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 these evolution when it comes to how many new species evolving; at the very 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 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 the main world towards the end of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata out of this area show evidence of many more different dinosaur types.
Hell Creek Formation Data
Certainly some of the finest known dinosaurs date from the very 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 of course Tyrannosaurus rex. Previously, these gigantic representatives of these dinosaur families, (Triceratops, Ankylosaurus and T. rex are only about the largest type of dinosaur from these three families), were thought to indicate that dinosaurs just got too big and lumbering to survive and for this reason they went extinct. Scientists now know that the reason why for the end Cretaceous mass extinction event, the extinction not only of the dinosaurs but additionally 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 present dinosaur fossil record it’s difficult to piece together a “dinosaur family tree” but a project to map dinosaur evolution and to highlight the main evolutionary shifts in Dinosauria has just been completed. The outcome with 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 friends 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 large percentage 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 during their entire existence, in certain periods, the evolution of new forms was speeded up. One particular period was early to mid Cretaceous which saw the emergence of a greater selection of Ornithischian dinosaurs – the rise of the Hadrosaurs, Ceratopsians and the Pachycephalosaurs, for example. These kinds of new dinosaur were evolving during an occasion when many life forms on Earth were diversifying. Dating from about 125 to 80 million years ago, 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 many types of mammals all evolved. It have been believed that the rapidly diversifying dinosaurs were part with this move towards greater biodiversity, the paper published by the Bristol team demotes dinosaur evolution during this period to a far more peripheral role. This new study shows that by the full time of the Cretaceous Terrestrial Revolution, all the main 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 a lot of the accepted thinking regarding dinosaur diversity. Most palaeontologists think that during 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 your terrestrial vertebrate life of the Mesozoic is extremely incomplete so it is difficult to trace evolutionary links between several types of animals. The job of the Bristol University team is obviously assisting to open up 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. Hardly any is famous concerning the evolution of birds, however they do seem to possess diversified and developed new species very quickly during the mid to late Cretaceous, a growth in speciation that was 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 planet 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 recuperate and those types 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 absolutely was after the Permian mass extinction event that several groups of vertebrates got a chance to diversify, including our personal mammalian ancestors.