Diverging Dinosaurs Some time before the beginning of all the Cretaceous
Study Shows Dinosaurs Diverged Long Ahead of the End of the Cretaceous
There’s a popularist view that the dinosaurs were at their most diverse and at the peak of their evolution with regards to the amount of 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 refers to 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 the amount of species of dinosaur was declining in this part of the world towards the end of the Cretaceous. Approximately ten different genera are known from the youngest Cretaceous sediments, whilst older strata using 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 needless to say Tyrannosaurus rex. Before, these gigantic representatives of their dinosaur families, (Triceratops, Ankylosaurus and T. rex are only about the largest form of dinosaur from these three families), were considered to indicate that dinosaurs just got too big and lumbering to survive and this is the reason they went extinct. Scientists now know that the causes for the end Cretaceous mass extinction event, the extinction not only of the dinosaurs but also the Ammonites, Plesiosaurs, Mosasaurs, Pterosaurs and an entire host of other plants and animals, were complex and probably involved numerous 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 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 another evolutionary surge in the Mid Jurassic (170 -160 million years ago). The scientists studied a big 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 through the Cretaceous. The established view is that although dinosaurs as friends diversified throughout their entire existence, using periods, the evolution of new forms was speeded up. One period was the early to mid Cretaceous which saw the emergence of a larger variety 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 ago, there seemingly have been a huge 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 kinds 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 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 that were to survive before the 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 believe that during the early to middle Jurassic there have been only four main categories 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 extremely incomplete therefore it is difficult to trace evolutionary links between various kinds of animals. The job of the Bristol University team is certainly helping to open the debate, but devoid of reviewed the particular 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 known in regards to the evolution of birds, but they do seem to have diversified and developed new species rapidly through 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 through the Late Triassic, the planet was just recovering from the Permian mass extinction (an event that saw an estimated 57% of marine families and 70% of terrestrial vertebrate genera becoming extinct). Life on Earth slowly began to recoup and those forms of organisms left begun to diversify to fill those environmental niches that were empty and those soon to be left empty by the “dead clades walking” such as the last of the Lystrosaurs. It was following the Permian mass extinction event that numerous categories of vertebrates got a chance to diversify, including our own mammalian ancestors.
Study Shows Dinosaurs Diverged Long Ahead of the End of the Cretaceous There’s a popularist view that the dinosaurs were at their most diverse and at the peak of their evolution with regards to the amount of new species evolving; at the very end of the Cretaceous. The Chicxulub impact then wiped out the fantastic…