#ratite

Southern Cassowary (Casuarius casuarius), father with chick, family Casuariidae, order Casuariiformes, northern QLD, Australia

Emus, Kalbarri WA.

Quantitative analysis of stem-palaeognath flight capabilities sheds light on ratite dispersal and flight loss

Klara Widrig, Fabio Alfieri, Pei-Chen Kuo, Helen James and Daniel J. Field

Abstract

Lithornithids are an assemblage of Palaeogene fossil birds thought to represent stem-group members of Palaeognathae. Among extant palaeognaths, which include flightless ratites such as ostriches, only tinamous can fly, though only in anaerobic bursts. Despite their limited dispersal capabilities, the phylogenetic interrelationships and geographic distributions of palaeognaths imply that their early relatives were capable of long-distance dispersal, although quantitative skeletal evidence has not been applied to this question. We investigate the flight capabilities and ecology of the Palaeogene lithornithid Lithornis promiscuus using a three-dimensional geometric morphometric dataset spanning the avian crown group. Our models reject the hypothesis that Lithornis would have relied on tinamou-like burst flight, and show that its sternum morphology is consistent with a range of aerobic, flapping flight styles—closely resembling those of many extant birds exhibiting pronounced dispersal capabilities. Our results are consistent with inferences from lithornithid wing shape, supporting the hypothesis that at least some stem palaeognaths were capable of long-distance flight, helping to clarify the origins of the transoceanic distributions of extant flightless ratites.

Read the paper:

[ID: an illustration of a fluffy brown kiwi bird facing to the left. The background is green with a pattern like the inside of a kiwi fruit. End.]

South Island giant moa (Dinornis robustus) - the largest species of moa, weighing over 200 kg and capable of reaching 3.6 metres above the ground. As their name suggests, they were native to the South Island of New Zealand, primarily inhabiting lowland areas.

Dinornis robustus were the second largest birds ever found, surpassed in weight and size only by their distant cousin, the elephant bird. They became extinct +-600 years ago, due to the arrival of humans, like other moas.

A major factor in the extinction of moas, especially the giant ones, was egg theft by humans. These birds could lay 1-2 eggs at a time, investing heavily in a small number of hatchlings.

This breeding strategy resulted in a population consisting mainly of long-lived, slow-breeding adults. Interestingly, despite their enormous size, moas eggs were very thin and fragile, only 1.4mm thick.

This may have led to another interesting adaptation, a major sexual dimorphism; males were much smaller than females, so much so that they were once thought to be different species.

Similar to some modern ratites, it's thought that males took care of eggs and young alone, the smaller size made it easier not to damage eggs, although they probably didn't sit on them but wrapped their necks around them.

They nested in holes in the ground or even in hollow tree trunks, probably reused for many years, suggesting that they lived in isolation rather than in a colony.

It is likely that females competed for males with the largest territories, perhaps physically or just by vocalisation. After hatching from the egg, baby moa were already able to walk and feed, probably not only on ferns and grasses but also on smaller animals.

Moas could reach sexual maturity in a few years, but probably social behaviour would prevent them from breeding until much later; much like the cassowary, which doesn't breed until it has its own territory.

Moas were once thought to be closely related to another New Zealand bird - the kiwi - but DNA sequencing has shown that their closest relative is actually the tinamou, a small flying ratite/paleognath from South America.

The two diverged about 60 million years ago, making the moa another example of a paleognath that lost its ability to fly independently after reaching a region without many other large herbivores and predators.