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One new pterosaur, Dendrorhynchus curvidentatus1, is morphometrically most similar to the Late Jurassic (Tithonian) Solnhofen form Rhamphorhynchus but does not fit within that taxon. Principal components analysis (by K. I. Warheit and K. P.) (Fig. 2) of the long bones of various pterosaurs indicates that Dendrorhynchus clusters most closely with Rhampho-rhynchus and has no obvious unique features, but its proportions differ from those of the ontogenetic trajectories of Rhampho-rhynchus. Instead, like Scaphognathus, it is distinct at the generic level. The generic name Dendrorhynchus is preoccupied by a nemertine3, so we propose replacing it with the name Dendrorhynchoides.

Figure 2: Principal components analysis (PCA).
figure 2

PCA plot of second and third major axes, comparing radius, wing metacarpal, first two wing phalanges, and tibia in Campylognathoides, Ctenochasma, Dendrorhynchoides1, Dorygnathus,“Eosipterus2, Gallodactylus, Germanodactylus, Pterodactylus, Rhamphorhynchus and Scaphognathus. Dendrorhynchoides differs significantly from Rhamphorhynchus along the third major axis; “Eosipterus ”falls within the cluster of points of the congenerics Pterodactylus, Germanodactylus and Ctenochasma4 for pairwise comparisons of PCAs 1-3, and so is probably a large specimen of Pterodactylus (including Germanodactylus).

The second new fossil, Eosipterus yangi2 (Fig. 1c), is a large pterodactylid with a wingspan of about 1.25 metres. The incomplete fusion of the carpals and tarsals indicates that this specimen, although large for a pterodactylid, was not fully adult. A plot of the second and third principal components (the first was size) of the preserved long bones of Eosipterus (Fig. 2) groups Eosipterus with the Late Jurassic Solnhofen pterodactylids Pterodactylus kochi, P. antiquus and Germanodactylus, which have been viewed as part of a single ontogenetic series4 of P. antiquu s, with which Eosipterus may be synonymous.

The age of the Liaoning beds has been argued to be Late Jurassic or Early Cretaceous, and radiometric dates give conflicting results5. The biostratigraphy of the fauna through the entire section of the Yixian and Chaomidianzi formations is ambiguous. At Sihetun (in the Beipiao area), fish, frogs, turtles, lizards and mammals have been found, as well as theropod and sauropod (saurischian) and psittacosaurid (ornithischian) dinosaurs6,7. Among the theropods, Sinosauropteryx, Protarchaeopteryx, Caudi-pteryx and Confuciusornis8,10 are of primary importance to studies of the origins of birds and avian features.

When exact faunal equivalents are not available, next-of-kin taxa can provide at least minimal divergence times. Psittacosaurid dinosaurs have so far been known only from the Early Cretaceous7, but the separation of these marginocephalians from other ornithischian dinosaurs was no later than Early Jurassic, perhaps much earlier11. Sinosauropteryx is the most closely related of the Liaoning coelurosaurs to the Late Jurassic basal coelurosaur Compsognathus from the Solnhofen limestones of Germany8. Protarchaeopteryx3 is a basal maniraptoran, as are avians such as the Solnhofen form Archaeopteryx, and the Liaoning form Caudipteryx has been linked basally to these taxa3. Confuciusornis is the next most basal bird known after Archaeopteryx. The coelurosaurian lineages therefore provide a biostratigraphic signal of sister-taxa rooted in the Late Jurassic. None of these specific genera is known from the Early Cretaceous, although related lineages persisted.

The two new Liaoning pterosaurs provide a similar signal by clustering with Late Jurassic relatives. Pterodactyloids are known from both the Late Jurassic and the Cretaceous, but non-pterodactyloid pterosaurs are not reliably known from any Cretaceous deposits12. The Jurassic-Cretaceous transition among pterosaurs may therefore be sharper than in some other tetrapod faunal components, and the available data from coelurosaurs and particularly pterosaurs suggest a Late Jurassic age for the beds in which they are found. In contrast, the earliest Cretaceous faunas, such as that of the Wealden, bear little resemblance to the Liaoning and Solnhofen faunas13. But the most basal Cretaceous faunas must be better known before any biostratigraphic hypothesis can be considered iron-clad.