Ordovician slab of brachiopod fossils

Brachiopoda Preservation


Above Image: Rock slab of fossil brachiopods from the Upper Ordovician Waynesville Formation of Warren County, Ohio (PRI 76881). Specimen from the Paleontological Research Collection, Ithaca, New York. Image by Jaleigh Q Pier.

Brachiopod Preservation

Instead of being able to directly observe living things as a biologist would, paleontologists must interpret fossils—and the rocks in which they are found—in order to understand ancient life. Rocks tell a story when you know how to read them, revealing the ancient habitats and environmental conditions that existed millions of years ago. Sometimes they can even hint at what led to the death of an individual or the extinction of a species. Being able to read rocks is important for the study of brachiopod fossils since they are commonly preserved as molds in sediments, their shell material long since altered or gone altogether.

Brachiopod fossils are commonly preserved in three main ways: Unaltered remains, internal molds, or external molds (learn more about fossil preservation here).

  • Unaltered remains preserve the original shell as if you picked it up off the ocean floor.
  • Internal molds preserve the inside of the shell including internal supports, hinge characteristics, and sometimes impressions of soft tissues.
  • External molds preserve the characteristics on the outside of a shell, most commonly shell ornamentation.

Unaltered Fossil: 

Fossil specimen of the brachiopod Atrypa devoniana from the Devonian Lime Creek Formation of Floyd County, Iowa (PRI 70763). Specimen is from the collections of the Paleontological Research Institutuion, Ithaca, New York. Longest dimension of specimen is approximately 3 cm.


Internal and External Molds:

A small slab full of brachiopod fossils, showing preserved shell, internal molds, and external molds. Specimen is from the teaching collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 13 cm.


Since brachiopods have two distinctly shaped valves, identification can be difficult with individuals of each species having potentially four unique molds: an external and internal mold for each valve. When preservation is poor, identifications can be a challenge. Below are three models of the same brachiopod species, showing the variability of preservation for both valves.


Fossil brachiopod specimen of Hipparionyx proximus from the Devonian Oriskany Sandstone Formation of New York (PRI 76876). Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 12 cm. Model by Jaleigh Pier.


Fossil brachiopod pedicle valve specimen of Hipparionyx proximus from the Devonian Oriskany Sandstone Formation of New York (PRI 76876). Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 12 cm. Model by Jaleigh Pier.


Fossil internal mold of the brachiopod Hipparionyx proximus from the Devonian Oriskany Sandstone Formation of New York (PRI 76921). Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 6 cm. Model by Jaleigh Pier.


Brachiopod features that can preserve in external or internal molds

Brachiopod features that can preserve in external or internal molds. A-C: Schizophoria striatula from the Devonian of Germany. D: Schizophoria vulvaria from the Late Devonian of Germany (Zittel 1913, Fig. 565). (Public Domain)


An additional, if less common, way in which brachiopods are preserved is the replacement of the original calcite shell material by other minerals, especially silica or pyrite. This type of preservation is referred to as replacement. Below are a couple of examples.


Replacement by Pyrite:

Pyritized fossil brachiopod specimen of Paraspirifer bownockeri from the Middle Devonian Silica Formation of Ohio (PRI 76880). Specimen is from the collections of the Paleontological Research Institution, Ithaca, New York. Longest dimension of specimen is approximately 4.5 cm.


Replacement by Silica:

Fossil brachiopod Hercosia uddeni from the Permian Word Formation of Brewster County, Texas (PRI 45537). Specimen is preserved as a silicified replacement. Specimen is on display at the Museum of the Earth, Ithaca, New York. Specimen is several cm in length.


Fossil specimen of a productid brachiopod replaced by quartz from the Permian Glass Mountains of southwest Texas (PRI 76879). From the collections of the Paleontological Research Institution. The longest dimension is 4 cm in length.

References and further reading

Benton, M.J., and Harper, A.T., 2009. Introduction to Paleobiology and the Fossil Record. First ed., Wiley-Blackwell Publishing, 592 pp.

Boardman, R.S., Cheetham, A.H., and Rowell, A.J. 1987. Fossil Invertebrates. Blackwell Scientific Publications. 713 pp.

Carlson, S.J. 2016. The Evolution of Brachiopoda. Annual Reviews of Earth and Planetary Sciences, 44:409-438.

Leighton, L.R. 2001. New Directions in the Paleoecology of Paleozoic Brachiopods, in Carlson, S.J. and Sandy, M.R. ed., Brachiopods Ancient and Modern. The Paleontological Society Papers, Volume 7:185-205.

Peck, L.S. 2001. Ecology of Articulated Brachiopods, in Carlson, S.J. and Sandy, M.R. ed., Brachiopods Ancient and Modern. The Paleontological Society Papers, Volume 7:171-183.

A. Selden ed., Treatise on Invertebrate Paleontology, Part H, Brachiopoda Revised, Volume 6. The University of Kansas and Geological Society of America. 3226 pp.

Tree of Life Web Project. 2002. Brachiopoda. Lamp shells. Version 01 January 2002 (temporary). http://tolweb.org/Brachiopoda/2494/2002.01.01 in The Tree of Life Web Project, http://tolweb.org/

Williams, A. and Carlson, S. J. 2007. Affinities of Brachiopods and Trends in their Evolution, in P. A. Selden ed., Treatise on Invertebrate Paleontology, Part H, Brachiopoda Revised, Volume 6. The University of Kansas and Geological Society of America. 3226 pp.

Zittel, K.A. 1913. Brachiopoda, in Eastman, C.R. ed., Text-Book of Paleontology. Macmillan and Co. Limited, London. 839 pp.

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Unless otherwise indicated, the written and visual content on this page is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. This page was written by Jaleigh Q. Pier. See captions of individual images for attributions. See original source material for licenses associated with video and/or 3D model content.