appConfigEntityId

bodyType

customContents

entityId

entityUuid

isVideo

articlePageQuery

article

articleSchemaContent

content

hooksArticlePageAdvertisementConfigArticle

hooksArticlePageFloatingButtonConfigArticle

appConfig

filter

json

liveArticle

Reuters

Everyone knows dinosaurs got really big. Some of ⁠the long-necked plant-eaters were the largest land animals ever on Earth, as shown by Argentinosaurus, perhaps 65 to 80 tonnes (70 to 90 tons) and upwards of 30 metres (around 100 feet) long. But why were there never tiny dinosaurs, like the size of a mouse? As far as we know, none ever existed.
New research investigates this phenomenon. Scientists employed mathematical models to explore the evolution of body size across vertebrate groups. They determined that energetics and physiology can account for the sizes of mammals, birds that fly and turtles, but these ‌factors fail to explain the absence of really small dinosaurs, aside from their avian descendants.
The researchers see other dynamics at play. They hypothesise that because early mammals – most of them puny and shrew-sized – had filled ecological niches for small animals, their presence prevented dinosaurs from evolving tiny body sizes adapted to such niches.
“We know based on observations of living animals and the fossil record that most animal groups have members that achieve very small body sizes, and that these small animals typically dominate their ecosystems,” says palaeontologist Stephanie Lechki, a postdoctoral fellow at Princeton University in New Jersey and co-leader of the study published in the journal Evolution.
“A small animal typically requires fewer resources and can achieve reproductive maturity and reproduce more quickly than ⁠a large-bodied animal,” Lechki adds.
The smallest dinosaurs included the likes of crow-sized Microraptor, weighing as little as 430 grams (15oz); Fruitadens, at 730 grams; and Anchiornis, at 530 grams. These were still much ‌larger than today’s smallest bird, the bee hummingbird (about 1.95 grams); smallest mammal, the Etruscan shrew (about 1.8 grams); and smallest lizard, the dwarf gecko (about 0.15 grams).

“Most living species are small, much smaller than us, and smaller than even the smallest dinosaurs,” says palaeontologist and study co-leader Roger Benson, curator of dinosaur palaeobiology at the ‌American Museum of Natural History in New York.
About 90 per cent of extant – still existing today – bird species and 75 per cent of extant mammal species are smaller than the smallest dinosaurs.
“Think of rodents, shrews, bats, songbirds, most lizards, frogs, ⁠so many small species. This suggests that ⁠there are many more niches available to small-bodied species. The absence of tiny dinosaurs means that all those abundant niches were closed to them,” Benson says.
Dinosaurs first appeared roughly 230 million years ago and eventually became the dominant land animals, holding that ‌status until an asteroid struck Earth 66 million years ago, causing a mass extinction of species. Mammals during the age of dinosaurs thrived in ecological niches perfect for small body sizes, like insectivores and seed eaters.
“It is likely that small-bodied early mammals outcompeted dinosaurs, preventing ‌them from ‌reaching small body sizes,” Lechki says. “Similarly, large dinosaurs likely outcompeted early mammals, preventing them from reaching large body sizes.”
It was only after the asteroid struck that mammals achieved larger body sizes and ‌expanded into ecological niches previously occupied by dinosaurs such as large plant-eaters and apex predators.
Another potential explanation for the lack of evidence of tiny dinosaurs is that they did exist but their fossils have been ⁠elusive. The researchers say this seems improbable because fossil deposits containing dinosaur remains often also preserve the remains of numerous small animals.
The mathematical models forecast how evolutionary forces drove body size based ⁠on the physiology of an animal’s energy uptake from ecosystem resources, and the rate at which the animal converted that to offspring. Evolutionary forces favour body sizes at which the rate of energy invested in offspring is maximum, Benson says.
Dinosaurs defied the models even though birds, which evolved from small feathered dinosaurs and first appeared about 150 million years ago, ‌conformed to the models – although flightless birds did not. Snakes ‌and crocodilians also deviated from the mathematical models.

