It is at this time in the earth's history that mammals first made their appearance, so these fossil remains provide a wonderful 
(these fossil; remains; provide a wonderful) (It; is; at this time in the earth's history; that mammals first made their appearance, so these fossil remains provide a wonderful)
these fossil It
remains is
provide a wonderful
at this time in the earth's history that mammals first made their appearance, so these fossil remains provide a wonderful