Crotalus morulus, or the Tamaulipan rock rattlesnake, is a species of rattlesnake from Mexico, closely related to and previously considered a subspecies of Crotalus lepidus.

[2][3] The name morulus comes from the Latin word morus for mulberry in reference to their mottled patterns.

[4] As juveniles, Crotalus morulus has a dark pattern with black blotches dorsally on a grey base, the dark colours blending between the patterns.

[4] They are distinguished from Crotalus lepidus by this dark colouration and higher number of blotches.

[3] Their rattle is also known to be fluorescent, although more dull in adults than neonates.