Dinosaurs’ legacy and the faunas that followed

The disappearance of non-avian dinosaurs near 66 million years ago changed terrestrial ecosystems, but it did not leave a blank planet. Birds, mammals, crocodilians, turtles, amphibians, insects and many plants survived. Their descendants formed later faunas through uneven recovery, diversification and further environmental change.

“Legacy” can mean several things. Birds preserve a direct dinosaur lineage. The extinction also removed large herbivores and predators from many food webs, changing ecological opportunities. A more specific proposal argues that dinosaurs had altered vegetation and river systems so strongly that their loss changed the landscape itself. These claims rest on different evidence and should not be treated as interchangeable.

What the boundary record shows

Rocks at the Cretaceous–Paleogene boundary preserve a global geochemical anomaly associated with the asteroid impact, along with abrupt turnover in many fossil groups. Non-avian dinosaurs disappear from the record above the boundary, while several lineages survive. The impact’s dust, aerosols, fires and disruption of food supply provide a strong explanation for the mass extinction. The fossil and chemical record identifies a major crisis, although its consequences were not identical in every habitat.

The fossil record is patchy. A local gap can reflect erosion or a lack of sediment, so scientists compare multiple sections, fossil groups and chemical markers. Recovery also differed among freshwater, marine and terrestrial communities. It did not happen everywhere on the same schedule, and some lineages rebounded sooner than others.

Surviving lineages and newly available roles

Mammals had coexisted with dinosaurs for more than 100 million years. Most were small, but the group already included varied body forms and diets. After the extinction, mammals expanded into many ecological roles, including larger herbivores and predators. This diversification was not immediate or uniform: it unfolded over millions of years, and different continents followed different paths.

Birds survived as the only living dinosaurs. Early Cenozoic bird fossils document substantial diversification, although the number and identity of lineages that crossed the boundary remain subjects of research. Crocodilians, turtles and some freshwater organisms also survived. Survival depended on more than one simple trait; food availability, habitat, body size and population structure likely mattered, with different factors acting in different groups.

The Cenozoic overview follows the longer succession of post-extinction ecosystems. The end of non-avian dinosaurs was a major turning point, not the only force shaping subsequent faunas. Later climate changes and new interactions continued to reorganise communities.

Did dinosaurs engineer their environments?

Large animals can influence landscapes. Modern elephants, for example, alter vegetation and move nutrients, offering one comparison for questions about large Mesozoic herbivores. Dinosaur feeding, trampling and movement could have affected local plant communities. Directly measuring the scale of those effects in deep time is much harder. A modern analogy suggests a possibility; it does not prove that extinct animals had the same effect in a different ecosystem.

A 2025 study proposed a “dinosaurs as ecosystem engineers” hypothesis to explain changes in continental sedimentary facies across the Cretaceous–Paleogene boundary. It suggests that the loss of large dinosaurs may have contributed to shifts in vegetation and river systems. This interpretation connects fossil ecology with deposits; it is not settled consensus and does not show that dinosaurs alone controlled rivers or forests.

Alternative and interacting causes include climate change, sea-level shifts, regional geology and changes in sediment supply. Strong evidence would include patterns repeated across well-dated basins and independent plant, animal and sediment records. The hypothesis is useful as a research question because it makes claims that can be tested. Future work can assess whether the signal appears in additional regions and whether it aligns with other environmental records.

What later faunas inherited

Later ecosystems inherited evolutionary branches, habitats and ecological relationships from survivors, while also developing new ones. Birds are the clearest living inheritance from dinosaurs. Mammal radiations followed the extinction, but mammals did not descend from dinosaurs. Plants and invertebrates have their own histories, and many groups crossed the boundary with little direct dependence on dinosaur lineages.

The legacy is therefore biological and ecological: a surviving branch, a changed distribution of roles and a long recovery through which new communities emerged. Fossils document turnover; evolutionary trees reconstruct relationships; ecological explanations are strongest when they connect several independent records. Keeping those levels separate makes the story more accurate and more interesting.