Study Shows Dinosaurs Diverged Long Before the End of the Cretaceous

There’s a popularist view that the dinosaurs were at their most diverse and at the peak of their evolution with regards to how many new species evolving; at ab muscles end of the Cretaceous. The Chicxulub impact then wiped out the truly amazing dinosaur dynasty leaving the world for the mammals to exploit. The Chicxulub impact refers to the asteroid impact event that led to 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 the main world towards the finish of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata from this area show evidence of many more different dinosaur types.

Hell Creek Formation Data

Certainly some of the finest known dinosaurs date from ab muscles end of the Mesozoic. Animals wandering the Hell Creek area at the conclusion of the Cretaceous include Triceratops, what dinosaur has 500 teeth  Ankylosaurus and obviously Tyrannosaurus rex. In the past, these gigantic representatives of their dinosaur families, (Triceratops, Ankylosaurus and T. rex are only about the largest kind of dinosaur from these three families), were considered to indicate that dinosaurs just got too big and lumbering to survive and for this reason they went extinct. Scientists now realize that the reason why for the finish Cretaceous mass extinction event, the extinction not only of the dinosaurs but in addition the Ammonites, Plesiosaurs, Mosasaurs, Pterosaurs and a whole host of other plants and animals, were complex and probably involved several factors.

A Family Tree for the Dinosauria

Given the limitations of the present 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 outcome with 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 a second evolutionary surge in the Mid Jurassic (170 -160 million years ago). The scientists studied a big percentage of the described dinosaur species and pieced together an evolutionary “family tree of dinosaurs” ;.The team estimate that their study covered something such as 70 percent of all 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 in their entire existence, using periods, the evolution of new forms was speeded up. One period was early to mid Cretaceous which saw the emergence of a better 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 seems to have been a huge surge of increased terrestrial biodiversity. Now period is known as the Cretaceous Terrestrial Revolution, life on Earth over this period changed dramatically. The Angiosperms (flowering plants), social insects, modern lizards, Mosasaurs and many types of mammals all evolved. It had been believed that the rapidly diversifying dinosaurs were part with this move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution during this period to an even more peripheral role. This new study shows that by the time of the Cretaceous Terrestrial Revolution, all the main dinosaur types which were to survive until the end of the Cretaceous were already established.

New Research Challenges Earlier Theories

This new work certainly contrasts with much of the accepted thinking regarding dinosaur diversity. Most palaeontologists feel that during early to middle Jurassic there have been only four main groups 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 the terrestrial vertebrate life of the Mesozoic is very incomplete so it’s difficult to trace evolutionary links between several types of animals. The work of the Bristol University team is unquestionably helping open the debate, but not having reviewed the actual 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. Hardly any is famous concerning the evolution of birds, nevertheless they do seem to own diversified and developed new species quickly 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 dealing with 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 started initially to diversify to fill those environmental niches which were empty and those soon to be left empty by the “dead clades walking” like the last of the Lystrosaurs. It was following the Permian mass extinction event that several groups of vertebrates got an opportunity to diversify, including our own mammalian ancestors.

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