{
  "id": 374947,
  "title": "Dinosaurs became giants — so why did they never become tiny?",
  "url": "https://urgent.news/2026/08/09/dinosaurs-became-giants-so-why-did-they-never-become-tiny",
  "topic": "science",
  "section": "Science",
  "published": "2026-08-09T10:15:11.000Z",
  "source": {
    "name": "ScienceDaily",
    "slug": "sciencedaily",
    "url": "https://www.sciencedaily.com/releases/2026/08/260807035137.htm"
  },
  "original_language": "en",
  "account": "Dinosaurs are renowned for their gargantuan size, with giants like Tyrannosaurus rex and Apatosaurus dominating popular imagination. However, new research published in the journal Evolution by scientists from the American Museum of Natural History and Princeton University seeks to answer an equally intriguing question: why did dinosaurs never become extremely small? Using mathematical models to analyze how body size evolved among vertebrates, researchers found that energy use and physiology can account for size ranges observed in mammals, birds, and turtles. Yet, these factors fail to explain why even the smallest dinosaurs, aside from birds, remained relatively large. The researchers propose that ecological factors, such as competition with early small mammals, may have imposed a lower size limit on dinosaurs. Competing with small mammals could have barred dinosaurs from occupying the tiny niches filled by modern creatures like mice and sparrows. The disparity between dinosaurs and modern animals is striking: the largest dinosaurs weighed over 80 tons, while the smallest known dinosaurs outside the bird lineage weighed just about one pound, comparable to a large rabbit. This is over 200 times heavier than the bee hummingbird, the smallest bird in the world, which weighs only 1.75 grams. To investigate this size constraint, researchers turned to mathematical models designed to predict how natural selection influences body size. While these models explained body size patterns in mammals, birds, and turtles, they could not account for the larger-than-expected sizes of most dinosaurs outside the bird lineage. This suggests that factors beyond physiology, likely ecological pressures like competition and predation, influenced dinosaur size limits. The findings also shed light on the rise of birds, which evolved from dinosaurs but can reach sizes far smaller than those of other dinosaurs. Birds' transition to powered flight transformed ecological possibilities, allowing them to escape the dinosaur size constraint and evolve into diverse, miniature forms. Understanding these ecological pressures could reveal why dinosaurs were unable to shrink to the sizes seen in modern small animals and small reptiles.",
  "summary": "Dinosaurs conquered the land at enormous sizes, but strangely, they almost never evolved into truly tiny animals. New research suggests that physiology alone can’t explain this missing miniature end of the dinosaur spectrum—and that early mammals may have been partly responsible. While dinosaurs kept mammals from becoming large, small mammals may have returned the favor by occupying ecological…",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}