[Photo] The tiny creature is the earliest recorded example of an axial bifurcation malformation. It did not survive long after birth (Image: Eric Buffetaut et al)

A remarkably well-preserved fossil of a two-headed reptile has been discovered in the Early Cretaceous Yixian rock formation in northeast China.

The tiny skeleton of a hatchling choristodere ??? a group of extinct aquatic reptiles with long necks ??? has two heads and two necks, fused at their base. The 120-million-year-old specimen is thought to be the oldest example of a developmental anomaly known as axial bifurcation.

While rare, this type of malformation has been seen before in living snakes, crocodiles, lizards and turtles ??? some of which have survived for several years in captivity.

However, judging from the extreme juvenility of the fossilised skeleton ??? its proportionally large head and eye orbits ??? the tiny creature did not survive for long, say its finders Eric Buffetaut at National Centre for Scientific Research in Paris, France, and colleagues.

As an adult, the choristodere could exceed 1 metre in length, although the neonate found was just 70 millimetres long.