This egg seems to be home to more than just the creature growing inside...
Terraturts like be in low-lying, wet areas where the water does not move that fast. There they do not have to worry about their environment changing too much and can focus on growing into their terrarium-like, glass shell. Terraturts actually shed their hard, outer shell once the glass has grown on the inside of the shell. After the glass casing matures, the shell simply drops off the creature's body.
A Terraturt's terrarium is primarily home to insects. Some of these insects can be found natively on Ark outside of the glass terrarium but others are Terraturt-only insects. It seems that there is something special about the Terraturt's biology and genes that gives rise to birth new life—perhaps we could call it a self-contained experiment in evolution and natural selection.