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522 FOSSIL VERTEBRATES/Mesozoic Amphibians and Other Non-Amniote Tetrapods continents Frog skeletons are readily recognizable; the skeleton is highly modified for jumping, the backbone is very short (seven to nine vertebrae), and the tail vertebrae are fused as a rodlike urostyle In the pelvis, the ilium is elongate, and in the hindlimb, the tibia and fibula are fused and the ankle bones are elongated Fossils with some of the characteristics of frogs appear in the Early Triassic as Triadobatrachus (Madagascar) (Figure 9A) and Czatkobatrachus (Poland) Triadobatrachus, known from a nearcomplete skeleton, had the long ilium and modified ankles but had not yet acquired the other features There are no other Triassic frogs or frog relatives, and the first frogs with the full suite of jumping adaptations are the Early Jurassic genera Prosalirus from Arizona and Vieraella from Argentina By the Upper Jurassic, there are frogs attributable to the primitive modern family Discoglossidae in Laurasia, and it appears that the diversification to the modern families was under way Cretaceous frogs are not well documented, but the limited record suggests that much of the diversification to extant families had taken place Discoglossids, pelobatids, rhinophrynids, and palaeobatrachids are known from Laurasia; leptodactylids and pipids are known from South America; and pipids are known from Africa The genus Gobiates, sometimes elevated to the family Gobiatidae, is abundant in the mid-Late Cretaceous of central Asia but disappears in the Campanian and may be the only major type of Cretaceous frog not to survive into the Cenozoic Rich assemblages of tadpoles of pipid frogs are known from the Lower Cretaceous of Makhtesh Ramon in Israel (Figure 9B) Salamanders The major diversity of living salamanders occurs in North America, central America, and Eurasia A few genera are found in South America and North Africa, and these are believed to represent Neogene range extensions Most of the Mesozoic record of salamanders is also restricted to Laurasia and the group appears to have been endemic to this region for much of its history Diagnostic remains of salamanders first appear in the Bathonian of England and central Asia, and by the Late Jurassic they were widespread throughout Eurasia and North America The known Jurassic salamanders are more primitive than most, if not all, living forms A single articulated skeleton (Karaurus) is known from the Kimmeridgian of Kazakhstan (Figure 9C) During the Cretaceous, the group diversified and basal members of some of the modern lineages appeared, and by the Maastrichtian, most modern Figure 10 The salamander Valdotriton gracilis, from the Lower Cretaceous, Las Hoyas, Spain Specimen at Las Hoyas Museum, Spain ß Andrew Milner families are represented in the record or can be inferred to have been present Articulated skeletons are known from the konservat-lagerstaă tten at Las Hoyas, Spain (Figure 10), and Liaoning, China, and there are large numbers of salamander-producing microvertebrate assemblages in Eurasia and North America Almost all salamanders were still restricted to the northern continents, but some reached the African region of Gondwana and are known from Israel (Ramonellus), Sudan, and Niger (Kababisha) Caecilians The caecilians are tiny, burrowing amphibians now found in moist soils and leaf litter in South America, Africa, the Seychelles, India, and South-east Asia They are superficially earthworm-like in shape, with no limbs or tail and with rudimentary eyes, and a scale distribution that gives them a segmented appearance They are poorly represented in the Mesozoic, with just three records The Lower Jurassic Eocaecilia from Arizona is known from articulated material and retained small limbs (Figure 9D) The two Cretaceous
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