Information on the first steps of the avian evolutionary history has dramatically increased during the last few years. The fossil record provides a general view of the morphological changes of the avian flight apparatus from non-volant ancestors (non-avian theropod dinosaurs) to the first derived fliers of the Early Cretaceous. The Las Hoyas bird record includes three genera: Iberomesornis, Concornis and Eoalulavis. This fossil material has yielded information about the early avian evolutionary history. These Early Cretaceous birds (some 120 Myr old) had a wingbeat cycle and breathing devices similar to those of extant birds. The function of the rectricial fan was also similar. In the evolutionary transition from cursorial ancestors to derived fliers it is possible to verify a trend to increase lift. Primitive wing aspect ratio morphotypes were elliptical ones, other derived morphotypes appeared, for example, in the Neornithes (extant birds). Some primitive fliers, like the Las Hoyas genus Eoalulavis, had an alula (feathers attached to the first digit of the hand) similar to that of present day birds, indicating braking and manoeuvring skills similar to those of their extant relatives. Primitive avian life habits are poorly understood. Some evidence from the Las Hoyas bird record indicates that Early Cretaceous birds were present in the trophic chains.
Pérez-MorenoB.P., SanzJ.L., BuscalioniA. D., MoratallaJ. J., OrtegaF., & Rasskin-GutmanD. (1994) A unique multitoothed ornithomimosaur dinosaur from the Lower Cretaceous of Spain. Nature, 370, 363–367.
2.
BriggsD. E. G., WilbyP. R., Pérez-MorenoB.P., SanzJ.L., & Fregenal-MartínezM. (1997) The mineralization of dinosaur soft tissue in the Lower Cretaceous of Las Hoyas, Spain. Journal of the Geological Society of London, 154, 587–588.
3.
OrtegaF., SanzJ. L., BarbadilloL., BuscalioniA. D., DiéguezC., EvansS. E., Fregenal-MartínezM. A., de la FuenteM., MaderoJ., Martín-ClosasC., Martínez-DelclòsX., MeléndezN., MoratallaJ. J., Pérez-MorenoB. P., Pinardo-MoyaE., Poyato-ArizaF.J, Rodríguez-LázaroJ., SanchizB., & WenzS. (1999). Las Hoyas. La huella del pasado. Fósiles de Castilla-La Mancha. (Aguirre, E. & Rábano, I., coords.), pp. 195–216. Junta de Comunidades de Castilla-La Mancha. Toledo, Spain.
4.
SanzJ.L., Fregenal-MartínezM.A., MeléndezN., & OrtegaF. (2001) Las Hoyas. Palaeobiology II (BriggsD. E: G., & CrowtherP. R., eds), pp. 356–359. Blackwell Science, Oxford.
5.
ChiappeL.M. (1997) Aves. The Encyclopedia of Dinosaurs (CurrieP., & PadianK. eds), pp. 23–28. Academic Press, New York.
6.
SanzJ. L., & BuscalioniA. D. (1992) A new bird from the Early Cretaceous of Las Hoyas, Spain, and the early radiation of birds. Paleontology, 35(4), 829–845.
7.
SanzJ. L., BonaparteJ. F., & LacasaA. (1988) Unusual Early Cretaceous birds from Spain. Nature, 331, 433–435.
8.
SanzJ. L., & BonaparteJ. F. (1992) Iberomesornis romerali, a fossil small bird articulated skeleton from the Early Cretaceous of Spain.Proc. II Int. Symp. Avian Paleontol., Los Angeles, 1988, pp. 39–49.
9.
SanzJ. L., Perez-MorenoB.P., ChiappeL.M., & BuscalioniA. D. (in press). The birds from the Lower Cretaceous of Las Hoyas (Province of Cuenca, Spain). Mesozoic Birds: Above the Heads of Dinosaurs (ChiappeL. M., & WitmerL. M., eds). The University of California Press, Berkeley.
10.
SerenoP. C. (2000) Iberomesornis romerali (Aves, Ornithothoraces) reevalu-ated as an Early Cretaceous enentiornithine. Neues Jahrbuch fur Geologie und Palaontologie Abhandlungen, 215, 365–395.
11.
