NREM/ZOOL 4464 Ornithology Dr. Tim O Connell Lectures 12 14 9 13 February, 2015 Modern hierarchy of life on earth: Domain Kingdom Phylum (plural phyla ) Class Order Family Genus (plural genera ) Species (plural species ) Prokaryotes no nucleus and no subcellular organelles. These are exceedingly tiny 0.1 10 microns diameter. Eukaryotes larger cells (10 100 microns) with DNA contained in a nucleus and numerous membranebound organelles like mitochondria, Golgi apparatus. Four kingdoms of the Eukarya: Protista - most unicellular, hetero- or autotrophic or both Plantae - multicellular, photosynthetic autotrophs Fungi - multicellular heterotrophs that feed by absorption Animalia - multicellular heterotrophs that feed by ingestion Within Animalia Phylum Chordata Subphylum Vertebrata Class Aves Paleontologist Phil Currie, commenting on recent fossil finds in China of dinosaurs with feathers: "This shows that dinosaurs are not extinct, but are well-represented by 10,000 species of birds." What did he mean? Are bird birds, or are birds really dinosaurs? The issue: Birds are obviously allied with reptiles, and specifically to dinosaurs. Ancestry ambiguous, however. Did birds descend from ancient reptiles that were NOT dinosaurs, or did birds descend DIRECTLY FROM dinosaurs? If the latter, then birds are technically considered dinosaurs according to a modern cladistic analysis. That is, dinosaurs did NOT die out at the end of the Cretaceous! Adaptive radiation - process through which one taxon gives rise to many others that exploit available niches. We need to go back to the Paleozoic the rise of the Tetrapods! ~450 million years ago (MYA), bony fish with cartilaginous rays in their fins appear. ~420 (blaze it!) MYA, some fish develop fleshy fins with bone and muscle inside, e.g., Coelocanth. ~410 MYA, some lobe-finned fish develop a structure of one proximal limb bone articulating with two distal limb bones in each limb. This is the beginning of humerus-radius/ulna. ~385 MYA, Tiktaalik shows a development of the pectoral girdle sufficient to bear its weight without the buoyancy of water! ~380 MYA, Acanthostega has digits at the end of its 4 limbs. ~370 MYA, amphibians appear 5 digits on 4 limbs these are the ancestral Tetrapods. 1
Kingdom Animalia, Phylum Chordata, (Subphylum Vertebrata), Class Reptilia adaptive radiation of reptiles in the Mesozoic Era, ~ 250 65 mya. From the basal stock of reptiles (cotylosaurs), at least SIX major groups developed: Turtles Plesiosaurs (long-necked marine reptiles) Icthyosaurs (dolphin-shaped marine reptiles) Pelycosaurs (ancestral to the therapsids from which we mammals descended) Eusuchians (ancestral to lizards, snakes, and the tuatara) Pseudosuchians (a.k.a. thecodonts, so-named because their teeth sit in individual sockets in the jaw). The pseudosuchians are ancestral to crocodilians, pterosaurs (flying reptiles), and the dinosaurs the group that underwent one of the most dramatic adaptive radiations the world has ever seen. 2
Dino-diversity: The dinosaur radiation led to the development of many wildly different forms. All dinosaurs had their limbs rotated to support the body from beneath like mammal limbs rather than splayed out to the sides as in lizards, turtles, and crocodilians. Significantly, dinosaurs radiated into ancestral quadrapedal forms and derived bipedal forms. The big split in dino-diversity involves the orientation of the bones in the pelvis: ilium, ischium, and pubis. In the ORNITHISCHIANS, the pubis bone points backwards, as it does in modern birds (although as we ll see, birds didn t descend from the ornithischians). The ornithischians include such familiar dinosaurs as Stegosaurus, Ankylosaurus, the ceratopsians like Triceratops, and the hadrosaurs, i.e., the duck-billed dinosaurs like Trachodon. Iguanodon Stegosaurus Opposite the ornithischians were the SAURISCHIANS, the lizard-hipped dinosaurs with the pubis bone pointed forward: The Saurischians radiated into the massive long-necked sauropods like Brachiosaurus and the meat-eating, bipedal theropods. The big theropods like Tyrannosaurus were the carnosaurs and the little vicious ones like Velociraptor were the coelurosaurs. 3
Seismosaurus Megalosaurus The structure of modern birds has been dramatically shaped by the demands of efficient, powered flight. That said, there are numerous similarities between birds and dinosaurs, especially those coelurosaurs. That s the issue: Did birds descend directly from some basal stock of reptiles like the pseudosuchians, or did they arise later, descending directly from the coelurosaur dinosaurs? If birds descended directly from the pseudosuchians, then the principle of monpohyleticism would dictate that birds be included with reptiles in the class Reptilia. If birds descended directly from the coelurosaurs, then birds are not just reptiles, they are a specific type of reptile dinosaurs! This is only really a big deal if we consider dinosaurs to have gone extinct at the end of the Cretaceous. If birds are dinosaurs, that means that the dinosaurs DID NOT die out at the end of the Cretaceous; thousands of them are still with us today. To examine this issue, we need to consider the anatomy of birds and reptiles specifically dinosaurs. To begin to appreciate the structure of birds, we need to have a basic understanding of skeletal structure in an ancestral reptile. Consider Euparkeria, a genus of Triassic pseudosuchian reptiles that predate the dinosaurs, from about 345 mya. 4
