Paleontologists have described a new genus and species of tropicbird from a fossilized partial skeleton found in New Zealand. The fossil represents the first unambiguous record of tropicbirds — a group of birds now restricted to the tropics — from the Paleocene of the southern hemisphere.
The red-billed tropicbird (Phaethon aethereus subsp. mesonauta) in the waters around Trinidad and Tobago. Image credit: Dominic Sherony / CC BY-SA 2.0.
Tropicbirds are members of the Phaethontiformes, an order of birds that includes one living (Phaethontidae) family and one extinct (Prophaethontidae) family.
“Tropicbirds are highly aerial, plunge-diving and predominantly piscivorous birds, which occur in tropical and subtropical seas,” said Dr. Paul Scofield, a paleontologist at the University of Canterbury and Canterbury Museum, and his colleagues.
“The three living species are classified into the genus Phaethon and mainly differ in size and plumage features.”
“These pelagic birds are relics of a once much more widespread and diverse group of birds, whose fossil record goes back into the earliest Paleogene.”
The newly-identified species, named Clymenoptilon novaezealandicum (or Zealandian tropicbird), lived in what is now New Zealand approximately 62 million years ago.
Its fossilized remains, including the skull, vertebral column, right wing and pectoral girdle elements, pelvis, were collected from the Waipara Greensand in the Canterbury region.
“It is the second tropicbird found in the Waipara Greensand (the first one was a smaller, unnamed specimen described in 2016),” the paleontologists said.
Clymenoptilon novaezealandicum has features that distinguish it from all other known fossil tropicbirds and suggest it was, evolutionarily speaking, an ancestral form of tropicbird.
Features of the skull, wing, and pelvis suggest it had different feeding/foraging habits from living and other extinct tropicbirds, but because the specimen has no legs, it is not possible to get a complete picture of its mode of life.
The age and ancestral characteristics of the new species suggest that tropicbirds may have originated in the southern hemisphere — up until now all other fossil species had been known from the northern hemisphere only.
“Paleocene Phaethontiformes had widely disparate geographic occurrences in New Zealand (Clymenoptilon), Northern Africa (Lithoptila), Europe (Prophaethon), western Asia (Zhylgaia), and North America,” the researchers said.
“These birds therefore seem to have rapidly dispersed across the globe, and potential geographic barriers, such as less productive marine zones around the equator, apparently did not constitute dispersal barriers.”
“The wide distribution of the Phaethontiformes and Pelagornithidae in the early Paleogene stands in sharp contrast to the geographic restriction of coeval diving seabirds, with taxa such as the Vegaviidae and Sphenisciformes having been, and still being in the case of the Sphenisciformes, restricted to the southern hemisphere.”
“Apparently, different factors limited the dispersal of aquatic and pelagic seabird taxa in the early Paleogene, but it has yet to be determined why, for example, penguins were not able to disperse into the northern hemisphere.”
Their paper was published in the Alcheringa: an Australasian Journal of Palaeontology.
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Gerald Mayr et al. Partial skeleton from the Paleocene of New Zealand illuminates the early evolutionary history of the Phaethontiformes (tropicbirds). Alcheringa: an Australasian Journal of Palaeontology, published online August 28, 2023; doi: 10.1080/03115518.2023.2246528
