Mesofossils

Mesofossils are fossils that are typically visible to the naked eye but require microscopic study to elucidate their morphology and anatomy. These fossils typically fall in the range of 200μm to 10mm in size. Mesofossils are often preserved as charcoal or lignite and can include flowers, fruits, seeds, leaves and other plant organs. However, mesofossils may also include cuticle fragments as well as un-charred seeds and megaspores. Mesofossils are frequently more abundant than macrofossils and often occur where typical compression floras do not. Further, mesofossils are normally preserved in three dimensions, sometimes with exceptional anatomical detail. Collectively, their abundance and exceptional preservation make mesofossils powerful tools for studying the evolution of plants and even plant-animal interactions.

The most extensively-studied mesofossils in the Field Museum collections were isolated from sediments deposited along the Atlantic and Gulf coastal plains of the eastern United States during the mid to late Cretaceous. These mesofossils include many examples of early angiosperms and have contributed significantly to our knowledge and understanding of their early evolution and diversification.

Charred fern pinnule from the Late Santonian, Gaillard Formation, Allon, Georgia.

Charred fern pinnules from the Late Santonian, Gaillard Formation, Allon, Georgia.

Charred flower from the Late Santonian, Gaillard Formation, Allon, Georgia.

Eopolytrichum antiquum capsule of moss sporophyte preserved as charcoal, from the Late Santonian, Gaillard Formation, Allon, Georgia.

Charred moss gametophyte from the Late Santonian, Gaillard Formation, Allon, Georgia.

Charred liverwort from the Albian, Patapsco Formation, Puddledock, Virginia.

Vessels in charred angiosperm wood from the Late Santonian, Eutaw Formation, Upatoi Creek, Georgia.