Early in the Cretaceous, a revolution was afoot. Not in the continents or climate but in the organisms themselves. To modern eyes, Jurassic floras would have looked like an odd mix of familiar ferns and conifers with tropical relicts like cycads and ginkgos. Most conspicuous would be the absence of any flowering plants: there were no broadleaf trees, no fruits or nuts, and no social insects to pollinate them (Benton). As these new plants spread with the continents (Gurung et al), there came an array of new herbivores, each specially adapted for feeding on them: first iguanodonts and ankylosaurs, later ceratopsians and hadrosaurs. And radiating out alongside them was an unprecedented diversity of theropods, including, for the first time, a wide range of non-predators (Zanno and Mackovicky). Where pencil-toothed diplodocids and narrow-mouthed stegosaurs had previously scraped pine needles and cropped cycads, there were now therizinosaurs munching leaves, oviraptorosaurs crushing seeds, and alvarezsaurs digging up ants.
A Beginner’s Guide to Theropods, Part 4: TYRANNOSAURS!
The tyrannosaurids of the late Late Cretaceous were in a unique position. While earlier theropods had spread freely across the continents, tyrannosaurs lived in a world of fragmented continents and inland seaways. In Asia and western North America, where they were restricted, rising mountains and ebbing seaways formed a huge diversity of habitats, inhabited by a huge diversity of hadrosaurs and ceratopsians. For the first time in theropod history, there were not only no other giant apex predators, but the next biggest carnivorous dinosaurs - dromaeosaurs and troodontids - were over an order of magnitude smaller than they were (Holtz). This meant they were free to not only inherit the role of big-game hunters but, throughout their ontogeny, to maintain their ancestral roles as mid-sized, long-legged pursuers of small, fast animals.
A Beginner’s Guide to Theropods, Part 3: Giant Killers and Lesser Tyrants
By the beginning of the Late Jurassic, the global supercontinent had begun to break up. Seaways had split off the Northern and Southern landmasses, Asia was an island, and Europe was a Tethys-spanning archipelago. And all of it, from the Chinese Shaximiao to the Tanzanian Tendaguru, was ruled by allosauroids.
A Beginner’s Guide to Theropods, Part 2: Crests, Horns and Sails
The Early Jurassic World was a very uniform one. After the extremes of heat and drought that characterized the Triassic, a brief period of global cooling had reduced their therapsid and croc-line competitors to a handful of small mammals and lizardlike creatures and allowed the formerly restricted dinosaurs to spread throughout the world (Dunne et al). With the continents joined together, there were no major barriers to their dispersal, and so for the first time in dinosaur history, faunas the world over looked much the same (Holtz). Some faunal elements would have been familiar, if rare, parts of a Late Triassic ecosystem: long-tailed pterosaurs in the air, ichthyosaurs and plesiosaurs in the sea, bipedal prosauropods and small coelophysids on land. Others were more novel: elephant-sized sauropods, bipedal and armored ornithischians, and hunting them all, the first truly large (6m+), apex-predator theropods.
A Beginner’s Guide to Theropods, Part 1: Setting the Scene
Theropods (meat-eating dinosaurs) permeate popular culture. Anyone who’s ever had a passing interest in dinosaurs knows T. rex and Velociraptor. They fill books and movies; they’re perpetual objects of childhood fascination for their size, power, and ferocity. They’re windows into a world lost forever, that we can only ever look dimly into. And, in the form of birds, they’re still around today. In this series, we’ll be looking at the Mesozoic through the eyes of theropods, taking a walk up the tree of life and through time to track the ever-changing Mesozoic world and our changing knowledge of it. We’ll see the roles they played in their ecosystems and look at their evolution and diversity, along with a number of historically important discoveries that helped enrich our view of the Age of Reptiles and the predators that stalked through it.
A Tale of Two Extinctions: What the Triassic Tells us about Who Lives, Who Dies and Why it Matters Today
About 250 million years ago, the worst mass extinction Earth has ever seen left a gaping hole in ecosystems the world over. The organisms that filled that hole would come to define the world of the Mesozoic and leave fundamental changes in their ecology that still shape the living world today. On land, there was an explosive diversification of reptiles, including among its array of weird wonders the ancestors of modern lizards, turtles, and crocodiles. In the seas, an invasion of new predators and shell-crushers set off an arms race that produced the diverse community of fast-moving fish and heavily-armored invertebrates we see today. And under the feet of the new ruling reptiles, a last gasp of the Permian world would make one of the most significant morphological innovations in mammalian history (Benton et al, Dal Corso et al). Then, after only 50 million years, the world would be wiped clean again, ending a range of Triassic experiments and giving way to the more recognizable world of the Jurassic and Cretaceous. Among the beneficiaries of this new world were the dinosaurs, who started as a small part of an already crowded fauna, but, by the beginning of the Jurassic, had come to dominate a newly-emptied ecosystem, and, with very little serious competition, radiated out into the variety of forms that characterized the later Mesozoic (Dunne et al). But what caused this change, from thriving ecosystems full of evolutionary novelties to barren landscapes monopolized by a small handful of survivors, and what advantage did they have that allowed them to make it through and recolonize this barren world?