Over 50,000 years ago, Leptoptilos robustus — an extinct species of large-bodied stork around 1.8 m tall — co-existed with mysterious miniature human relatives Homo floresiensis, dwarf proboscideans Stegodon florensis insularis, Komodo dragons (Varanus komodoensis), and vultures Trigonoceps sp., on the Indonesian island of Flores. Paleontologists previously thought that Leptoptilos robustus evolved from a smaller ancestor and may have been flightless. According to new research, the prehistoric bird was capable of active flight.
A possible scene at Liang Bua Cave around 70,000 years ago: Leptoptilos robustus challenges a juvenile Komodo dragon for access to the carcass of a dwarf proboscidean while other giant marabou storks, vultures and hominins look on. Image credit: Gabriel Ugueto.
Leptoptilos is a genus of very large tropical storks containing three living and almost ten extinct species.
One of the extinct members of the genus, Leptoptilos robustus, lived on Flores — an oceanic island that is part of the Wallacea biogeographical region — during the Pleistocene epoch.
This bird was first described in 2010 on the basis of four bones found in the limestone cave of Liang Bua.
It was estimated to have weighed approximately 16 kg, larger than any living Leptoptilos species.
Previous research suggested that Leptoptilos robustus evolved from a smaller Middle Pleistocene ancestor and may have been flightless.
“Extinct giant marabou storks were broadly distributed across continental Africa and Eurasia during the Plio-Pleistocene,” said University of Bergen researcher Hanneke Meijer and her colleagues.
“Of these, Leptoptilos falconeri is the best known with fossils of this species recovered at sites in Africa and Eurasia.”
“Relatively younger sites in northeastern China and Java preserve evidence of Leptoptilos lüi (260,000 years ago) and Leptoptilos titan (Late Pleistocene), respectively.”
“In some instances, these giant carnivorous birds have been found in association with proboscideans, vultures, and even hominins, suggesting a possible symbiotic relationship existed among these species.”
“The emergence and expansion of grasslands in East Africa during the Late Pliocene likely facilitated the dispersal of large mammalian species from Africa into Asia (and vice versa), and subsequently during the Pleistocene from mainland Asia into Southeast Asia,” they said.
“As opportunistic scavengers, giant marabou storks and vultures almost certainly would have also dispersed along with their primary sources of food (i.e. large mammal carcasses).”
“Adding to this interesting story is yet another extinct giant marabou stork species, Leptoptilos robustus, discovered on the Indonesian island of Flores, an oceanic island that has never been connected to either the Asian or Australian continental land masses,” they added.
In the new study, Dr. Meijer and co-authors examined 21 additional skeletal elements of Leptoptilos robustus from Liang Bua Cave.
“Although Leptoptilos robustus elements are extremely rare at Liang Bua, comprising less than 1% of the total faunal assemblage, together these remains represent one of the best samples in the world of an extinct giant marabou stork species,” the researchers said.
“With its shady overhang and recurring water pools (due to frequent flooding from the nearby river, the Wae Racang), Liang Bua likely was a comfortable shelter from the heat for local wildlife,” they added.
“Such a sheltered watering hole would have provided ample hunting and scavenging opportunities for Komodo dragons, marabou storks, vultures and Homo floresiensis.”
“The fragmentary nature of the Leptoptilos robustus assemblage suggests there may have been intense competition for Stegodon carcass access among these various species.”
“However, the Leptoptilos robustus remains thus far do not show any signs of either Komodo dragon tooth marks or hominin butchery.”
The authors found that the wing bones of Leptoptilos robustus were well-developed and the species was almost certainly capable of active flight.
“The close association of giant marabou storks with hominins, proboscideans and even vultures, at sites in Kenya, Chad and Ethiopia, northeastern China, Java, and Flores suggests that the dispersal of these birds into Island Southeast Asia probably happened as part of a larger scale faunal community dispersal tied to the expansion of drier, savannah-like ecosystems across the Sunda shelf during the Pleistocene,” they said.
“Future findings of giant marabou stork and vulture remains in association with those of hominins and proboscideans from the region would confirm such a scenario, as would their absence from islands never colonized by proboscideans and/or hominins other than Homo sapiens (e.g. Timor).”
“As the remains of Leptoptilos titan and Leptoptilos robustus appear to be the most recent representatives of these once plentiful giant marabou storks, Island Southeast Asia likely acted as a refugium for the last surviving members of these enigmatic birds.”
The findings were published in the July 2022 issue of the journal Royal Society Open Science.
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Hanneke J.M. Meijer et al. 2022. More bones of Leptoptilos robustus from Flores reveal new insights into giant marabou stork paleobiology and biogeography. R. Soc. Open Sci 9 (7): 220435; doi: 10.1098/rsos.220435
