The history of dinosaurs is often defined by giants, but the other extreme of the size spectrum holds scientific fascination. Identifying the single smallest dinosaur challenges the boundaries of paleontology and our understanding of evolution. The search for the smallest non-avian species involves scrutinizing fragmentary remains, interpreting growth stages, and drawing a fine line between dinosaurs and their descendants, the birds. The answer remains dynamic, reflecting the latest fossil finds and analytical techniques.
Identifying the Primary Candidate
The current candidate for the smallest known non-avian dinosaur specimen is Parvicursor remotus, a swift-running theropod from the Late Cretaceous period in Mongolia. Its name, “small runner,” is fitting for an animal whose known fossil measured only about 39 centimeters long. Its estimated weight was a mere 162 grams, comparable to a small house cat and less than a can of soda.
Parvicursor belonged to the Alvarezsauridae family, characterized by long, slender legs and very short forelimbs ending in a single, robust claw. Living approximately 85 million years ago, it likely consumed insects, using its specialized claw to break into termite mounds.
The single known specimen exhibits skeletal features suggesting it was not fully mature when it died. This highlights the complexity of distinguishing a genuinely small species from a juvenile of a larger one. The Parvicursor specimen currently represents the smallest measured body size for a non-avian dinosaur.
Why Determining the Smallest is Difficult
Pinpointing the absolute smallest dinosaur is challenging because the fossil record is incomplete and skewed toward larger individuals. Smaller, more delicate bones are less likely to survive fossilization, and they are more susceptible to destruction by geological forces. Fossils of small creatures are also harder for paleontologists to locate and extract.
A major hurdle is determining the ontogenetic status of a specimen—deciding if a small fossil represents a fully grown adult or a juvenile of a larger species. Paleontologists use techniques like bone histology, which involves slicing the bone to examine growth rings, to estimate age and maturity. However, a lack of consistent skeletal maturity indicators across all dinosaur groups complicates this analysis.
The definition of a “non-avian dinosaur” also creates ambiguity along the evolutionary line leading directly to birds. The smallest extinct dinosaurs generally fall into the Maniraptoran group, which includes creatures morphologically very close to the earliest birds (Avialans). Some tiny feathered fossils, such as Anchiornis, have unstable classifications, altering the pool of candidates for the “smallest non-avian” title.
Other Notable Miniature Species
Beyond Parvicursor, other species frequently enter the discussion. Epidexipteryx hui, a theropod from the Jurassic period of China, is a contender based on its remains. This animal had a body length of about 25 centimeters, excluding its long ornamental tail feathers.
The weight estimate for Epidexipteryx is 164 grams, nearly identical in mass to Parvicursor, though it lived millions of years earlier. This species possessed the earliest evidence of ornamental feathers, which were ribbon-like structures likely used for display. Epidexipteryx belonged to the Scansoriopterygidae family, known for having long fingers adapted for climbing.
A slightly larger, but historically significant, small dinosaur is Compsognathus longipes, a well-known predator from the Late Jurassic of Europe. Compsognathus was considered the smallest dinosaur for decades after its discovery in the 1850s. It reached a length of about 0.8 to 1 meter and weighed between 2 and 2.8 kilograms, roughly the size of a large chicken.
The Science of Dinosaur Miniaturization
The existence of small dinosaurs demonstrates that not all species followed the path to gigantism, instead undergoing evolutionary miniaturization. This size reduction was particularly pronounced in the theropod lineage that eventually led to birds. This sustained shrinkage allowed the ancestors of birds to evolve new anatomical features at an accelerated rate compared to their larger relatives.
Miniaturization often occurs due to environmental pressures, allowing a species to fill a specific ecological niche, a concept known as niche partitioning. For example, the specialized forelimbs of Parvicursor suggest an adaptation for myrmecophagy (eating ants and termites), a food source accessible to smaller animals. In other cases, such as the sauropod Magyarosaurus, small size resulted from island dwarfism, where large mainland animals evolve to be smaller when confined to resource-limited islands.