Westlothiana’s hidden gills overturn its reptile ancestry
X-ray scans of Westlothiana lizziae, a Scottish fossil dating back 345 million years, revealed internal gills and a fish-like mouth. The anatomy moves the animal away from its familiar position near reptile ancestors and toward earlier relatives of four-limbed vertebrates. Its five digits and claw-like bones also complicate how scientists identify the earliest land-adapted animals from fossil footprints.
Science··Morning
Scans reveal gills inside the fossil
A new examination of Westlothiana lizziae, a fossil from Scotland nicknamed Lizzie, has revised its place in vertebrate evolution. Hidden internal gills and primitive skull features moved the animal away from its longstanding classification near the ancestors of reptiles. The peer-reviewed study was published on September 30.[1], [2]
The specimen dating back 345 million years was found in 1984. It is compressed between two rock slabs, which concealed much of its anatomy. Researchers used X-ray tomography to reconstruct bones hidden inside the rock.[1]
A fish-like mouth changes the family tree
The scans exposed an ossified internal gill skeleton and a mouth lined with many small teeth. A phylogenetic analysis, which compares anatomical relationships, placed Westlothiana among stem tetrapods: early relatives of four-limbed vertebrates. The team interprets its lifestyle as aquatic or amphibious rather than wholly terrestrial.[1]
Claw-like feet complicate ancient trackways
Westlothiana still had five digits and claw-like terminal bones. Those traits show that features commonly associated with life on land appeared in a patchwork across early lineages. Claw-shaped impressions in fossil trackways therefore cannot alone identify an amniote, the group containing modern reptiles, birds and mammals. Earlier tetrapod relatives could also have made such tracks.[1]
