Wooster Geologists

This post of Wooster’s Fossil of the Week marks five years of this feature. If you’re counting, that is 260 entries, with never a week missed. To celebrate, I’m returning to the very first fossil in the series, a beautiful encrusting tabulate coral. The original entry is below, with some updates and added links.

This week’s fossil was collected by Brian Bade of Sullivan, Ohio, and donated to Wooster as part of my hederelloid project.  It is a beautiful specimen of the tabulate coral Aulopora encrusting a brachiopod valve from the Silica Shale (Middle Devonian — about 390 million years old) of northwestern Ohio.  [Update: I now know the species is A. microbuccinata Watkins, 1959.] Auloporid corals are characterized by an encrusting habit, a bifurcating growth pattern, and horn-shaped corallites (individual skeletal containers for the polyps).

What is especially nice about this specimen is that we are looking at a well preserved colony origin.  The corallite marked with the yellow “P” is the protocorallite — the first corallite from which all the others are derived.  You can see that two corallites bud out from the protocorallite 180° from each other.  These two corallites in turn each bud two corallites, but at about 160°.  This pattern continues as the colony develops (a process called astogeny).  The angles of budding begin to vary depending on local obstacles; they never again go below 160°.

The polyps inside the corallites are presumed to have been like other colonial coral polyps.  Each would have had tentacles surrounding a central opening, and all were connecting by soft tissue within the skeleton.  They likely fed on zooplankton in the surrounding seawater.  This type of coral went extinct in the Permian, roughly 260 million years ago.

Again, we thank our amateur geologist friends for such useful donations to the research and educational collections in the Geology Department at Wooster.

Later I began to add information about a notable paleontologist associated with the highlighted fossil. I especially wanted to put a face and brief biography with a name we may often see in our taxonomic pursuits but know little about. We can now add this German gentleman from a previous entry —
Aulopora was first described in 1826 by Georg August Goldfuss (1782-1848), a German paleontologist and zoologist. (Goldfuß is the proper spelling, if I can use that fancy Germanic letter.) He earned a PhD from Erlangen in 1804 and later in 1818 assumed a position teaching zoology at the University of Bonn. With Count Georg zu Münster, he wrote Petrefacta Germaniae, an ambitious attempt to catalog all the invertebrate fossils of Germany (but only got through some of the mollusks). The 1841 portrait above is by Adolf Hohneck (1812-1879).

Since the first few entries I began to add a few critical references for the fossils and related stratigraphy. At first these were for me so that I could remember where I got the information used in the text. Later I noted that students and others were finding these entries online and using them as brief introductions to particular taxa. A few references made each entry a starting point for someone else’s paleontological explorations. Here are some added citations for Aulopora —

References:

Fenton, M.A. 1937. Species of Aulopora from the Traverse and Hamilton Groups. American Midland Naturalist 18: 115-119.

Fenton, M.A. and Fenton, C.L. 1937. Aulopora: a form-genus of tabulate corals and bryozoans. American Midland Naturalist 18: 109-115.

Goldfuß, G.A. 1826-1844. Petrefacta Germaniae. Tam ea, quae in museo universitatis Regia Borussicae Fridericiae Wilhelmiae Rhenanae servantur, quam alia quaecunque in museis Hoeninghusiano Muensteriano aliisque extant, iconibus et descriptionibus illustrata = Abbildungen und Beschreibungen der Petrefacten Deutschlands und der angränzenden Länder, unter Mitwirkung von Georg Graf zu Münster, Düsseldorf.

Helm, C. 1999. Astogenese von Aulopora cf. enodis Klaamann 1966 (Visby-Mergel, Silur von Gotland). Paläontologische Zeitschrift 73 (3/4): 241–246. [Courtesy of Paul Taylor]

Scrutton, C.T. 1990. Ontogeny and astogeny in Aulopora and its significance, illustrated by a new non‐encrusting species from the Devonian of southwest England. Lethaia 23: 61-75.

