Menarana

Menarana nosymena was a snake from the Maastrichtian Maevarano Formation of northwestern Madagascar. Its holotype, UA 9684, is an associated but incomplete set of vertebrae, rib fragments and part of the braincase. That cranial fragment is unusual among madtsoiid snakes: several bones at the rear of the skull are fused together. The structure led researchers to suggest forceful head-first burrowing, but the fossil preserves anatomy rather than behaviour. Menarana is one of the fossil snakes in the ancient lizard and snake catalogue.

Quick facts

A partial skeleton with an informative skull fragment

Thomas LaDuke, David Krause, Jason Scanlon and Nicholas Kley named the genus and species in their 2010 study of the Maevarano snake fauna. UA 9684 was collected at locality MAD93-14. The authors treated the vertebrae, ribs and braincase fragment as one individual because they share preservation and size and came from a small area, about two square metres. The specimen is associated, but it is not a fully articulated skeleton.

For description, the authors labelled elements within the holotype: a mid-trunk vertebra, a posterior trunk vertebra, the braincase piece, part of the atlas and a proximal rib fragment. Keeping these parts distinct matters because they preserve different anatomical evidence. The atlas and ribs are fragmentary, and the skull is represented only by its rear basal region.

The name Menarana comes from the Malagasy word for snake. The species epithet refers to the Malagasy words for island and red, a reference to Madagascar's familiar nickname. The name does not encode an ecological trait; the anatomy is what supports the evolutionary and functional interpretations.

Vertebrae and madtsoiid relationships

The trunk vertebrae have the zygosphene–zygantrum joints typical of snakes. Their neural arches and spines are relatively low, while the prezygapophyseal facets and haemal keel have a distinctive form. The broad, flattened keel on mid and posterior vertebrae, together with the shape of the articular surfaces, helps distinguish the species from other large madtsoiids.

The 2010 authors placed Menarana nosymena in Madtsoiidae, an extinct snake family known from several Gondwanan regions. A later phylogenetic analysis recovered Menarana among large southern madtsoiids, but relationships within the family remain sensitive to which incomplete taxa and characters are included. A family-tree position is an inference from comparative anatomy, not a feature visible on the specimen.

The incomplete vertebral series does not provide a direct full-body length. Scaling a few vertebrae to a modern snake would require assumptions about how many vertebrae are missing and how proportions varied along the spine. The specimen supports a substantial snake, but it does not justify a precise metre figure.

Why researchers proposed burrowing

The basicranium, or rear underside of the braincase, preserves several fused elements, including parts of the parabasisphenoid, basioccipital and otico-occipital region. Its integrated construction is uncommon among snakes. The 2010 study compared this condition with living groups that push their heads through soil and other confined substrates.

Such comparisons offer a functional hypothesis: a reinforced skull base may have helped resist loads during head-first digging. The fossil itself does not show a digging stroke. There is no associated tunnel, scratch surface, distinctive burrow fill or body pose that records Menarana moving through sediment. Nor does the partial skull preserve the snout well enough to reconstruct the exact digging motion.

A reinforced skull can have more than one mechanical explanation, and similar structures can evolve independently. The strongest account therefore keeps the observation and the inference separate: the braincase is fused; a fossorial lifestyle is plausible and was proposed by the authors; the exact behaviour remains unobserved.

Maevarano setting and missing evidence

Maevarano fossils accumulated in a seasonal river and floodplain system. Channel deposits, overbank muds and rapid burial created a varied record of land animals near the end of the Cretaceous. The small-area association of UA 9684 makes its bones more convincingly attributable to one snake than loose vertebrae spread across a broad deposit.

The holotype has no known teeth or complete jaws, and no stomach contents or prey remains can be assigned to it. A snake was a predator, but the prey size, feeding method and use of burrows cannot be specified from this material. Madtsoia and other snakes in the same regional fauna provide comparisons, not a direct record of Menarana's interactions.

The partial skeleton gives a rare look at the rear of an ancient snake skull alongside vertebrae and ribs. It cannot reveal skin pattern, colour, a full head shape, reproductive mode or exact body length. New material preserving a more complete skull or associated trunk could test both the diagnosis and the digging hypothesis.