The large extinct flightless birds referred to in the title question are a group of species belonging to an order called the ratites. The ratites were a diverse group of flightless birds that inhabited parts of the world up until their extinctions within the last several hundred years. The most well-known ratites include the ostrich, emu, cassowary, rhea, kiwi, and the famously extinct dodo and elephant bird. These large flightless birds filled an important ecological niche in their environments and had unique adaptations that enabled their flightless lifestyles. While most ratites are now extinct, the ostrich, emu, cassowary, rhea and kiwi have survived to the present day.
Overview of Ratites
The ratites are a group of flightless birds that make up the order Struthioniformes. There are around 5-6 families, 9 genera and 15 existing species of ratites alive today. However, many ratite species have gone extinct over the last few hundred years following human settlement of their environments. Ratites are characterized by their large size, flightless nature, lack of a keeled breastbone, distinctive palate structure, and feathers with soft and downy plumage. While they have wings, these are vestigial and not suitable for flight. Without the ability to fly, ratites evolved adaptations for running, including strong leg muscles and fusion of certain bones in their pelvis. Most ratites have small heads and long powerful legs with just two or three toes. Ostriches are the largest living ratites, standing up to 9 feet tall. Ratites are found natively on every continent except Antarctica and Europe. Here is a breakdown of the living ratite species by family:
Struthionidae – Ostriches
- Common ostrich – Africa
- Somali ostrich – Africa (extinct in wild)
- Arabian ostrich – Middle East (extinct)
Casuariidae – Cassowaries and Emu
- Southern cassowary – Australia and New Guinea
- Northern cassowary – New Guinea
- Dwarf cassowary – New Guinea
- Emu – Mainland Australia
Rheidae – Rheas
- Greater rhea – South America
- Lesser rhea – South America
- Darwin’s rhea – South America
Apterygidae – Kiwis
- Great spotted kiwi – New Zealand
- Little spotted kiwi – New Zealand
- Rowi – New Zealand
- Tokoeka – New Zealand
Some key extinct ratite species include:
- Elephant bird – Madagascar (largest known ratite)
- Moa – New Zealand
- Dodo – Mauritius
Evolutionary History
The evolutionary origins of ratites date back to the Cretaceous period, over 65 million years ago. Early ratite ancestors were flying birds related to waterfowl and fowl. Flightless ratites began evolving on the ancient southern supercontinent Gondwana, which included South America, Africa, Australia, Antarctica, and New Zealand. As Gondwana broke up, ratites became isolated on different landmasses where they independently lost the ability to fly and grew much larger in size. Their wings became vestigial while their legs adapted for running. Without flying predators, large size provided ratites evolutionary advantages on islands and isolated environments. The different ratite lineages continued evolving independently into the diverse species known today.
Key Points in Ratite Evolution
- Late Cretaceous (~80-66 million years ago) – Earliest ratite ancestors evolved flight on Gondwana.
- Paleogene Period (~66-23 million years ago) – Gondwana broke up isolating ratites lineages across multiple continents.
- Neogene Period (~23-2.6 million years ago) – Ratites lost flight capabilities and grew much larger.
- Pleistocene Epoch (~2.6 million – 11,700 years ago) – Further ratite diversification and gigantism.
- Holocene Epoch (~11,700 years ago – present) – Widespread extinction from overhunting and habitat loss.
Molecular evidence suggests that the ostrich lineage was the first to diverge from other ratites based on its basal position in the ratite evolutionary tree. The kiwi split next, followed by the emu and cassowaries. The rheas were the last major ratite lineage to branch off. While flightless ratites no longer needed their wings, they kept small vestigial wings with claw-like fingers for balance, steering, and displays.
Extinct Giant Ratites
While all ratites are considered large birds, some extinct species evolved to massive proportions in the absence of predators. On islands like Madagascar and New Zealand where mammals were scarce or absent, ratites took advantage by occupying mammal niches and growing to gigantic sizes. The largest known ratite was the elephant bird of Madagascar, weighing over 1000 lbs (500 kg) and standing over 10 feet (3 meters) tall! New Zealand was home to several species of moa, the tallest reaching 12 ft (3.6 m) high. Other sizable extinct ratites include the Australian mihirungs and thunder birds. These giant ratites went extinct within the last several hundred years following human colonization of their island homes. Hunting and habitat destruction led to their demise. Here are some key facts about giant extinct ratites:
Elephant Bird
- Native to Madagascar
- Up to 10 ft (3 m) tall and 1,000 lbs (500 kg)
- Laid largest known bird egg – 9-14 lbs (4-6 kg)
- Went extinct around 1000 AD
Moa
- Native to New Zealand
- Up to 12 ft (3.6 m) tall
- Weighed around 500 lbs (230 kg)
- Went extinct around 1500 AD
Thunder Bird
- Native to Australia
- Up to 9 ft (2.7 m) tall
- Weighed around 400 lbs (180 kg)
- Went extinct around 1850 AD
These giant ratites filled niches similar to large mammalian herbivores, serving as important grazers, browsers and seed dispersers in their insular ecosystems. Their immense size was likely an evolutionary response to the lack of predators and abundance of resources on islands.
