The incisors are orthodont; the rostrum is short and the braincase is wide.
The tympanic bullae are less inflated and less protruded from the braincase.
The braincase of the skull is crushed in three places as though by a raptor's beak.
These dimensions indicate that the braincase reaches full size early.
It is distinguishable by greater general breadth and by the depth of the braincase, which perceptibly exceeds that of S. notatus.
That part of the braincase immediately above posterior root of zygoma is more conspicuously inflated.
The braincase is nearly as broad as in the Bornean species, but the zygomatic width is distinctly less.
From M. occultus, M. fortidens differs in having the rostrum (viewed from above) smaller in relation to the braincase.
The limbs and braincase are more primitive than those so far described in any amphibian.
Anterior to the otic capsule the lateral wall of the braincase cannot be seen, and may not have been ossified.