A very short history of Dinosaurs.

Evolutionary relationships of dinosaurs. From Benton 2018.

On 20 February 1824, William Buckland published the first report of a large carnivore animal: the Megalosaurus. The description was based on specimens in the Ashmolean Museum, in the collection of Gideon Algernon Mantell of Lewes in Sussex, and a sacrum donated by Henry Warburton (1784–1858). One year later, the Iguanodon entered in the books of History followed by the description of Hylaeosaurus in 1833. After examined the anatomy of these three genera, Richard Owen erected the clade Dinosauria in 1842.

Dinosaurs likely originated in the Early to Middle Triassic. The closest evolutionary relatives of dinosaurs include flying pterosaurs and herbivorous silesaurids. Early ecological divergences in dinosaur evolution are signaled by disparity in dental morphology, which indicates carnivory in early theropods, herbivory in ornithischians, and omnivory in sauropodomorph (subsequently sauropodomorphs underwent a transition to herbivory).

Eoraptor lunensis, outcropping from the soil. Valle de la Luna (Moon Valley), Parque Provincial Ischigualasto, Provincia de San Juan, Argentina.

The oldest dinosaurs remains are from the late Carnian (230 Ma) of the lower Ischigualasto Formation in northwestern Argentina. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation. Two further early dinosaur-bearing formations, are the lower (and upper) Maleri Formation of India and the Pebbly Arkose Formation of Zimbabwe. These skeletal records of early dinosaurs document a time when they were not numerically abundant, and they were still of modest size.

During the Late Triassic period numerous extinctions, diversifications and faunal radiations changed the ecosystems dynamics throughout the world. Nevertheless, dinosaurs exhibited high rates of survival. According to the competitive model, the success of dinosaurs was explained in terms of their upright posture, predatory skills, or warm-bloodedness. In the opportunistic model, dinosaurs emerged in the late Carnian or early Norian, and then diversified explosively. The current model contains some aspects of both the classic competition model and the opportunistic model. In this model, the crurotarsan-dominated faunas were replaced by a gradual process probably accelerated by the ecological perturbation of the CPE (Carnian Pluvial Episode).

Ingentia prima outcropping from the soil.

In the Jurassic and Cretaceous dinosaurs achieved enormous disparity. Sauropodomorphs achieved a worldwide distribution and become more graviportal and increased their body size. Gigantism in this group has been proposed as the result of a complex interplay of anatomical, physiological and reproductive intrinsic traits. For example, the upright position of the limbs has been highlighted as a major feature of the sauropodomorph bauplan considered an adaptation to gigantism. However, the discovery of Ingentia prima, from the Late Triassic of Argentina, indicates that this feature was not strictly necessary for the acquisition of gigantic body size.

Ornithischian were primitively bipedal, but reverted to quadrupedality on at least three occasions: in Ceratopsia, Thyreophora and Hadrosauriformes. The presence of early armored dinosaurs (thyreophorans) in North America, Asia, and Europe, but their absent from the southern African record, suggests some degree of provinciality in early ornithischian faunas.

Archaeopteryx lithographica, specimen displayed at the Museum für Naturkunde in Berlin. (From Wikimedia Commons)

Theropod dinosaurs also increased their diversity and exhibit a greater range of morphological disparity. The group underwent multiple parallel increases in brain size. The volumetric expansion of the avian endocranium began relatively early in theropod evolution. For instance, the endocranium of Archaeopteryx lithographica is volumetrically intermediate between those of more basal theropods and crown birds. The digital brain cast of Archaeopteryx also present an indentation that could be from the wulst, a neurological structure present in living birds used in information processing and motor control with two primary inputs: somatosensory and visual. The extensive skeletal pneumaticity in theropods such as Majungasaurus demonstrates that a complex air-sac system and birdlike respiration evolved in birds’ theropod ancestors. Anatomical features like aspects of egg shape, ornamentation, microstructure, and porosity of living birds trace their origin to the maniraptoran theropods, such as oviraptorosaurs and troodontids. In addition, some preserving brooding postures, are known for four oviraptorosaurs, two troodontids, a dromaeosaur, and one basal bird providing clear evidence for parental care of eggs.

Nonavian dinosaurs disappeared more or less abruptly at the end of the Cretaceous (66 mya). Birds, the only living dinosaurs, with more than 10,500 living species are the most species-rich class of tetrapod vertebrates.

