Brahmic scripts such as devanāgarī, Gurmukhī, and Bengali are noted for joining glyphs with a long horizontal line across the top (shirorekhā). However, other examples such as Tamil use more curls and curves, and lack the shirorekhā.
I am told that one reason for this change was because manuscripts in certain regions used parchment or vellum, and in other regions used palm leaves. Writing on a palm leaf, if you made long, straight horizontal marks on it, you could split the fibers.
