when we think about the Mesozoic and the world the dinosaurs lived in we often think about warm elevated temperatures of a greenhouse world a world that has very little if any ice at the poles and as we saw in the paleogeography segment earlier this semester we can track the shifting climate zones using geological Clues like the distribution of coal and evaporites and tillites and glacial drop stones and these Clues point to a rather warm ice-free World from most of the Mesozoic we also soften the chemistry of fossils preserved in Ocean sediments that the oceans were generally warmer in the Mesozoic than they were in the older Paleozoic and in the younger cenozoic we live in today although the Mesozoic was overall warmer there were some times that were cooler than others such as in the early Jurassic and spanning the Jurassic Cretaceous boundary we saw our first dinosaur fossils and Triassic rocks from South America deposited during a Triassic Hot House interval but if we look at a reconstruction of the climate zones and think about where that early dinosaur site would have been during the Triassic we see that they would have lived in temperate forests and not in the hottest tropical regions each of these plots is a Paleo climate map for a different time interval the Mesozoic the blues are tropical regions and the greens are temperate grasslands and forests and the reds are deserts and the Deep green represents a cooler Boreal climate zone looking at the distribution of dinosaur fines dated to the lake Triassic folks have noticed that many of the fossils are restricted to places outside of the tropics and primarily in the Region's reconstructed as temperate zones while both herbivorous and carnivorous dinosaurs are found in temperate regions the few dinosaur finds in the tropics are only small carnivores and sometimes these fines are based on Footprints and trackways alone and no body fossils are preserved at all this is not due to a lack of fossil preservation though because we see a higher diversity of non-dinosaurs and near relatives in tropical regions the larger beverage dinosaurs like prosauropods at the time were simply not there and were instead living at mid-latitudes somewhere between 24 and 60 degrees in both hemispheres so perhaps it was so warm that the most mild climates were nearer to the poles than they are today and most dinosaur species simply did not live in the two Hot Tropics despite all this warmth new sedimentological evidence from the high Northern latitudes a Paleo latitude of about 71 degrees north suggests that perhaps Winters were cooler than we might have thought we discussed ice Raptor debris and drop stones in Marine sediments as a way to support the presence of glaciers ice rapid debris can also be deposited in lakes and is recognizable by the particular bimodal distribution of grain sizes we see in this figure the authors examined the grain size distributions of sediments from lakes that were approximately 202 million years old and compared them to Modern Lake basins and isolated Seas the grain sizes they see 202 million years ago in this Lake are quite similar to what we see in these modern analog environments suggesting that seasonal ice also influenced this location which is reconstructed as a boreal Zone in the paleoclimate map we know from Modern settings that the ice wrapped debris or ird is created when seasonal ice freezes to the Shoreline picking up coarse grains in its bottom which is then deposited when the ice begins to melt and break up rafting debris out to where the finer grained Lake sediment is deposited so perhaps like many temperate climates today think places like the Upper Midwest and the Northeast United States some regions of the globe were seasonally cold with freezing temperatures for part of the year this would mean that dinosaurs would have experienced and lived in these conditions and would have to have the physiology necessary to allow for their survival during cold Winters conditions were likely even a bit colder in the early Jurassic when geochemical data like Delta o18 measured from the shells of cephalopods suggests a brief interval of Ice House conditions temperatures during this interval were probably cool enough for Continental ice to form at least seasonally at the poles and for Highland regions to form ice on high mountain peaks at low latitudes when we were learning about archosaurs we mentioned two groups the Ave metatarsalia which includes dinosaurs and pterosaurs and the kuritarsi which includes relatives of today's crocodiles at the end Triassic there was a major Extinction event that diminished the diversity of the kuritarsi but left the avettarsalia relatively unscathed this was a massive turnover event in which the dominant archosaurus on the planet changed we also know from looking at the distribution of fossils that the kuritarsi were the most dominant in the low latitudes near the equator and the dinosaurs did better at middle to high latitudes other tetrapods living in Middle to high latitudes also preferentially survive this Extinction event whereas extinctions were concentrated in taxa that were restricted to the tropics this pattern of Extinction selectivity were organisms in the tropics were harder hit suggest that the extinction was related to a major Cooling this figure on the right shows that the concentration of CO2 in the atmosphere was much higher than it is today and was probably greater than 2000 PPM this likely explains the overall climate warmth relative to the modern world the atmospheric concentration of CO2 can be estimated using the chemistry of soil carbonates or paleosols if CO2 levels were that high today we'd expect to have much warmer temperatures and Ice free poles but in the early Jurassic cold interval we clearly see evidence for ice in the sedimentary deposits and for cooler temperatures in the oxygen isotopes although a minor cooling event in the latest Triassic is related to a decrease in CO2 the early Jurassic has quite high CO2 a rise associated with Camp volcanism however these volcanic events also introduced a huge amount of sulfur aerosols into the atmosphere these aerosols interfere with incoming solar radiation causing an overall cooling effect on the planet that counteracted the effect of high CO2 during this cooler time in the early Jurassic basal sore potomorphs migrated South appearing in North American lower latitudes for the first time consistent with a shift cooler early Jurassic Global climates if we look more broadly at the tetrapods living before and after the entras extinction we also see some patterns in the traits of the winners and losers of this Extinction not only did the Ave meta tarsalia suffer less Extinction the kuritarsi which are labeled on the phylogenes of pseudosuccio sometimes we just don't use the same name but the mammals were also less affected by this Extinction event both these groups the mammals and the Ave metatarsalia have some form of insulation that allows them to conserve heat in cool times in mammals this was of course fur and in some dinosaurs this insulation was Fluffy Proto feathers but groups that only had scales and were large bodied were a clear disadvantage during this Extinction event again pointing to global cooling as a driver of the extinction by the late Jurassic the icy regions were simply cool temperate and tropical seasonal environments were narrowly restricted to the equator so clearly the Mesozoic was not all warm wet Tropics even if it was on average warmer than today because climates were cool for much of the time following the n-triosi extinction the dinosaurs maintained their competitive advantage over the kuritarsi and diversified into new ecological roles as they Rose to ecological dominance among the arcosource during this time in the cooler late Jurassic we see that temperature was not the primary environmental Factor driving differences in some dinosaur faunas instead aridity and the amount of precipitation in a region received may have had a stronger impact large browsing dinosaurs like sauropods were able to live in more arid conditions whereas more moist regions with denser vegetation supported a higher diversity of dinosaur communities the distribution of dinosaurs and their success in cold intervals that drove Extinction other diapses suggests that they had some adaptations that gave them an advantage over other groups one hypothesis is that the dinosaurs had a bit more insulation than other diopsides and perhaps they had a physiological ability to control their internal temperature that allowed them to live in cooler conditions as well in the next few weeks we'll be talking about aspects of dinosaur physiology and as we do keep in mind how the biogeography of dinosaurs and their ability to avoid Extinction and instead of diversify during cold intervals might lend support to some of these hypotheses and refute other hypotheses about how dinosaurs functioned and behaved