Fossil of the month: Barycrinus(?) holdfast
What is this strange fossil? You might think it’s some kind of plant root, but it’s not from a plant. This month’s fossil is a root to a sea lily, which sounds like a plant, but is actually a type of organism called a crinoid. Rather than plants, crinoids are marine invertebrates (animals without backbones), which include sea urchins and starfish.
Description. This month’s fossil is part of a crinoid. Crinoids consist of a cup (called a calyx), which is covered in skeletal plates. Arms attach to the cup. Many modern crinoids are stemless, but in the past, most crinoids had stems (called columns), which connected to the cup at one end, and a holdfast at the other. Holdfasts are the attachment structures of crinoids. Some crinoids attached to the sediment on the sea floor, while others attached to other objects, even other crinoids. Crinoid holdfasts have many shapes and sizes (Ubaghs, 1978; Brett, 1981; Guensberg, 1992; Seilacher and Mcclintock, 2005). In some cases, holdfasts have distinctive shapes that were given genus (form-genus) names. In other cases, they are just termed holdfasts of the larger crinoid. Some holdfasts are found as part of the whole crinoid, so the genus name of the whole crinoid based on the calyx and crown applies. This month’s holdfast was not attached to a whole crinoid but other, very similar specimens, have been found attached to the crinoid Barycrinus in the same deposit (the Fort Payne Formation), so it is tentatively assigned to Barycrinus (?).
Different views of another Barycrinus holdfast with multiple roots from the Fort Payne Formation in the Kentucky Geological Survey collection. This specimen was collected from Cumberland County. The fossil of the month was collected in Clinton County.
Ubaghs (1978) and Brett (1981) have both proposed classifications for different types of holdfasts. Both call the roots of branching root-like holdfasts (as seen in this month’s examples) radices. The shape of these multiple-branched holdfasts is sometimes termed radicular because it is composed of multiple radices.
Four species of Barycrinus are known from the Fort Payne Formation (Krivicich and others, 2014), but species can’t be determined for holdfasts unless they are attached to the rest of the crinoid. For crinoids species are generally based on details of the calyx and crown.
Holdfasts have been a part of crinoids for as long as crinoids have been in existence. In Kentucky, fossil crinoid holdfasts can be found in Late Ordovician through Pennsylvanian strata, although they are most common in Late Ordovician, Silurian, Devonian, and Mississippian strata. Barycrinus is a genus of crinoids which was common in eastern North America during the Middle Mississippian (Late Osagean to early Meramecian) (Kammer and Ausich, 1996). In Kentucky, Barycrinus is found in the Borden and Fort Payne Formations (e.g., Lee and others, 2005; Meyer and others, 1989). This month’s fossil is from the Fort Payne Formation. Barycrinus holdfasts in original growth position are found in crinoidal packestones (a type of limestone) in the Fort Payne Formation (Meyer and others, 1989). The Fort Payne is approximately 345 million years old. It outcrops at the surface in 12 counties in south-central Kentucky.
Barycrinus stems sometimes have star-shaped lumens (axis of the column or stalk). This sample is in the KGS collection and was collected in Clinton County.
Holdfast shapes and paleoecology
Crinoid holdfasts had many different sizes and shapes to help them anchor on different substrates in different marine environments. Some of these shapes suggest permanent attachment through the life of the crinoid, while others suggest the possibility of detachment and reattachment if disturbed. Some crinoids may have had different types of holdfasts at different stages of their lives. Research suggests that juvenile Barycrinus started life with simpler encrusting holdfasts on hard substrates. Later in life, they detached from the hard surface and as adults were attached to softer substrates where they grew stout radicular root systems (Hollis and Ausich, 2009). These would have provided a sturdy attachment to the sea floor.
Examples of different shapes of crinoid holdfasts which can be found in Kentucky (terms modified from data in Parichthyocrinus; Brett (1981)). See more information for example crinoid genera.
Many stout, Barycrinus holdfasts have been reported from crinoidal buildups in the Fort Payne Formation (Meyer and others, 1989). The Fort Payne Formation was deposited in relatively deep water of the Middle Mississippian seas that covered much of central and eastern North America. The Fort Payne Formation contains mounds of crinoidal and bryozoan debris which grew above the sea floor (e.g., Greb and others, 2008). Undersea gardens of hundreds or thousands of Barycrinus and other crinoids would have covered the Fort Payne mounds as well as parts of the submerged Borden delta to the east during the Middle Mississippian.
Special thanks. The fossil of the month and many other Fort Payne crinoids in the KGS fossil collections were donated by Dr. David Meyer from the University of Cincinnati. We thank Dave for his donation.
Greb, S.F., Potter, P.E., Meyer, D.L., and Ausich, W.I., 2008, Mud mounds, paleoslumps, crinoids, and more; the geology of the Fort Payne Formation at Lake Cumberland, south-central Kentucky: Field trip for the Kentucky Chapter of the American Institute of Professional Geologists, May 17-18, 2008: 45 p.
Hollis, K.A. and Ausich, W.I., 2009, Ontogeny and life‐history strategy of Barycrinus (Crinoidea, Mississippian): Lethaia, v. 42, no. 2, p. 138-145.
Kalllmeyer, J., no date, Beginners guide to identifying Cincinnatian crinoids: Cincinnati, Drydredgers website, http://drydredgers.org/crinoids_disparida.htm.
Kammer, T.W. and Ausich, W.I., 1996, Primitive cladid crinoids from upper Osagean-lower Meramecian (Mississippian) rocks of east-central United States: Journal of Paleontology, v. 70, no. 5, p. 835–866.
Krivicich, E.B., Ausich, W.I., and Meyer, D.L., 2014, Crinoid assemblages from the Fort Payne Formation (late Osagean, early Viséan, Mississippian) from Kentucky, Tennessee, and Alabama: Journal of Paleontology, v. 88, no. 6, p. 1154–1162.
Lee, K.G., Ausich, W.I. and Kammer, T.W., 2005, Crinoids from the Nada Member of the Borden Formation (Lower Mississippian) in eastern Kentucky: Journal of Paleontology, v. 79, no. 2, p. 337–355.
Meyer, D.L., Ausich, W.I. and Terry, R.E., 1989, Comparative taphonomy of echinoderms in carbonate facies: Fort Payne Formation (Lower Mississippian) of Kentucky and Tennessee: Palaios, v. 4, no. 6, p. 533–552.
Ubaghs, G. 1978, Skeletal morphology of fossil crinoids, in Moore, R.C., and Teichert, C. (eds.): Treatise on Invertebrate Paleontology, Part T, Echinodermata 2, Crinoidea: Geological Society of America and University of Kansas Press, v. 2–3, p. 58–216.