Biology subjects

Couzens, A.

Publications and source records attributed to Couzens, A..

3 recordsLinked to original sources

bioRxiv2026

Contingency Inverts Mammalian Herbivore Evolution in Australia

The rise of Neogene herbivores with high-crowned (hypsodont) molar teeth has been viewed as a mostly predictable response to abrasive grazing diets. Using kangaroos, an isolated marsupial radiation, we show that the ancestral vertical slicing function of grazing kangaroo molars prompted heavy investment from the late Miocene in thickened enamel, rather than hypsodonty. Grazing kangaroo enamel thickness overlaps some robust hominins, evincing an eclectic, thick-enamelled grazer guild. The success of vertically-chewing marsupials contrasts with their placental counterparts, which were overwhelmingly replaced by transversely-chewing ungulates. This inversion is explained by the pre-grassland extinction of most transversely-chewing marsupials, and the crucial advent of thick enamel. These results challenge the determinism of the browser-grazer transition, and implicate extinction, and ensuing innovation, as causes of unpredictability in evolution.

paleontology↗

bioRxiv2019

PREDICTING EVOLUTIONARY TRANSITIONS IN TOOTH COMPLEXITY WITH A MORPHOGENETIC MODEL

The extent to which evolutionary transitions are shaped by developmental bias remains poorly understood. Classically, morphological variation is assumed to be abundant and continuous, but if morphogenesis biases how traits vary than evolutionary transitions might follow somewhat predictable steps. Compared to other anatomical structures, teeth have an exceptional fossil record which documents striking evolutionary trajectories toward complexity. Using computer simulations of tooth morphogenesis, we examined how varying developmental parameters influenced transitions from morphologically simple to complex teeth. We find that as tooth complexity increases, development tends to generate progressively more discontinuous variation which could make the fine-tuning of dietary adaptation difficult. Transitions from simple to complex teeth required an early shift from mesiodistal to lateral cusp patterning which is congruent with patterns of dental complexification in early mammals. We infer that the contributions of primary enamel knot cells to secondary enamel knots which are responsible for patterning lateral cusps may have been an important developmental innovation in tribosphenic mammals. Our results provide evidence that development can bias evolutionary transitions and highlights how morphogenetic modelling can play an important role in building more realistic models of morphological character evolution.

evolutionary biology↗

bioRxiv2018

Rapid Pliocene Diversification of Modern Kangaroos

AbstractDifferentiating between ancient and rapidly-evolved clades is critical for understanding impacts of environmental change on biodiversity. Australia possesses many aridity-adapted lineages, the origins of which have been linked by molecular evidence to late Miocene drying. Using dental macrowear and molar crown-height measurements spanning the past 25 million years, we show that the most iconic of Australias terrestrial mammals, true kangaroos and wallabies (Macropodini), diversified in response to Pliocene grassland emergence. In contrast, low-crowned short-faced kangaroos radiated into browsing niches as the late Cenozoic became more arid, contradicting the view that this was a period of global decline among browsers. Our results link warm intervals with bursts of diversification and undermine arguments attributing Pleistocene megafaunal extinction to aridity-forced dietary change.

paleontology↗