#avialans

Silvereye/tauhou/Zosterops lateralis

Doing an art challenge for bird of the year 2025. Prompt list is by a mutual on cara.

After the K-T extinction, the last remaining dinosaurs began to diverge, trying on many different shapes and sizes. While most birds stayed in the small forms that had kept them alive for so long, some achieved massive sizes. Some even reached these sizes while still retaining their ability to fly. One such genus was Pelagornis, a group of “pseudotooth birds.” While the gene for teeth was lost in birds, the Pelagornithids found a work-around, evolving tooth-like edges to their beaks. These were seabirds, using their saw-edged beaks to grip onto slippery fish and squid. The largest species of Pelagornis was Pelagornis sandersi. P. sandersi was not only the largest Pelagornis, but also had the widest wingspan of any known bird, estimated at 6.06 to 7.38 m (19.9 to 24.2 ft) long. P. sandersi had short, stumpy legs, and likely spent most of its time on the wing. It would have had to take off by dropping from cliffs, utilizing air currents to glide into the air. It would have been able to travel long distances like this, without landing, similar to modern day albatrosses.

Fossils of Pelagornis have been found worldwide, including in the Aridal Formation of Morocco, the Chandler Bridge Formation of South Carolina, the Bahía Inglesa Formation of Chile, the Black Rock Sandstone of Australia, the Molasse Coquilliere Formation of France, the Calvert Formation in Virginia, the Pisco Formation of Peru, the Castillo Formation and Capadare Formation of Venezuela, the Greta Formation of New Zealand, and the Purisima Formation of California. This worldwide distribution means they would have been living alongside a large variety of Eocene to Early Pleistocene animals, and eating a large variety of fish species. It is unknown why these giant seabirds went extinct, but they may have been encountered by archaic humans in the Early Pleistocene.

#Archovember Day 19 - Kelenken guillermoi

The Phorusrhacids, commonly known as “terror birds” were the last dinosaurian apex predators to hunt on land. The largest known phorusrhacid, Kelenken guillermoi, lived in the Middle Miocene of Argentina. It is known only from a skull (though it is one of the most complete large phorusrhacid skulls) and a leg and toe bone, so the rest of its anatomy must be inferred from other phorusrhacids. The skull, the largest of any known bird, is 716 mm (2.3 ft) long, allowing us to estimate Kelenken’s height at around 3 m (9.8 ft) tall. Kelenken would have lived in an open, grassland environment. Its long, slender tarsometatarsus suggests that it was a fast runner, likely adapted for chasing down small animals like rodents, marsupials, and lizards. While large, its skull was relatively weak, so it would have had difficulty gripping onto and subduing large, struggling prey. Instead, it likely preyed on animals it could swallow whole and/or, if targetting larger prey, used repetitive, targeted pecks with its beak. It could have also used its feet to restrain prey. While only Kelenken’s phalanx toe bone has been found, other large phorusrhacids (as well as their living relatives, the seriemas) have a “sickle claw” on their second digits, similar to dromaeosaurs. These claws could have also been used to restrain prey, or to kick out and strike.

Dinosaur Kumimanu fordycei, of Early Paleogene, New Zealand!

For a few million years after the K–Pg mass extinction, the last remaining avialans, the birds, began to “experiment” more with their forms as the larger dinosaurs died off. With all these new niches opened up, someone had to fill them. One of these experimental forms were the Sphenisciformes, the “penguins”. These semi-aquatic dinosaurs spread across much of the Southern Hemisphere, from the tropics to the subantarctic, developing unique adaptions for life in the ocean, and are successful to this day. One of the oldest and largest was Kumimanu, meaning “monster bird" in Māori. There were two species, K. biceae and K. fordycei, with Kumimanu fordycei being the larger of the two, with an estimated weight of 148–159.7 kg (326–352 lb). This large size would have allowed Kumimanu to take advantage of larger fish and squid, diving deeper and surviving colder waters than its relatives. This is eventually what allowed giant penguins to spread farther north into the Antarctic. The extinction of giant penguins seems to coincide with the spread of seals around the Southern Hemisphere, as both large aquatic predators would have had to compete for prey and breeding sites.

Kumimanu fordycei was found in the Moeraki Formation, 55.5–59.5 million years ago in New Zealand. It would have lived alongside other penguin species like its relative Kumimanu biceae, as well as another penguin that was about half its size (but still a bit taller and heavier than today’s Emperor Penguin), Petradyptes stonehousei.

Dinosaur Palaelodus ambiguus, of Late Paleogene, France and Germany!

The Oligocene is often considered an important time of transition, a link between the “archaic” world of the tropical Eocene and the more “modern” ecosystems of the Miocene. During this time one group of dinosaurs, the bizarre Eocene Phoenicopteriformes, which today are represented only by the living family Phoenicopteridae (flamingoes), slowly began to diversify. The genus Palaelodus, a long-necked semi-aquatic phoenicopteriforme, was highly successful, living worldwide, and surviving from the Oligocene to the Miocene, with records indicating at least one species (or at least a relative) survived into the Pleistocene of Australia. Palaelodus’ skull shares ancestral traits with both flamingos and grebes (the closest living relative of flamingos). Their bills are straight and lack the internal spongy texture of flamingos, but their skull clearly shows the presence of salt glands, a trait shared with flamingoes. Although still relatively long, Palaelodus’ legs were not nearly as elongated as those of modern flamingos. It did not seem to have developed the mechanisms yet for filter feeding, and was likely more adept at swimming and using its long neck for foraging for small invertebrates like caddisflies and snails. The species we are looking at here is Palaelodus ambiguus, from the Late Oligocene to Middle Miocene of France and Germany. Known from thousands of bones, P. ambiguus is one of the best known species of Palaelodus.

Social behavior for Palaelodus seems to have varied between species. Species from Australia and New Zealand may have been less social, as their fossils are less commonly found, while species from Europe, like Palaelodus ambiguus, likely lived in large flocks due to their bones being found in great numbers. Similar to flamingos, they inhabited saline and brackish lakes. Fossils of Palaelodus ambiguus have been found in the Saint-Gérand-le-Puy area in France and the Mainz Basin in Germany. Material from the Oligocene to Miocene Taubuté Basin (Tremembé Formation) of São Paulo, Brazil, has also been tentatively assigned to this species.