Ichthyornis
Name:
Ichthyornis
(Fish bird).
Phonetic: Ik-fee-or-niss.
Named By: Othniel Charles Marsh - 1872.
Synonyms: Angelinornis, Colonosaurus,
Graculavus anceps, Graculavus agilis, Ichthyornis agilis,
Ichthyornis anceps, Ichthyornis antecessor, Ichthyornis tener,
Ichthyornis victor, Ichthyornis validus, Plegadornis,
Classification: Chordata, Aves, Ornithurae,
Carinatae, Ichthyornithes, Ichthyornithiformes, Ichthyornithidae.
Species: I. dispar (type).
Diet: Piscivore.
Size: Skeletal
wingspan 43 centimetres long, in life would have been more with
the addition of the feathers.
Known locations: Canada, including Alberta and
Saskatchewan. USA, including Alabama, Kansas, New Mexico
& Texas.
Time period: Cenomanian to Campanian of the
Cretaceous.
Fossil representation: Multiple specimens including
adult and juvenile individuals.
Ichthyornis - A brief history
of the discovery and classification.
Ever
since its first description in 1872, Ichthyornis
has been one of
the most important prehistoric birds known to us, but one that has
been frequently mired in controversy. The very first specimen of
Ichthyornis was first recovered in 1870 by
Benjamin Franklin
Mudge. Those who know their paleontological history will already know
that at this time in North America the Bone Wars were in full swing.
The Bone Wars were basically just the rivalry between two
palaeontologists of the time named Edward Drinker Cope and Othniel
Charles Marsh, and while they resulted in a great many discoveries,
the period is usually held as an example of how not to conduct
palaeontology.
In
1870 Mudge was supplying his fossil discoveries to Cope but then
things changed. Mudge had been a friend of Marsh in his younger years
and Marsh decided to take advantage of this. This was always Marsh’s
advantage over Cope in that he knew people in the right places to
secure positions and work, and when he wrote to Mudge he asked him to
send anything that he thought was significant to him instead of Cope.
To sweeten the deal Marsh offered to do this for free and promised to
give Mudge sole credit for the discovery. When Mudge received Marsh’s
letter the first Ichthyornis specimen was already
prepared for shipping
to Cope; it ended up going to Marsh instead.
In
their eagerness to outdo one another both Cope and Marsh missed several
key things, and here Marsh failed to realise the importance of his
bird specimen. Upon first study, Marsh thought that he had the
remains of two creatures. The skeleton he thought belonged to a
bird, no doubt about that, but there were long jaws had sharp teeth
included with the pot cranial skeleton. At this time Marsh thought
that these belonged to some reptile, possibly something like a small
mosasaur.
Marsh noted the unusual vertebrae of the bird skeleton and
noted that they were concave (curved inwards) at both ends like
those of fish. This yielded the rather simple name of Ichthyornis
which means ‘fish bird’. The jaws were attributed to their own
genus, Colonosaurus mudgei.
By
early 1873 Marsh had realised that he had made a big mistake.
Further preparation of the rock that held the bones resulted in
further exposure of the remains that yielded a very startling
discovery; the toothed jaws were not those of a reptile, they
belonged to the bird. Marsh immediately created the Odontornithes
(toothed birds) and Ichthyornithes groups to classify his new
discovery which was already sending shockwaves through the
paleontological world. Ichthyornis became the
first bird known to
have had teeth within its jaws. For clarity, while Archaeopteryx
was named in 1861 and was the first bird to be known from the
Mesozoic age, the genus was not known to have had teeth as well until
a specimen with a skull was described in 1884.
Ichthyornis
was controversial. Charles Darwin’s Upon the Origin of Species had
been first printed in 1859 and had upset a lot of people,
particularly those with strong religious views who saw it as a
challenge to the teachings of the Christian bible. Marsh’s specimen
of Ichthyornis was a clear indicator that birds had
a reptilian origin
(today we now know this to be the theropod dinosaurs), and some
people actually asked Marsh to hide the specimen away because it was
such strong proof of evolution in action.
