Common Name: Ropen
Latin Name: Neopterodactylus luminosus
IUCN Status: Least Concern
An adult male ropen in breeding coloration.
Description: Ropen are one of the larger modern pterosaurs, with wingspans reaching up to two and a half meters. As is typical for pterosaurs, only the feet are scaled. Adults are lightly built, and their wings have an exceptionally high aspect ratio, as is typical for pelagic flying creatures. They have a "prey grab" of elongated teeth in the front of their jaw. All of their body except the underside and the wing membranes are covered in a thin layer of feathers, colored white and gray. During the breeding season, males grow a premaxillary crest and the front two teeth of their premaxillary lengthen substantially. Older males often bear scars from other males' teeth.
Younger ropen have lower aspect ratios than adults, more similar to agile forest-dwellers, and slightly more robust skeletons. Their jaw is shorter and while they have teeth, their teeth are shorter and peg-like. Like adults, they have an extensive covering of feathers, but their pattern is mottled brown. The wrist and fingers are much better developed; juvenile ropen are capable of exerting a much stronger grip than adults.
Diagram of ropen photophore. Bioluminescent bacteria are concentrated in the photocyte but distributed throughout the entire photophore. The color filter is vestigial.
The most interesting aspect of the ropen, however, is their bioluminescent underside. Ropen have photophores colonized with bioluminescent bacteria lining their belly. These bacteria originate from the fish and squid ropen feed upon. While after establishment the colonies are self-sustaining, ropen fed on an inappropriate diet won't develop bioluminescence.
The color of light emitted varies somewhat. Ropen on Sulawesi and the Maluku Islands have a noticeable green tinge to their bioluminescence, while populations on New Guinea and the Bismarck Archipelago are cyan. This isn't due to genetics. If you raise ropen from one population in the other population's range, their bioluminescence is the same color. We're pretty sure the bacterial symbionts are different, but haven't been able to culture the bioluminescent bacteria.
Distribution: While the bulk of the ropen population lives in New Guinea and Sulawesi, small populations live in the Bismarck Archipelago and the Maluku Islands. Sulawesi's population has decreased in recent years, as have the populations on the smaller islands, due to habitat destruction and direct persecution. In recent years this population decrease has slowed but has not fully stopped. They remain abundant on New Guinea.
Evolutionary History: Fossil records in the Wollemi Plains, a small world accessible through a Way in New South Wales, indicate that members of Anhangueridae had colonized the area at least five million years before the Cretaceous–Paleogene extinction event. As the only flying lifeforms other than insects in the Plains, they underwent an evolutionary radiation.1 Neopterodactylus is one of the less derived genera.
While it's believed that the K-Pg extinction cut off access through the Way, lifeforms from the Wollemi Plains were migrating back to Earth five thousand years ago at the latest. The abrupt ecological transition from the Wollemi Plains to the forests of New South Wales are thought to have inhibited dispersal, but genetic data proves that the ropen had spread to the Indo-Pacific two thousand years ago. Initially, the species colonized New Guinea.2 From there, they spread to nearby islands.
Bioluminescence isn't known from any other species of pterosaur. It's implausible that ropen developed it so quickly. Initially biologists suspected anomalous interference in their evolution. The trait may be older than first thought, however. Recent genetic analyses have suggested that Neopterodactylus is more properly split into three genera that split apart millions of years ago but underwent little morphological change. Under this classification scheme, ropen would be a monospecific genus. They may be the last survivors of a bioluminescent lineage.
Ethology: Adult ropen generally do not form large groups. However, the species is monogamous and mates for life. These pair-bonds endure throughout the year, with both animals roosting and hunting together. Only when nesting do adult ropen gather in large numbers. Then they will group in colonies of dozens. In comparison, juvenile ropen are intensely social and gather in flocks of hundreds for mutual protection. These linger close to nesting colony sites.
All life stages of ropen are exclusively nocturnal. While modern pterosaurs are typically extremely vocal, ropen are nearly silent. Instead, they primarily use their bioluminescence to communicate by flashing in different patterns. In addition to territorial and mating displays, ropen (usually juvenile ones) use this to tell each other about food. The only vocalizations ropen make are the alarm calls of juvenile ropen, and even then in contrast to most pterosaurs they don't have separate alarm calls for different threats. Instead, while giving the alarm call a juvenile ropen flashes distinct patterns of light on their belly, alerting others of the threat. Other juveniles then make the same flashes. The light show that results disorients predators.
There is some evidence of adult ropen using their bioluminescence to attract fish. Occasionally one half of a mated pair has been sighted tightly circling a school of fish while lit up. Their mate then feeds by skimming. The circling may simply be to attract their mate's attention to a good food source, however. There are no records of juvenile ropen using their boluminescence to attract insect prey.
Life Cycle: Ropen reach sexual maturity at two years. They mate in late April and lay two to three eggs shortly afterwards at the start of the dry season; this ensures that parents can forage at sea without fear of storms. Come the start of the wet season in December, the young have left the nest and will have an easier time hunting due to the seasonal abundance of insects.
Ecology: Adult ropen feed on fish and squid. Their habit of roosting inland makes them extremely effective nutrient pumps for upland forests. Plant biomass around ropen roosts is much higher, and around nesting colonies it is higher still. Animal biodiversity and biomass around ropen nesting colonies is noticeably higher, and this helps support the juvenile ropen, which feed mostly on insects and other arthropods.
In-Situ Conservation Efforts: Ropen benefit from conservation efforts to reduce deforestation and maintain fish stocks in Oceania, as do many other species. Direct persecution of the species is uncommon and not a significant threat.
Ex-Situ Conservation Efforts: None are necessary at this time.