A new study suggests that the evolutionary ancestors of humans lived with dinosaurs for a short time before the reptilian beasts died out.
As reported by the New York Post, a team of paleobiologists from the University of Bristol (UK) and the University of Freiburg (Germany), have thoroughly analyzed the fossils of the group of species that populated the planet during the period cretaceous, between 145 and 72 million years ago. This covered placental mammals, including the ancestors of humans, dogs and bats (among others), revealing that these was born before the mass extinction.
Evolution earlier than expected
The researchers concluded in their study that when the destructive asteroid hit Earth 66 million years ago, it killed all dinosaurs except birds and other small animals, such as lizards and frogs, a event called the Cretaceous-Paleogene (K-Pg) mass extinction. However, when paleobiologists examined the fossil record, they reached a point where they revealed that placental mammals already existed before the destruction that led to extinction.
The lead author of the study, Emily Carlisle, from the Bristol School of Earth Sciences, said“We collected thousands of placental mammal fossils and were able to see the patterns of origin and extinction of the different groups and, Based on this, we were able to estimate when placental mammals evolved.“.
According to research, primates (the human lineage), lagomorphs (rabbits and hares) and carnivores (dogs and cats) evolved just before the extinction of the ancient large species.
Currently, placental mammal fossils have only been found in rocks less than 66 million years old, a timeline that coincides with the impact of the asteroid that caused the extinction of the dinosaurs. However, molecular data suggest a later age for the emergence of this group of animals.
Thus, the researchers identified seven families of mammals with fossils dating back 66 million years, which means that they must have descended from a pre-asteroid common ancestor.
A controversial theory
The research opens a debate on when did true placental mammals first evolve and if they co-existed with the dinosaurs.
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Some experts have proposed a model in which mammalian evolution patiently waited for dinosaurs to leave the scene and then they appeared. While another model assumes the process started deep in the Cretaceous, concluding that it started later in the period.
The study says its findings support the theory that there was a brief overlap between dinosaurs and mammals. The results of their analyzes suggest that the mystery of whether our ancestors coexisted with dinosaurs has finally been solved.
“The model we used estimates ages of origin based on when lineages first appear in the fossil record and the pattern of species diversity over time for the lineage,” shared the co- research author, Daniele Silvestro from the University of Fribourg.
Additionally, researchers believe that the loss of competition from dinosaurs allowed placental mammals to diversify and evolve more rapidly, giving rise to many of the species we know today.
The study was published in the journal Current biology.
References: Very interesting / History.
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