Study Shows Dinosaurs Diverged Long Prior to 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 very end of the Cretaceous. The Chicxulub impact then wiped out the fantastic dinosaur dynasty leaving the entire world for the mammals to exploit. The Chicxulub impact describes 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 area 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 best known dinosaurs date from the very 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 the dinosaur families, (Triceratops, Ankylosaurus and T. rex are simply about the greatest kind of dinosaur from these three families), were considered to indicate that dinosaurs just got too large and lumbering to survive and this is why they went extinct. Scientists now know that the reasons for the finish Cretaceous mass extinction event, the extinction not only of the dinosaurs but additionally the Ammonites, Plesiosaurs, Mosasaurs, Pterosaurs and a whole 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 task to map dinosaur evolution and to highlight the key evolutionary shifts in Dinosauria has just been completed. The results of 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 an organization 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 part 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 of 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 an organization diversified during their entire existence, using periods, the evolution of new forms was speeded up. One particular period was the first 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 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 a massive surge of increased terrestrial biodiversity. This time 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 kinds of mammals all evolved. It have been believed that the rapidly diversifying dinosaurs were part of this move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution in this period to an even more peripheral role. This new study shows that by the time of the Cretaceous Terrestrial Revolution, all the key dinosaur types that have been 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 first to middle Jurassic there were only four main categories 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 very 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 could 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, however they do seem to own diversified and developed new species very 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’s not surprising that the dinosaurs diversified during the Late Triassic, the entire world was just dealing 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 recoup and those types of organisms left started to diversify to fill those environmental niches that have been 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 a number of categories of vertebrates got a chance to diversify, including our personal mammalian ancestors.