What is the giant dinosaur looking bird?

The giant dinosaur looking bird refers to a group of large flightless birds that lived in the past and resembled dinosaurs in some ways. These birds are part of a group called ratites, which includes modern day ostriches, emus, rheas, cassowaries, and kiwis.

Ratites are a group of flightless birds that have existed since the Cretaceous period over 60 million years ago. They were once distributed across the continents but today are found natively only in Australia, New Zealand, and South America. The ratites alive today include ostriches, emus, rheas, cassowaries, and kiwis.

These large flightless birds share many similarities with dinosaurs in their appearance, especially in relation to their size, feathers, long necks and legs, and claw-tipped toes. Some of the largest ratites like the moa and elephant bird grew up to 10-12 feet tall and weighed over 500 lbs, comparable in height and mass to some theropod dinosaurs.

While not directly descended from dinosaurs, ratites and dinosaurs shared a common maniraptoran ancestor during the Late Cretaceous period. They evolved similar adaptations for a cursorial, flightless lifestyle. Their imposing stature and dinosaur-like profile lead them to be described as giant dinosaur-looking birds.

Ratite Evolutionary History

The evolutionary origins of ratites can be traced back to prehistoric flying birds in the maniraptoran group of theropod dinosaurs which includes birds and their closest dinosaurian relatives. Maniraptorans like dromaeosaurs, troodontids, and early birds evolved feathered wings and the ability to fly during the Jurassic and Cretaceous periods.

During the Late Cretaceous period around 80-70 million years ago, several lineages of maniraptorans lost the ability to fly and evolved into large flightless forms. These included ancestral palaeognaths, which would later diversify into ratites, tinamous, and the extinct lithornithids and mihirungs.

The absence of flight in palaeognaths allowed them to evolve extreme cursorial adaptations. Their forelimbs became smaller while their hindlimbs grew massive and muscular with feet adapted for running. Many lineages increased dramatically in body size as well. The earliest definitive ratite fossils date to the Paleocene epoch around 60 million years ago after the extinction of the dinosaurs.

Timeline of Ratite Evolution

• Late Jurassic/Early Cretaceous (~150 million years ago) – Earliest maniraptoran theropods evolve feathers and flight capabilities.
• Late Cretaceous (~80 million years ago) – Multiple maniraptoran lineages become secondarily flightless leading to palaeognath ancestors of ratites.
• Cretaceous/Paleogene boundary (~66 million years ago) – Non-avian dinosaurs become extinct but palaeognaths survive.
• Paleocene (~60 million years ago) – Earliest undisputed ratite fossils appear after the extinction of non-avian dinosaurs.
• Eocene (~50 million years ago) – Proto-ratites diversify across northern continents. Giant ratites like gastornithids emerge.
• Oligocene (~30 million years ago) – Ratites become widespread in Europe, North America, and Asia.
• Miocene (~15 million years ago) – Ratite lineages dwindle across northern continents. Surviving lineages are isolated in Gondwana landmasses.
• Pliocene/Pleistocene (~5 million to 12,000 years ago) – Megafaunal ratites evolve in Australia and Madagascar before mass extinctions.
• Holocene (~12,000 years to present) – Most giant ratites go extinct, leaving the 5 remaining smaller species today.

Giant Ratites of the Past

While the ratites of today are relatively modest in size, some ancient ratite lineages evolved into giant flightless birds standing over 10 feet tall and weighing upwards of 500 lbs. These megafaunal ratites were apex herbivores and occupied ecological niches similar to large ungulates or theropod dinosaurs in their environments.

Some notable giant ratites of the past include:

• Elephant Birds – Endemic to Madagascar. The largest elephant bird, Aepyornis maximus, stood over 10 feet tall and weighed over 1,000 lbs. They went extinct around 1,000 years ago likely due to human activity.
• Moa – Endemic to New Zealand. The largest moa, Dinornis robustus, reached heights of 12 feet and weighed over 500 lbs. They went extinct around 600 years ago after the island was colonized by humans.
• Gastornithids – Inhabited Europe, North America, and Asia beginning in the Eocene. The largest species was Gastornis gigantea which stood over 6 feet tall. They went extinct in the late Miocene.
• Dromornithids – Endemic to Australia. The largest species, Dromornis stirtoni, may have weighed over 1,100 lbs. They survived until the late Pleistocene era.

These giant ratites are examples of “island gigantism” where island-dwelling species can evolve larger body sizes in the absence of large competing herbivores. Human colonization of these islands inevitably led to the extinction of most giant ratites.

Characteristics of Giant Ratites

While varied across different lineages, giant ratites shared some key anatomical and ecological similarities due to their extreme adaptations towards a flightless, cursorial lifestyle:

• Large body size – Giant ratites commonly reached heights of 8-12 feet and weights over 500 lbs, comparable in mass to many large dinosaurs.
• Long muscular legs – Their legs were elongated with thick, muscular thighs adapted for powerful running.
• Reduced forelimbs – The wings became much smaller and more vestigial compared to flying ancestors.
• Loss of flight muscles and keeled breastbone – With no need for flight muscles or anchoring point for wing muscles, the breastbone became flat and obtuse.
• Long neck and small head – The neck tended to elongate to enable greater reach when foraging on vegetation at ground level.
• Toothless beak – Adapted for herbivorous grazing on tough vegetation.
• Cursorial feet – Usually three-toed feet with strong claws for running.

