Twitter has a new look on mobile. It has swapped it's URLs for clickable images and text. It makes sense for advertisers because richer media will now be embedded in the stream. However, it is also a bit of an acknowledgement that the 140 character format that was the origin of the platform has moved on.
The new format makes things less complicated for end users. Not only is the URL gone — just click on the card to open the link — but the new display allows Twitter to show more information about a link to users before they open it. That does impinge on your timeline — bigger cards means you see less information on your screens — but it certainly looks a lot slicker and is more informative to boot.