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A feathered skeleton of a Lower Cretaceous enantiornithine bird from Spain indicates that the modified diapsid skull of modern birds did not evolve until late in their evolution: Basal birds retained an essentially primitive diapsid design. The fossil provides data clarifying long-standing debates on the cranial morphology of the basalmost bird,Archaeopteryx. It also reemphasizes the notion that the early morphological transformations of birds were focused on the flight apparatus. This fossil was a nestling and suggests that early postnatal developments in the Cretaceous enantiornithine birds and those in their extant counterparts are comparable.

AVIAN flight is one of the most remarkable achievements of vertebrate evolution, yet there is little evidence of its early phases. Specimens of Archaeopteryx shed important (albeit controversial) light on this evolutionary phenomenon, but the large morphological (and almost certainly functional) gap between Archaeopteryx and modern avians remained virtually empty until recently. Here we report a new, exquisitely preserved, bird from the Lower Cretaceous Konservat-Lagerstatte of Las Hoyas (Cuenca, Spain) which provides evidence for the oldest known alula (bastard wing). Crustacean remains found inside its belly also provide the oldest direct evidence of feeding habits in birds. The new specimen has numerous synapomorphies with the Enantiornithes, but its unique sternal morphology, along with other autopomorphies in the furcula and vertebral centra, support the recognition of a new enantiornithine taxon, Eoalulavishoyasi. The combination in Eoalulavis of a decisive aerodynamic feature, such as the alula, with the basic structures of the modern flight apparatus indicates that as early as 115 million years ago, birds had evolved a sophisticated structural system that enabled them to fly at low speeds and to attain high manoeuvrability.

Although famous as a fossil lagerstatte that has produced numerous well-preserved vertebrates, recent discoveries indicate that the lithographic limestones of Las Hoyas (Calizas de la Huerguina Formation) also contain vertebrate trackways. We herein report on at least two distinctive tetrapod track types tentatively assigned to crocodilians and to turtles. Turtle tracks are isolated while the crocodile ones are forming a trackway showing an animal walking with a very regular step and stride length on an emergent surface. It is interesting to note the similarity between the inferred turtle tracks from Las Hoyas and those from the Late Jurassic lithographic limestones of Cerin, France. The occurrence of tracks in both environments suggests that the ichnofaunas are similar.

A dinosaur tracksite has been discovered comprising three types of tridactyl footprints at Regumiel de la Sierra (province of Burgos, north‐central Spain). The rocks belong to Lower Cretaceous Wealden deposits of the Western Cameros Basin and two ichnological levels comprising 8 trackways and several isolated tracks were noted. All the footprints are tridactyl, although there are three types. Level 1 holds a trackway of which the footprints belong to a big iguanodontid dinosaur. Level 2 has yielded 6 trackways and several isolated tracks of Iguanodon‐like morphology, and also a theropod trackway. One iguanodontid trackway of level 2 has manus impressions suggesting that the dinosaur used a quadrupedal gait. The degree of inward rotation of footprints (similar to that of the other ones) suggests that this did not significantly modify the slight rotation of the pelvic girdle or the role of the tail during progression. The shape of manus prints suggests that the digit II was almost free and the III and TV on...

A quadrupedal ornithopod trackway has been discovered at Cabezon de Cameros (La Rioja, Spain). The strata at the Valdemayor site is Early Cretaceous in age (probably Hauterivian). The trackway is formed by five footprints and four manus impressions. Size and footprint structure suggest that it has been produced by an iguanodontid dinosaur using a quadrupedal gait. The estimated speed is 4 km/h. The lesser depth of manus prints suggests that the center of gravity is located near the hindlimbs. Ornithopod dinosaurs used a similar type of locomotion in both bipedal and quadrupedal gaits, showing inward rotation of pes prints. This fact suggests that the use of such an optional locomotion does not modify significantly the role of the tail during progression. The structure of the manus prints indicates that there is probably not an unique soft-tissue structure enclosing the digits II, III, and IV.

The discrimination of ornithopod from theropoddinosaur footprints can sometimes be problematical. In order to obtain discriminatory criteria, an analysis BMDP (4M, 7M) on a sample of 66 Lower Cretaceous tridactyl footprints of diverse geographical origins has been carried out. The more significant ichnological parameters explaining sample variability are related with the digital widths and with the whole dimensions of the footprints. Some other parameters, such as digital angulation (often used as an important discriminatory criterion), seem to be of limited significance. Based on the more significant ichnological parameters, some indices have been proposed. These indices are used in bivariate analyses which allow to discriminate ornithopod from theropod footprints with a different degree of confidence.

THE Lower Cretaceous lithographic limestones from Las Hoyas (province of Cuenca, Spain) have yielded important vertebrate fossil remains. We report here a new specimen, the first ornithomimosaur theropod found in Europe. Pelecanimimus polyodon gen. et sp. nov., has some striking elements preserved, such as the hyoid, sternum and integumentary impressions. The fossil has revealed other unexpected features, including a derived hand in an ancient ornithomimosaur, and a large number of teeth (over 200) with a distinctive morphology. This specimen suggests an alternative evolutionary process towards the toothless condition in Ornithomi-mosauria, which could be explained by an exaptation. Pelecanimimus polyodon stresses the relationship between Troodontidae and Ornithomimosauria.