Bohaiornithidae

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Bohaiornithidae are an early group of enantiornithean “stem birds” known from the Early Cretaceous of China, about 125–120 million years ago. All well-supported specimens come from the northeastern part of modern China, in the eastern and southern foothills of the Greater Khingan mountains, and they were a prominent part of the Jehol Biota.

What they looked like
- Unlike modern birds, bohaiornithids had teeth. Their teeth were large, strong, and somewhat cone-shaped with sharp tips that curved backward. The front teeth were larger than those toward the back, and the first teeth in the upper jaw were smaller than the others.
- Their skeletons show several distinctive features: a sternum with lateral projections that extended backward and outward, wide, rounded tips on the furcula (wishbone), and a scapula (shoulder blade that curves downward). They also had gradually tapering pygostyles (the tail bone at the end of the spine).
- The toes were arranged so the innermost toe was thicker than the others, while the middle toe was long and thin, and all claws were long and curved.
- Adults were generally similar in size across species, about the size of a pigeon, which is large for many Jehol enantiornitheans. The smallest individuals were about half the size of the largest.
- Many bohaiornithids preserved feathers. Some specimens show long, ribbon-like tail feathers with barbs only at the tips. A subadult with iridescent head and body feathers has also been described.

Feathers, display, and digestion
- The long tail feathers might have been used in courtship display, a feature seen in several enantiornitheans.
- In at least one specimen, rocks found in the stomach region were once thought to be gastroliths (stomach stones used for grinding food). Later study showed these were mineral concretions, not evidence of a particular diet.

Lifestyle and diet
- The footprint and bone structure suggest a balance between tree-dwelling and ground-walking abilities, with long claws indicating they were not specialized climbers like some modern perching birds.
- Their teeth imply they fed on hard-shelled prey, and some researchers have suggested a possible fish-eating habit, but the anatomy does not point to a single, clear lifestyle. The exact diet remains uncertain.

Classification and phylogeny
- The family Bohaiornithidae was defined by Wang and colleagues in 2014 as all descendants of the common ancestor of Bohaiornis guoi and Shenqiornis mengi. Bohaiornis guoi is the type species.
- Over time, other genera such as Zhouornis, Parabohaiornis, and possibly Linyiornis and Fortunguavis have been discussed in relation to Bohaiornithidae, but their exact placement has been debated.
- Phylogenetic analyses place bohaiornithids among the enantiornitheans, a large and diverse group of early birds that were not modern birds. Some studies suggest bohaiornithids form a polytomy (an unresolved branching pattern) with Linyiornis and Fortunguavis, indicating ongoing questions about how these genera are related within the family.

In short, Bohaiornithidae were distinctive, toothy early birds from a narrow time and place in China, notable for their strong teeth, peculiar skeletal features, and a mix of plumage traits that hint at display behaviors. While they were common in their ecosystem, their exact relationships within the early bird family tree remain a topic of study.