Madtsoiidae is a speciose family of extinct snakes that achieved a wide
Gondwanan and trans-Tethyan distribution by the Late Cretaceous, surviving until the late
Pleistocene. Gigantophis garstini, the first and largest described madtsoiid, was recovered
from the upper Eocene of Fayum, Egypt. The twenty vertebrae that comprise the syntype
have only received a brief description, hindering the referral of specimens to this taxon and
our understanding of madtsoiid interrelationships in general. A detailed re-description of
the syntype material demonstrates the validity of Gigantophis, based on two
autapomorphies (including a strongly depressed neural canal in posterior trunk vertebrae)
and a unique combination of characters. Referred material from the lower Paleocene of
Pakistan differs significantly, and we restrict Gigantophis to the middle–late Eocene of North
Africa. Using a model of morphological variation in extant snakes, we estimate that
Gigantophis was 6.9 ± 0.3 m long. A phylogenetic analysis using the largest sample of
putative madtsoiids (20 OTUs) and a revised and augmented matrix (148 characters), places
Gigantophis as sister taxon to the latest Cretaceous Indian snake Madtsoia pisdurensis.
Whereas our topology might suggest that a dispersal route was present between India and
North Africa in the latest Cretaceous–early Paleogene, an evaluation of putative dispersal
routes leads us to conclude that the paleobiogeography of Madtsoiidae is best explained by
a poorly sampled, earlier widespread distribution in Africa, Indo-Madagascar and South
America. In contrast, latest Cretaceous madtsoiid occurrences in Europe might be explicable
by trans-Tethyan dispersal from Africa across the Apulian Route.