OG 2018New RC
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- Conodonts, the spiky phosphatic remains (bones
and teeth composed of calcium phosphate) of
tiny marine animals that probably appeared about
520 million years ago, were once among the most
- controversial of fossils. Both the nature of the
organism to which the remains belonged and the
function of the remains were unknown. However,
since the 1981 discovery of fossils preserving not
just the phosphatic elements but also other remains
- of the tiny soft-bodied animals (also called conodonts)
that bore them, scientists' reconstructions of the
animals' anatomy have had important implications
for hypotheses concerning the development of the
vertebrate skeleton.
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- The vertebrate skeleton had traditionally been
regarded as a defensive development, champions of
this view postulating that it was only with the much
later evolution of jaws that vertebrates became
- bodied, would have been easy prey for numerous
invertebrate carnivores, especially if these early
vertebrates were sedentary suspension feeders.
Thus, traditionalists argued, these animals developed
coverings of bony scales or plates, and teeth were
- secondary features, adapted from the protective
bony scales. Indeed, external skeletons of this
type are common among the well-known fossils of
ostracoderms, jawless vertebrates that existed from
approximately 500 to 400 million years ago.
- However, other paleontologists argued that many of
the definitive characteristics of vertebrates, such as
paired eyes and muscular and skeletal adaptations
for active life, would not have evolved unless the
- first vertebrates were predatory. Teeth were more
primitive than external armor according to this view,
and the earliest vertebrates were predators.
The stiffening notochord along the back of the
body, V-shaped muscle blocks along the sides,
- and posterior tail fins help to identify conodonts as
among the most primitive of vertebrates. The lack of
any mineralized structures apart from the elements
in the mouth indicates that conodonts were more
primitive than the armored jawless fishes such as the
- ostracoderms. It now appears that the hard parts that
first evolved in the mouth of an animal improved its
efficiency as a predator, and that aggression rather
than protection was the driving force behind the origin
of the vertebrate skeleton.
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