Let s look at its skeleton: Axial skeleton Includes skull, all vertebrae (cervical, dorsal {thoracic, lumbar}, sacral and caudal, ribcage, and sternum. Appendicular skeleton Includes limb bones plus scapula, coracoid, clavicles and pelvis. Euparkeria s ancestral condition shows a long, bony tail, teeth in the jaw, at least 10 pairs of ribs, and in the limbs, a solid bone (femur and humerus) proximally and distally paired bones (tibia and fibula in the hindlimbs; radius and ulna in the forelimbs) that end in feet with five digits. A real theropod dinosaur: Compsognathus. This is a much more derived skeleton than that of Euparkeria. Many of a bird s unique features are modifications associated with the demands for flight. Still, despite numerous modifications for the demands of flight, birds are remarkably reptilian. Scales, lay eggs, single urogenital opening... FEATHERS are the key: If it s got feathers, then it s a bird. 5
Exceptional birds: Hoatzin - (extant in South America) nestlings have claws on their wings. Hesperornis regalis: A Cretaceous bird that was structurally similar to a loon or cormorant, though flightless. Its bony beak had teeth. Charles Darwin publishes his Origin of Species in which he describes his theory of evolution by natural selection - 1859. Predicted by that theory: intermediate forms in the fossil record (and around today). Thomas Henry Huxley, citing skeletal similarities between dinosaurs and modern birds was the first to publish his idea that birds descended from dinosaurs. [Not just reptiles, but specifically descended from the dinosaurs.] Enter Archaeopteryx lithographica in 1862 - after Huxley s proclamation: Skeletons of Archaeopteryx (left) and a modern pigeon (Columba) (right). Skeletally, almost identical to small coelurosaurs. One important difference, though... Archaeopteryx had feathers. Fully formed and modern feathers including asymmetrical vanes on the flight feathers that are presumed to be an advanced character compatible with flight. 6
Birds and feathered dinosaurs. These reconstructions from Matthew Martyniuk: Here s what our most advanced reconstructions of Archaeopteryx suggest it probably looked like: A group of coelurosaurs called the maniraptors were skeletally similar to Archaeopteryx: sickle-claw toe, semi-lunate carpal, posterior orientation of pubis, large eyes & braincase, hollow bones, 3-fingered hand, 4-toed foot, fused clavicles, bladelike scapula, secondary bony palate, and... Feathers! Some of the synapomorphies between modern birds, Archaeopteryx, and maniraptors: *Secondary palate *3-fingered hand, 4-toed foot *Semi-lunate carpal *Furcula *Bladelike scapula *Hingelike ankle - no lateral movement *High metabolism *Big eyes, big brains *FEATHERS! Based mostly on spectacular fossil finds from quarries in China, we now have at least 13 different genera of coelurosaurs known to have had feathers or protofeathers and many other species, e.g., Velociraptor, are suspected of having been feathered as well. Sinornithosaurus: 7
Gigantoraptor and related feathered dinosaurs (Cretaceous Period): Here s what Velociraptor probably really looked like: So, according to John Ostrom, Phil Currie, Jack Horner, Bob Bakker, and every thinking cladist out there, birds must share a common ancestor with the coelurosaurs, i.e., birds are descended from dinosaurs and therefore ARE dinosaurs. A small, but vocal group stands in opposition: Alan Feduccia, Sankar Chatterjee, Peter Dodson Concerned about timeline primarily, but also dispute some of the feathered fossils: Are those REALLY feathers? Which specific digits were lost/retained on the 3-fingered hand? Presence of feathers on ALL maniraptors is still conjectural. Maybe birds aren t dinosaurs, maybe those feathered dinosaurs are really flightless birds... Are a birds hand bones digits 2, 3, and 4 or like all theropods 1, 2, and 3? 8
Timeline of modern birds, Archaeopteryx, and feathered maniraptors: Modern birds appear ~ 60 mya Archaeopteryx ~ 150 mya Earliest coelurosaurs ~ 165 mya Feathered dinosaurs, raptors ~ 135-80 mya If Archaeopteryx is older than the Cretaceous feathered dinosaurs, and unequivocally a true bird, then the REAL intermediate reptile/bird must be much older than Archaeopteryx! Contrary to the media frenzy, NONE of the feathered dinosaurs discovered to date was ancestral to birds! The media impression created by these discoveries is that the feathered dinosaurs were ancestors to birds. That can t be because Archaeopteryx from the Jurassic Period was already more birdlike that the feathered dinosaurs that appeared later. Are there any candidates for bird-like reptiles much older than Archaeopteryx? Longisquama, Triassic age - 220 mya. This lizard-like creature was NOT a dinosaur OR a bird, but it had feather-like projections growing out of its spine, and probably glided among trees. It shows few synapomorphies with Archaeopteryx, but does illustrate that feathers could have evolved more than once, and much earlier than currently presumed. But no one seriously considers Longisquama ancestral to birds because it is otherwise so different in structure and so much more similar to lizards. The most widely held ancestry of birds these days looks something like this: Even more recent discoveries, however, start to fill in some of the blanks: older than Archaeopteryx. Many more feathered dinosaurs now discovered, including hundreds of individual specimens Xiaotingia, 155 MYA 9
Epidexipteryx, 160 MYA Anchiornis, 160 MYA Unlikely that all the bird/coelurosaur synapomorphies are mistakes, lies, or convergence To suggest that coelurosaurs are derived birds ignores the synapomorphies between the feathered and non-feathered theropods - that is, if Composgnathus was a bird, then Tyrannosaurus was too. Little evidence for an earlier proto-bird than Archaeopteryx - Longisquama is too distant to forge a defensible link to modern birds Parsimony and cladistics dictate that birds are indeed, living dinosaurs. 10