Levin: Reptiles At The Feeder

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(Host) They may be the same old birds at the feeder, but nature writer,
photographer and commentator Ted Levin tells us that the knowledge of
their pedigree has changed.

Long, long ago, crocodiles and birds sprang from a common ancestor. In
fact, modern evolutionary science has shown that an alligator is more
closely related to a chickadee then it is to a turtle or a lizard. You
might even say that birds are late blooming reptiles or alligators are
latent birds. Here’s the drill.

I was an undergraduate studying comparative vertebrate anatomy in the
late 60s, I learned that during at least some stage of development all
members of the phylum Chordata possess a notochord, a cartilaginous
skeletal rod that supports the body. This phylum includes a diverse
array of animals, from worm- like creatures called sea squirts to
sharks, bony fish, amphibians, reptiles, birds, and mammals. In the more
highly evolved chordates – fish through mammals – a column of vertebrae
made up of either cartilage or bone, is the body’s central joist. In
us, it’s the spine.

subphylum Vertebrata or backboned chordates were divided into eight
classes, four of which represent "fish." Two of these are obscure and
two are eminently recognizable: the cartilaginous sharks and rays; and
the pinnacle of fish evolution, the statistically abundant and diverse
boney fish, which includes virtually everything else – from guppies to
swordfish. The remaining four classes represent the terrestrial
vertebrates – amphibians, reptiles, birds, and mammals.

tracing Abraham’s descendents in the Book of Genesis, the relationship
between the classes of vertebrates is easy to plot. Follow all the
"begots" and we discover that amphibians emerged from a group of
lung-bearing, boney fish called lobefins.

300 million years ago, during the steamy Carboniferous Period, when the
Earth was much hotter than it is today, and all the landmasses of the
planet were joined into one huge equatorial belt; amphibians begot
reptiles. Eventually, reptiles begot birds and mammals during the Age of

My comparative
anatomy course subdivided reptiles into sixteen orders. Dinosaurs
comprised two of them, and only four still exist today. Of those four,
three represent turtles, crocodiles, lizards and snakes. The fourth, a
lizard-like group of two living species called tuatara, make their last
stand today on islands off the coast of New Zealand.

But like
the animals themselves, our classification system has evolved over time.
Once, we grouped animals into an ascending pyramid with humans at the
apex. Now, through sophisticated molecular research, we’re able to track
the actual evolutionary relationships between groups of animals based
on genetic markers, biogeography, and fossil history.

vertebrates are grouped together as Tetrapoda – that’s the four-limbed
crowd: amphibians, reptiles, birds, and mammals. Unlike amphibians,
however, reptiles, birds, and mammals also have eggs with a shell and
embryos protected by three membranes. So they’re given a new label that
reflects that relationship. Collectively, they’re known as Amniota.

birds and reptiles are very close cousins. In fact, birds are
"feathered reptiles" – an idea that’s utterly transformed my
appreciation of the daily drama at the feeder in my yard.

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