It was found that the fish species Dascyllus flavicaudus contributes to faster recovery of damage in corals of the genus Pocillopora where they live. The presence of these fish reduces wound healing time by 38–55 percent and also helps maintain photosynthesis at an optimal level.
Fish living in symbiosis with corals use them as shelter from predators. This mutually beneficial alliance benefits the corals themselves: the fish improve water circulation by moving and flapping their fins inside the coral structure. Furthermore, they help corals resist temperature stress and bleaching when water temperatures rise, and they stimulate growth by supplying nitrogen released by the fish through urine. Symbionts also provide protection against coral-eating predators, allowing corals to save energy that they would otherwise spend on regeneration.
Despite the general benefits of symbiosis, it was previously unknown whether it influences wound healing if damage occurs. A team of researchers led by Adrian Stayer from the University of California, Santa Barbara, decided to test this question. Scientists took branches of Pocillopora corals from six healthy large colonies located in a lagoon on the northern coast of Moorea Island (French Polynesia) and distributed them into six aquariums, twelve specimens in each. Three aquariums were placed with six adult Dascyllus flavicaudus fish caught from the same reefs, while three aquariums were kept as a control group.
After inflicting controlled wounds on the corals using an airbrush (sized 1.48 ± 0.40 or 3.82 ± 1.08 square centimeters) and leaving four intact samples in each aquarium, scientists observed for 21 days. It was noted that in the presence of fish, wounds healed significantly faster: the area of small injuries decreased approximately 38.6 percent faster, and large ones by 55.7 percent. After three weeks, complete healing was observed in 16 out of 24 wounds in the fish aquariums, compared to 9 out of 23 in the aquariums without fish. Moreover, the fish maintained the photosynthetic activity of the damaged corals at a normal level, although this did not depend on their presence in healthy corals. It was also noted that the fish prevented the attachment of filamentous algae to the wounds; by the end of the experiment, such algae remained on eight damaged corals, seven of which were in the aquariums without fish.
The authors suggest that the influence of fish on regeneration may be related to already known protective functions, such as providing ventilation, supplying nitrogen, and reducing competition with algae. Nevertheless, the scientists pointed out some limitations of their study, including the small number of replicates, conducting the work in laboratory conditions, and the limited duration of the experiment. In particular, they could not detect any influence of the symbionts on coral skeleton growth, which might only appear after several months.
Researchers described the fossil of a six-to-seven-meter ichthyosaur, Platypterygius australis, which inhabited the inland Eromanga Sea in Australia during the Early Cretaceous period, approximately 105–106 million years ago. Among the scattered bones of this ancient reptile, fossilized remains of stomach contents were found. Analysis of this content showed that shortly before P. australis died, it had swallowed a pterosaur. There are two versions: either the ichthyosaur caught the winged reptile on its own, or it fed on its carcass. This marks the first documented case of an ichthyosaur feeding on a pterosaur.
Furthermore, based on tooth marks on the vertebrae, it is suggested that P. australis itself might have been killed and eaten by an even larger marine animal—the pliosaaur Kronosaurus queenslandicus. These research findings were published in the scientific journal Gondwana Research.
Periodically, paleontologists come across fossil remains of ancient animals containing coprolites—that is, preserved parts of stomach and intestinal contents. Such finds allow for the direct study of the diet and feeding behavior of long-extinct species. For example, previously, a coprolite was discovered belonging to a sauropod, young specimens of Diamantinasaurus matildae, which lived in Australia about 100 million years ago. Analysis of this sample confirmed that sauropods were herbivores and ingested food without much chewing.
A team of paleontologists led by Matt Andrew White from Northeastern University presented data on another discovery of a fossil animal with preserved gastrointestinal tract contents. The focus was on remains under identification number KK F1435, which were found in the Tulubook formation in Queensland, Australia. The age of this specimen is estimated at 105–106 million years. During that era, most of Australia was covered by the shallow inland Eromanga Sea.
Specimen KK F1435 consists of the remains of a large reptile, including a nearly complete skull with teeth and fragments of the postcranial skeleton, such as vertebrae, ribs, and limb bones. By studying this specimen, White and his colleagues classified the remains as belonging to the ichthyosaur Platypterygius australis of the family Ophthalmosauridae, which is well known to paleontologists and was described in 1972. It was established that this individual could reach a length of six to seven meters when alive.
About half a meter from the skull of KK F1435, White and his co-authors discovered a spherical mass, which they interpreted as fossilized stomach content that had fallen out of the abdominal cavity. From this structure, two fragments of pterosaur tooth bone from the family Anhangueridae were extracted, whose wingspan was presumably about four meters. The most likely scenario is that P. australis caught the pterosaur while it was flying over the sea and ate it. An alternative version suggests that the ichthyosaur fed on the carcass of a winged reptile that fell into the water.
According to researchers, this is the first known example of an ichthyosaur feeding on a pterosaur. Nevertheless, coprolites also contained (using neutron tomography) remains of more typical ichthyosaur food: several belemnites, as well as fish vertebrae and ribs and shell fragments. The stomach contents of P. australis indicate that members of this species, and possibly other Cretaceous ichthyosaurs, were generalist predators consuming a wide range of prey.
Notably, deep tooth marks were observed on the vertebrae of KK F1435, and some vertebrae were broken or missing. Judging by the size and shape of these marks, they were left by the pliosaaur Kronosaurus queenslandicus—an even larger marine reptile that reached over ten meters in length and occupied the position of apex predator in the Eromanga Sea. According to the most plausible version, the pliosaaur hunted the ichthyosaur, killed it, after which it fell to the seabed, damaging its skull from the impact. Then this same pliosaaur consumed the body of the victim, scattering the remains across the seabed over a distance of more than ten meters (possibly its relatives later acted as scavengers).
The research results demonstrate the presence of a complete food chain in the Eromanga Sea: large ichthyosaurs consumed mollusks, fish, and pterosaurs, and in turn became prey for more massive pliosaurs. Several years ago, paleontologists found a fragment of a lower jaw of an unknown pterosaur on the Tulubook formation, based on which a new genus and species—Thapunngaka shawi—was described. Scientists estimated the wingspan of this reptile to be six to seven meters, making it the largest pterosaur in Australia. There is a possibility that the bone found in P. australis's stomach belonged to T. shawi.
