A group of scientists has unearthed a nearly 130-million-year-old fossilized skull of a reptile-like mammal species that continued to evolve as it migrated across several continents.
The age of the fossilized skull hinted that the new species could be the link that completed the transition of reptiles to the earliest mammal relatives.
The discovery revealed that species of ancient reptile-like mammals were already ecologically diverse aside from being anatomically similar. They could already be classified into different groups the way modern mammals are classified today. The new species, as well as its contemporaneous that existed 66 to 145 million years ago, already belonged to different niches of insectivores, herbivores, carnivores, swimmers, and gliders.
Based on the unearthed skull, it could also be hypothesized that evolution of ancient mammals continued to happen while they migrate from Asia to Europe, into North America, and further to bigger Southern continents.
This pattern of migration also suggested that the separation of the ancient landmass Pangea continued to about 15 million years later than what was previously believed.
Fossil Skull From Utah Named Cifelliodon Wahkarmoosuch
The skull was incidentally unearthed at a site north of Arches National Park in eastern Utah. The paleontologists initially brought a rock for a different study but surprisingly discovered the fossilized skull.
Adam Huttenlocker, the lead author of the study and assistant professor of clinical integrative anatomical sciences at the Keck School of Medicine of the University of Southern California, named the new species Cifelliodon wahkarmoosuch.
Huttenlocker and colleagues from the Utah Geological Survey and University of Chicago grouped the Cifelliodon with the Haramiyida, an extinct branch of mammals that is closest to the present-day mammals.
"Here we report, to our knowledge, the first cranium of a large haramiyidan from the basal Cretaceous of North America," the scientists wrote in the study published in the journal Nature. Cifelliodon became the first of its particular subgroup found in North America, the Hahnodontidae.
The skull showed that Cifelliodon had a small brain but large olfactory bulbs where its sense of smell, used for looking for food, was located. It also had small tiny eye sockets, which suggested that it had either poor eyesight or poor color vision.
The scientists estimated that Cifelliodon weighed about 2.5 pounds, a body weight that was comparatively smaller than contemporary mammals but heaviest compared to ancient mammals during the Cretaceous period.
In comparison, an adult Cifelliodon was about the size of a small hare or a pika. The species' teeth resemble that of the fruit-eating bats.
"Cifelliodon is unique in that it is one of the only near-complete skulls of a mammal relative from the basal Cretaceous of North America and is the only fossil of early mammal relatives from this time interval in Utah," explained Huttenlocker.
The Pangea Landmass
The Americas, Eurasia, Africa, Antarctica, Australia, and India used to be one huge continent called Pangea. The exact timing of Pangea's breakup into different continents continues to be under discussion.
Huttenlocker and his team said the Cifelliodon closely resembled another species in Africa. This could suggest that the breakup of Pangea continued to happen 15 million years later than what was previously believed. This could particularly be true since northern and southern continents as well as Europe and North America were believed to have completely separated by the end of the Jurassic period or about 145 million years ago.
Cifelliodon was unearthed from Utah deposits that were found to be about 125 to 130 million years. Huttenlocker and his team, therefore, concluded that there might be a "North Atlantic land bridge" that may have connected the Old and New Worlds into the Cretaceous.