At a time of immense proliferation of species, they were only a modest addition to the biosphere, and there was nothing to suggest that they would become the lords of the planet.
Around the end of the Triassic period, around 230 million years ago, in a region that much later would be called by certain mammals of South America, the first dinosaurs appeared. A literal translation of the name, derived from Greek and Latin, would be something like “terrible lizards” – more than appropriate for creatures like the most famous of all dinosaurs, the fearsome tyrannosaurus rex. The origins of this fascinating lineage, however, did not inspire such confidence.
Take, for example, the eoraptor, which lived 231.4 million years ago in Argentina. From tip of tail to head, 1 meter long. Standing upright, this bipedal creature measured no more than 50 centimeters. This is an excellent example of the main characteristic that marked the origin of dinosaurs: they started small, modest.
From the same period is the Herrerasaurus, another Argentine dinosaur. In length, it could even impress, with an imposing 3 meters. At the height, not much more than 1.8 meters. The relatively small size is explained by the great competition for space that marked that time.
In addition to dinosaurs, several other creatures sought their place in the sun. Among them, many amphibians, crocodilians, cynodonts (reptiles halfway to becoming mammals) and, running around, the first real mammals, which also appeared there. A remarkable – and random – event would decide this fierce dispute for dominance.
Known since the 19th century, it has already caused a lot of confusion. Its skeleton is difficult to interpret, and there were even those who suggested it was a quadruped, or that it jumped like a kangaroo. Modern biomechanical analysis show that it could only be bipedal.
Plateosaurus reached up to 8 meters in length and could weigh up to 4 tons. And, that’s all by eating leaves.
Everything seems to point to the fact that the first dinosaurs must have walked on two legs. And they quickly evolved to divide into two groups, one with a pelvis (the famous pelvis) that most resembled that of birds (the ornithischians) and another that had this bone constitution closer to the lizard style (the saurischians).
Interestingly, modern birds are descendants of this second group, showing how natural selection produces twists and turns, playing haphazardly with characteristics of living beings. It was precisely one of these comings and goings that caused some of the most famous dinosaurs of later times to revert to a quadrupedal posture.
With a modest skull and a light, bipedal build, Herrerasaurus had a movable neck and adequate dentition to give deadly bites to its victims. Fossilized faeces indicate that he probably did not eat plants.
Versatile, this creature was probably omnivorous, as indicated by the two types of teeth it had. Those in the upper jaw were serrated like a predator’s, and those in the lower jaw seemed better for plant consumption.