Early mammals existed alongside dinosaurs before a massive asteroid struck the Earth 66 million years ago, as revealed in a recent study.
These resilient creatures included early ancestors of humans, dogs, rabbits, cats, and any mammal that gives birth with a placenta. They managed to survive until the Cretaceous Period came to an end with the impact of an asteroid, which also marked the extinction of larger dinosaurs.
Placental Mammals and Dinosaur Coexistence
Following this event, these early mammals experienced a remarkable burst of diversification, ultimately leading to the diverse array of species we observe today.
The conclusions of the study published in the journal Current Biology were drawn through a statistical examination of the existing fossil record, predominantly comprising rocks that are less than 66 million years old. Carlisle and other researchers from the University of Bristol and the University of Fribourg successfully identified seven mammalian families whose fossil remains can be traced back to 66 million years ago.
This implies that these mammalian families likely share a common ancestor that existed before the asteroid impact. The study delves into a continuous scientific debate concerning the origin of genuine placental mammals and the possibility of their coexistence with dinosaurs.
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Challenging Fossil Evidence
Various theories have been proposed, each offering different perspectives. One model proposes an explosive scenario where mammalian evolution awaits the exit of dinosaurs before rapidly diversifying.
Additionally, the paper challenges the assertion made by some researchers that a well-known fossil specimen called Brasilodon quadrangular provides evidence of placental mammal existence as far back as 225 million years ago, during the Triassic Period.
The animal in question, resembling a shrew, likely lived underground, coexisting alongside dinosaurs. However, the paper refutes the claim that it is a true mammal, despite its classification as an early mammalian relative.
The analyzed fossils comprise three jawbones, one juvenile, and two adult, all belonging to a roughly 8-inch creature that once inhabited Brazil. Upon examination of the jaw, researchers discovered indications of a second set of developing teeth, a characteristic known as diphyodont.
Mammals possess this trait, whereas other species like lizards have polyphyodont dentition, allowing them to continuously replace their teeth. In humans, the first set of teeth, commonly known as baby teeth, is shed between the ages of 6 and 12 before the second set emerges.
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