Rapid Pliocene adaptive radiation of modern kangaroos

Abstract

Differentiating between ancient and younger, more rapidly evolved clades is important for determining paleoenvironmental drivers of diversification. Australia possesses many aridity-adapted lineages, the origins of which have been closely linked to late Miocene continental aridification. Using dental macrowear and molar crown height measurements, spanning the past 25 million years, we show that the most iconic Australian terrestrial mammals, “true” kangaroos (Macropodini), adaptively radiated in response to mid-Pliocene grassland expansion rather than Miocene aridity. In contrast, low-crowned, short-faced kangaroos radiated into predominantly browsing niches as the late Cenozoic became more arid, contradicting the view that this was an interval of global browser decline. Our results implicate warm-to-cool climatic oscillations as a trigger for adaptive radiation and refute arguments attributing Pleistocene megafaunal extinction to aridity-forced dietary change.

Incorporating uncertainty is essential to macroecological inferences: Grass, grit, and the evolution of kangaroos

“…Divergence analyses using fossil tips and all five node priors result in date estimates 270 which are at odds with recent molecular results (Dodt et al 2017;Nilsson et al 2018;Couzens and Prideaux 2018;Celik et al 2019). This is primarily driven by the hard minimum prior age of Ganguroo bilamina which limits the divergence of the Lagostrophinae and Macropodinae to 17.79 MYA (Neville's Garden Site (Woodhead et al 2016)), and to a lesser extent, the minimum prior age of Ngamaroo archeri (Fig.S1-S2).…”

“…The timing of the radiation of modern kangaroos remains a topic of debate. Most recently it has been suggested that kangaroos speciated rapidly in response to the expansion of C 4 grasses in the Pliocene (Nilsson et al 2018;Couzens and Prideaux 2018). This hypothesis conflicts with a number of molecular and morphological dating studies (Phillips et al 2013; package (Gavryushkina et al 2014).…”

“…Because of this, the convergent evolution of high-crowned teeth across many groups has traditionally been associated with the global expansion of grasslands in the Miocene (Badgley et al 2008). This idea has also been applied to macropods, in which high-crowned molars have been suggested to have developed alongside the expansion of C 4 grasses and a transition to grazing in the Pliocene (Couzens and Prideaux 2018). However, the relationship between increasing crown height and endogenous (fiber, silica) dietary abrasives has more recently been disputed.…”

“…For example, the genus Macropus comprises 13 living species, but we are aware of at least as many described extinct taxa. To account for this disparity between the sampled and known diversity of the Macropodinae, I also ran analyses incorporating all fossil macropodin taxa included in 155 the trait data of Couzens and Prideaux (2018). These 38 taxa (Table 2) were incorporated as tips by including them in all molecular and morphological alignment files, and scored as missing data for all characters.…”

Increased diversification rates are coupled with higher rates of climate space exploration in Australian Acacia (Caesalpinioideae)

“…Macroevolutionary patterns have been linked to historical trends in global and regional climate in many Australian lineages, including elevated speciation in arid‐zone pygopodoid geckos (Brennan & Oliver, ), macropods (Couzens & Prideaux, ), cockroaches (Beasley‐Hall et al , ), and cicadas (Owen et al , ). In plants, the eucalypts provide evidence that climate and historical events are important in explaining species distribution and turnover at the continental scale (Ladiges et al , ; Bui et al , ), and Hakea has expanded coincident with a transition to more open, drought and fire‐prone habitats promoted by aridification (Lamont et al , ; Cardillo et al , ).…”