A giant armoured skink from Australia expands lizard morphospace and the scope of the Pleistocene extinctions

Abstract

There are more species of lizards and snakes (squamates) alive today than any other order of land vertebrates, yet their fossil record has been poorly documented compared with other groups. Here, we describe a gigantic Pleistocene skink from Australia based on extensive material that includes much of the skull and postcranial skeleton, and spans ontogenetic stages from neonate to adult. Tiliqua frangens substantially expands the known ecomorphological diversity of squamates. At approximately 2.4 kg, it was more than double the mass of any living skink, with an exceptionally broad, deep skull, squat limbs and heavy, ornamented body armour. It probably filled the armoured herbivore niche that land tortoises (testudinids), absent from Australia, occupy on other continents. Tiliqua frangens and other giant Plio-Pleistocene skinks suggest that small-bodied groups that dominate vertebrate biodiversity might have lost their largest and often most morphologically extreme representatives in the Late Pleistocene, expanding the scope of these extinctions.

The late-Quaternary megafauna extinctions: Patterns, causes, ecological consequences and implications for ecosystem management in the Anthropocene

“…In addition, multiple crocodiles (Ristevski et al, 2023), large monitor lizards (Varanus spp.) (Hocknull et al, 2009), a large snake (Wonambi naracoortensis), and a giant armored lizard (Thorn et al, 2023) went extinct in Australasia (Palci et al, 2018), and an enormous freshwater turtle disappeared in Amazonia (Ferreira et al, 2024).…”

New Lizard Specimens from the Campanian Wapiti Formation of Alberta, Canada

“…Although cephalic osteoderms occur in a range of non-monstersaurian squamates, and are prevalent in Scincoidea and various anguimorph groups other than Monstersauria, monstersaurian osteoderms are morphologically distinctive [44,[48][49][50]. Non-monstersaurian osteoderms tend to be flatter, thinner and more plate-like, and may be keeled, overlapping, relatively small in area, unfused to the skull roof, and/or composed of multiple smaller ossifications [17,20,49,[51][52][53][54][55][56][57]. The cephalic osteoderms of Cenozoic glyptosaurine anguids bear discrete tubercles rather than the ridge-and-pit ornamentation typical of monstersaurs, and in some glyptosaurines, the cephalic osteoderms are proportionally very large [58][59][60][61].…”

Compound osteoderms preserved in amber reveal the oldest known skink

“…Among extant scincoids (Xantusiidae, Gerrhosauridae, Cordylidae, Scincidae), members of Scincidae exhibit the greatest range in body length, including some miniaturized forms having a body length (SVL) of only a few centimetres (e.g. Scincella macrotis , 24 mm SVL 9 ) to the extinct Tiliqua frangens , which may have reached half a meter or more 10 . Skinks also show great variation in the number of presacral vertebrae, ranging from 26 to 108 11 which, in combination with cycloid scales and compound osteoderms, may have facilitated the repeated evolution of fossorial and limbless morphotypes 7 , 12 , 13 .…”