On testwiki wmf.9 the suggested image for Thanatotheristes is the small-sized (9x17 px) image - File:Arrow_for_fossil_range_17x9.png.
Clicking 'yes' to insert the image produces a broken caption view:
Click on the animated gif :
This task is for making sure the image is not stretched to the full width if its width is smaller than the device width. Image suggestions that don't meet the minimum width requirements should not be shown (this is handled separately via T296218: Add image: Set a minimum width for image suggestions).