Compound osteoderms preserved in amber reveal the oldest known skink

Area of Science:

• Paleontology
• Herpetology
• Evolutionary Biology

Background:

• Scincidae (skinks) are a highly diverse and widespread group of reptiles.
• Fossil evidence for early crown-skinks is scarce, with no complete pre-Cenozoic specimens known.
• Disarticulated fossils are common, but their definitive assignment to Scincidae is challenging.

Purpose of the Study:

• To describe the first unambiguous fossil crown-skink specimen.
• To investigate the evolutionary origins of key skink features, such as compound osteoderms.
• To understand the role of morphological innovations in skink diversification.

Main Methods:

• Analysis of a well-preserved fossil specimen from 99-million-year-old Burmese amber.
• Comparative morphological analysis with extant skink species.
• Phylogenetic placement within Squamata based on key anatomical features.

Main Results:

• The fossil represents the oldest definitive crown-skink, dated to the Cretaceous period.
• It possesses compound osteoderms, formed from articulated osteodermites, a characteristic feature of extant skinks.
• The specimen exhibits a unique combination of dorsal and ventral compound osteoderms and overlapping cycloid scales.

Conclusions:

• Compound osteoderms likely evolved in response to increased scale overlap and reduced dermal armor stiffness.
• This innovation may have been a crucial factor enabling the evolutionary success and diversification of the Scincidae family.
• The discovery provides critical insights into the early evolution and paleobiogeography of skinks.