A team of paleontologists has discovered and described the nearly complete fossilized skull of a previously unknown mammal relative that lived about 130 million years ago (Early Cretaceous epoch). The study appears in the journal Nature.
Cifelliodon wahkarmoosuch. Image credit: Jorge A. Gonzalez / Keck School of Medicine of the University of Southern California, Los Angeles.
The 130-million-year-old fossil skull was found at the Cedar Mountain Formation, a rock formation in Utah dated to between 139 million and 124 million years ago.
It was analyzed by a group of experts from the University of Chicago, the Natural History Museum of Utah, the Utah Geological Survey, and the University of Southern California, Los Angeles.
The researchers used an imaging technique called micro-computed tomography to reveal anatomical details about the skull.
“With an estimated body weight of up to 2.5 pounds (0.9 kg), the ancient creature — named Cifelliodon wahkarmoosuch — would seem small compared to many living mammals, but it was a giant among its Cretaceous contemporaries,” they said.
“A full-grown Cifelliodon wahkarmoosuch was probably about the size of a small hare or pika (small mammal with rounded ears, short limbs and a very small tail).”
“It had teeth similar to fruit-eating bats and could nip, shear and crush. It might have incorporated plants into its diet.”
“The animal had a relatively small brain and giant ‘olfactory bulbs’ to process sense of smell. The skull had tiny eye sockets, so the animal probably did not have good eyesight or color vision. It possibly was nocturnal and depended on sense of smell to root out food.”
“For a long time, we thought early mammals from the Cretaceous were anatomically similar and not ecologically diverse,” said study lead author Dr. Adam Huttenlocker, from the Keck School of Medicine at the University of Southern California, Los Angeles.
“This finding by our team and others reinforce that, even before the rise of modern mammals, ancient relatives of mammals were exploring specialty niches: insectivores, herbivores, carnivores, swimmers, gliders. Basically, they were occupying a variety of niches that we see them occupy today.”
The nearly complete skull of Cifelliodon wahkarmoosuch. Image credit: Huttenlocker et al, doi: 10.1038/s41586-018-0126-y.
The scientists also found that Cifelliodon wahkarmoosuch belonged to a long-lived and widespread group of early mammal relatives called Haramiyida. These early mammal relatives included the closest relatives of the common ancestor of all true living mammals.
The fossil was the first of its particular subgroup — Hahnodontidae — found in North America. This subgroup was previously known only from the Cretaceous of Northern Africa.
“Based on the unlikely discovery of this near-complete fossil cranium, we now recognize a new, cosmopolitan group of early mammal relatives,” Dr. Huttenlocker said.
The fossil discovery emphasizes that haramiyidans and some other vertebrate groups existed globally during the Jurassic-Cretaceous transition.
It suggests that the divide of the ancient landmass Pangaea continued for about 15 million years later than previously thought and that mammal migration and that of their close relatives continued during the Early Cretaceous (145 to 101 million years ago).
“It’s generally thought that the northern and southern continents, as well as Europe and North America, were completely separated by the end of the Jurassic period (about 145 million years ago),” Dr. Huttenlocker said.
“The problem is that the earliest Cretaceous record is not as well studied in North America or in Africa, making it difficult to compare continental vertebrate assemblages.”
“Based on intense fieldwork taking place now in the basal Cretaceous of Utah and in Europe, there is evidence of a ‘North Atlantic Land Bridge’ that may have connected the Old and New Worlds into the Cretaceous.”
“Shared dinosaur groups found in Africa and Europe further present the possibility that similar connections existed between the southern and northern continents, transforming our understanding of the timing and order of the Pangaean supercontinent’s breakup.”
“The study reveals that the early mammal precursors migrated from Asia to Europe, into North America and further onto major Southern continents,” added senor author Professor Zhe-Xi Luo, a paleontologist at the University of Chicago.
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Adam K. Huttenlocker et al. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature, published online May 23, 2018; doi: 10.1038/s41586-018-0126-y
