocurrents and the slope of the ancient bed. The wider geographical context is explored in the world dinosaur fossil map.

Even a good trackway does not give water depth to the centimetre or reveal how high the back stood above the surface. It confirms a body unloaded by water and repeated limb movements. Whether the animal floated freely throughout or occasionally pushed from the bottom depends on preservation along that specific route.

How the legs and tail may have worked

The alternating Spanish traces fit hind-limb strokes that resembled exaggerated walking. A foot moved backwards relative to the trunk, the toes combed the sediment, and the leg recovered forwards for another cycle. Current displaced the animal, leaving the two sides slightly asymmetrical.

This action does not require flippers. A terrestrial foot with spread toes can push water, although less efficiently than a broad webbed limb. A long tail could stabilise direction and resist unwanted trunk rotation. Ordinary theropods provide no direct evidence that powerful side-to-side tail beats supplied most of the thrust, so that mechanism should not be added automatically.

Large size does not itself prevent swimming. Buoyancy depends on total volume, air spaces and tissue density, while control depends on limb proportions and the relative positions of mass and buoyancy. Size alone cannot identify either an excellent swimmer or an animal unable to remain afloat.

Most dinosaurs were not aquatic

Older reconstructions placed sauropods in deep lakes, assuming water had to support their weight. Terrestrial trackways, limb construction and respiratory mechanics made that picture unnecessary. Trackways containing only forefoot prints were also interpreted as swimming sauropods whose hind feet missed the bottom. Differential penetration into layered mud and later erosion can create the same pattern without swimming.

A sauropod could still enter a river. Tracks on floodplains show animals around water, not an entire group confined to swamps. The same caution applies to hadrosaurs: a broad bill, large tail and frequent recovery from river sediment do not establish permanent swimming.

Marine rock is also misleading when removed from its taphonomic context. A terrestrial carcass may be carried offshore, and coastal land may later flood. Dinosaur bone in a marine deposit is evidence about burial, not automatically about habitat.

Spinosaurus was connected to water, but how did it swim?

Spinosaurus is more closely associated with aquatic food than most large theropods. Its long narrow jaws and conical teeth could grip slippery prey, the external nostrils sat back from the snout tip, the hind limbs were relatively short and the tail had tall spines supporting a deep soft-tissue outline. Physical models published in 2020 found that the reconstructed tail produced more thrust in water than tails of ordinary terrestrial theropods.

Agreement becomes narrower beyond those observations. A 2022 analysis of bone density grouped Spinosaurus and Baryonyx with animals capable of feeding underwater. Critics noted that density varies with body size, bone selection and statistical method. Separate calculations of buoyancy, stability and drag portrayed a slow, unstable surface swimmer that would struggle to submerge and pursue fish efficiently.

The secure synthesis is therefore specific. Spinosaurus was a fish-eating theropod with unusual aquatic adaptations and could swim. Whether it was a sustained underwater pursuit predator remains disputed. Hunting from a bank or in shallow water requires fewer unsupported assumptions than depicting the animal diving continuously like a sea lion.

Halszkaraptor and Natovenator suggest another experiment

Halszkaraptor was described in 2017 as a possible semiaquatic dromaeosaurid. Its long neck, flattened snout, numerous small teeth, dense sensory canals in the rostrum and forelimb proportions were compared with aquatic hunters. Later work showed that several features also occur among terrestrial maniraptorans and that the hand was not a true flipper. Swimming remains plausible, but a specialised diving fish-eater is not demonstrated.

Natovenator, described in 2022, provides a stronger anatomical clue. Its articulated ribs sweep backwards, producing a dorsoventrally flattened, streamlined ribcage comparable in outline with diving birds. The authors interpreted it as a capable swimmer. Only one skeleton is known, no trackway can be assigned to this genus and neither stroke mechanics nor dive duration is preserved.

Deinocheirus lived near water without proving regular swimming

Deinocheirus had broad feet, an enormous body and a toothless bill. Gastroliths and fish remains occur in the abdominal region of one specimen, while the Nemegt Formation included moist channels and floodplains. These data support an omnivore feeding in or beside shallow water.

Broad feet and fish in the diet do not by themselves establish swimming. The feet could spread weight on soft sediment, and fish can be caught from a bank. Deinocheirus is a useful reminder that ecological association with water and specialised aquatic locomotion are separate propositions.

Marine reptiles do not answer the dinosaur question

Ichthyosaurs generated thrust with the tail, plesiosaurs used four hydrofoil-like flippers, and mosasaurs combined body motion with a developed tail fin. These animals shared the Mesozoic with dinosaurs but belonged to other reptile branches. Their transformed limbs and streamlined bodies represent a much deeper commitment to marine life.

The distinction matters because “dinosaur” is not a label for every extinct reptile. Our guide to Mesozoic seas follows the genuinely marine lineages. No securely known non-avian dinosaur matches their complete set of open-ocean adaptations.

Why swimming tracks are rare

A swimmer usually leaves no footprint because it never reaches the bottom. When toes do score soft mud, waves, currents and later animals can erase the grooves. Preservation requires a narrow sequence: plastic substrate, rapid burial under new sediment, little erosion and eventual conversion of the layer into rock.

This bias makes raw trackway counts a poor comparison between groups. Hundreds of traces at one locality may reflect an ideal surface crossed repeatedly, not hundreds of species or a permanent aquatic population. Carreras Pampa shows that rare behaviour can look abundant when preservation conditions are unusually favourable.

Could every dinosaur swim?

For an individual animal, the answer would depend on size, health, current, water temperature and distance. Many living terrestrial vertebrates cross short stretches without aquatic anatomy. That comparison makes ordinary dinosaur swimming physically plausible, but it cannot replace fossil evidence.

Theropods supply direct trackways. Other groups have disputed traces and biomechanical estimates. For a genus lacking both tracks and specialised bones, the careful statement is a possible general capacity, not confirmed behaviour. Claims about speed, maximum depth and crossing range are especially weak because fossils almost never preserve those values.

What is observed and what is reconstructed

Direct observations include furrow positions on a rock surface, the anatomy of preserved bones and the sedimentary setting. From them researchers infer a buoyant body, a sequence of foot motions and skeletal features useful in water. These are testable conclusions with different confidence levels.

Soft-tissue outlines, the exact stroke, tail angle and head height usually come from comparisons and models. Colour, water clarity and the moment of hunting are artistic choices. The cover presents a plausible crossing by a generalised theropod, not a portrait of a known maker of one particular trackway.

Conclusion

Some non-avian dinosaurs definitely moved by swimming. Long alternating sequences of toe scratches are the clearest direct record, especially for theropods. They show a body supported by water and hind feet repeatedly contacting the bottom.

That evidence does not turn dinosaurs into a marine radiation or every genus into a strong swimmer. Spinosaurus shows a pronounced connection with water, but underwater pursuit remains contested. Natovenator offers an unusual streamlined trunk, while Halszkaraptor illustrates the danger of assigning a lifestyle from a few strange bones. The defensible answer is not a single category but a spectrum from occasional crossings to debated specialisation.