Complex sentence: Their bodies had settled in anoxic mud and were soon covered with further extremely fine silty sediments; without oxygen, their remains resisted decay: these specimens preserved remains of flight feathers and traces of the webbing between their toes.
Split into simpler sentences: Their bodies had settled in anoxic mud and were soon covered with further extremely fine silty sediments. Without oxygen, their remains resisted decay: these specimens preserved remains of flight feathers and traces of the webbing between their toes.