Live birth in a 47-million-year-old snake.

Viviparity is a widespread reproductive trait in snakes, although fossil evidence bearing on its evolution is extremely sparse. Here, we report an exceptional specimen of the minute booid snake Messelophis variatus recovered in the paleolake of the Messel Formation (early-middle Eocene, Germany). This gravid female contains at least two embryos located in the posterior third of the trunk region. The morphology, size, and degree of ossification of the cranial and postcranial remains indicate they correspond with late embryos. This specimen documents the first occurrence of viviparity in a fossil snake and extends the temporal distribution of this reproductive strategy in booid snakes by over 47 Ma. The evolution of viviparity in squamates has traditionally been associated with cold climates, but its presence at the dawn of the evolution of booids during early Palaeogene thermal peaks indicates that viviparity may have evolved under different selective pressures in this clade.

Paleontology: It's a bird, it's a plane, it's Oculudentavis!

Few animals have experienced such jarring taxonomic whiplash as has Oculudentavis, a tiny tetrapod preserved in amber. A new specimen of this perplexing lineage now shows that it is a lizard unlike any ever discovered.

A model of digestive tooth corrosion in lizards: experimental tests and taphonomic implications.

Corrosion patterns induced by gastric fluids on the skeleton of prey animals may depend on the nature of the corrosive agents (acid, enzymes) as well as on the composition of the hard parts and the soft tissues that surround them. We propose a framework for predicting and interpreting corrosion patterns on lizard teeth, our model system, drawing on the different digestive pathways of avian and non-avian vertebrate predators. We propose that high-acid, low-enzyme systems (embodied by mammalian carnivores) will lead to corrosion of the tooth crowns, whereas low-acid, high-enzyme systems (embodied by owls) will lead to corrosion of the tooth shafts. We test our model experimentally using artificial gastric fluids (with HCl and pepsin) and feeding experiments, and phenomenologically using wild-collected owl pellets with lizard remains. Finding an association between the predictions and the experimental results, we then examine corrosion patterns on nearly 900 fossil lizard jaws. Given an appropriate phylogenetic background, our focus on physiological rather than taxonomic classes of predators allows the extension of the approach into Deep Time.

Pythons in the Eocene of Europe reveal a much older divergence of the group in sympatry with boas.

Extant large constrictors, pythons and boas, have a wholly allopatric distribution that has been interpreted largely in terms of vicariance in Gondwana. Here, we describe a stem pythonid based on complete skeletons from the early-middle Eocene of Messel, Germany. The new species is close in age to the divergence of Pythonidae from North American Loxocemus and corroborates a Laurasian origin and dispersal of pythons. Remarkably, it existed in sympatry with the stem boid Eoconstrictor. These occurrences demonstrate that neither dispersal limitation nor strong competitive interactions were decisive in structuring biogeographic patterns early in the history of large, hyper-macrostomatan constrictors and exemplify the synergy between phylogenomic and palaeontological approaches in reconstructing past distributions.

The Only Known Jawed Vertebrate with Four Eyes and the Bauplan of the Pineal Complex.

The pineal and parapineal organs are dorsal outpocketings of the vertebrate diencephalon that play key roles in orientation and in circadian and annual cycles. Lampreys are four eyed in that both the pineal and parapineal form eyelike photosensory structures, but the pineal is the dominant or sole median photosensory structure in most lower vertebrate clades. The pineal complex has been thought to evolve in a single direction by losing photosensory and augmenting secretory function in the transitions from three-eyed lower vertebrates to two-eyed mammals and archosaurs [1-3]. Yet the widely accepted elaboration of the parapineal instead of the pineal as the primary median photosensory organ [4] in Lepidosauria (lizards, snakes, and tuataras) hints at a more complex evolutionary history. Here we present evidence that a fourth eye re-evolved from the pineal organ at least once within vertebrates, specifically in an extinct monitor lizard, Saniwa ensidens, in which pineal and parapineal eyes were present simultaneously. The tandem midline location of these structures confirms in a striking fashion the proposed homology of the parietal eye with the parapineal organ and refutes the classical model of pineal bilaterality. It furthermore raises questions about the evolution and functional interpretation of the median photosensory organ in other tetrapod clades.

Variation in the position of the jugal medial ridge among lizards (reptilia: squamata): its functional and taxonomic significance.

The course of the medial ridge in the lizard jugal shows considerable morphological variation. There are four basic configurations: (1) the medial ridge is located ventral to mid-height on the suborbital process and anterior to mid-length on the postorbital process; (2) the medial ridge is located ventrally on the suborbital process (as above), but posteriorly on the postorbital process; (3) the medial ridge is located dorsally on the suborbital process and anteriorly on the postorbital process; and (4) the medial ridge is centrally located along the entire length of the jugal. Ancestral character state reconstruction shows that type 1 is plesiomorphic for Squamata regardless of the broad-scale phylogenetic topology. Type 3 is present in chamaeleonids and convergently in Anolis barbatus. Type 3 is a synapomorphy of the chamaeleonids. Type 2 is considered plesiomorphic for Anguidae, Heloderma and Xenosaurus, although it is independently modified in some extant members. These taxa form a clade in molecular phylogenies of Squamata, and the course of the medial ridge of the jugal therefore provides some measure of morphological support for this arrangement. The course of the medial ridge may be best explained by the position of the eye and by the angle of the jugal; its relations with other bony orbital structures (supraocular osteoderms, palpebral, supraorbital flanges) and the posterior extent of the maxilla are also discussed.