Study Shows Dinosaurs Diverged Long Before the End of the Cretaceous

There is a popularist view that the dinosaurs were at their most diverse and at the peak of the evolution with regards to how many new species evolving; at the end of the Cretaceous. The Chicxulub impact then wiped out the great dinosaur dynasty leaving the world for the mammals to exploit. The Chicxulub impact refers to the asteroid impact event that resulted in the demise of the dinosaurs sixty-five million years ago. Fossil evidence doesn’t support this idea, studies in the Hell Creek Formation (Maastrichtian faunal stage), of the western United States indicate that how many species of dinosaur was declining in this part of the world towards the end of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata out of this area show proof a lot more different dinosaur types.

Hell Creek Formation Data

Certainly some of the greatest known dinosaurs date from the end of the Mesozoic. Animals wandering the Hell Creek area by the end of the Cretaceous include Triceratops, what dinosaur has 500 teeth  Ankylosaurus and obviously Tyrannosaurus rex. Previously, these gigantic representatives of the dinosaur families, (Triceratops, Ankylosaurus and T. rex are just about the biggest type of dinosaur from these three families), were thought to indicate that dinosaurs just got too big and lumbering to survive and for this reason they went extinct. Scientists now understand that the reason why for the end Cretaceous mass extinction event, the extinction not just of the dinosaurs but also the Ammonites, Plesiosaurs, Mosasaurs, Pterosaurs and an entire host of other plants and animals, were complex and probably involved several factors.

A Family Tree for the Dinosauria

Given the limitations of the prevailing dinosaur fossil record it’s difficult to piece together a “dinosaur family tree” but a task to map dinosaur evolution and to highlight the main evolutionary shifts in Dinosauria has just been completed. The outcomes of this study, led by a group of researchers from the University of Bristol has just been published in the British Journal Proceedings of the Royal Society B.

This study shows that the dinosaurs as friends diversified rapidly in the Late Triassic (225 – 200 million years ago) and then underwent another evolutionary surge in the Mid Jurassic (170 -160 million years ago). The scientists studied a sizable part of the described dinosaur species and pieced together an evolutionary “family tree of dinosaurs” ;.The team estimate that their study covered something like 70 percent of all of the known and described dinosaur species.

Bursts of Evolution

This new study contradicts earlier research that shows the dinosaurs diversifying throughout the Cretaceous. The established view is that although dinosaurs as friends diversified during their entire existence, in certain periods, the evolution of new forms was speeded up. One such period was the early to mid Cretaceous which saw the emergence of a larger number of Ornithischian dinosaurs – the rise of the Hadrosaurs, Ceratopsians and the Pachycephalosaurs, for example. These kind of new dinosaur were evolving during an occasion when many life forms on Earth were diversifying. Dating from about 125 to 80 million years back, there seemingly have been a huge surge of increased terrestrial biodiversity. This time around period is called the Cretaceous Terrestrial Revolution, life on Earth over this period changed dramatically. The Angiosperms (flowering plants), social insects, modern lizards, Mosasaurs and various kinds of mammals all evolved. It have been believed that the rapidly diversifying dinosaurs were part of this move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution in this period to an even more peripheral role. This new study shows that by the full time of the Cretaceous Terrestrial Revolution, all the main dinosaur types that were to survive before the end of the Cretaceous were already established.

New Research Challenges Earlier Theories

This new work certainly contrasts with a lot of the accepted thinking regarding dinosaur diversity. Most palaeontologists think that during the early to middle Jurassic there have been only four main categories of dinosaurs, whilst throughout the Cretaceous this expanded to nine, namely:

Megalosaurs/Allosaurs, Tyrannosaurs, Sauropods, Hysilophodontids, Hadrosaurs, Pachycephalosaurs, Ceratopsians, Ankylosaurs and Stegosaurs.

The fossil record for all your terrestrial vertebrate life of the Mesozoic is quite incomplete so it’s difficult to trace evolutionary links between several types of animals. The job of the Bristol University team is obviously assisting to start the debate, but lacking reviewed the particular paper we cannot really comment any further. It would be interesting to discover how the evolution of non-avian dinosaurs, the birds has been assessed in this study. Very little is known in regards to the evolution of birds, however they do seem to possess diversified and developed new species rapidly throughout the mid to late Cretaceous, a growth in speciation which was largely unchecked by the Cretaceous mass extinction event.

Late Triassic Diversification

Certainly, it’s not surprising that the dinosaurs diversified throughout the Late Triassic, the world was just recovering from the Permian mass extinction (an event that saw an estimated 57% of most marine families and 70% of most terrestrial vertebrate genera becoming extinct). Life on Earth slowly began to recuperate and those forms of organisms left began to diversify to fill those environmental niches that were empty and those soon to be left empty by the “dead clades walking” including the last of the Lystrosaurs. It absolutely was after the Permian mass extinction event that several categories of vertebrates got a way to diversify, including our personal mammalian ancestors.

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