A new genus and species of bohaiornithid enantiornithine bird has been identified from a nearly complete and articulated skeleton preserved with traces of feathers found in northeastern China.
Holotype of Neobohaiornis lamadongensis. Image credit: Shen et al., doi: 10.1038/s41598-024-82869-8.
Enantiornithes, or ‘opposite birds,’ are named for a feature in their shoulder joints that is ‘opposite’ from what’s seen in modern birds.
These birds had teeth and clawed wings and occupied various ecological niches, comparable with the Neornithes.
They were once the most diverse avian group, but they went extinct 66 million years ago following the meteor impact that killed most of the dinosaurs.
The newly-identified enantiornithine species lived during the Cretaceous period, approximately 119 million years ago.
Scientifically named Neobohaiornis lamadongensis, the bird belonged to an early enantiornithine family called Bohaiornithidae.
“The most diverse Mesozoic clade of birds was the Enantiornithes,” said Field Museum paleontologist Dr. Jingmai O’Connor and colleagues.
“With over one hundred named genera described to date, fossils referable to this group of predominantly arboreal birds have been described from nearly all continents and account for half the known Mesozoic avifauna.”
“Although restricted to smaller body sizes in the Early Cretaceous, by the Late Cretaceous Enantiornithes achieved a significant size range and occupied a diversity of ecological niches.”
“The greatest number of enantiornithine fossils comes from deposits that record the Early Cretaceous Jehol Biota in northeastern China, accounting for slightly more than half of the known Mesozoic avian diversity (130 to 120 million years ago).”
“Bohaiornithids are characterized by a distinct robust tooth morphology,” they added.
“The teeth are apically pinched, gently apicodistally curved, and mesiodistally robust near the basal portion.”
“The rostral-most teeth are typically reduced in size compared to the remainder of the tooth row.”
“Like most enantiornithines, bohaiornithids were likely arboreal based on their pedal morphology, in which the pedal phalanges elongate distally within each digit ending in large, recurved unguals.”
“However, compared to other species their claws were proportionately larger and more recurved.”
“The largest members of the clade (Bohaiornis) likely approached similar sizes to extant diminutive accipitrids (200 g).”
“The largest known bohaiornithids are 167% the size of the smallest previously described specimen, an unnamed juvenile.”
The fossilized skeleton of Neobohaiornis lamadongensis was recovered from the Jiufotang Formation near Lamadong in the Chinese province of Liaoning.
“The fossil preserves a halo of feather traces extending from the caudal margin of the external nares down the neck, from the shoulder and pelvic regions, crural feathers, remiges, and a pair of rachis-dominated tail feathers,” the paleontologists said.
According to the researchers, Neobohaiornis lamadongensis is estimated to have a body mass of around 50 g.
“In contrast to Neobohaiornis lamadongensis, all other bohaiornithids are estimated to have body masses that exceed 100 g,” they said.
“The discovery of Neobohaiornis lamadongensis therefore considerably increases the body size range and diversity of bohaiornithids.”
“This hints at greater ecological diversity, although there currently exists no direct evidence concerning diet or ecological niche in this clade.”
Neobohaiornis lamadongensis also preserves new information pertaining to the plumage in bohaiornithid birds.
Along with another specimen, the fossil indicates the primary feathers of bohaiornithids were approximately twice the length of the humerus, with rounded feather margins, suggesting broad wings as in most other Early Cretaceous enantiornithines.
“The new specimen represents a new species that contributes to the considerable recognized diversity of bohaiornithid enantiornithines in the Jiufotang Formation, especially with regards to body size,” the scientists said.
“This specimen highlights the skeletal adaptations, such as the reduction of the alular and major digit and possible increase in sacral vertebrae, evolved within this lineage, as they evolved more refined flight capabilities in parallel to other enantiornithine lineages, like the Longipterygidae.”
“The new specimen preserves the best-known plumage of any bohaiornithid, which demonstrates that rachis-dominated tail feathers were likely widespread in this clade, as were crural feathers, and that the rostrum lacked feathers.”
The work appears in the journal Scientific Reports.
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C. Shen et al. 2024. A new diminutive species of bohaiornithid enantiornithine (Aves: Ornithothoraces) from the Lower Cretaceous Jehol Group, northern China. Sci Rep 14, 31363; doi: 10.1038/s41598-024-82869-8