The dinosaurs from which birds evolved were from a lineage called theropods to which giants like Tyrannosaurus rex – which reached roughly 12 metres in height and weighed perhaps eight tonnes – belonged. Some flightless birds became sizeable. For instance, the elephant birds that inhabited Madagascar until about a millennium ago could weigh up to 500kg (1,100lbs).
“Birds evolved most of their flight adaptations around 130 million years ago and immediately became small,” Benson says.
“We think that flight might have allowed birds to escape from ecological competition and invade tiny body sizes. This ultimately explains the tremendous biodiversity of living birds, which have more than 12,000 species.”


Neurobiologist Ye Bing says his return to China is not spurred by Michigan campus tragedy

China’s stealth fighters, critical minerals from lithium waste: 7 science highlights

China launches its first commercial radio-tracking satellites in electronic warfare leap

China’s cancer breakthrough on CAR-T cell therapy shows progress

Science

Why were there no teeny-tiny dinosaurs like we have with mammals and birds?

A model of a Microraptor (front) is wheeled out for display at the American Museum of Natural History in New York. The crow-sized Microraptor was one of the smallest-known dinosaurs, weighing about 430 grams. Photo: Reuters

A hummingbird drinks from a flower in a garden. The smallest hummingbird weighs less than two grams. Photo: AP

This feathered dinosaur, Anchiornis huxley, which lived in what is now China about 161 million years ago, embodies the gradual transition from non-avian dinosaurs to birds. Illustration: Zhao Chuang/Peking Natural Science Organisation

What to see at the Shenzhen Natural History Museum, from dinosaur fossils to meteorites

Fossils of a Mammuthus primigenius is displayed at the Evolution Hall of Shenzhen Natural History Museum.

25JUL26 SCMP / Elson Li

The Shenzhen Natural History Museum’s Dinosaur Hall is crowded with visitors on its soft opening day on July 25. Photo: Elson Li

The Cosmos Hall at the Shenzhen Natural History Museum is crowded with visitors on its soft opening day on July 25, 2026. Photo: Elson Li

A woolly mammoth skeleton on display in the Evolution Hall. Photo: Elson Li

The exterior of the museum, which is located in the Pingshan district in Shenzhen’s northeast. Photo: Edmond So

Why Singapore’s record-breaking giant fire dragon goes up in smoke every 3 years

Spectators watch the Fire Dragon Dance of Sar Kong Mun San Fook Tuck Chee in March 2026. Every three years, the dragon is offered back to the deities through fire, reducing its physical form to ashes. This act is not an end but a renewal. Photo: Yeo GT

Fire billows during a performance of the Sar Kong Mun San Fook Tuck Chee Fire Dragon Dance in 2025. Photo: Ivan Fu

A performance of the Sar Kong Mun San Fook Tuck Chee Fire Dragon Dance in 2024.

Zhen Meng Chye is one of only two remaining artisans in Singapore capable of constructing the fire dragon’s intricate head and tail, which he sews with a metal hook. Photo: Angela Sim 

Inside the black-and-white panda-monium in Chengdu, China’s panda capital

Stuffed panda dolls inspired by Hua Hua, the most popular panda living at the Chengdu Research Base of Giant Panda Breeding in China, are displayed at a gift shop at the research base. Photo: The Korea Times

A visitor takes a photo of a giant panda at the Chengdu Research Base of Giant Panda Breeding in Chengdu, China. Photo: The Korea Times

Giant panda structures welcome travellers at the Chengdu Tianfu International Airport in China. Photo: The Korea Times

Panda-themed souvenirs at a traditional teahouse in Chengdu. Experts estimate that panda-themed tourism and merchandise in Sichuan constitute a business worth 1 billion yuan annually. Photo: The Korea Times

Lifestyle

Travel & Leisure

New research investigates why there were never any dinosaurs the size of, say, a mouse, and it seems like mammals could be to blame


New research investigates why there were never any dinosaurs the size of, say, a mouse, and it seems like mammals could be to blame.


Archaeology and palaeontology

History

Animals

Why were there no teeny-tiny dinosaurs like we have with mammals and birds?

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}New research investigates why there were never any dinosaurs the size of, say, a mouse, and it seems like mammals could be to blame

New research investigates why there were never any dinosaurs the size of, say, a mouse, and it seems like mammals could be to blame