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 their evolution when it comes to how many new species evolving; at the end of the Cretaceous. The Chicxulub impact then wiped out the fantastic dinosaur dynasty leaving the planet for the mammals to exploit. The Chicxulub impact describes the asteroid impact event that generated the demise of the dinosaurs sixty-five million years ago. Fossil evidence does not 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 out of this area show proof of a lot more different dinosaur types.
Hell Creek Formation Data
Certainly some of the finest known dinosaurs date from the end of the Mesozoic. Animals wandering the Hell Creek area at the end 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 simply about the greatest type of dinosaur from these three families), were thought to indicate that dinosaurs just got too large and lumbering to survive and this is the reason they went extinct. Scientists now know that the reason why for the finish 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 several factors.
A Family Tree for the Dinosauria
Given the limitations of the prevailing dinosaur fossil record it is difficult to piece together a “dinosaur family tree” but a task to map dinosaur evolution and to highlight the key evolutionary shifts in Dinosauria has just been completed. The outcomes 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 indicates 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 large part 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 during the Cretaceous. The established view is that although dinosaurs as friends diversified in 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 better variety of Ornithischian dinosaurs – the rise of the Hadrosaurs, Ceratopsians and the Pachycephalosaurs, for example. These kinds of new dinosaur were evolving during a period when many life forms on Earth were diversifying. Dating from about 125 to 80 million years back, there seems to 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 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 indicates that by enough time of the Cretaceous Terrestrial Revolution, all the key 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 think that during the early to middle Jurassic there were only four main groups 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 all the terrestrial vertebrate life of the Mesozoic is extremely incomplete so it is difficult to trace evolutionary links between several types of animals. The work of the Bristol University team is obviously helping open up the debate, but devoid of 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. Hardly any is known about the evolution of birds, however they do seem to have diversified and developed new species quickly 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 is not surprising that the dinosaurs diversified during the Late Triassic, the planet was just coping with 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 recuperate and those kinds of organisms left begun to diversify to fill those environmental niches which were empty and those soon to be left empty by the “dead clades walking” such as the last of the Lystrosaurs. It was after the Permian mass extinction event that several groups of vertebrates got an opportunity to diversify, including our own mammalian ancestors.