It wasn't easy for mammals to stand upright.
The passage of mammals from walking as reptiles to staying upright was a complex, nonlinear transition, which occurred much later than expected. Two researchers from Harvard University (USA) came to this conclusion in a study published in the journal Science Advances.
The shift from the reclining position of the reptiles to the tense attitude of modern mammals was a turning point in evolution. Important changes in the anatomy and function of the extremities from the synapses to the therium. Synapsids are a group of primitive mammals and non-mammalian ancestors (mammalian reptiles), and terium are current mammals (marsupial and placental). Until now it was not clear when and how this evolutionary leap took place.
Now, coupled by advanced biomechanical models and fossil data, you've seen that path was very complex. First, he studied the biomechanics of five modern species representing the entire spectrum of the attitudes of the extremities, such as a lizard (italics), an alligator (semi-erent) and a galgo (errant). Thus, they were able to better understand the relationship of anatomy with the attitude and form of movement of these animals. Subsequently, the analysis was extended to eight fossil species, with an evolution of over 300 million years. The biomechanical model that they developed allowed simulations to be carried out to calculate the force that the posterior extremities could exert on the earth. In fact, they observed that the strength that the legs can do is determinant for the evolution of locomotion.
The researchers conclude that the performance of locomotion did not have a linear evolution, but suffered large oscillations over millions of years. And finally, the traits associated with the tense behavior of today's mammals evolved much later than predicted, probably very close to the common ancestor of the therium.
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