NREM/ZOOL 4464 – Ornithology
Dr. Tim O’Connell
Lecture 14
8 February 2013
Last time:
•avian systematics
•phenetics and cladistics
This time:
•genetic structuring in Black-capped Vireo
•are birds . . . dinosaurs?
Readings this week:
•Gill: Ch. 19, 2
•Exam 1 – Monday, Feb. 11. Will cover all lecture material and associated readings up to and including
Friday, Feb. 8. This is Gill chapters 1, 2, 3, 18 (just pages 558–569), 19, and 21, plus Millican et al. 2012.
th
•Field trip #2: tomorrow, 8:00 am, OSU Arboretum and Botanical Garden. Meet at Rt. 51/6 St. entrance
(just east of Sangre Rd.) for a bird walk of ~ 2 hours’ duration.
•Wed. Feb. 13 will be Literature Discussion of a paper from The Auk. Bayly, et al. 2012.
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
•We will see that the class Aves might not be what it seems . . .
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.
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.
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 meateating, bipedal theropods. The big theropods like Tyrannosaurus were the “carnosaurs” and the little
vicious ones like Velociraptor were the “coelurosaurs.”
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.
Notes from the BBC’s “Life of Birds”
Jurassic Period (150 mya) fossils from an ancient seabed in what is now Germany have revealed at least
10 fossils of an early bird, Archaeopteryx. Like its reptilian contemporaries, this creature ran on its hind
legs, had three-fingered claws at the end of each forelimb, small and sharp teeth in its jaws, and it had a
long bony tail. But what it also had was more remarkable: feathers. Not only was its body covered with
feathers, its forelimbs supported feathers with asymmetrical vanes – compelling evidence that this
creature could fly.
We see in the hoatzin of Venezuela some indication of how Archaeopteryx might have used the claws on
its wings. Nestling hoatzins have two functional claws on their wings today, and those claws are a
tremendous aid to the young birds as they climb around their home in the mangrove swamps.
Feathers are made of the protein keratin, just like reptilian scales, mammalian hair, and claws. The
filamentous structure of feathers allows them to be puffed up to trap warm air close to the skin when cold
or sleeked down to release air close to the skin when hot. Down feathers especially are excellent
insulation.
Fully modern birds (with horny beaks and no teeth) and feathered tails without a bony center were flying
around T. rex and Triceratops in the late Cretaceous. By 50 million years ago (Cenozoic Era), non-avian
dinosaurs and pterosaurs were gone, and mammals hadn’t yet undergone their impressive adaptive
radiation. Birds, on the other hand, were quite diverse in from and function. Some had even already
secondarily lost the power of flight. Why? Flight is energetically expensive. Birds that don’t need to fly,
won’t. Those that can obtain their food and defend themselves from predators without flying to do so,
have repeatedly given up flight. Notable examples include ostriches and allies, rails, penguins, etc.
Without the need to fly, some species have secondarily lost the microscopic features of their feathers that
allow the vanes to be zipped together, e.g., the fluffy, hairlike plumage of ostriches, emus, and kiwis.