Researchers have identified a new small mammal species that lived on the Pacific Coast about 75 million years ago. The find adds evidence about how some mammals survived the mass extinction 66 million years ago that killed 75% of life on Earth.
A team led by the University of Washington studied a fossil discovered at a research site in Baja California in 2009. The fossil was found by field assistant Michael de Sosa VI. The researchers recovered teeth, a skull, jaws and parts of the skeleton, including a femur and an ulna. They named the species Cimolodon desosai. It was about the size of a golden hamster and likely moved on the ground and in trees, eating fruits and insects.
Scientists used digital imaging and micro-computed tomography to make high-resolution images of the fossil and compared the teeth to related species to show it is new. The genus was common in the Late Cretaceous across western North America and the team says this species was ancestral to the survivors of the extinction event; being small and omnivorous was advantageous.
Difficult words
- species — a group of similar living organisms
- fossil — the preserved remains of an organism
- mass extinction — a time when many species die
- recover — to get something back after lossrecovered
- skull — the bones that protect the head
- femur — the large bone in the upper leg
- genus — a group of related species
- omnivorous — eating both plants and animals
- ancestral — related to earlier generations or species
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- Do you agree that being small and omnivorous helped some mammals survive the mass extinction? Why or why not?
- Which tools mentioned in the article (for example digital imaging or micro-computed tomography) seem most useful to study fossils? Why?
- Which fossil parts (teeth, skull, femur or other bones) do you think help most to identify a species? Explain your choice.
Related articles
Molecules in million‑year‑old fossils show a warmer, wetter past
Researchers extracted metabolism molecules from fossil bones aged 1.3–3 million years. Analyses of animal and plant metabolites reveal diets, infections and local environments and suggest the study sites were warmer and wetter than today.
