The largest terrestrial predators on the Late Miocene Gargano-Scontrone island(s) were unusually big hedgehog-relatives, and likewise the local aerial predators also increased in size compared to most of their cousins on the mainland.
Tyto gigantea was a massive barn owl, estimated to have been at least as large as the modern eagle-owl – probably measuring somewhere around 80cm in length (2′7″). It likely grew so big thanks to the lack of competition and in order to keep up with the larger sizes of its prey, since the rodents and pikas of Gargano-Scontrone were also comparative giants.
Alongside the slightly smaller species Tyto robusta it would have been the dominant nocturnal predator on the island(s), while during the daytime the golden-eagle-sized buzzard Garganoaetus occupied the same large-carnivorous-bird niche.
While some of the main big herbivores on the Late Miocene Gargano-Scontrone island(s) were the larger species of Hoplitomeryx, they weren’t the only animals filling that ecological niche.
Garganornis was an enormous anatid bird, closely related to modern ducks, geese, and swans. Although only known from fragments of its skeleton it’s estimated to have stood up to 1.5m tall (4′11″), making it the largest known waterfowl to have ever lived.
It probably reached such a size thanks to the lack of large terrestrial predators, and possibly also as protection against the island eagles and owls – literally growing too big for them to be able to eat.
It was flightless, with small wings, and had reduced webbing between its toes, suggesting it spent most of its time walking around on land. It also had bony knobs on its wrists that would have been used to give some extra force to wing-slaps when fighting with each other over territory or mates.
Thanks to the absence of large terrestrial carnivores on the Gargano-Scontrone island(s) during the Late Miocene, animals that were usually small had the opportunity to become larger, moving into the vacant ecological niches and evolving into predators unlike anything existing on the mainland.
Deinogalerix was a giant member of the gymnures – close relatives of hedgehogs without the quills – with a proportionally big head and a long snout full of large fangs at the front and bone-crushing molars at the back.
Several different species have been found, with the largest Deinogalerix koenigswaldi having a head-and-body length of around 60cm (2′). Along with its tail that would have made it at least 90cm long (2′11″), making it the biggest eulipotyphlan ever discovered.
It would probably have hunted smaller mammals, birds, and reptiles, filling a niche on the island similar to dogs or cats.
During the mid-Miocene, about 15 million years ago, a region of central and southeast Italy around Gargano and Scontrone was cut off from the mainland by rising sea levels.
For the next 7-10 million years this island (or perhaps a cluster of islands) was left isolated, and an unusual ecosystem developed known as the “Mikrotia fauna”. With the island starting off lacking large predators, small herbivorous animals like rodents, pikas, and waterfowl became huge – and then small predators like gymnures and carnivorous birds also grew to keep up with the increasing size of their prey.
One of the strangest residents of the island(s) was Hoplitomeryx, an early type of ruminant that resembled a deer or pronghorn. Nicknamed the “prongdeer”, it had a total of five horns on its head and large protruding fangs similar to some modern deer.
Multiple species of Hoplitomeryx have been identified, representing four different size classes ranging from huge down to tiny insular dwarfs. The largest is estimated to have been similarly sized to modern moose, standing around 2m tall at the shoulder (6′6″), while the smallest would have been under 50cm (1′8″).
Each of these size classes was specialized for slightly different ecological niches, eating different types of vegetation to avoid directly competing with each other for the limited amount of food on the island.