Others
were less kind and instead accused Marsh of making a deliberate attempt
at a hoax, and these claims have been as recent as 1967. As
always however, time has allowed the truth to be determined without
doubt. Ichthyornis is now known by many
specimens; in fact it is
one of the best represented fossil birds currently known. Other
toothed birds of varying degrees of primitiveness are now also known,
including Hesperornis,
a genus of toothed bird that was different
but lived in the same time and locations as Ichthyornis.
Darwin
himself considered both Hesperornis and Ichthyornis
to represent
important links in our understanding of evolution.
Due
to the large number of fossil remains, Ichthyornis
now has many
synonyms accredited to it. Obviously Colonosaurus mudgei,
the name
given to just the jaws in 1872 is a synonym but so is Angelinornis
and two species of Graculavus, G.
anceps and G. agilis.
Ichthyornis was one broken down into many species
but today only the
type species is universally considered as valid. Older species are
either synonyms to the type species or have been moved to other
genera. Remains from Uzbekistan once thought to belong to the
genus were later named as Austinornis.
Ichthyornis
- The bird.
In
the simplest terms, Ichthyornis was a sea bird
that was probably very
similar to modern gulls in terms of ecological niche. As already
mentioned, remains from Uzbekistan are no longer thought to belong to
the genus, so the distribution of Ichthyornis is
now the central
portion of North America. This indicates that Ichthyornis
lived along
the coastline of the old Western Interior Seaway. This was a shallow
sea that submerged most of central North America during the late
Cretaceous.
By
the time of Ichthyornis birds had become competent
flyers. The wing
structure of Ichthyornis is more or less the same
as in modern bird
forms meaning that the wings were capable of performing efficient
flight strokes. The skeletal wingspan of Ichthyornis
is about
forty-three centimetres long, but in life this would have been
extended by the presence of flight feathers. The exact size of the
wing is still uncertain because the flight feathers are still unknown.
The
sternum of Ichthyornis also display a strongly
developed keel-like
growth that projects forward. This bone would have been the main
attachment point for strong pectoral muscles that would have enabled
repetitive flapping of the wings to keep the bird in the air. The
addition of fused metacarpals in the wings and presence of a pygostyle
also indicate that Ichthyornis could make finer
flight controls while
in the air than far more primitive forms earlier in the Cretaceous and
Jurassic. These features would have allowed Ichthyornis
to fly out
over the open sea for extended periods as well as possibly exploit air
currents over the water’s surface.
Rather
than being a single sheet of keratin, the beak of Ichthyornis
was
composed of several segments that formed a whole, the beak of the
albatross would be a modern analogy to this. The teeth of Ichthyornis
were laterally compressed (flattened to the sides) and the tips
were recurved so that they pointed towards the rear of the mouth. A
key note about the teeth is that they were only present in the middle
portion of the mouth, the front portion is completely lacking. The
teeth themselves likely facilitated prey capture of marine organisms
such as late Cretaceous fish that swam too close to the surface.
Further reading
- Notice of a new reptile from the Cretaceous - Othniel Charles
Marsh - 1872.
- Notice of a new and remarkable fossil bird - Othniel Charles
Marsh - 1872b.
- On a new sub-class of fossil birds (Odontornithes) - Othniel
Charles Marsh - 1873.
- The jaws of the Cretaceous toothed birds, Ichthyornis
and
Hesperornis - J. T. Gregory - 1952.
- Marsh was right: Ichthyornis had a beak -
J. P. Lamb Jr
- 1997.
- Bone microstructure of the diving Hesperornis
and the volant
Ichthyornis from the Niobrara Chalk of western
Kansas - A.
Chinsamy, L. D. Martin & P. Dobson -1998.
- Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara
Formation) and the Sharon Springs Member (Pierre Shale) - K.
Carpenter - 2003.
- Morphology, phylogenetic taxonomy, and systematics of
Ichthyornis and Apatornis
(Avialae: Ornithurae) - J. A.
Clarke - 2004.
- Ichthyornis sp. (Aves:
Ichthyornithiformes) from the lower
Turonian (Upper Cretaceous) of western Kansas - K. Shimada
& M. V. Fernandes - 2006.
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