Amazing stuff! Once they found the right place, they settled down! Just kidding!
"... When the theory of plate tectonics became widely accepted in the 1960s, an answer seemed within reach. All of the continents were once united as the supercontinent Pangea, which slowly broke apart during the time of the dinosaurs, starting to split around 200 million years ago. Scientists wondered whether different populations of flightless palaeognaths could have just drifted apart from each other along with the continents they lived on.
However, this once-popular theory has since been discredited for two reasons. One is that the flying tinamous are genetically closer to some flightless palaeognaths than they are to others. This means that ostriches, rheas, emus, cassowaries and kiwi did not share a flightless common ancestor. Instead, in a remarkable case of parallel evolution, they all became flightless separately from each other. ..."
From the 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."
Quantitative analysis of stem-palaeognath flight capabilities sheds light on ratite dispersal and flight loss (open access)
A cassowary
Figure 1. Morphospace of the first three axes of sternum shape variation. Convex hulls represent the approximate area of morphospace occupied by each flight style.
Figure 2. Time-calibrated phylogenetic relationships of taxa in our geometric morphometric analysis highlighting the top 10 most similar sterna to Lithornis promiscuus by Euclidean distance.
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