Eucritta

Eucritta (meaning "true creature") is an extinct genus of stem-tetrapod from the Viséan epoch in the Carboniferous period of Scotland. The name of the type and only species, E. melanolimnetes, ("true creature from the black lagoon") is a homage to the 1954 horror film Creature from the Black Lagoon.

Eucritta possessed many features in common with other generalized Carboniferous tetrapods and tetrapod relatives. With a short, wide skull, large eyes, and strongly-built limbs, Eucritta proportionally resembled Balanerpeton, a contemporary terrestrial tetrapod which was one of the earliest members of Temnospondyli, a successful tetrapod group which may have produced modern amphibians. However, Eucritta lacked key temnospondyl adaptations, while also not showing certain adaptations of reptiliomorphs (the tetrapod lineage that would lead to reptiles and other amniotes).

Eucritta's mosaic possession of characters seen in baphetids, "anthracosaurs" (early reptiliomorphs), and temnospondyls suggests that these three groups diverged in the Carboniferous rather than earlier, in the Devonian. Its limb proportions support terrestrial preferences while skeletal features suggest that it utilized buccal pumping, the type of breathing used by modern amphibians.

Discovery

Eucritta is known from five specimens found in a layer of black rock at East Kirkton Quarry in Scotland. Four of these specimens were described by paleontologist Jenny Clack in 1998. The most complete specimen, called the holotype, includes a skeleton and skull. Another specimen has just a skull, which is larger than the holotype. These fossils were discovered by fossil collector Stan Wood in the late 1980s. By 2001, a fifth specimen had also been found.

Description

The skull of Eucritta was broad with a short, rounded snout and large eye sockets close together. Skulls ranged from about 30 mm to 90 mm long. It had 38-40 teeth in the upper jaw, with the largest teeth near the front. The rear of the skull had large, rounded temporal notches and included all the bones typical of early tetrapods.

The body had a robust shoulder girdle and an irregularly shaped forearm bone similar to other early tetrapods. The pelvic girdle was typical for its time, with a two-pronged ilium and plate-like ischium. The legs were rectangular, and the feet had five toes each. The body was likely short and squat, with rows of small, needle-like belly scutes running down the middle.

orbits
tempnospondyl
Balanerpeton
temporal notches
intertemporal bone
supratemporal bone
squamosal
postparietal
plesiomorphic
anthracosaurs
tabular
postorbital bone
cleithrum
scapulocoracoid
interclavicle
clavicles
humerus
Baphetes
amniote
ulna
radius
olecranon process
unguals
ilium
ischium
pubis

Paleobiology

Eucritta is special because scientists found many fossils of different sizes, showing how it grew. Its skull stayed about the same shape as it grew, but its eye sockets got smaller compared to the rest of the skull. Unlike some of its friends, Eucritta seems to have lived in its home, East Kirkton, at many ages, not just as an adult. It had long legs, which suggests it could move well on land.

Eucritta likely used a special way to breathe called buccal pumping. This means it used muscles in its neck to fill its mouth with air and push the air into its lungs. This is similar to how modern amphibians breathe. Eucritta had a short, wide skull and straight ribs, which fits with this breathing method. Other creatures from the same place had different skull shapes and curved ribs, suggesting they used another breathing method called costal ventilation, which uses the ribs to help breathe, like many modern animals do.

Classification

Eucritta was recognized as a unique animal when it was first described in 1998. Early studies suggested it was closely related to a group called baphetids, but its exact position was unclear. Later research in 2001 included another reptile-like tetrapod, Gephyrostegus, and found that Eucritta might be closer to a different group called temnospondyls.

Additional studies over the years have tried to pin down Eucritta's place in the family tree of early four-legged animals. Some place it close to baphetids, while others suggest it might be one of the earliest reptiliomorphs or temnospondyls. Despite some uncertainty, Eucritta consistently appears near the common ancestors of several early tetrapod groups, including baphetids, colosteids, and temnospondyls.