Study Shows Dinosaurs Diverged Long Ahead of 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 in terms of the number of new species evolving; at the 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 identifies the asteroid impact event that generated 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 the number of species of dinosaur was declining in this area of the world towards the conclusion of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata from this area show proof a lot more different dinosaur types.
Hell Creek Formation Data
Certainly some of the best known dinosaurs date from the 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 of course Tyrannosaurus rex. In the past, these gigantic representatives of their dinosaur families, (Triceratops, Ankylosaurus and T. rex are just about the greatest type of dinosaur from these three families), were thought to indicate that dinosaurs just got too big and lumbering to survive and this is why they went extinct. Scientists now realize that the reason why for the conclusion Cretaceous mass extinction event, the extinction not just of the dinosaurs but additionally 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 prevailing dinosaur fossil record it’s difficult to piece together a “dinosaur family tree” but a project 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 team 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 an additional evolutionary surge in the Mid Jurassic (170 -160 million years ago). The scientists studied a large portion 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 the known and described dinosaur species.
Bursts of Evolution
This new study contradicts earlier research that shows the dinosaurs diversifying during the Cretaceous. The established view is that although dinosaurs as friends diversified throughout their entire existence, using periods, the evolution of new forms was speeded up. One period was the first 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 kinds of new dinosaur were evolving during a time when many life forms on Earth were diversifying. Dating from about 125 to 80 million years back, there seemingly have been a massive surge of increased terrestrial biodiversity. Now 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 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 a far more peripheral role. This new study shows that by the time of the Cretaceous Terrestrial Revolution, all the main dinosaur types that were to survive before 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 think that during the first to middle Jurassic there have been only four main sets of dinosaurs, whilst during 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 is difficult to trace evolutionary links between different types of animals. The task of the Bristol University team is unquestionably helping to open the debate, but lacking reviewed the particular paper we cannot really comment any further. It could be interesting to discover how the evolution of non-avian dinosaurs, the birds has been assessed in this study. Very little is famous in regards to the evolution of birds, but they do seem to possess diversified and developed new species rapidly during the mid to late Cretaceous, a growth in speciation that has been largely unchecked by the Cretaceous mass extinction event.
Late Triassic Diversification
Certainly, it’s not surprising that the dinosaurs diversified during the Late Triassic, the world was just coping with the Permian mass extinction (an event that saw an estimated 57% of marine families and 70% of 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 that were empty and those soon to be left empty by the “dead clades walking” including the last of the Lystrosaurs. It absolutely was following the Permian mass extinction event that several sets of vertebrates got an opportunity to diversify, including our own mammalian ancestors.