This guest post was contributed by David Moscato, a freelance science writer. This guest post reflects the views solely of its author, which are not necessarily shared by PLOS. Thank you, David, for contributing to the PLOS Paleo Community!
When it comes to evolution, islands are weird places. Species living on islands often experience fascinating changes in their lifestyle and anatomy. Famously, many small creatures experience “island gigantism,” as in the case of the huge rats of Flores, the big lizards of San Esteban, or the massive lemurs of Madagascar. In recent years, fossil evidence has revealed another island oddity: the giant goose of Gargano.
Garganornis ballmanni was an odd duck – literally. It didn’t fly, possibly spent a lot of its time away from the water, and had a habit of fighting with its wings. On top of that, it was big, estimated at up to 23kg (50lbs). For a living comparison, that’s the size of a greater rhea, South America’s largest extant bird.
Dr. Hanneke Meijer of the University of Bergen, Norway, has been studying island evolution for a long time. She explained to me that big predators often cannot make it to islands, and this is a big deal for island denizens. “There’s a very strong selection pressure that basically is lifted without those predators present,” she said. So island animals can evolve traits that might be detrimental in a more threatening continental ecosystem.
Which brings us to Gargano. Today, this region is part of the Italian mainland, but during the late Miocene, around 5–7 million years ago, it consisted of one or more isolated islands. Fossils from the area tell of an ancient insular fauna, including many small rodents, a “moon-rat” of unusual size, a five-horned deer, and of course plenty of birds.
Meijer recounted seeing Gargnornis for the first time. “I remember that one of my colleagues … showed me this really big tibia fragment,” she told me. “He thought it was a mammal because it was so big.” She originally identified and named the big bird in 2013 from just that bone. This year, she and colleagues have published on new Garganornis fossils, including more leg pieces as well as wing bones.
The new fossils helped to confirm aspects of the big bird’s lifestyle and relationships. Garganornis is identified as a member of the Anatidae, the family that includes ducks, swans, and geese, though it’s significantly heavier than the largest anatids alive today. And its wing bones are so reduced that it was certainly not doing any flying.
Large flightless island birds are a classic evolutionary product. They include the extinct dodo (a pudgy pigeon); the living kakapo (a grounded parrot); and the elephant birds and moa (the largest birds of all time). Garganornis isn’t the only member of its family to adapt this way. Up until very recently, for example, both New Zealand and Hawaii were also home to large flightless ducks and geese.
So what was this huge honker doing on Gargano? “I think it had the role of a large herbivore,” Meijer said. With few (if any) other big herbivores on the island, Gargnornis had an open niche to fill. Like its relatives on other islands, it likely took to a terrestrial life of plant-eating, taking on the role that medium-to-large mammals typically occupy on continents.
It was probably also a convenient source of food; Garganornis wasn’t the only big bird of Gargano. Its ecosystem was home to the eagle Garganoaetus and the owl Tyto gigantea, both also quite large, though still flighted. Just as the moa of New Zealand were food to the preposterously-large Haast’s eagle, the great goose of Gargano may have had its own birds of prey to contend with – a young Garganornis would make a nice meal. In fact, Meijer and colleagues suspect its large size may have evolved in part to provide protection against the local birds of prey.
As if its size weren’t impressive enough, Garganornis also had weaponized wings. Close examination of the goose’s wrist bones revealed a small outgrowth – a “carpal knob.” These are actually surprisingly common among birds, from ducks to pigeons to jacanas; some have small knobs, other large knobs, and some have even developed elaborate spikes or spurs. These structures typically serve to add some extra oomph to a combative wing-slap.
It’s likely that wing-fighting in Garganornis was mainly reserved for members of its own species, as a means for settling territorial or mating disputes, as is the case with many birds today. But it’s certainly possible a predator may have received a beating now and then.
“If you look at swans – swans can be very aggressive, especially during breeding time,” Meijer said, speaking from experience growing up in the Netherlands, where getting too close to a defensive swan could invoke the bird’s ire. “And they come out with wings spread. They could easily just smack you.” This struck a familiar chord with me as well; I grew up in North America, where dwells the dreaded Canadian Goose.
The fossil evidence, compared with insights from relatives of Garganornis, paints an impressive picture. This was a very large goose (or duck, or swan; it’s hard to say for sure), roaming its island keeping the vegetation in check, and armed with massive girth, knobby wings, and – most likely – a typical anatid attitude.
Like I said, islands are weird places.
Pavia M, Meijer HJM, Rossi, MA, Göhlich UB (2017) The extreme insular adaptation of Garganornis ballmanni Meijer, 2014: a giant Anseriformes of the Neogene of the Mediterranean Basin. Royal Society Open Science 4: 160722
David Moscato is a freelance science writer from Long Island, NY with a background in paleontology. He is a contributor for Earth Touch News, and you can follow him on his blog, The Meniscus, or on Twitter @DMos150.
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