Researchers have described a new species of small mammal that lived alongside dinosaurs on the Pacific Coast about 75 million years ago. The discovery helps explain 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 found in 2009 at a research site in Baja California; field assistant Michael de Sosa VI located the specimen. The team recovered teeth, a skull, jaws and parts of the skeleton, including a femur and an ulna. They named the new species Cimolodon desosai. The animal was about the size of a golden hamster, likely scampered on the ground and in trees, and probably ate fruits and insects. The species belongs to the Cimolodon genus and to the wider group of multituberculates, which first appeared in the Jurassic and survived for more than 100 million years before going extinct.
Scientists used digital imaging and micro-computed tomography (micro-CT) to produce high-resolution images of the fossil and compared the teeth of C. desosai to those of related Cimolodon species to demonstrate it is new. As Gregory Wilson Mantilla, senior author and UW professor, notes, “That far back in time everything is named based on their tooth characteristics.” He also says, “This new species, Cimolodon desosai, was ancestral to the species that survived the extinction event. It and its descendants were relatively small and omnivorous—two traits that were advantageous for surviving.”
The research, published in the Journal of Vertebrate Paleontology, involved coauthors from UW and the Universidad Nacional Autónoma de México. Funding came from UC MEXUS-CONACYT; Dirección General de Asuntos del Personal Académico PAPIIT IN111209-2; the UW College of Arts and Sciences; the UW biology department; and the American Philosophical Society. The discovery improves understanding of early mammal anatomy, ecology and evolutionary history and fills gaps about multituberculate environments.
Difficult words
- species — group of similar organisms that can breed
- fossil — preserved remains or traces of ancient life
- multituberculate — extinct group of early mammals with many teethmultituberculates
- genus — taxonomic group above species level
- ancestral — relating to an earlier ancestor or form
- omnivorous — eating both plants and animals
- micro-computed tomography — imaging method for detailed internal structuresmicro-computed tomography (micro-CT)
- extinction — permanent loss of a species from Earth
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Discussion questions
- Why might small size and an omnivorous diet be advantageous during a mass extinction? Give reasons.
- How do modern imaging methods like micro-CT change what scientists can learn from fossils?
- What further questions about early mammal ecology could researchers investigate after this discovery?
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