Unique Adaptations
As flightless birds, ratites evolved a variety of anatomical and physiological adaptations for their terrestrial lifestyles:
Skeletal Adaptations
- Did not develop a keeled breastbone to anchor flight muscles
- Lost most of their wing bones
- Developed long, strong leg bones
- Fused sacral vertebrae for strength
- Flattened sternum
- Reduced number of caudal vertebrae
Muscular Adaptations
- Powerful leg muscles for running and kicking
- Reduced pectoral muscles
- Enlarged pelvic limb muscles
Organ Adaptations
- Enlarged heart and lungs for endurance running
- Expanded gastrointestinal tract to digest fibrous diet
- Lower basal metabolic rate to conserve energy
Behavioral Adaptations
- Fast sprinting to escape predators
- Skill at maneuvering through dense vegetation
- Good eyesight and hearing to detect threats
- Use of feet for defense through kicking
These adaptations allowed ratites to thrive as herbivores and omnivores in their terrestrial environments, exploiting niches usually occupied by mammals. The loss of flight led to enlarged size as well as unique defensive behaviors using the feet, reinforced by sturdy skeletal reinforcements. Ratites serve as a prime example of convergent evolution as distantly related lineages adapted in similar ways for life on the ground.
Ecology and Behavior
As large terrestrial birds, ratites play important roles in their native ecosystems. Here are some key elements of ratite ecology and behavior:
Habitats
- Open grasslands and savannas
- Scrublands
- Woodlands and open forests
- Alpine areas
- desert fringes
Feeding
- Herbivorous diet of grasses, leaves, seeds, fruits
- Omnivorous species feed on insects and small vertebrates
- Use beak to selectively browse vegetation
- Gizzard helps grind and digest fibrous foods
Behavior
- Crepuscular activity patterns
- Males may form harems of multiple females
- Males defend large territories
- Loud booming and drumming for communications
- Rhea and emu known for speed; ostriches powerful kick
Breeding
- Ratites have high egg mortality in the wild
- Females lay eggs in simple ground nests called scrapes
- Incubation 30-60 days depending on species
- Precocial young can walk and feed shortly after hatching
As predominant herbivores and omnivores, ratites help shape the vegetation communities of their native habitats. Their large size and abundant eggs provide food sources for predators as well. Unfortunately, habitat loss poses one of the biggest current threats to wild ratite populations today.
Role of Ratites for Humans
For thousands of years, humans have interacted with ratites in a variety of ways. Here are some of the key relationships between people and ratites:
Food Source
- Meat, eggs, feathers and oil used historically by native peoples
- Early sailors hunted ratites for provisions on islands
- Ostrich farming today provides red meat yield without methane emissions
Material Uses
- Feathers made into clothing, blankets, ornaments
- Hides used for leather
- Bones carved into tools and decorations
- Eggshells used for cups and vessels
Cultural Significance
- Mythological and spiritual importance for native cultures
- Symbolic meaning of wealth, status and power
- Trade of feathers and artifacts over long distances
- Iconic flightless birds depicted in art and stories
Ecotourism
- Birding tours draw tourists hoping to spot wild ratites
- Zoos and wildlife parks allow visitors to view captive ratites
- Ostrich rides and racing offered in some areas
From ancient times up to today, ratites have provided subsistence, materials and inspiration for many human societies. Their large size and unique appearance makes them popular subjects for zoos and naturalists as well. Sadly, overexploitation led to the extinction of the moa, elephant bird and other giant ratites. Ongoing conservation efforts now seek to preserve remaining wild ratite populations.
Surviving Ratite Species
While many ratites have gone extinct in recent centuries, several species have managed to survive into the modern era. Here is an overview of ratites that can still be found in the wild today:
Ostriches
- World’s largest living bird
- Native to Africa
- Can reach 9 feet tall and 350 lbs
- Renowned for high speed running
- Herbivores that inhabit savannas and deserts
Emus
- Second tallest living bird after ostrich
- Native to Australia
- Can reach 6 feet tall and 110 lbs
- Omnivorous diet including plants, insects, larvae
- Found in woodlands and bushland
Cassowaries
- Large forest-dwelling ratites of New Guinea and Australia
- Can reach 5-6 feet tall and 120 lbs
- Mostly frugivorous, feeding on fallen fruit
- Shy but can deliver dangerous kicks when threatened
Rheas
- Medium-sized ratites of South America
- Can reach 4-5 feet tall and 55 lbs
- Herbivores inhabiting savannas and grasslands
- Cryptic plumage helps camouflage in vegetation
Kiwis
- Smallest living ratite
- Native to New Zealand
- Can reach 20 inches tall and 7 lbs
- Nocturnal, hiding in burrows during the day
- Omnivores feeding on invertebrates and plants
These surviving ratites employ an array of foraging strategies and occupy diverse habitats on multiple continents. However, many ratite populations remain threatened by habitat destruction and invasive predators. Continued conservation efforts are needed to ensure the long-term survival of these unique flightless birds.
Conclusion
In conclusion, the large extinct flightless birds referred to in the original question were the diverse members of the ratite lineage. Evolving on the ancient supercontinent Gondwana, groups of ratites independently lost the ability to fly as they adapted to cursorial terrestrial life. In the absence of predators, ratites grew to massive sizes on islands, including the 500 kg elephant birds and 12 ft tall moas. Highly adapted for running and kicking, ratites occupied mammal-like niches as herbivores and omnivores in their ecosystems. Their large size and abundant eggs made them important food sources for humans, leading to overhunting and the extinction of the largest species. Today just 5 families and 15 species of ratites survive worldwide, though habitat loss continues to threaten populations. The massive elephant birds and moas remind us of the impacts humans can have on naïve island species, while also illustrating the remarkable evolutionary journey of flightless ratites over millions of years.