This body plan allowed giant ratites to exploit fast running speeds and the ability to forage on tough fibrous plant material that other herbivores could not digest effectively. In some cases, giant ratites filled similar niches to hadrosaurs, ceratopsians, sauropods, and other large dinosaurian herbivores.

Ecological Role of Giant Ratites

As apex herbivores, giant ratites played important roles in shaping the ecosystems they inhabited:

• They grazed extensively on grasses, leaves, seeds, fruit, and other plant matter. Their powerful beaks could shred tough vegetation.
• As megaherbivores, they impacted vegetation structure through browsing, grazing, and seed dispersal.
• Their fast running likely helped stamp down trails over grasslands.
• Being flightless, adults were vulnerable to large predators where present. Juveniles could fall prey to smaller carnivores as well.
• Their eggs provided an abundant food source for predators and scavengers.
• Their disappearance led to ecological cascades and new niches opening up on islands.

In many ways, giant ratites assumed the ecological roles of large dinosaurian herbivores during the Cenozoic era in the absence of those dinosaurs. Their presence shaped the vegetation and predator-prey dynamics of their environments.

Surviving Ratite Lineages

Today, only 5 ratite species in 4 genera survive across 3 isolated landmasses:

While still impressive in their own right, none match the epic proportions of their giant extinct cousins. They represent the last living remnants of an ancient and once much more diverse lineage.

Flightlessness in Ratites

A key question around ratites is why they lost the ability to fly. There are several hypotheses:

• The cursorial advantage hypothesis suggests that becoming larger and flightless allowed ratites to run faster without the aerodynamic constraints and muscle tradeoffs required for flight.
• The vegetation structure hypothesis proposes that dense forests in the past selected for flightlessness and running adapted to move through cluttered habitats.
• The island rule states that island species tend to evolve either larger or smaller body sizes. In the absence of predators, becoming larger was advantageous.
• The phylogenetic constraint hypothesis posits that ratites inherited strong genetic and developmental constraints from flightless dinosaur ancestors that predisposed them towards flightlessness.

The actual evolutionary drivers were likely a combination of these factors. Flight had high energy costs and competing demands on skeletal structure and muscles. Selection for running efficiency relaxed constraints on increasing body size and losing flight adaptations like keeled breastbones, robust wings, and flight muscles. Isolation on islands also enabled increases in size due to lower predation pressures and abundance of resources.

Ratite Distribution and Habitats

Today, living ratites are restricted to Australia, New Zealand, Africa, and South America. This fragmented distribution is a relic of the breakup of the ancient supercontinent Gondwana:

• Ostriches – Africa was once part of Gondwana and still houses ancestral ratite lineages.
• Emus and cassowaries – Australia was formerly connected to Antarctica as part of Gondwana.
• Rheas – South America was initially connected to Africa and Antarctica as part of Gondwana.
• Kiwis – New Zealand split off from Gondwana later and was colonized by ratites more recently.

Ratites inhabit open grasslands, savannas, woodlands, scrublands, and other open habitats that accommodate their cursorial lifestyle. They are mostly absent from dense forested environments. Ostriches thrive in African savannas while rheas occupy South American pampas grasslands. Emus and cassowaries range across Australia’s bushlands and woodlands.

Shared Ratite Characteristics and Biology

Despite spanning different continents, living ratites share many anatomical, physiological, and behavioral similarities:

• Large flightless bodies with long muscular legs adapted for running.
• Small vestigial wings with long claws used for displays and defense.
• Long S-shaped necks and small heads with large eyes.
• Covered in shaggy plumage with soft feathers consisting of downy barbs but no barbules.
• Most have simple plumes arising from their heads, wings, and/or tails.
• Toothless beaks adapted for plant grazing and seeds.
• Simple gut without crop structure to allow swift digestion of fibrous foods.
• Powerful pedal claws used for kicking in defense.
• Fast development with precocial young that can run soon after hatching.
• Male displays for courtship using plumage, vocalizations, and ritualized behaviors.
• Only males incubate and raise eggs and young in most species.

These shared characteristics reflect their common ancestral origins and ecological similarities. As dominant avian herbivores, ratites evolved under analogous selection pressures across different regions.

Conclusion

In summary, the giant dinosaur-looking birds refer to the diverse extinct lineages of megafaunal ratites that once inhabited continents across the globe. While flightless, they assumed similar ecological niches as large herbivorous dinosaurs. Their imposing size, cursorial limbs, and feathered appearance evoked their dinosaurian heritage. Today just 5 smaller species survive in Australia, New Zealand, Africa and South America representing relics of a once far more widespread and spectacular avian radiation.