摘要:

The question of the origin of birds can be equated with the origin ofArchaeopteryx, the oldest known bird. Analysis of the five presently known skeletal specimens ofArchaeopteryx.and comparison with the skeletal anatomy of the several reptilian groups that have been proposed as possible ancestors of birds (Ornithopoda, Theropoda, Hseudosuchla and Sphenosuchidac), confirm the conclusions (long rejected by most subsequent workers) of Heilmann (1926), Lowe (1935, 1944) and Holmgren (1955), namely, that the skeletal anatomy ofArchaeopteryxis extraordinarily similartothat of contemporaneous and succeeding coelurosaurian dinosaurs. Rejection of these similarities as adaptive structures only (parallel or convergent similarities), and therefore of no phylogenetic importance, is here considered invalid. Heilmann was the first to identify the only evidence that has been cited so far for dismissing coelurosaurian‐avian ancestral–descendant relationships, the supposed absence of clavicles in all theropods, and on that basis suggested a commonArchaeopteryx–dinosaur ancestry among pseudosuchian reptiles. That evidence is negative and thus inconclusive, and is now known to be false.With the exceptionof fusedclavicles and unique ischial morphology, virtually every skeletal feature ofArchaeopteryxis known in several contemporaneous or near‐contemporary coelurosaurian dinosaurs and many of these conditions are unrelated, specialized features (the detailed morphology of the manus, metacarpus, carpus, humerus, scapulocoracoid, pes, metatarsus, tarsus, femur, pubis, ilium, skull and mandibles). The presence of so many derived characters in common clearly establishes that the closest ancestral affinities otArchaeopteryxare with coelurosaurian theropods. There is no contrary evidence and any other explanation is illogical.All available evidence indicates unequivocally thatArchaeopteryxevolved from a small coelurosaurian dinosaur and that modern birds are surviving dinosaurian descendants. Stated simply, avian phylogeny was: Pseudosuchia CoelurosauriaArchaeopteryxhigher birds.SUMMARYThe question of the origin of birds can be equated with the question of the origin ofArchaeopteryx.This last question evokes two possible answers, depending upon how one views the importance of “primitive versus derived characters” in assessing phylogenetic relationships. One possible answer is:Archaeopteryxis a direct descendant of some unknown, but presumablyEuparkeria‐likepseudosuchian. This answer is predicated on the belief thatArchaeopteryxonly parallels or converges with various coelurosaurs in certain skeletal similarities. This is the view now held by the majority of biologists– a view that I find unacceptable. The second possible answer is:Archaeopteryxis directly descendant from a small unknownOrnitholestes‐likecoelurosaurian dinosaur. This answer assumes that skeletal similarities between coelurosaurs andArchaeopteryxare derived from a common ancestor, itself a coelurosaur. This is the view advocated here.There is no evidence to support an ornithischian ancestry of birds. The pubis ofArchaeopteryxapparently was not reflected backward as in ornithischians and modern birds, and in any case, the ornithischian pubis is only superficially like that of living birds. Nor is the so‐called ornithopod foot like that of birds.Evidence of close theropod–Archaeopteryxrelationships, however, is abundant: the presence of the same, multiple, specialized adaptations in bothArchaeopteryxand various coelurosaurs (tridactyl manus, metacarpus and carpus morphology, forelimb and pectoral girdle structure, four‐toed pes, reversed hallux, metatarsal morphology, mesotarsal joint, hindlimb construction, pelvic form, plus elongated forelimbs, bipedal posture, vertebral structure and formula, and basic cranial morphology).The presence inArchaeopteryx, coelurosaurs and pseudosuchians of several primitive characters in common (thecodont dentition, sclerotic ring, possibly amphicoelous vertebrae, long caudal series, gastralia, pubic symphysis, short coracoids) indicates only a probable common ancestry. It does not establish that the Coelurosauria could not have given riseto Archaeopteryx–and higher birds. There is no evidence (outside ofLagosuchusandLagerpeton)of shared derived characters to suggest a close evolutionary relationship between classic pseudosuchians andArchaeopteryx.Similarly, there is no clear‐cut evidence in the form of shared derived characters to linkArchaeopteryxwithSphenosuchus.The absence of clavicles in theropods (now known to be false), once considered as conclusive evidence against a coelurosaurian ancestry of birds, is no more significant than is the absence of a sternum in all known pseudosuchians as evidence against a pseudosuchian ancestry of all other archosaurs. The absence of any known “ideal” coelurosaurian pre‐Archaeopteryxis only negative and inconclusive evidence, especially in view of our meagre and exceedingly deficient knowledge about Early and Middle Jurassic terrestrial vertebrates.All available evidence indicates that the immediate ancestor ofArchaeopteryxwas a small coelurosaurian dinosaur and that the phylogeny of avian ancestry was: Pseudosuchia–Coelurosauria–Archaeopteryx:– higher birds.Ornithopod‐Archaeopteryx ancestral‐descendant affinities may be dismissed because of the false “avian” organization of the pelvis in the Berlin specimen ofArchaeopteryxand the merely superficially bird‐like construction of the ornithisehian pelvis. The suite of specialized characters unique to ornithischians (e.g., predentary, tooth morphology), that occur even in Triassic representatives, is further evidence for dismissing close affinity between ornithopods andArchaeopteryx.The supposed close relationship between birds and pseudosuchians is judged to be remote at best, due to the completely primitive nature of the few anatomical features which pseudosuchians have in common withArchaeopteryx. Sphenosuchus, a primitive and early archosaur, is also a potential avian ancestor, but existing evidence consists of primitive archosaurian features plus a few similarities with certain modern birds. These similarities, which are present in two groups that are separated from each other by more than 200 million years, and which cannot be demonstrated inArchaeopteryx, are considered irrelevant t

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00244.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY