Kiwis and elephant birds may seem like an unlikely pair to be related. After all, kiwis are small, flightless birds that live in New Zealand today, while elephant birds were giant, flightless birds that lived in Madagascar until they went extinct within the last few thousand years. However, despite their differences in size and geography, kiwis and elephant birds do in fact share a common ancestor.
Both kiwis and elephant birds belong to an ancient group of birds called palaeognaths. The palaeognaths originated over 80 million years ago and were once widespread across the southern supercontinent Gondwana. As Gondwana broke up and the continents drifted apart, different lineages of palaeognaths became isolated and evolved independently in Australia, New Zealand, and Madagascar.
Kiwis and elephant birds both lost the ability to fly as they adapted to life on the ground without predators. However, in the absence of competition from mammals, elephant birds grew to enormous sizes, becoming the largest birds to ever live. Kiwis remained small, using their reduced size to maneuver through dense vegetation. Despite these adaptations, kiwis and elephant birds retain similarities in their DNA, bone structure, and other anatomical features that reveal their shared ancestry.
When did kiwis and elephant birds diverge?
Kiwis and elephant birds diverged over 50 million years ago as the ancient continent of Gondwana broke apart. At that time, the ancestors of both groups were small, flying birds. After New Zealand and Madagascar separated, the kiwi ancestors remained in New Zealand while the elephant bird ancestors ended up in Madagascar.
For tens of millions of years, these bird groups evolved independently on their respective islands without mammals to compete against. In New Zealand, kiwis lost the ability to fly and remained small, filling an ecological niche similar to small mammals. In Madagascar, elephant birds grew to gigantic sizes in the absence of mammalian competition, with some species weighing over 1,000 pounds.
Despite evolving for eons on opposite sides of the globe, molecular evidence confirms that kiwis and elephant birds are each other’s closest living relatives. Their divergence dates back to the Cretaceous period when today’s continents were still joined as Gondwana.
The breakup of Gondwana
The supercontinent Gondwana originally formed over 500 million years ago and included the landmasses that are now South America, Africa, Australia, Antarctica, the Arabian Peninsula, and the Indian subcontinent. By 160 million years ago in the Jurassic period, Gondwana started to break apart as tectonic plates drifted.
First, Africa and South America separated from the rest of Gondwana. Next, Australia and Antarctica split off around 100 million years ago. Finally, India began slowly migrating northward towards Eurasia. This continental drift explains how ancient bird groups like palaeognaths came to inhabit different landmasses.
Evidence that kiwis and elephant birds are related
Several key lines of evidence confirm that kiwis and elephant birds descend from a common ancestor despite their dramatic differences in size and habitat.
Molecular evidence
Analyses of DNA sequences have consistently placed kiwis and elephant birds together within the palaeognaths. In fact, genetic studies indicate that kiwis and elephant birds are each other’s closest living relatives. Their genetic divergence matches the timing of the breakup of Gondwana.
Anatomical evidence
Kiwis and elephant birds share distinctive anatomical features found only in palaeognaths, such as:
- Large palatine bones in the palate
- A perforated septum between the nostrils
- A small vomer bone
- Single-headed thigh muscles
- Large yolk sacs
These ancient anatomical traits support a close evolutionary relationship between kiwis and elephant birds.
Oological evidence
The structure of kiwi and elephant bird eggshells is almost identical. Their eggshells are exceptionally thick, which is a trait shared by all ratites (flightless birds). This provides additional oological evidence of their relationship.
| Feature | Kiwi eggshell | Elephant bird eggshell |
|---|---|---|
| Thickness | 2-3 mm | 2-3 mm |
| Texture | Porous | Porous |
| Color | White | White |
Key differences between kiwis and elephant birds
Despite evidence that kiwis and elephant birds share a close evolutionary relationship, they appear superficially quite different due to millions of years evolving in isolation. Some of the major differences between kiwis and elephant birds include:
Size
Kiwis range from 15-50 inches tall and weigh 2-9 pounds. Elephant birds were 8-12 feet tall and weighed over 1,000 pounds. Elephant birds were similar in size to ostriches, while kiwis are closer to chickens. The largest elephant bird, Vorombe titan, was nearly 3 meters (9 feet 6 inches) tall.
Habitat and geography
Kiwis live in forests and scrublands on New Zealand. Elephant birds lived in the forests and woodlands of Madagascar. New Zealand and Madagascar are over 7,000 miles apart.
Diet
Kiwis eat insects, worms, fruit and seeds. They probe the ground with their long bills searching for food. Elephant birds were herbivores, feeding on plants like fruits, seeds, and leaves. Their shorter bills were better adapted for browsing.
Time period
Kiwis still survive today, though some species are endangered. Elephant birds went extinct around 1,000 years ago, likely due to human hunting and habitat loss. The last remaining elephant bird species survived until the 17th century.
Eggs
Kiwi eggs are about 15% of the female bird’s weight. At 450 grams, they are one of the largest in proportion to the mother’s size. Elephant bird eggs reached 9-12 kg, the largest single cells ever known. To visualize how massive that is, a single elephant bird egg could feed around 150 people.
Could elephant birds and kiwis ever have encountered each other?
Since elephant birds and kiwis evolved separately for over 50 million years on different landmasses, they never would have encountered each other in the wild. Even when the first humans arrived on Madagascar around 2,000 years ago, the elephant birds were already extinct.
However, humans did once have the opportunity to see both kiwis and elephant birds. Ancient Polynesians first discovered New Zealand around 1300 AD. Centuries later, European explorers arrived in Madagascar in the 1500s and saw remnants of the giant elephant birds that had disappeared. Early European drawings of elephant birds were informed by folk memory and subfossil remains.
So while kiwis and elephant birds evolved independently for eons in isolation, their paths did briefly cross through the voyages of early seafaring human explorers. These explorers inadvertently connected the palaeognath lineages by discovering the wildly different paths kiwis and elephant birds took in the absence of competition and predators.
Conclusion
Kiwis and elephant birds exemplify the amazing transformations that can occur in isolated island ecosystems. While flightless island birds today are typically much smaller than their ancestors, Madagascar’s elephant birds exploded in size to take advantage of vacant ecological niches. They became the titans of Madagascar while kiwis remained petite.
Yet despite the differences enabled by isolation, kiwis and elephant birds still retain the common heritage that connects them to their shared ancestry millions of years ago when their forebears inhabited the ancient supercontinent Gondwana. Their striking similarities in anatomy, egg-morphology, and DNA all confirm that these unlikely birds are in fact close evolutionary cousins.
