進化学：卵の殻の化石がエレファントバードの知られざる系統を探り出す

New insights into extinct elephant birds from Madagascar, gained from DNA analysis of fossil eggshells that are over 1,000 years old, are reported in a Nature Communications paper. The findings improve our understanding of elephant bird evolution and distribution on the island, and suggests that there may have been a previously unknown lineage of the bird.

The elephant bird was a large, flightless bird that went extinct around 1,000 years ago when humans arrived in Madagascar. The limited bones available suggest that there were four species of elephant bird, but the evolutionary history of this group remains unclear. The analysis of ancient DNA preserved in eggshells is known to be a promising source of information when skeletal fossils are limited. For example, in previous research, such analyses have supported that the elephant and kiwi birds were related.

Alicia Grealy and colleagues analysed 960 elephant bird eggshell fragments found at 291 locations across Madagascar. The eggshells were between 6,190–1,290 years old, consistent with when these birds lived. By measuring the thickness of the eggshells, the authors estimated that the eggs weighed between 0.86–10.47kg, and the size of the birds that laid them ranged between 41–1,000kg. DNA analysis showed that elephant birds in southern Madagascar had low genetic diversity, with fewer species than estimated from skeletal fossils. However, the authors suggest the possibility of a previously unknown lineage of elephant bird in northern Madagascar, of which no skeletal remains have yet been found.

The findings demonstrate how eggshells can preserve important information, and highlights the complexity of the evolution of the elephant bird.