#clymenoptilon

During the start of the Cenozoic, the oceans were relatively empty. Gone were the great marine reptiles like mosasaurs and plesiosaurs, as were ammonites and many large predatory fish. As soon as birds could, they entered the ocean to reap its bounties, whether by flying over the surface or diving to the depths. This is especially evident in Aotearoa (New Zealand), where lots of early seabirds, including the first penguins, were found in Paleocene sediments dating about 62 million years ago.

Kumimanu: One of the largest known penguins, and one of the earliest, standing over 1,5 metres tall and weighing 90-150 kilograms.

Sequiwaimanu: Another early penguin, known from a skull that preserves a long, spear-like beak.

Muriwaimanu: A relatively small early penguin. Like other early penguins, it had relatively long legs and somewhat flexible wings.

Kupoupou: A small early penguin with derived traits, like a flipper-like wing and short legs.

Waimanu: The earliest known penguin, and also relatively large at the size of the modern king penguin (Aptenodytes patagonicus)

Protodontopteryx: The earliest known pelagornithid, large soaring marine birds. This earliest member of the family sports a "modest" 2-metre wingspan.

(Type specimen of Clymenoptilon novaezealandicum [scale bar = 50 mm], from Mayr et al., 2023)

Meaning of name: Clymenoptilon = Clymene [mother of Phaethon in Greek mythology, referencing the extant tropicbird genus Phaethon] feather [in Greek]; novaezealandicum = from New Zealand

Age: Paleocene (Danian–Thanetian)

Where found: Waipara Greensand, Canterbury, New Zealand

How much is known: Partial skeleton of one individual, including the skull, the right wing, and several vertebrae.

Notes: Clymenoptilon was a close relative of extant tropicbirds, a group of seabirds with long, streamer-like tail feathers. Modern tropicbirds are restricted to equatorial regions, but fossils of their close relatives have been found all over the world, with Lithoptila from the Paleocene–Eocene of Morocco and Prophaethon from the Eocene of the United Kingdom being the most completely known. Although a previously described fossil of a smaller bird from the Waipara Greensand may represent another proto-tropicbird, Clymenoptilon provides the clearest evidence to date that members of this lineage were present in the Paleocene of New Zealand as well.

Clymenoptilon is one of the oldest proto-tropicbirds known and appears to have been less closely related to modern tropicbirds than Lithoptila and Prophaethon. Whereas Prophaethon was probably better adapted for swimming than modern tropicbirds (which may rest on the water's surface but primarily catch prey by diving from the air), Clymenoptilon may have been a less specialized swimmer than Prophaethon based on its hip anatomy, though further assessment of its swimming capabilities will depend on the discovery of its hindlimb bones, which are currently unknown.