Razanandrongobe sakalavae,a gigantic mesoeucrocodylian from the Middle Jurassic of Madagascar, is the oldest known notosuchian

Abstract

Razanandrongobe sakalavae Maganuco, Dal Sasso & Pasini, 2006 is a large predatory archosaur from the Middle Jurassic (Bathonian) of the Mahajanga Basin, NW Madagascar. It was diagnosed on the basis of teeth and a fragmentary maxilla, but its affinities were uncertain. Here we describe new cranial remains (above all, an almost complete right premaxilla and a caudally incomplete left dentary) that greatly improve our knowledge on this enigmatic species and reveal its anatomy to be crocodylomorph. The right premaxilla indicates that the rostrum was deep, wide, and not pointed; it bears five teeth that are sub-vertical and just slightly curved lingually; the mesial teeth are U-shaped in cross-section and have serrated carinae on the lingual side; the aperturae nasi osseae (external bony nares) are confluent and face rostrally; and there is no lateral groove at the premaxillomaxillary suture for reception of a hypertrophied lower caniniform tooth. The preserved portion of the left dentary has an edentulous tip and bears eight large mandibular teeth of which the mesial (1–3) are the largest, but none is a hypertrophied caniniform tooth; the mandibular (dentary) symphysis extends caudally to the level of the third tooth; the splenial is not preserved, but its sutural marks on the dentary indicate that it contributed to the mandibular symphysis for at least 20% of the symphyseal length in dorsal aspect. On the basis of this new data, some previously uncertain features of the holotype maxilla—such as the margin of the suborbital fenestra, the contact surfaces for the palatine, the ectopterygoid, and the jugal—are now apparent. Testing of the phylogenetic position of the species within Crocodylomorpha indicates that R. sakalavae is a mesoeucrocodylian. It also represents one of the earliest events of exacerbated increase in body size along the evolutionary history of the group. In addition, it is by far the oldest notosuchian. A cranial reconstruction of this gigantic predator is also attempted here. The very robust jaw bones of R. sakalavae, coupled with its peculiar dentition, strongly suggest a diet that included hard tissue such as bone and tendon.

A small Cretaceous crocodyliform in a dinosaur nesting ground and the origin of sebecids

“…The main topology of the strict consensus tree (Fig. S3 ) agrees with other previous phylogenetic hypotheses 12 , 32 , 34 .

Figure 3 Time-calibrated evolutionary tree for Sebecosuchia.

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Spatiotemporal sampling patterns in the 230 million year fossil record of terrestrial crocodylomorphs and their impact on diversity

“…The recent reinterpretation of fragmentary cranial remains (CCM = 7%) from the Bathonian (Middle Jurassic) of Madagascar as the earliest known notosuchian (Dal Sasso et al . ) is in keeping with this view. Furthermore, although their ‘sudden’ appearance in the Aptian of Africa (e.g.…”

Environmental drivers of body size evolution in crocodile-line archosaurs

“…The evolutionary rate increase associated with the Middle Jurassic notosuchian Razanandrongobe is exceptional, especially when compared to the relatively low evolutionary rates observed among other notosuchians. Razanandrongobe has been described as an island-dweller, with a fossil range coinciding with the separation of Madagascar from mainland Africa 37 . Increased evolutionary rate among island species is well documented 38 .…”

“…This is not a representative sample, since long-snouted and short-snouted forms are known across a range of body sizes; for example, a highly elongated snout is observed in both the modest-sized Isisfordia duncani 42 and the giant Sarcosuchus imperator 43 . Likewise a short-snouted morphology occurs in the small-bodied Shamosuchus djadochtaensis 44 and the exceptionally large Razanandrongobe sakalavae 37 . Therefore, this regression does not address the possibility that skull length may over-estimate body size in long-snouted taxa, and under-estimate it in short-snouted taxa.…”