 

References:

Benson, R. B. J. (2018). Dinosaur Macroevolution and Macroecology. Annual Review of Ecology, Evolution, and Systematics, 49(1).  doi:10.1146/annurev-ecolsys-110617-062231

Michael J. Benton et al. The Carnian Pluvial Episode and the origin of dinosaurs, Journal of the Geological Society (2018). DOI: 10.1144/jgs2018-049

Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

 

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The real Jurassic World.

Global paleogeographic reconstruction of the Earth in the late Jurassic period 150 Ma. From Wikimedia Commons

Global paleogeographic reconstruction of the Earth in the late Jurassic period 150 Ma. Credit: Dr Ron Blakey

The transition from Triassic to Early Jurassic is marked by a major biotic crisis in the marine and terrestrial realms. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In land, most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. During the Jurassic (201-145 mya) the breakup of the supercontinent Pangaea continued and accelerated with the opening of the North Atlantic by the rifting of Africa and North America, giving rise to the supercontinents of Laurasia and Gondwana. The sea level rise flooded continental areas around Pangaea, forming huge epicontinental seas, especially in northern Africa and eastern Laurasia (modern China). The world was predominantly warm with at least four times the present level of atmospheric CO2. The period is also characterized by the explosive adaptive radiation of dinosaurs and the diversification of the cycads.

The Early Jurassic climate was characterized by a global warming, with average summer temperatures that exceeded  35°C in low-latitude regions of western Pangaea where eolian sandstones testify to the presence of vast deserts (Holz, 2015). The early Toarcian Oceanic Anoxic Event  (T-OAE; ∼183 mya) is considered as one of the most severe of the Mesozoic era. It’s associated with a major negative carbon isotope excursion, mass extinction, marine transgression and global warming (Huang, 2014, Ullmann et al., 2014). The T-OAE has been extensively studied in the past three decades although there is no consensus about the causes or triggering mechanisms behind this event.

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

After the extinction of many carnivorous crurotarsan lineages (phytosaurs, ornithosuchids, rauisuchians) at the Triassic–Jurassic boundary, theropod dinosaurs increased their diversity and exhibit a greater range of morphological disparity. Sauropodomorphs also achieved a worldwide distribution and become more graviportal and increased their body size. The presence of early armored dinosaurs (thyreophorans) in North America, Asia, and Europe, but their absent from the southern African record, suggests some degree of provinciality in early ornithischian faunas (Brusatte et al., 2010).

By the Mid-Jurassic, Gondwana started to break up in different blocks: Antarctica, Madagascar, India, and Australia in the east, and Africa and South America in the west, with relatively warm sea-surface conditions (26–30◦C) from Mid-Jurassic (∼160Ma) to the Early Cretaceous (∼115Ma) in the Southern Ocean.  There was a drastic climatic decline during the Late Callovian. This decline in temperature lasted about 2.6My and is know as the “Callovian Ice Age”. It has been interpreted in terms of an inverse greenhouse effect, triggered by drawdown of CO2 consequent upon excess carbón burial (Dromart et al, 2003).  The Puchezh-Katunki impact crater in Russia is prior to the Callovian extinction event and is not considered as a factor for this biotic extinction event.

During the Late Jurassic, North America completed its separation from Gondwana, and Gondwana was split into a northern and southern continent by the rift system opening the proto-Indian Ocean. The geological and geochemical record suggest that low-latitude environments were arid and tropical ever-wet conditions were absent. Maximum plant diversity was concentrated at midlatitudes, whith forests dominated by a mixture of conifers, cycadophytes, pteridosperms, ferns, and sphenophytes.

References:

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and Norell, M. A. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews, 101, 68-100

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Jenkyns, H. C. (2010), Geochemistry of oceanic anoxic events, Geochem. Geophys. Geosyst., 11, Q03004, doi: 10.1029/2009GC002788.

Sellwood, B.W. & Valdes, P.J. 2006. Mesozoic climates: General circulation models and the rock Record. Sedimentary Geology 190:269–287.

Corwin Sullivan et al. 2014. The vertebrates of the Jurassic Daohugou Biota of northeastern China. Journal of Vertebrate Paleontology, vol. 34, no. 2; doi: 10.1080/02724634.2013.787316