Blog

Moa than meets the eye

How extinct broken eggs in Auckland Museum's collections continue to inform science across the millennia

Blog by Matt Rayner, Senior Research Fellow, Land Vertebrates

The moa, Aotearoa’s famous giant birds were only recently lost due to hunting occurring after the arrival of the first New Zealanders within the past 500-600 years, sometime after 1250AD. The loss of this diverse community of 9 species of flightless giants is tragic, but the remains of moa has provided palaeobiologists with a wealth of material long after death, allowing us to understand the biology of these animals in more detail. 

After moa bones, eggshell fragments from broken moa eggs are the second most common remains of the extinct moa. The Land Vertebrates collections of Auckland Museum have thousands of moa eggshell fragments, often found at sand-dunes and caves, or rock-shelter sites both archaeological and natural in origin. It was previously believed that moa eggshell had little value for research, but technological breakthroughs of the past few decades are presenting new opportunities for understanding the biology of the moa and their relatives even through small pieces of broken eggs.

Emeritus Curator of Land Vertebrates Brian Gill began studying moa eggshell within the Auckland Museum collection in the 1990s. First, he investigated whole moa eggs, or those whole enough that total length could be measured. There are only 36 of these more-or-less whole eggs in museum collections globally, and three of them are at Auckland Museum. 

Many of the eggs are damaged, which actually provides a good opportunity to get even closer to the secrets contained within the eggs. By being able to access the inside of the egg, measurements can be taken to study the thickness of the shells. Generally, there is a positive correlation between shell thickness and egg length; meaning that larger eggs have thicker shells, and these were likely laid by larger species of moa. With the increasing power of DNA-based techniques, Ancient DNA researchers were able to swab DNA from eggshells and identify which species of Moa the fragments belonged to. The research showed that though species vary greatly in shell thickness, there is still a trend for the shells of increasingly larger species to have increasingly thicker shells on average.

Amazingly, sex-specific DNA recovered from lighter, more breakable, eggshells suggest that in these species it was the smaller and lighter males that did most of the incubating. Brian then looked at large groups of eggshell fragments collected from single localities, taking one thickness measurement from each of many fragments.

Looking at 6,000 eggshell fragments from 13 North Island sites, Brian found that the shells were 0.54–1.74 mm thick. South Island moa eggshell is up to 1.89 mm thick, which overlaps with the thickness of ostrich eggs.

There seemed to be a connection between the spread and relative abundance of shell thicknesses at a site and the presence or absence of moa species of different sizes, as determined by the moa bones recovered at the same site. Where there were moa bones, the eggs related to their species were not far away. For example, at Tokerau Beach, Northland, a sample of 1042 eggshell fragments collected over many years in the sand-dunes was about 80% "thin" shell (<1.1 mm thick) and 20% "thick" shell (≥1.1 mm thick). We already know from bones found in the area that there were smaller species of moa living in this part of the country, with larger moa being much rarer. This means that a sample of eggshell thicknesses at a site can stand in for what we might know from analyses of bones. Moa eggshell fragments have therefore a greater importance in helping us to understand the past distribution of moa species at natural sites, or their frequency in the diet of early Māori at archaeological sites.

From measurements of shell thickness to more complicated digital methods, researcher Seung Choi from Montana State University and his colleagues recently used moa eggshell from the Land Vertebrates collection as part of a global review of the evolution of eggshell in moa and their relatives. Around 50 birds on the planet today do not belong to the same group as the other 10,000 or so species in existence. Known as palaeognaths, from the Greek meaning old (palaiós) jaw (gnáthos) they are named for a characteristic, complex architecture of the bones in the bony palate -but that’s another story. The palaeognath group includes the largest and heaviest flightless birds in existence such as ostriches, rheas, emus, cassowaries and the extinct, and equally large, elephant birds of Madagascar and the moa of New Zealand. The smaller flightless kiwi and anomalously flighted tinamous of South America round out the group.

Choi and his colleagues were interested in the evolution of palaeognath eggs which differ from the rest of their avian brethren, being larger and with thicker shells. In the late 2000s new genetic analyses of the evolution of eggshell microstructure radically changed scientists’ understanding of the evolution of palaeognaths and how they related to each other. Seung Choi and his team analyzed eggshells of all major groups of palaeognaths including moa eggshell from the Auckland Museum collection.

They used an electron microscopic technique called electron backscatter diffraction (EBSD), which shows the biological building blocks of the eggshells. They concluded that among three previously recognized distinct types of palaeognath eggshells, one type from a common ancestor to palaeognaths and the remaining two were likely independently acquired by the respective groups.

Equipped with this knowledge, it may become possible for ornithologists to decipher how eggshells evolved in other lineages of flightless birds, and for palaeontologists to better interpret fossil bird and other dinosaur eggs where eggshell microstructure is often preserved in fossils.

The work of these researchers shows that although moa are long extinct, their remains, meticulously preserved and protected in museum collections, can still make contributions to scientific research addressing amazing questions about how animals lived in the past and their evolution across millennia.

 

Image LB4005 – This near complete egg of the Coastal Moa Euryapteryx curtus is over 800 years old and was collected from the sand dunes of Te Tai Tokerau, Northland in c. 1900, and presented to the Museum in 1931. It is one of three whole or nearly whole Moa eggs in the Auckland Museum collection and one of 36 in the world.