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.
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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.
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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.”
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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.
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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.
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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.
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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:
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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?
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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
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•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.
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