Giant Terror Birds Once Ruled Antarctica, Study Suggests
New research answers a long-standing mystery around Antarctic apex predators
Terror birds were wretched creatures. They grew up to nine feet tall. They crushed prey with their horse-sized skulls. They stalked ecosystems and created misery for almost everything.
A new discovery by Carolina Acosta Hospitaleche and Washington Jones, published in the journal Palaeontologia Electronica, suggests terror birds might have once ruled Antarctica.
Antarctica today is an inhospitable place. To quote the US Antarctica Program, “it is the coldest, windiest, [and] harshest continent.” Over 98% of its land is covered by thick ice sheets. Temperatures near the South Pole average -28°C (-18°F) in summer and -60°C (-76°F) in winter. Not an ideal location for your next vacation home.
Hospitaleche and Jones did their digging on Seymour Island, a small island off the northernmost tip of the Antarctic Peninsula. As they note:
This island, characterized by a fossil rich uppermost sequence, remains devoid of ice cover during the austral summer [summer in the southern hemisphere], enabling the extensive exposure of Cretaceous-Paleogene outcrops.
Cretaceous-Paleogene outcrops are 146 to 23 million years old. Hospitaleche and Jones dug in the La Meseta Formation, which dates to the Eocene (56 to 34 million years ago).
Eocene Antarctica was vastly different than Antarctica today. The land and surrounding water was warm. Fossil evidence indicates temperate rainforests like those in Chile and New Zealand. Ice core samples show temperatures around 14°C (57.2°F). Toward the end of the Eocene, things got colder.
This from another paper:
The change from a warm, ice-free greenhouse world to the glacial Antarctic icehouse occurred during the latest Eocene. … Prior to this, during the Early-Middle Eocene, Antarctica experienced warm climates... Overall, evidence from fossils, sediments and geochemistry … indicates generally warm and ice-free conditions during the earliest part of the Eocene … followed by gradual cooling.
Fossil evidence from Eocene Antarctic rock reveals abundant bird, mammal, and marsupial species. Paleontologists find ancestral penguin, duck, turtle, and starfish species. Mammals and marsupials were mostly small and herbivorous.
This from Hospitaleche and Jones:
Herbivorous groups dominated the community of land mammals and were represented by ungulates [hoofed mammals] of various sizes with dental adaptations for feeding on different types of plants. … The diversity of marsupials included small species with diverse dietary habits, including insectivores, frugivores, and folivores.
Conspicuously, Hospitaleche and Jones note, “the representation of top predators in Eocene Antarctica remains relatively under-represented.” Who were the predators?
After the Eocene, Antarctica broke from Australia and South America. The Antarctic Circumpolar Current formed, which reduced temperatures around the continent. Glaciation ebbed and flowed, but eventually formed large ice sheets. Ice sheets now cover land that would otherwise reveal details about Antarctic predators.
To see what predators might have dominated Antarctica, paleontologists look to Southern South America. South America and Antarctica were previously connected by the Paleogene Weddellian Isthmus, so Southern South America offers clues about which predators paleontologists might find.
Predator niches in South America were occupied by crocodiles, massive snakes, mid-size marsupials, and — drum roll please —Phorusrhacidae, also known as terror birds.
Terror bird remains are found throughout South America and parts of North America. Species have been identified in Argentina, Brazil, and most recently Uruguay. The largest of them, weighing over 300 kg (661 lbs), is Titanis walleri, which is from Texas and Florida in the United States.
This from the authors:
[Terror] birds are amongst the largest birds that have ever existed on the planet, ranging in height from approximately 1 to 3 meters. … They most likely preyed on small- and medium-sized vertebrates. These birds would be active hunters that fulfilled the role of continental apex predator…
Terror birds used their formidable legs, large skulls, hooked beaks, and razor-sharp ungual phalanxes to kill prey. The ungual phalanx is a distinctive, claw-like appendage used by many birds to ensnare their victims. The authors elaborate:
Hypercarnivorous birds, like Phorusrhacos, typically develop a strongly curved ungual phalanx in the second digit to capture prey during hunting.
Hospitaleche and Jones found two ungual phalanxes in the La Meseta Formation. They compared the claws with similarly aged bird species, including each of the terror birds. Their results show the claws belonged to a species that closely resembles Phorusrhacos longissimus, a terror bird from South America.
P. longissimus weighed between 117 to 134 kg, suggesting the Antarctic specimen weighed at least 100 kg (220 lbs).
More from the authors:
It is highly likely that this bird was an active predator, hunting and feeding on small marsupials and medium-sized ungulates. This finding fundamentally changes our understanding of the dynamic within the Antarctic continental ecosystems during the early Eocene. … Birds similar in size … would have been capable of preying on similarly sized prey, approximately up to 100 kg.
Modern Homo sapiens, it should be noted, weigh 60 to 80 kg on average. If there was any overlap between us and them (and fortunately there was not), we might have been on the menu.
Several Antarctic discoveries over the past decade were initially mistaken for terror birds, but later reclassified as other taxa. Hospitaleche and Jones found the first “unequivocal” evidence of terror bird species in Antarctica.
Terror birds are thought to have gone extinct in part from the Great American Biota Interchange, a process that unfolded after a land bridge formed between Panama and Colombia. While the land enabled terror birds to migrate into North America, it also allowed panthers, Smilodon (i.e., saber-toothed tigers), and a formidable short-faced bear species to venture south. These predators might have stolen terror bird territory.
Future research will invariably reveal further details about Antarctic ecosystems and their apex predators. For now, we know terror birds ruled as they once did in parts of North and South America. We should pity the animals they terrorized.
