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 the evolution with regards to the amount of 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 the amount of species of dinosaur was declining in this part of the 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 additional 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 conclusion 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 only about the greatest 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 reasons 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 numerous 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 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 indicates that the dinosaurs as an organization 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 sizable percentage 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 throughout the Cretaceous. The established view is that although dinosaurs as an organization diversified in their entire existence, in certain periods, the evolution of new forms was speeded up. One particular period was the early to mid Cretaceous which saw the emergence of a better selection of Ornithischian dinosaurs – the rise of the Hadrosaurs, Ceratopsians and the Pachycephalosaurs, for example. These types 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 a huge 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 many types of mammals all evolved. It had been believed that the rapidly diversifying dinosaurs were part of the 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 full time of the Cretaceous Terrestrial Revolution, all the key dinosaur types which 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 genuinely believe that during the early to middle Jurassic there were only four main sets 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 all the terrestrial vertebrate life of the Mesozoic is extremely incomplete therefore it is difficult to trace evolutionary links between several types of animals. The work of the Bristol University team is certainly assisting to open the debate, but devoid of 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. Almost no 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 that was largely unchecked by the Cretaceous mass extinction event.
Late Triassic Diversification
Certainly, it is not surprising that the dinosaurs diversified throughout the Late Triassic, the planet 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 types 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” such as the last of the Lystrosaurs. It absolutely was following the Permian mass extinction event that numerous sets of vertebrates got a chance to diversify, including our personal mammalian ancestors.