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Introduction

At the very back of many dinosaur books I had when I was a kid, there was usually a brief one or two-page section discussing Mesozoic era birds. Flapping and scurrying around the dinosaurs, prehistoric birds were not as charismatic as the more well-known Mesozoic flyers, the pterosaurs, which is why they usually got the short shrift in children's books and popular media. The discovery that birdhood extended to more popular dinos like "raptors" helped spark my interest in drawing those animals; when I noticed that most illustrations of the newly birdified dinosaurs did not match what the scientists were saying about them or even what the fossils feathers showed, I started attempts to draw scientifically accurate and up-to-date alternatives. Nowadays, prehistoric birds make up the majority of my online art gallery here.

A few notes on terminology and classification: "Bird" on this site refers to any member of Aves, as defined by Charig in 1985. This is my personally preferred, publushed definition, which is also the earliest 'modern-style' (phylogenetic) definition of the group. Charig defined Aves as "the clade that is demarcated from its antecedents by the appearance of the evolutionary novelty ‘feathers’." Since Charig didn't provide a definition of "feather," I'm taking this to mean feathers of a modern aspect, with a central rachis and a vane composed of barbs and barbules. This corresponds with the apomorphy-based clade Averemigia defined by Gathier and de Queiroz.

Technically, birds are dinosaurs in classification systems based on strict genealogy, because birds descended from members of the group Dinosauria. I tend to think that the traditional ranked classifications are useful for illustrating biological diversity, and can compliment the newer genealogical methods, so I use ranks like 'Class Aves' on this site, though most technical papers no longer use this terminology.

Some of the family names used here may seem unfamiliar, because I prefer to follow the guidelines for naming priority set in place by the International Code of Zoological Nomenclature (ICZN). In many cases, names that should have priority are ignored or unjustifiably replaced over time, for a variety of reasons. Examples from this site are given below.

Ornithodesmidae (Hooley 1913) has priority over the better-known Dromaeosauridae (Matthew & Brown 1922). The scrappy type specimen of Ornithodesmus, though initially (correctly) identified as a primitive bird, was soon confused with the much better remains of the pterosaur now known as Istiodactylus. Hooley named Ornithodesmidae as a family of pterosaurs, but it became a theropod family when Ornithodesmus was again recognized as a maniraptoran in 1993. Naish & Martill (2007), as well as Makovicky & Norell (1995), and Mortimer (online) have shown that Ornithodesmus falls into the same family as Dromaeosaurus. So, unless Dromaeosauridae is re-defined to include only Dromaeosaurus and a few closely related taxa such as Achillobator or trated as a synonymous but differently goverened clade (under the future PhyloCode), Ornithodesmidae has clear priority of name under the ICZN.

Atlantosauridae (Marsh 1877) has clear priority of name over the more well known Diplodocidae (Marsh 1884), and Hay (1902) argued that it has priority over Amphicoelidae (Cope 1877). Again, Atlantosauridae has not yet been defined as a clade, so if Diplodocidae is defined first under parallel systems such as PhyloCode, a situation will arise where Atlantosauridae is valid under one code but not the other--Diplodocidae will be a valid name but for a clade, not a family. Olshevsky (1991) incorrectly labelled Atlantosauridae a nomen oblitum (forgotten name). The ICZN states that to be a nomen oblitum, a name must not be treated as valid in the scientific literature after 1899. However, Atlantosauridae was in use in papers by Steel (1970) and Nowinsky (1971) well into the 20th Century.

Deinodontidae (Cope 1866) is a slightly more complicated case than the above. It was in clear, widespread use through the mid 20th Century (as in Maleev 1955) and almost always treated as the senior synonym of Tyrannosauridae (Osborn 1905). However, Russel (1970) argued that Deinodontidae be abandoned, because he considered the type specimens of Deinodon (isolated teeth) not diagnostic, rendering the name a nomen dubium. However, the teeth are clearly diagnostic at the family level and possibly even genus and species, as they must have come from either Daspletosaurus or (more likely) Gorgosaurus, and the rocks those dinosaurs come from are well enough sampled to rule out the presence of a third large tyrannosaur species unless such compelling evidence is found. Similarly, it is questionable whether or not the pertinant ICZN rules allow for abandoning a name due to a dubious type genus. Even if this is the case, it is only followed sporadically in the literature, and many family names remain in use that are based on dubious type material, including Hadrosauridae, Ceratopsidae, and Troodontidae (the latter is also based exclusively on teeth of questionable diagnosability at the genus and species levels). Olshevsky (1991) recognized this, but argued that the name is still invalid because Cope initially spelled it Dinodontidae, and the name Deinodontidae was an emended spelling not published until 1914, after Tyrannosauridae. He concluded that therefore Deinodontidae (with an e) is a junior synonym and Dinodontidae (no e) is a nomen oblitum. However, Olshevsky's argument is incorrect because the ICZN clearly mandates that any family names based on misspellings or unjustified spelling changes of their type genus (Cope spelled the name Dinodon) can and must be emended by any subsequent revisor, and that this does not change the original authorship or date of the name (ICZN Article 35.4.1). Also, note that even if Deinodontidae and Deinodontoidea are ignored, several studies have found Coelurus fragilis to be a "tyrannosauroid", and so the next available name for that group after Deinodontoidea is Coeluroidea (Marsh 1881).

References:
Charig, A.J. (1985). "Analysis of the several problems associated with Archaeopteryx." Pp. 21–31 in Hecht, M.K., Ostrom, J.H., Viohl, G., and Wellnhofer, P. (eds.). The Beginnings of Birds. Freunde des Jura-Museums, Eichstätt. Journal of Paleonology, 17: 989-1013.