The Cretaceous Short Armed Alvarezsauridae

NORELL, AND JAMES M. CLARK The discovery of Mononychus olecranus (Perle et al., 1993a later emended to Mononykus olecranus, see Perle et al., 1993b) from the Late Cretaceous of the Gobi Desert stimulated a fruitful new discussion about the origin and early diversification of birds and the evolution of their flight. Mononykus not only led to the recognition of a previously unknown clade of theropod dinosaurs but also suggested, through its phylogenetic placement as the...

Cladistics and the Fossil Record of Theropods

Critics of the hypothesis that birds are theropod dinosaurs have claimed that the stratigraphic record supports their view, by indicating that the relevant theropod taxa occur too late in time. Feduccia (1996 90), for example, states, Birds are supposed to be derived from the coelurosaurian dinosaurs, and the form initially used to relate dinosaurs to birds, Deinonychus, is from the early Cretaceous, some 40 million years after Archaeopteryx, and the most birdlike dinosaurs are from the late...

The Logic of Cladistics

Science endeavors to explain natural phenomena with the fewest untestable notions, and this methodological truism underlies the widespread acceptance of cladistic methods. The main premise of cladistic analysis, indeed any method of phylogenetic inference, is that characteristics shared by organisms provide the strongest evidence of their evolutionary relationships (Farris, 1983 Rieppel, 1988 Kluge, 1997). Many of the criticisms leveled at cladistic analysis either are true of any method of...

Cladistic Analyses of Coelurosaurian Theropods

Cladistics was developed as a formal analysis only within the past three decades, so the relationships of extant birds to fossil archosaurs were not subjected to cladistic analysis until the mid-1980s (e.g., Thulborn, 1984 Gauthier, 1986). But the groundwork of comparisons was laid by Ostrom (1976), who cataloged the many similarities of Archaeop-teryx to theropod dinosaurs, dromaeosaurids in particular, and explicitly interpreted them in terms of synapomorphies (shared derived characters). The...

The Status of the Theropod Hypothesis

The only explicit hypothesis for the phylogenetic relationships of birds states that avian ancestry is fully embedded somewhere within the nexus of maniraptoran theropod dinosaurs, probably nearest to Dromaeosauridae and or Troodontidae among known groups. As such, it is the only game in town. As mentioned previously, opponents of theropod relationships have regarded the hypothesis as basically an unfortunate outcome of sloppy application of phylogenetic systematics. However, the idea was...

New Analysis of Coelurosaurian Relationships

The distribution of 197 characters among 37 species of coelurosaurian theropods and two outgroup taxa was analyzed by Norell et al. (2001), based on detailed study of specimens of nearly all taxa. The analysis presented here (see Hwang et al., in press) expands the data set to 208 characters and 46 theropod taxa (see Appendix 2.2 for the character list and data matrix). Recently discovered specimens of Troodontidae, Dromaeosauridae, Ornithomimi-dae, and Oviraptoridae from the Early Cretaceous...

Lawrence M Witmer

Ever since the time of Huxley 1868 , the Ijgjjlllj debate on the place of birds within vertebrate Ipigfes phylogeny has been one of the highest-profile and hotly contested of all evolutionary debates. What makes the origin of birds so contentious Why can we not agree and then move on to other issues Will we ever regard the problem as solved It would seem that establishing the ancestry of birds would be a relatively simple, empirical task, but, despite abundant data, the debate rages like never...

The Status of Alternatives to the Theropod Hypothesis

There is no question that the theropod origin of birds is by far the most popular hypothesis on avian ancestry. The question then arises,Are there credible alternatives In most previous reviews e.g., Ostrom, 1976 Gauthier, 1986 Wit-mer, 1991 Feduccia, 1996 Padian and Chiappe, 1998b , the debate on avian origins was divided into three competing hypotheses 1 the theropod hypothesis, 2 the crocodylo-morph hypothesis, and 3 the basal archosauriform or thecodont hypothesis. However, in recent years...

The Relationship of the Origin of Flight to the Origin Of Birds

The origin of birds is, at its core, a matter of genealogy. That is, regardless of your systematic philosophy whether it be cladistic, phenetic, or eclectic avian ancestry is a question of phylogeny, or, more precisely, phylogenetic reconstruction. For most biologists, phylogenetic reconstruction has become more or less synonymous with phylogenetic sys-tematics or cladistics, whereby the distribution of attributes among taxa forms the primary raw data used to develop hy potheses of...

The Significance of Protoavis

A particularly difficult question is whether this ensemble cast should rightly include the Texas fossils known as P.tex-ensis. These fossils, whose discovery was announced only in 1986, have had a troubled and controversial history. In a long series of published works, Sankar Chatterjee 1987, 1988, 1991,1995,1997a, 1998b, 1999 argued that the Protoavis fossils are not only those of a bird but from a bird that lived 75 million years before Archaeopteryx The fossils are generally attributed to...

The Significance of the Feathered Chinese Dinosaurs

The 1990s will go down in history as a time when one of the most significant fossil deposits ever discovered was brought to light. The Lower Yixian Formation Chaomidianzi Formation of some and allied rock units in western Liaoning Province, People's Republic of China, have yielded a wealth of fossil vertebrates, preserving in often astounding abundance an entire fauna in all its diversity Luo, 1999 Swisher et al., 1999 . The basal birds from these deposits are discussed in this volume by Zhou...