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 their evolution when it comes to the amount of new species evolving; at ab muscles end of the Cretaceous. The Chicxulub impact then wiped out the truly amazing dinosaur dynasty leaving the planet 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 the amount of 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 using this area show proof additional different dinosaur types.
Hell Creek Formation Data
Certainly some of the greatest known dinosaurs date from ab muscles 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 of course Tyrannosaurus rex. In the past, these gigantic representatives of their dinosaur families, (Triceratops, Ankylosaurus and T. rex are only about the greatest type of dinosaur from these three families), were thought to indicate that dinosaurs just got too large and lumbering to survive and this is why they went extinct. Scientists now understand that the reasons for the end Cretaceous mass extinction event, the extinction not just 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 task to map dinosaur evolution and to highlight the key 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 suggests that the dinosaurs as a group 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 portion 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 of 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 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 larger 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 back, there appears to have been a massive surge of increased terrestrial biodiversity. Now 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 during this period to a far more peripheral role. This new study suggests that by the full 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 think that during early to middle Jurassic there have been only four main groups 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 the terrestrial vertebrate life of the Mesozoic is quite incomplete so it is difficult to trace evolutionary links between several types of animals. The job of the Bristol University team is certainly helping to start the debate, but not having reviewed the actual paper we cannot really comment any further. It could be interesting to discover how the evolution of non-avian dinosaurs, the birds has been assessed in this study. Almost no is famous in regards to the evolution of birds, however they do seem to have diversified and developed new species very 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 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 kinds of organisms left started to diversify to fill those environmental niches that were empty and those soon to be left empty by the “dead clades walking” like the last of the Lystrosaurs. It had been following the Permian mass extinction event that several groups of vertebrates got a chance to diversify, including our personal mammalian ancestors.