Little Early Birds – The Tiny Descendants of Archaeopteryx

Updated July 09, 2015 with a new image of Archaeopteryx.

Archaeopteryx, one of the most primitive birds, was among the smallest of all adult dinosaurs. But what followed Archaeopteryx was even smaller (Fig. 1).

Figure 1. Archaeopteryx and several other basal birds. Here Archaeopteryx is a relative giant. This is an older illustration, predating all of the recent and now, not so recent, finds from China. The wings, sternum and tail are derived in the smaller birds. That's the smallest Archaeopteryx, the Eichstätt specimen.

Figure 1. Archaeopteryx and several other basal birds. Here Archaeopteryx is a relative giant. This is an older illustration, predating all of the recent and now, not so recent, finds from China. The wings, sternum and tail are derived in the smaller birds. That’s the smallest Archaeopteryx, the Eichstätt specimen.

Size reduction in early birds
Early maturation produces smaller adult birds. They cycle through life and reproduce quickly, before reaching the size of their parents and grandparents. And if their chicks mature even more quickly they will have smaller hips to produce smaller eggs. Smaller eggs produce smaller chicks that reproduce quickly. On and on, well, you get the idea.

The wings lost their individual fingers in these early birds. The tail shortened, developing a pygostyle (fused tail bones). The rostrum was shorter. The orbit was relatively larger. The sternum deepened, developing toward its modern shape. These little guys were smaller, lighter and stronger flyers. They were probably very hard for a predator to catch. They could lay eggs in otherwise inaccessible places. They may have had a higher, more bird-like metabolism, with greater needs for food, and more rapid reactions. They weighed only a fraction of Archaeopteryx, so the little birds could jump and fly easier.

Evolution happens more quickly in small taxa because they grow and reproduce at a faster rate. More generations appear in less time. By flying, birds can access more environments, from trees to seashores, which also has selective effects.

Parallels in pterosaurs
Earlier we talked about various pterosaur lines that shrank and evolved into new forms prior to ultimately producing larger forms. However, pterosaur ancestors, like Cosesaurus, were not larger than early pterosaurs. They did not develop wings through serial size reduction.

Parallels in bats
Today there are megabats and microbats. The most primitive bats were small. Bat ancestors, like Ptilocercus were likewise small.

Juveniles vs. Adults
Gobipteryx was considered an embryo. If so, it would have grown to the size of Archaeopteryx. Not sure about the possible juvenile status of the others. Since birds grew up so quickly and are all about the same size, the odds are the rest represent adults.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Dames W 1884. Ueber Archaeopteryx. Palaeontologische Abhandlungen, 2 (3):119-198.
Heller F 1959. Ein dritter Archaeopteryx Fund aus den Solnhofener Plattenkalken von Langenaltheim/Mfr. Erlanger Geologische Abhandlungen, 31: 1-25; Erlangen
von Meyer H 1861. Archaeopteryx litographica (Vogel-Feder) und Pterodactylus von Solenhofen. Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefakten-Kunde. 1861: 678–679.
Owen R 1863. On the Archaeopteryx von Meyer, with a description of the fossil remains of a long-tailed species from the lithographic stone of Solnhofen. Philosophical Transactions of the Royal Society, London 153: 33-47.
Paul G 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press. 460 pp.
Wellnhofer P 1974. Das fünfte Skelettexemplar von Archaeopteryx. Palaeontographica Abt. A Vol. 147 S: 168-216.

wiki/Archaeopteryx

3 thoughts on “Little Early Birds – The Tiny Descendants of Archaeopteryx

  1. Does the illustration use the London Archaeopteryx for scale? As I recall, there are complete and apparently mature specimens that are markedly smaller and larger — overall something like 2x range in linear dimensions.

  2. The Neuquen City bird has since been named Neuquenornis.

    Gobipteryx’s type (Elzanowski, 1974, 1976 and 1977) is generally considered adult, but since it’s just a skull that’s hard to say. The embryos were referred to Gobipteryx by Elzanowski (1981), but have been proposed to be a new species “Gobipipus reshetovi” (see http://home.comcast.net/~eoraptor/Ornithothoraces.htm#Gobipipusreshetovi). I don’t have an opinion on the matter yet. New Gobipteryx specimens like the Nanantius valifamovi type are large but have some subadult features like partially fused tibiotarsi.

    Of the others, I’d say Concornis, Cathayornis and Neuquenornis are adults (e.g. complete tibiotarsal and carpometacarpal fusion). Sinornis probably close to adulthood (less fused carpometacarpus). Iberomesornis is controversial, with Sereno claiming adulthood and Sanz claiming a less fused status.

    The general trend you describe is still probably true, with Shenzhouraptor, Jixiangornis, Yandangornis and Sapeornis also being large (though if some recent studies are right in placing Saoeirnis closer to Aves than confuciusornithids, that complicates things). Confuciusornithids are Neuquenornis-size or smaller, but the large Vorona and Patagopteryx might also complicate matters if they are basal ornuthuromorphs (though others like Chaoyangia, Archaeorhynchus, Hongshanornis and Jianchangornis are small).

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