A conserved tooth resorption mechanism in modern and fossil snakes.

Whether snakes evolved their elongated, limbless bodies or their specialized skulls and teeth first is a central question in squamate evolution. Identifying features shared between extant and fossil snakes is therefore key to unraveling the early evolution of this iconic reptile group. One promising candidate is their unusual mode of tooth replacement, whereby teeth are replaced without signs of external tooth resorption. We reveal through histological analysis that the lack of resorption pits in snakes is due to the unusual action of odontoclasts, which resorb dentine from within the pulp of the tooth. Internal tooth resorption is widespread in extant snakes, differs from replacement in other reptiles, and is even detectable via non-destructive µCT scanning, providing a method for identifying fossil snakes. We then detected internal tooth resorption in the fossil snake Yurlunggur, and one of the oldest snake fossils, Portugalophis, suggesting that it is one of the earliest innovations in Pan-Serpentes, likely preceding limb loss.

Live birth in Cretaceous marine lizards (mosasauroids).

Although live-bearing (viviparity) has evolved around 100 times within reptiles, evidence of it is almost never preserved in the fossil record. Here, we report viviparity in mosasauroids, a group of Cretaceous marine lizards. This is the only known fossil record of live-bearing in squamates (lizards and snakes), and might represent the oldest occurrence of the trait in this diverse group; it is also the only known fossil record of viviparity in reptiles other than ichthyosaurs. An exceptionally preserved gravid female of the aigialosaur Carsosaurus (a primitive mosasauroid) contains at least four advanced embryos distributed along the posterior two-thirds of the long trunk region (dorsal vertebrae 9-21). Their orientation suggests that they were born tail-first (the nostrils emerging last) to reduce the possibility of drowning, an adaptation shared with other highly aquatic amniotes such as cetaceans, sirenians and ichthyosaurs; the orientation of the embryos also suggests that they were not gut contents because swallowed prey are usually consumed head-first. One embryo is located within the pelvis, raising the possibility that the adult died during parturition. Viviparity in early medium-sized amphibious aigialosaurs may have freed them from the need to return to land to deposit eggs, and permitted the subsequent evolution of gigantic totally marine mosasaurs.

Toxicity, ultrastructural effects, and metabolic studies with 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2-dichloroethane(o,p'-DDD) and its methyl analog in the guinea pig and rat.

Effects of 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2,2-dichloroethane (o,p'-DDD) (Lysodren; Mitotane) (I) and 1-(o-chlorophenyl)-1-(p-chlorophenyl)-2, 2-dichloropropane (Mitometh) (II) were investigated. Ultrastructural and toxicity studies were conducted with male Hartley outbred guinea pigs given 300 mg/kg/day ip for 14 days. Profound mitochondrial damage in the guinea pig adrenal cortex, an index of Lysodren's action as a cancer chemotherapeutic, reversible necrosis of the zona fasciculata and zona reticularis with swelling, disrupted cristae, and organelles destroyed in the mitochondria from these areas. Yet guinea pigs given Mitometh tolerated the drug better than those given an equivalent amount of Lysodren. In general the animals treated with Mitometh showed less alopecia, diarrhea, and weakness. The only deaths recorded in our study were in the Lysodren group. In addition po administration of these two drugs to male Sprague-Dawley rats and male Hartley guinea pigs for 4 days allowed for a direct comparison of urinary metabolites. Metabolites were identified from urine extracts by computerized mass spectrometry interfaced with capillary gas chromatography. Both compounds were shown to undergo dehydrohalogenation and side-chain cleavage to a limited extent; however, only Lysodren afforded side-chain oxidation metabolites. In fact, the dominant metabolite from Lysodren biotransformation was the corresponding carboxylic acid o,p'-DDA (III). On the other hand, Mitometh resisted side-chain oxidative metabolism and was less toxic than Lysodren. Therefore, when given to guinea pigs and rats, Mitometh had Lysodren-like biologic activity, did not undergo rapid inactivation, and was less toxic than Lysodren. Mitometh represents a potential alternative to Lysodren which should be investigated further for its possible use in the treatment of adrenal cortical carcinoma and Cushing's syndrome.