In contrast to the stratified squamous epithelium of the skin, the intestinal barrier is composed of a single layer of columnar epithelial cells However, this single layer of intestinal epithelial cells is made of diverse cell types with absorptive, secretory, and immune function
Fossils provide solid evidence that organisms from the past are not the same as those found today; fossils show a progression of evolution. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. This approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years.
