VERTEBRATE INCLUSIONS IN AMBER: A UNIQUE PRESERVATION PROVIDING A WEALTH OF PALEONTOLOGICAL INFORMATION

Burmese amber (~98.8 Ma) contributes in an outstanding manner to our knowledge of terrestrial Cretaceous ecosystems. Over the past few years, multiple discoveries in Burmese amber have highlighted the exceptional preservation and scientific interest of vertebrate inclusions in amber. Here we describe a complete bird foot as well as sample sets of isolated feathers trapped in Burmese amber.

The bird foot DIP-V-19354, shows complete metatarsals and digits, including the claws. Osteological features support a placement among the Enantiornithes, an extinct clade of avialans considered the most abundant and diverse of the Mesozoic era. The detailed study of the integumentary structures reveals that the bones are entirely encased in soft tissues. Scutellate scale filaments are present along the metatarsals and digits. Their distribution and size on the longest digit suggest a mechanosensory tactile role of these structures.

One of the most peculiar feather morphotypes discovered to date are rachis dominated feathers (RDFs). Detailed study of specimens trapped in amber demonstrates that RDFs form a distinct feather morphotype having a ventrally open rachis. Significant variability in microstructure, pigmentation, and symmetry is reported. In large sample sets of isolated feathers, several structural types can be differentiated, including flight feathers, contour feathers, semiplumes, and filoplumes. In some cases, peculiar pigmentation patterns and structural features can be documented. Additionally, different developmental stages have been captured in the assemblages with some examples of erupting feathers or neoptile plumage.

Vertebrate inclusions in amber provide the unique opportunity of combining osteological information with details on integumentary structures, such as soft tissues and plumages. Nonetheless, even in the absence of associated skeletal material, isolated vertebrate remains such as feathers remain of high scientific interest. The remarkable preservation of these delicate structures in amber implies a remarkable potential for significantly improving our knowledge of feather evolution and diversity.