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, means "true creature from the black lagoon" and is inspired by an old movie.

Eucritta had many features like other Carboniferous tetrapods and their close relatives. It had a short, wide skull, large eyes, and strong limbs. It looked a bit like Balanerpeton, an early land tetrapod that was one of the first members of Temnospondyli, a group that may have led to modern amphibians. But Eucritta did not have some special traits of temnospondyls or reptiliomorphs (the group that would later lead to reptiles and other amniotes).

Eucritta's mix of traits from baphetids, "anthracosaurs" (early reptiliomorphs), and temnospondyls shows that these three groups likely split apart during the Carboniferous, not earlier in the Devonian. Its limb shape suggests it lived on land, while some skull features show it may have used buccal pumping, a type of breathing seen in modern amphibians.

Discovery

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

Description

The skull of Eucritta was wide with a short, round snout and big eye holes close together. Skulls were from about 30 mm to 90 mm long. It had 38-40 teeth in the top jaw, with the biggest teeth at the front. The back of the skull had large, round temporal notches and included all the bones typical of early four-legged animals.

The body had a strong shoulder area and an odd-shaped forearm bone like other early four-legged animals. The hip area was normal for its time, with a two-part ilium and a flat ischium. The legs were square, and the feet had five toes each. The body was probably short and stout, with rows of tiny, sharp belly plates 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. This shows how it grew. Its skull stayed about the same shape as it grew, but its eye sockets got smaller. 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. This suggests they used another breathing method called costal ventilation, which uses the ribs to help breathe, like many modern animals do.

Classification

Eucritta was identified as a special animal in 1998. At first, scientists thought it was related to a group called baphetids, but they were not sure. Research in 2001 added another animal, Gephyrostegus, and showed that Eucritta might be closer to a group called temnospondyls.

More studies have tried to find where Eucritta fits among early four-legged animals. Some think it is close to baphetids, while others think it might be one of the first reptiliomorphs or temnospondyls. Even though there is some uncertainty, Eucritta is always found near the ancestors of several early groups, including baphetids, colosteids, and temnospondyls.