Reconstructing the Evolving PaleoEcology of Mesozoic Gondwana

Gondwanan Mesozoic biotas and bioevents

Authors:

McLoughlin et al

Abstract:

This special issue draws together presentations and related studies arising from both the symposium on “Mesozoic bioevents and Gondwanan biotas” at the 34th International Geological Congress in Brisbane, 2012, and the “Southern Hemisphere floras: unique insights into the biology and ecology of Southern Hemisphere ecosystems” meeting of the joint 13th International Palynological Congress and 9th Palaeobotanical Conference held in Tokyo, 2012. The theme also builds upon recent specialist compilations of similar works on Mesozoic biotas from the Northern and Southern hemispheres (Vajda and Turner, 2009; McLoughlin and Kear, 2010), and emphasizes the continuing high level of interest in events and processes that shaped the world’s faunas and floras between two of the greatest mass extinctions in Earth’s history.

The Mesozoic (251–66 Ma) is arguably one of the most spectacular intervals of biotic evolution in the Phanerozoic. The era began in the depths of Earth's most severe biotic crisis – the end-Permian extinction event, which was followed by prolonged and climatically harsh hothouse conditions of the Early Triassic (Retallack, 2013; Metcalfe et al., 2013). New radiometric data are now providing a precise means of calibrating the individual stages of decline and recovery associated with this mass extinction event (Metcalfe et al. in press). The slow recuperation of biotic diversity through the Middle and Late Triassic saw the rise of two animal groups that would compete for dominance of the terrestrial faunas for the remainder of the Phanerozoic –dinosaurs and mammals. Further mass extinctions and marine anoxia events at the end of the Triassic and in the Toarcian punctuated the evolution of life through the mid-Mesozoic (Hesselbo et al., 2002; Huang and Hesselbo, 2014). The Jurassic was also marked by episodic asteroid impacts, regionally intensive volcanism and the early stages of continental rifting (Vajda and Wigforss-Lange, 2009). Nevertheless, the mild, equable climates and broad connections between landmasses in the Jurassic saw the development of relatively cosmopolitan floras and faunas during the dinosaurian ‘heyday’ (Meyen, 1987; Novas, 2009). The subsequent, Late Jurassic–Cretaceous fragmentation of Pangaea and of Gondwana (Chatterjee et al., 2013; Torsvik and Cocks, 2013) saw progressive isolation of biotas, particularly in the Southern Hemisphere, and had a major influence on endemism and overall levels of biodiversity (Lloyd et al., 2008). Accompanying this fragmentation, new groups of vertebrates evolved to take advantage of niches arising through the constantly changing environmental pressures. These changes are evident not only on land, where new groups of dinosaurs (including birds), squamates, and mammals thrived, but also in the oceans where there were major radiations amongst coccolithophorids, dinoflagellates and centric diatoms, where modern lamniform sharks and teleosts rose to the fore, and gigantic mosasaurid lizards ultimately claimed dominance as the ocean’s apex predators (Cloudsley-Thompson, 2005).

Within the terrestrial flora, one insignificant and possibly aquatic group – the flowering plants – made their first appearance in the Early Cretaceous. These opportunistic colonizers possessed seeds protected in ovaries, and in many cases developed showy appendages to encourage a special relationship with insects as pollination vectors. During their rapid diversification and rise to dominance through the mid-Cretaceous, the flowering plants evolved a bewildering array of forms, from minute single-leafed floating plants to some of the world's tallest trees. By the end of the Cretaceous, these formerly obscure plants had claimed dominance of the vegetation and had transformed the face of the landscape (Friis et al., 2011). In turn, the new vegetation types, including closed damp forests, offered opportunities for other plant lineages, such as polypodialean ferns, to undergo evolutionary radiations of their own (Pryer et al., 2004).

The end of the Cretaceous saw another of Earth's great catastrophes – the impact of an asteroid in the Yucatan Peninsula region. This event witnessed the demise of the great (non-feathered) dinosaurs and radically altered life in both the seas and the terrestrial forests, thus bringing the final chapter of the Mesozoic to an abrupt close (Schulte et al., 2010).