Attaching is the best word I can come up with because it cleary shows (to me at least) that in extreme ancient times martians had to do massive clean-up work to deal with the extreme hardship of cleaning up after their dead creatures died in a major calamity that ruined their atmosphere and destroyed the surface of their planet, causing them to go underground. Through the eyes of Curiosity Rover, there truly appears to be a diagram in "outside floor sculpture form", of segmented sections "attaching" to each other. So the dead creatures would be in one total section and not all over the place causing more disease than they already had.