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 in terms of 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 identifies 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 part 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. Previously, these gigantic representatives of the dinosaur families, (Triceratops, Ankylosaurus and T. rex are only about the biggest kind 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 merely of the dinosaurs but also the Ammonites, Plesiosaurs, Mosasaurs, Pterosaurs and a complete host of other plants and animals, were complex and probably involved a number of 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 key evolutionary shifts in Dinosauria has just been completed. The results of the 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 a group 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 sizable 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 through the Cretaceous. The established view is that although dinosaurs as a group diversified during their entire existence, in certain periods, the evolution of new forms was speeded up. One such period was the first to mid Cretaceous which saw the emergence of a greater variety 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 seems to have been an enormous surge of increased terrestrial biodiversity. This time period is referred to as 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 thought that the rapidly diversifying dinosaurs were part of the move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution during this period to a more peripheral role. This new study shows that by the full time of the Cretaceous Terrestrial Revolution, all the key 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 much of the accepted thinking regarding dinosaur diversity. Most palaeontologists believe that during the first to middle Jurassic there were only four main groups of dinosaurs, whilst through the Cretaceous this expanded to nine, namely:
Megalosaurs/Allosaurs, Tyrannosaurs, Sauropods, Hysilophodontids, Hadrosaurs, Pachycephalosaurs, Ceratopsians, Ankylosaurs and Stegosaurs.
The fossil record for all the terrestrial vertebrate life of the Mesozoic is quite incomplete therefore it is difficult to trace evolutionary links between different types of animals. The task of the Bristol University team is unquestionably helping to start the debate, but devoid of reviewed the particular paper we cannot really comment any further. It could be interesting to find out how the evolution of non-avian dinosaurs, the birds has been assessed in this study. Hardly any is famous about the evolution of birds, nevertheless they do seem to possess diversified and developed new species very quickly through 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 through the Late Triassic, the world was just recovering from the Permian mass extinction (an event that saw an estimated 57% of all marine families and 70% of all terrestrial vertebrate genera becoming extinct). Life on Earth slowly began to recover and those types of organisms left begun to diversify to fill those environmental niches that were empty and those soon to be left empty by the “dead clades walking” like the last of the Lystrosaurs. It absolutely was after the Permian mass extinction event that a number of groups of vertebrates got a chance to diversify, including our personal mammalian ancestors.