Why do fossil birds matter for geology

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Archaeopteryx, the commonly accepted oldest known bird from the JurassicIchthyornis, a toothed sea-bird from Cretaceous North AmericaA Cenozoic phorusrhacid, a derived big flightless meat-eating group of modern birds now extinct, maybe related to railsConfuciusornis, toothless fossil forest birds from the Early Cretaceous of China
Archaeopteryx, the commonly accepted oldest known bird from the Jurassic
Archaeopteryx, the commonly accepted oldest known bird from the Jurassic
Ichthyornis, a toothed sea-bird from Cretaceous North America
Ichthyornis, a toothed sea-bird from Cretaceous North America
A Cenozoic phorusrhacid, a derived big flightless meat-eating group of modern birds now extinct, maybe related to rails
A Cenozoic phorusrhacid, a derived big flightless meat-eating group of modern birds now extinct, maybe related to rails
Confuciusornis, toothless fossil forest birds from the Early Cretaceous of China
Confuciusornis, toothless fossil forest birds from the Early Cretaceous of China

To what extent do birds influence geological processes? And since
when? Can fossil birds be helpful for stratigraphy or for
interpreting environmental settings? Do fossil avian remains play
any economic role?
Or is, after all, fossil bird research merely a task for
biologists?

These questions arose when I was realizing that the profs of my
school taught palaeontology mainly as a device for analysing
geological processes. What to answer when being asked about the
usefulness of a group of vertebrates whose bones are found once in a
blue moon? As if the keenness for fossil birds (as wells as for
dinosaurs) were a children's disease you have to overcome in order to
advance to the serious fields of palaeontology!

In fact, fossil birds are geologically relevant in several ways:

1) Rocks composed of avian remains

Seamount phosphorites are mainly formed by the accumulation of
phosphate-rich seabird excrements, called guano. Since guano is a
valuable fertilizer and can be used in the chemical industry, these
deposits (which may contain avian bones) have been mined for more
than 100 years.* 

In shallow marine (to fluviatile) environments with low sedimentation
rates, a relatively low oxygen concentration, and a high
concentration of nutrients (especially in upwelling areas) bones,
fish scales, and shells can accumulate to form phosphorite bonebeds.
These phosphorites can contain a high proportion of avian bones.


2) Fossil bird communities as environmental indicators

Attempts have been made to reconstruct Pleistocene environments on
the basis of their faunal compositions: An assemblage with a
composition similar to that of a well known present-day fauna is
likely to have inhabited the same environment.

TYBERG** used seabirds to reconstruct the climatic conditions of Late
Pleistocene European coasts. In contrast with mammals birds appear to
have evolved only slightly since the Miocene*** and they are less
affected by dispersal barriers and can migrate more freely in
response to climatic changes. On the other hand the higher vagility
of birds (the European avifauna includes a high percentage of long-
distant migrants) may limit the reliability of interpreting avian
assemblages. However TYBERG's analysis was successful in
illustrating the changing distributions of seabird populations which
imply climatic and environmental shifts during times of glaciation.

It's worth mentioning that the number of discovered bird species
and localities is particularly high in the Quaternary and decreases
significantly with increasing geological age****. Older avifaunas are
more rarely preserved and perhaps less meaningful concerning
environment reconstructions. But even if comparison with recent forms
is unsuccessful or limited, the presence of fossil birds will add to
the overall picture of an ancient ecosystem and thus may contribute
to the environmental analysis of a deposit.


3) Birds as fossil treasures

There is no doubt about the importance of exceptionally preserved
fossils for our understanding of the function, ecology and evolution
of extinct animals. But do they also raise or answer geological
questions? Of course, the preservation of feather imprints or the
accumulation of hundreds of bird specimens needs a taphonomical
explanation and might imply certain geological processes.

(Interestingly enough the Lower Cretaceous Jehol Group of Liaoning,
China has yielded hundreds of valuable bird skeletons. Many of them
have been collected illegally and smuggled to countries throughout
the world. For example 80% of 1000 unearthed Confuciusornis specimens
are thought to have been sold illegally to foreign collectors, each
for thousands of dollars. This illustrates that sometimes even fossil
birds prove to be economically significant.*****)


*Cronan, D.S.(1992): Marine Minerals in exclusive Economic Zones.-
chapman & hall, London, pp. 67-73;

**Tyrberg, T.(1999): Seabirds and Late Pleistocene Marine
Environments in the Northeast Atlantic and in the Mediterranean. In:
Olson, S.(ed.): Avian Paleontology [...]: Proceedings of the 4th
International meeting of the Society of Avian Paleontology and
Evolution [...].– Smithsonian Contributions to Paleobiology 89,
Washington, D.C., pp. 139- 157;

***compare: Feduccia, A.(1996): The Origin and Evolution of Birds.-
Yale University Press, New Haven, pp. 167-171;

**** for example: Benton, M. J.(1997): Vertebrate Palaeontology.-
London, pp. 285;

***** Schleich, H. H.(ed.)(2001): Fossil Treasures from China.-
Fuhlrott-Museum, Wuppertal, pp. 53- 55;

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