Lindwurmia, a new genus of Plesiosauria (Reptilia: Sauropterygia) from the earliest Jurassic of Halberstadt, northwest Germany.

This paper offers a re-description of one of the oldest (Lower Hettangian, Lower Jurassic) plesiosaurians (Reptilia: Sauropterygia) from Germany and discusses its phylogenetic relevance. Lindwurmia thiuda, new genus and species, is a moderately sized plesiosaur (estimated size between 2 and 3 m long) exhibiting several plesiomorphic features. Although it presents a short and robust premaxillary rostrum, constricted at the premaxilla-maxilla suture as observed in Rhomaleosauridae, its skull and skeleton share a great number of characters with basal sauropterygians and basal plesiosaurians: premaxillae and maxillae in contact posterior to the external nares, absence of contact between the vomers and the maxillae posterior to the internal nares, cervical zygapophyses wider than the vertebral centrum width and curved anterior border of the humerus. Phylogenetic analyses variably place Lindwurmia as sister taxon to Anningasaura and in a basal position to all other plesiosaurians or recover it among rhomaleosaurids. Most of the oldest plesiosaurians are known from the Hettangian or Hettangian-possibly Sinemurian strata of the UK (Lyme Regis and Street); Lindwurmia thus represents one of the oldest European taxa found outside of the UK.

Unique pelvic fin in a tetrapod-like fossil fish, and the evolution of limb patterning.

All living tetrapods have a one-to-two branching pattern in the embryonic proximal limb skeleton, with a single element at the base of the limb (the humerus or femur) that articulates distally with two parallel radials (the ulna and radius or the tibia and fibula). This pattern is also seen in the fossilized remains of stem-tetrapods, including the fishlike members of the group, in which despite the absence of digits, the proximal parts of the fin skeleton clearly resemble those of later tetrapods. However, little is known about the developmental mechanisms that establish and canalize this highly conserved pattern. We describe the well-preserved pelvic fin skeleton of Rhizodus hibberti, a Carboniferous sarcopterygian (lobe-finned) fish, and member of the tetrapod stem group. In this specimen, three parallel radials, each robust with a distinct morphology, articulate with the femur. We review this unexpected morphology in a phylogenetic and developmental context. It implies that the developmental patterning mechanisms seen in living tetrapods, now highly constrained, evolved from mechanisms flexible enough to accommodate variation in the zeugopod (even between pectoral and pelvic fins), while also allowing each element to have a unique morphology.

The Smallest Diplodocid Skull Reveals Cranial Ontogeny and Growth-Related Dietary Changes in the Largest Dinosaurs.

Sauropod dinosaurs were the largest terrestrial vertebrates; yet despite a robust global fossil record, the paucity of cranial remains complicates attempts to understand their paleobiology. An assemblage of small diplodocid sauropods from the Upper Jurassic Morrison Formation of Montana, USA, has produced the smallest diplodocid skull yet discovered. The ~24 cm long skull is referred to cf. Diplodocus based on the presence of several cranial and vertebral characters. This specimen enhances known features of early diplodocid ontogeny including a short snout with narrow-crowned teeth limited to the anterior portion of the jaws and more spatulate teeth posteriorly. The combination of size plus basal and derived character expression seen here further emphasizes caution when naming new taxa displaying the same, as these may be indicative of immaturity. This young diplodocid reveals that cranial modifications occurred throughout growth, providing evidence for ontogenetic dietary partitioning and recapitulation of ancestral morphologies.