Earliest Example of a Giant Monitor Lizard (<em>Varanus</em>, Varanidae, Squamata)

Abstract

<div><h3>Background</h3><p>Varanidae is a clade of tiny (<20 mm pre-caudal length [PCL]) to giant (>600 mm PCL) lizards first appearing in the Cretaceous. True monitor lizards (<em>Varanus</em>) are known from diagnostic remains beginning in the early Miocene (<em>Varanus rusingensis</em>), although extremely fragmentary remains have been suggested as indicating earlier <em>Varanus</em>. The paleobiogeographic history of <em>Varanus</em> and timing for origin of its gigantism remain uncertain.</p> <h3>Methodology/Principal Findings</h3><p>A new <em>Varanus</em> from the Mytilini Formation (Turolian, Miocene) of Samos, Greece is described. The holotype consists of a partial skull roof, right side of a braincase, partial posterior mandible, fragment of clavicle, and parts of six vertebrae. A cladistic analysis including 83 taxa coded for 5733 molecular and 489 morphological characters (71 previously unincluded) demonstrates that the new fossil is a nested member of an otherwise exclusively East Asian <em>Varanus</em> clade. The new species is the earliest-known giant (>600 mm PCL) terrestrial lizard. Importantly, this species co-existed with a diverse continental mammalian fauna.</p> <h3>Conclusions/Significance</h3><p>The new monitor is larger (longer) than 99% of known fossil and living lizards. <em>Varanus</em> includes, by far, the largest limbed squamates today. The only extant non-snake squamates that approach monitors in maximum size are the glass-snake <em>Pseudopus</em> and the worm-lizard <em>Amphisbaena</em>. Mosasauroids were larger, but exclusively marine, and occurred only during the Late Cretaceous. Large, extant, non-<em>Varanus</em>, lizards are limbless and/or largely isolated from mammalian competitors. By contrast, our new <em>Varanus</em> achieved gigantism in a continental environment populated by diverse eutherian mammal competitors.</p> </div

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