ChiappeL.M. (in press.). Basal bird phylogeny: problems and solutions. Mesozoic Birds: Above the Heads of Dinosaurs (ChiappeL. M., & WitmerL. M., eds). The University of California Press, Berkeley.
12.
SanzJ.L., ChiappeL. M., Pérez-MorenoB.P., MoratallaJ.J., Hernádez-CarrasquillaF., BuscalioniA.D., OrtegaF., Poyato-ArizaF.J., Rasskin-GutmanD., and Martínez-DelclósX. (1997) A Nestling Bird from the Lower Cretaceous of Spain: Implication for Avian Skull and Neck Evolution. Science, 276, 1543–1546.
13.
SanzJ. L., ChiappeL. M., & BuscalioniA. D. (1995) The osteology of Concornis lacustris (Aves: Enantiornithes) from the Lower Cretaceous of Spain and a reexamination of its phylogenetic relatioships. American Museum Novitates, 3133, 23 pp.
14.
ZhouZ. (1995) The discovery of Early Cretaceous bird in China. Courier Forschunsinstitut Senckenberg, 181, 9–22.
15.
SanzJ. L., ChiappeL. M., Pérez-MorenoB.P., BuscalioniA. D., MoratallaJ. J., OrtegaF., & Poyato-ArizaF. J. (1996). A new Lower Cretaceous bird from Spain: implications for the evolution of flight. Nature, 382, 442–445.
16.
ChiappeL.M., & CalvoJ. O. (1994) Neuquenornis volans, a new Upper Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. J. Vertebr. Paleontol., 14(2), 230–246.
17.
ChiappeL. M. (1995) The first 85 million years of avian evolution. Nature, 378, 349–355.
18.
PadianK., & ChiappeL.M. (1998). The early evolution of birds. Biological Reviews, 73(1), 1–42.
19.
GatesyS. M., & DialK. P. (1996) Locomotor modules and the evolution of avian flight. Evolution, 50(1), 331–340.
20.
BurgersP., & ChiappeL.M. (1999). The wing of Archaeopteryx as a primary thrust generator. Nature, 399, 60–62.
21.
PooreS. O., Sanchez-HaimanA., & GoslowG. E. (1997). Wing upstroke and the evolution of flapping flight. Nature, 387, 799–802.
22.
ChiappeL.M., JiS.-A., JiQ., & NorellM.A. (1999) Anatomy and Systematics of the Confuciusornithidae (Theropoda: Aves) from the Late Mesozoic of the Northeastern China. Bull. American Mus. Nat. Hist., 242, 1–89.
23.
BaileyJ. P., & DeMontM. E. (1991) The function of the wishbone. Can. J. Zool., 69, 2751–2758.
24.
NorbergU. M. (1990) Vertebrate Flight.Springer-Verlag. 291 pp.
25.
TennekesH. (1997) The Simple Science of Flight. From Insects to Jumbo Jets.The MIT Press, 137 pp.
26.
PennycuickC.J. (1989) Bird flight performance. A practical calculation manual.Oxford University Press.153 pp.
27.
OlmosM. (1988) Investigaciones sobre la alometría funcional en las extremidades de las aves. Ph. Dissertation. Universidad de Barcelona. 258 pp.
28.
JiQ., CurrieP., JiS-A., & NorellM.A. (1999) Two feathered dinosaurs from Northeastern China. Nature, 393, 753–761.
29.
SavilleD.B.O. (1957) Adaptative evolution in the avian wing. Evolution, 11, 212–224.
30.
HouL., MartínD., ZhouD., & FeducciaA. (1999) Archaeopteryx to opposite birds-missing link from the Mesozoic of China. Vertebrata PalAsiatica, 37(2), 88–95.
31.
McLellandJ. (1989). Anatomy of the lungs and airsacs. Form and Function in Birds (KingA. S., & McLellandJ., eds) vol. 3, pp. 221–279Academic Press, New York.
32.
Schmidt-NielsenK. (1993) Animal Physiology. Adaptation and Environment, 602 pp. Fourth Edition. Cambridge University Press.
33.
SanzJ. L., ChiappeL. M., Fernández-JalvoY., OrtegaF., Sánchez-ChillónB., Poyato-ArizaF. J., Pérez-MorenoB. P. (2001) An Early Cretaceous pellet. Nature, 409, 998–999.
