What is the Age of the Dinosaurs?
How would one understand dinosaurs without having a concept of time? To understand how a species of dinosaur fitted into the greater scheme of things it is important to know when it lived. Yet estimates of ‘Deep Time’, spanning millions of years, are frequently bandied about, making it easy to lose sight of the bigger picture of the history of life.
The Age of the Dinosaurs was the Mesozoic Era
The so-called ‘Age of the Dinosaurs’ refers to the Mesozoic area, which stretched from ca. 250 million to 66 million years before present. This conjures up an image of a long, endless summer that allowed the dinosaurs to flourish. Books usually paint a picture of one of three periods during this stretch of time to depict the life of dinosaurs, which gives the impression that stretches of millions of years seem shorter than it is. The Triassic is associated with the small Coelophysis; the Jurassic is synonymous with the large therapods and sauropods that were discovered in the Morrison Foundation; and the Cretaceous is known for Tyrannosaurus and Triceratops.
Detailing the Age of the Dinosaurs
Looking at time in more detail, we find that about 150 million years ago – during the latter part of the Jurassic – western North America was home to Allosaurus, Apatosaurus, Diplodocus and Stegosaurus. Tyrannosaurus and Triceratops – the most famous inhabitants of the Cretaceous era, only evolved about 67 million years before present. If one were to imagine an evolutionary timeline, these dates fall alongside and show, for example, that the time space between Tyrannosaurus and Apatosaurus was 83 million years, and that the same holds for Triceratops and Allosaurus.
The Age of the Mammals
The extinction of the non-avian dinosaurs saw the start of the ‘Age of Mammals’, which happened ca. 66 million years ago. This means that there is less time between us and Tyrannosaurus rex, than there is between Stegosaurus and T. rex. This is a sobering thought when one thinks about how much life has changed over the past 66 million years. Ancient mammals came, flourished, and went before the advent of our modern fauna. These included knobbly-headed and sabre-fanged herbivores (e.g. Uintatherium), lemur-like primates (e.g. adaptiforms), carnivores with razor jaws (e.g. creodonts), and a multitude of other strange creatures. Even some lineages that we know from modern times (e.g. rhinos, elephants, horses) have become more diverse through evolution and what we see now represents the leftover fragments of what once was.
Consider the enormous evolutionary changes seen between the last Triceratops and the present, and then imagine the 83 million years that separate the giants of the Jurassic and the Cretaceous eras. This stretch of time saw the first flowering of the angiosperms; it witnessed the disappearance of the fish-like ichthyosaurs and the rise of mosasaurs and plesiosaurs as dominant sea-predators; sauropods that dominated certain areas made way for large herds of ceratopsids and hadrosaurs; small dinosaur tyrants became apex predators; and the early forms of birds increased in variety and established themselves amongst their dinosaur relatives.
We Can Only View the Age of the Dinosaurs in Highlighted Events
Highlights. That is what the above gives us, and that is what makes it both wonderful and so frustrating to track history for life on our planet. We only see glimpses of a picture that keeps changing and when seen in isolation these glimpses make us forget that they are all ultimately related to each other. We need to take a step back to see how all the glimpses fit together to reveal the wonderfully long and constantly changing history of life that has been supported by our planet including the age of the dinosaurs.
