Chapter 5 Outline

HISTORY OF DINOSAURIA

• SIR RICHARD OWEN
  • CREATED "DINOSAURIA" IN 1842 TO ENCOMPASS A GROUP OF EXCEEDINGLY LARGE, PACHYDERMOUS REPTILES FROM THE SECONDARY AGE (MESOZOIC ERA)
    • Iguanodon , Megalosaurus & Hylaeosaurus were the first members
• DINOSAURS ­ THE MESOZOIC UNNATURALS
  • H. G. SEELEY CONCLUDED IN 1887 THAT DINOSAURIA WAS NOT MONOPHYLETIC
    • Saurischian (lizard hipped) dinosaurs had a separate origin among the "Thecodontia" from Ornithischian (bird hipped) dinosaurs according to Seeley
  • F. VON HUENE CONTINUED & EMBELLISHED SEELEY'S CONCEPT INTO THE 1960'S
    • Among saurischians, sauropods and theropods had separate origins, and among ornithischians, ankylosaurs and other ornithischians had separate origins, among the "Thecodontia" according to von Huene
  • A. J. CHARIG CARRIED ON VON HUENE'S IDEAS INTO THE 1970'S
• DINOSAURIA ­ IT'S A NATURAL
  • ROBERT T. BAKKER AND P. M. GALTON IN 1974 RESURRECTED DINOSAURIA AS A MONOPHYLETIC TAXON, AND INCLUDED BIRDS WITHIN DINOSAURIA
    • Met with great resistance, as did speculation by J. F. Bonaparte in 1976 that Dinosauria is a clade
  • CLADISTIC ANALYSIS OF ARCHOSAURIA COMMENCED IN 1984 ALONG 4 RESEARCH FRONTS
    • Disbanding of "Thecodontia"
    • Origin of Dinosaurs
    • Relationships within Saurischia and Ornithischia
    • Relationship of Birds to Dinosaurs
  • J. A. GAUTHIER IDENTIFIED MORE THAN 10 DERIVED FEATURES THAT ESTABLISHED THE CLADE DINOSAURIA (SEE FIGS. 5.4 AND 5.5) IN 1986
    • Herrerasaurus and Staurikosaurus are the most basal dinosaurs, but not members of Saurischia or Ornithischia according to Gauthier
    • Herrerasaurus and Staurikosaurus , plus Eoraptor ( a new dinosaur) are members of Saurischia and are Theropods according to newer research by Paul C. Sereno & co-workers
  • DINOSAURIA IS A WELL-SUPPORTED MONOPHYLETIC CLADE ACCORDING TO DINOSAUR PALEONTOLOGISTS NOW

ORIGINS

• CLOSEST ARCHOSAURIAN RELATIVES
  • ACCORDING TO GAUTHIER AND KEVIN PADIAN = PTEROSAURIA
    • Pterosauria + Dinosauria = Ornithodira
    • Ornithodira + Lagosuchus = Ornithosuchia
    • LAGOSUCHUS = SMALL (<1 M), LONG-LEGGED BIPEDAL CARNIVORE OR INSECTIVORE
  • ACCORDING TO SERENO = LAGOSUCHUS + LAGERPTON + PSUEDOLAGOSUCHUS
    • LAGOSUCHUS + LAGERPTON + PSUEDOLAGOSUCHUS + Dinosauria = Dinosauromorpha
    • Dinosauromorpha + Pterosauria = Ornithodira
  • ACCORDING TO THE SERENO PHYLOGENY, DINOSAURS WERE PRIMITIVELY OBLIGATE BIPEDS
    • All quadrapedal dinosaurs (like Apatosaurus , Triceratops , Ankylosaurus and Stegosaurus ) secondarily evolved (reevolved) their quadrupedal stance [the primitive stance for archosaurs is quadrupedal]
      • REMNANT OF BIPEDAL ANCESTRY - BACK LEGS OF STEGOSAURS AND CERATOPSIANS MUCH LONGER THAN FRONT LEGS

THE RISE OF DINOSAURS: SUPERIORITY OR LUCK

• EARLY TRIASSIC PERIOD (245 - 240 MILLION YEARS AGO)
  • LAND FAUNA WAS DOMINATED BY THERAPSIDS
    • Sleek, dog-like predators
    • Rotund, beaked and tusked herbivores (see Color Plate IA)
• MIDDLE & FIRST PART OF LATE TRIASSIC PERIOD (240 - 225 MILLION YEARS AGO)
  • LAND FAUNA WAS DOMINATED BY COMBINATION OF THERAPSIDS & ARCHOSAUROMORPHS
    • Herbivorous archosauromorphs (rynchosaurs)
    • Carnivorous crocodile-like archosaurs (see Fig. 15.3)
• LAST PART OF LATE TRIASSIC PERIOD (225 - 208 MILLION YEARS AGO)
  • LAND FAUNA WAS DOMINATED BY COMBINATION OF DINOSAURS (newly-evolved) & ARCHOSAUROMORPHS FOLLOWING EXTINCTION OF MOST SYNAPSIDS (except for newly-evolved mammals)
    • Herbivorous archosaurs (aetosaurs) and prosauropod & ornithischian dinosaurs
    • Carnivorous crocodile-like archosaurs and theropod dinosaurs
• LATE TRIASSIC RISE OF DINOSAURS ATTIBUTED EITHER TO EVOLUTIONARY ADVANTAGE (COMPETITIVE EDGE) OR TO OPPORTUNISTIC REPLACEMENT FOLLOWING MASS EXTINCTION
  • CHARIG SUGGESTS FULLY ERECT POSTURE OF DINOSAURS (Allowed longer stides and more effective walking & running ability) IS THE COMPETITIVE EDGE, WHILE BAKKER SUGGESTS "WARM-BLOODEDNESS" OF DINOSAURS IS THE COMPETITIVE EDGE
  • M. J. BENTON, P. E. OLSEN AND H.-D. SUES ARGUE THAT A MASS EXTINCTION ~225 MILLION YEARS AGO ALLOWED THE OPPORTUNISTIC REPLACEMENT OF THE THERAPSID - ARCHOSAUROMORPH LAND FAUNA BY DINOSAURS
    • some archosauromorphs, most synapsids and several major groups of predatory archosaurs were decimated at this time
    • also coincides with major extinction of the Dicroidium flora (seed ferns, horsetails, ferns and gymnosperms)
  • BENTON SUGGESTS THAT CLIMATE CHANGE (FROM MOIST & EQUABLE TO ARID & HOT) ALTERED THE FLORA WHICH AFFECTED THE HERBIVORES AND THEN THE PREDATORS
  • OLSEN & COLLEAGUES SUGGEST THAT AN ASTEROID IMPACT CAUSED THE MASS EXTINCTION ~225 MILLION YEARS AGO
    • Manicouagan crater in northern Quebec is about the right age and big enough (70 km in diameter)
• IN ANY EVENT, DINOSAURS SUPPLANTED SYNAPSIDS AS THE DOMINANT LAND ANIMALS, A DOMINANCE THEY HELD FOR 160 MILLION YEARS, UNTIL THEIR OWN EXTINCTION