Fossils may reveal 20-million-year history of penguins in Australia

Stratigraphically calibrated phylogeny of Sphenisciformes correlated with tectonic movements and changing ocean circulation in the southern hemisphere showing how: (1) the Australian taxa are dispersed across the phylogeny temporally; (2) the Australian continent becomes progressively more isolated from other southern continents; and (3) a strengthened ACC (indicated by the black arrows) provides a new dispersal vector to Australia despite the presence of a strengthening Antarctic Polar Front (APF). The bottom palaeomaps are based on reconstructions in Lawver & Gahagan [9]. Penguin silhouettes show overall trend for decreasing body size in penguin evolution: Top, archaic giant stem penguin taxa; middle medium-sized stem penguin taxa; bottom, smaller crown penguin taxa (silhouette credit: Fir0002/Flagstaffotos (original photo), John E. McCormack, Michael G. Harvey, Brant C. Faircloth, Nicholas G. Crawford, Travis C. Glenn, Robb T. Brumfield & T. Michael Keesey, used under a CC BY 3.0 Attribution Unported Licence (http://creativecommons.org/licenses/by/3.0/))). Palaeoceanographic reconstructions after [9,72-74]. Palaeoceanographic abbreviations: EAC = East Australian Current, pEAC = palaeo-East Australian Current, pRG = palaeo-Ross Sea Gyre/Tasman Current, RG = Ross Sea Gyre. The relative strength of the ACC and APF is shown by thickening arrows and lines though time. Black arrow = cold currents, red arrows = warm currents.
Credit: Park et al.; CCAL

Multiple dispersals of penguins reached Australia after the continent split from Antarctica, including 'giant penguins' that may have lived there after they went extinct elsewhere, according to a study published April 26, 2016 in the open-access journal PLOS ONE by Travis Park from Monash University, Australia, and colleagues.

Penguin evolution in Australia following the continent's pre-historic split from Antarctica is not well-understood, but the fossil record shows that Australia was home to a number of penguin species.
Only the little penguin remains today, and pre-Quarternary evidence of this species and its ancestors in Australia is lacking. To update our understanding of Australian penguin evolutionary history, the authors of the study analysed recently collected penguin fossils and compared them to known species, including now-extinct 'giant penguins,' and presented a new phylogenetic tree in the context of biogeographical events on the Australian continent.

The authors propose that Australia's unique biogeographical history allowed for multiple dispersals of penguins to the continent during the Cenezoic or Age of Mammals, and that ancestors of the modern little penguins arrived in Australia with the help of a strengthened Antarctic Circumpolar Current.

While evolutionary trees are constructed as best estimates based on sometimes-limited fossil records, the authors suggest these findings shed new insights into the evolutionary trajectory of penguins in Australia.

Reference:
Travis Park, Erich M. G. Fitzgerald, Stephen J. Gallagher, Ellyn Tomkins, Tony Allan. New Miocene Fossils and the History of Penguins in Australia. PLOS ONE, 2016; 11 (4): e0153915 DOI: 10.1371/journal.pone.0153915

Note: The above post is reprinted from materials provided by PLOS.

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Fossil teeth suggest that seeds saved bird ancestors from extinction

Date:

April 21, 2016

Source:

Cell Press

Summary:

When the dinosaurs became extinct, plenty of small bird-like dinosaurs disappeared along with giants like Tyrannosaurus and Triceratops. Why only some of them survived to become modern-day birds remains a mystery. Now, researchers suggest that abrupt ecological changes following a meteor impact may have been more detrimental to carnivorous bird-like dinosaurs, and early modern birds with toothless beaks were able to survive on seeds when other food sources declined.

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A number of bird-like dinosaurs reconstructed in their environment in the Hell Creek Formation at the end of the Cretaceous. Middle ground and background: two different dromaeosaurid species hunting vertebrate prey (a lizard and a toothed bird). Foreground: hypothetical toothless bird closely related to the earliest modern birds. Credit: Danielle Dufault

 

When the dinosaurs became extinct, plenty of small bird-like dinosaurs disappeared along with giants like Tyrannosaurus and Triceratops. Why only some of them survived to become modern-day birds remains a mystery. Now, researchers reporting April 21 in Current Biology suggest that abrupt ecological changes following a meteor impact may have been more detrimental to carnivorous bird-like dinosaurs, and early modern birds with toothless beaks were able to survive on seeds when other food sources declined.

"The small bird-like dinosaurs in the Cretaceous, the maniraptoran dinosaurs, are not a well-understood group," says first author Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and PhD candidate at the University of Toronto. "They're some of the closest relatives to modern birds, and at the end of the Cretaceous, many went extinct, including the toothed birds--but modern crown-group birds managed to survive the extinction. The question is, why did that difference occur when these groups were so similar?"

The team of researchers, which also included David Evans of the Royal Ontario Museum and the University of Toronto and Caleb Brown of the Royal Tyrrell Museum of Paleontology, began by investigating whether the extinction at the end of the Cretaceous was an abrupt event or a progressive decline simply capped off by the meteor impact. The fossil record holds evidence to support both scenarios, depending on which dinosaurs are being examined.

Delving into the bird-like dinosaurs, Larson collected data describing 3,104 fossilized teeth from four different maniraptoran families. Some were already published, but much of the information came from Larson's own work at the microscope, cataloging the shape and size of each tooth.

Larson and his colleagues were looking for patterns of diversity in the teeth, which spanned 18 million years (up until the end of the Cretaceous). If the variation between teeth decreased over time, the team reasoned, this loss of diversity would indicate that the ecosystem was declining and may have paralleled a long-term species loss. If the teeth maintained their differences over time, however, that would indicate a rich and stable ecosystem over millions of years and suggest that these bird-like dinosaurs were abruptly killed off by an event at the end of the Cretaceous.

In the end, the tooth data favored the latter interpretation. "The maniraptoran dinosaurs maintained a very steady level of variation through the last 18 million years of the Cretaceous," says Larson. "They abruptly became extinct just at the boundary."

The team suspected that diet might have played a part in the survival of the lineage that produced today's birds, and they used dietary information and previously published group relationships from modern-day birds to infer what their ancestors might have eaten. Working backwards, Larson and his colleagues hypothesized that the last common ancestor of today's birds was a toothless seed eater with a beak.

Coupled with the tooth data indicating an abrupt Cretaceous extinction, the researchers suggest that a number of the lineages giving rise to today's birds were those able to survive on seeds after the meteor impact. The strike would have affected sun-dependent leaf and fruit production in plants, but hardy seeds could have been a food source until other options became available again.

"There were bird-like dinosaurs with teeth up until the end of the Cretaceous, where they all died off very abruptly," says Larson. "Some groups of beaked birds may have been able to survive the extinction event because they were able to eat seeds."

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Story Source:
The above post is reprinted from materials provided by Cell Press. Note: Materials may be edited for content and length.

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Journal Reference:

1. Larson et al. Dental disparity and ecological stability in bird-like dinosaurs prior to the end-Cretaceous mass extinction. Current Biology, 2016 DOI: 10.1016/j.cub.2016.03.039

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Cell Press. "Fossil teeth suggest that seeds saved bird ancestors from extinction." ScienceDaily. ScienceDaily, 21 April 2016. <www.sciencedaily.com/releases/2016/04/160421133639.htm>.