Diverging Dinosaurs Some time before the beginning of your Cretaceous
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 entire 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 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 area of the world towards the finish of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata using 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 needless to say Tyrannosaurus rex. In the past, 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 considered to indicate that dinosaurs just got too large and lumbering to survive and this is the reason they went extinct. Scientists now understand that the reason why for the finish Cretaceous mass extinction event, the extinction not merely 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 existing dinosaur fossil record it is 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 outcomes 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 indicates that the dinosaurs as a group 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 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 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 in their entire existence, in certain periods, the evolution of new forms was speeded up. One such period was 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 kind of new dinosaur were evolving during a period when many life forms on Earth were diversifying. Dating from about 125 to 80 million years ago, there seemingly have been an enormous surge of increased terrestrial biodiversity. This time around 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 various types of mammals all evolved. It have been thought that the rapidly diversifying dinosaurs were part with this move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution in this period to a far more peripheral role. This new study indicates that by the time of the Cretaceous Terrestrial Revolution, all the key dinosaur types which 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 early 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 the terrestrial vertebrate life of the Mesozoic is quite incomplete so it is difficult to trace evolutionary links between several types of animals. The work of the Bristol University team is unquestionably assisting to start the debate, but not having reviewed the specific paper we cannot really comment any further. It would be interesting to find out 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 own diversified and developed new species 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 is not surprising that the dinosaurs diversified through the Late Triassic, the entire world was just coping 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 recoup 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” like 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.