Watkins, J.L. 1959. Middle Devonian auloporid corals from the Traverse Group of Michigan. Journal of Paleontology 33: 793-808.

Not all of our featured fossils are particularly beautiful, or even entire, but they are interesting in some way. Above is the broken cross-section of a rostroconch mollusk known as Hippocardia Brown, 1843. It was found somewhere in Ohio by the late Keith Maneese and kindly donated to the department by his widow Cameron Maneese. From its preservation and the kind of rock making up the matrix inside, we can tell that it almost certainly came from the Columbus Limestone (Middle Devonian, Eifelian).

In the top image it is apparent that this fossil has bilateral symmetry, a heart-shaped cross-section, and a ribbed calcitic shell. This is the dorsal view.
Flipping the specimen upside-down, we now have a view of the ventral portion. Again we see the ribs and bilateral symmetry.
This side view shows that the ribs extend from the dorsal to the ventral sides and are angled to the axis of the shell. That’s about all we can tell. (And this is the best specimen of a rostroconch we have! Thank you again, Cameron.)
This diagram of a complete rostroconch (from the Czech Virtual Museum). This is a side view of a species that does not have the dorsal-ventral ribbing. The shell is superficially like that of a bivalve (clam), but the valves are fused together and their is a distinctive tube (rostrum) extending to the posterior. Much study and debate about the rostroconchs has at least confirmed that these are a class of mollusks separate from the bivalves. They lived semi-infaunally with the rostrum extending into the seawater to channel a flow of water into the body chamber for filter-feeding, much like infaunal bivalves today that have siphons. Rostroconchs and cephalopods appear to be sister groups, and some rostroconchs may have evolved into the scaphopods. Plenty of arguments to go around, though, on the evolution and diversification of mollusks
Captain Thomas Brown (1785-1862) named the genus Hippocardia in 1843. He was a Scottish naturalist who studied many topics, including mollusks. Above are the sections of his book The Elements of Fossil Conchology that describe and illustrate Hippocardia (considering it a bivalve). Captain Brown was born in Perth and went to school in Edinburgh. He joined the militia at 20, becoming a captain at 26. When he was transferred to Manchester, England, Brown acquired an interest in nature. He bought a flax mill after leaving the military, but it burned down while still uninsured. He thus turned to nature writing for support. He was became a Fellow of the Royal Society of Edinburgh in 1818, and in 1840 he was appointed curator of the Manchester Museum. He retained this position for the rest of his life. He was later a Fellow of the Linnean Society and a member, in classic 19th Century fashion, of several other groups, including the Wernerian, Kirwanian and Phrenological Societies. (I love the addition of phrenology to his interests!) The marine gastropod Zebina browniana d’Orbigny, 1842, was named after him. An interesting character, this Captain Brown, but I’ve been unable to find a single portrait of him.

References:

Brown, T. 1843. The elements of fossil conchology according to the arrangement of Lamarck; with the newly established genera of other authors. Houlston & Stoneman, London; 133 pages.

Hoare, R.D. 1989. Taxonomy and paleoecology of Devonian rostroconch mollusks from Ohio. Journal of Paleontology 63: 838-846.

Pojeta, J., Jr., Runnegar, B. 1976. The paleontology of rostroconch mollusks and the early history of the phylum Mollusca. United States Geological Survey Professional Paper 968: 1-88.

Pojeta, J., Jr., Runnegar, B., Morris, N.J. and Newell, N.D. 1972. Rostroconchia: a new class of bivalved mollusks. Science 177: 264-267.

Runnegar, B., Goodhart, C.B. and Yochelson, E.L. 1978. Origin and evolution of the Class Rostroconchia [and discussion]. Philosophical Transactions of the Royal Society B: Biological Sciences 284(1001): 319-333.

Wagner, P.J. 1997. Patterns of morphologic diversification among the Rostroconchia. Paleobiology 23: 115-150.