Differentiating the Devonian Tabulate Corals Favosites and subgenus Emmonsia*
by Alan Goldstein Interpretive Naturalist Falls of the Ohio State Park
*Based on an article published in the MAPS "Digest" in 1983.
In common parlance, the tabulate coral genera Favosites (Lamarck, 1816) and its subgenus Emmonsia (Edwards & Haime, 1851) are called “honeycomb corals.” They have polygonal walls separated by horizontal shelf-like tabulae (described below) giving them the appearance of petrified honeycomb. Depending on the degree of preservation, they can be difficult to differentiate without a general knowledge of their anatomy, and that is the purpose of this article.
Until recently, Emmonsia had genus standing equivalent to Favosites (see Hill, 1981, for instance). It has been lowered to the subgenus level according to William A. Oliver, Jr. (personal communication). Investigators often confused them, even after Emmonsia was established by Edwards and Haime, probably because of the lack of access or understanding of their work published in French.
Favosites has tabula, a horizontal skeletal element that span the width of each chamber (corallite) from wall to wall. The walls and tabula define an individual corallite, of which colonies contain hundred to many thousands depending on size. Separation of tabulae between individual corallites varies by and even within a species. Some have chambers 1 – 2 mm high, while others are a fraction of a millimeter.
Figure 1. Tabulae
The most conspicuous anatomical difference is the presence of squamulae (sgl. squamula) in Emmonsia. The Treatise on Invertebrate Paleontology (volume F supplement, Coelenterata, p. 445) describes them as “tongue-shaped or spoon-like projections from the wall” toward the center of the corallite. In some Emmonsia species the tabulae may be absent or inconspicuously attached to the center of the squamulae. The various species of Emmonsia have squamulae with different characteristics, but invariably give chambers a “cluttered” appearance. (Whereas, Favosites tends to be open.)
Figure 2. Squamulae
While Favositids (the general term for Favosites-like corals) with squamulae range from the Upper Silurian through the Lower Permian and have world-wide distribution, the subgenus of Emmonsia is restricted to the Lower and Middle Devonian of Asia and North America. Favosites ranges from the Upper Ordovician (Manitoba) through the Middle Devonian. The Lower Silurian through Middle Devonian distribution of Favosites is cosmopolitan. “Honeycomb” corals younger than Devonian age are not genus Favosites, nor are there any in the U.S. older than Lower Silurian (outside of Manitoba).
Among the similarities between Favosites and Emmonsia:
Figure 3. Mural pores (triserial) Falls Area Species List The following species list belongs to the subgenus Emmonsia in the Devonian Jeffersonville (Eifelian age) or Beechwood Limestone (Givetian age). Note that the lower coral zone is upper Emsian age (uppermost Lower Devonian) according to Oliver. Many species are illustrated here.
1) Favosites (Emmonsia) amplissima Davis Hemispherical, polygonal corallites 4.5 – 5.3 mm wide, prominent squamulae, tabulae set 0.1 – 1mm apart, mural pores bi- or triserial (coral zone)
2) Favosites (Emmonsia) arbuscula Hall Irregular, knobby, (rarely branching) colony, polygonal corallites 1.4 – 2.5 mm wide, abundant squamulae, thin tabulae 1 – 1.5 mm apart (Beechwood Limestone)
3) Favosites (Emmonsia) bacula Davis Elongate to cylindrical colonies up to 2 cm thick, up to 12 cm long, thin-walled polygonal corallites 1.5 – 2 mm wide with scattered smaller corallites, tongue-shaped squamulae, tabulae 1 mm apart, mural pores uniserial (coral zone)
4) Favosites (Emmonsia) convexa Davis Small, irregularly hemispherical, somewhat dimorphic – larger 2.5 mm corallites nearly round, smaller 1 mm polygonal, triangular-shaped squamulae, mural pores uniserial (coral zone)
5) Favosites (Emmonsia) cymosa (Davis) Knob-like projections, corallites thin-walled, 1.5 mm wide, with 2 – 3 tabulae per mm, short, well-developed squamulae, mural pores uniserial
6) Favosites (Emmonsia) emmonsi Rominger Hemispherical colonies when found in-situ can be 1 – 5 meters across, polygonal 1.5 – 2 mm wide corallites, moderately thick walls, prominent squamulae, tabulae thin, 1 mm apart, mural pores variable (coral zone)
7) Favosites (Emmonsia) epidermata Rominger Low hemispherical to flat colony, 2.3 – 2.8 tetragonal to hexagonal thick-walled corallites, smaller interspersed, squamulae short, tabulae closely set, mural pores uniserial or offset biserial (coral zone)
8) Favosites (Emmonsia) eximia Davis Hemispherical to globular colonies often surrounding crinoid columns, corallites 3 mm polygonal to nearly round, interspersed with 1 – 2 mm polygonal corallites, short, shelf-like squamulae, closely set tabulae, mural pores uniserial in smaller corallites or biserial in larger coralites (Beechwood Limestone) 9) Favosites (Emmonsia) ocellata Davis Club-shaped colonies, somewhat dimorphic, 4 mm nearly round corallites surrounded by one or two layers of 0.5 – 2 mm polygonal corallites, tabulae closely set (coral zone)
10) Favosites (Emmonsia) radiciformis Rominger Irregular knob-like branches, somewhat dimorphic corallites 2-3 mm interspersed with 1 mm diameter, walls thin, squamulae short and broad, closely set tabulae, mural pores uniserial or biserial (coral zone)
11) Favosites "Emmonsia" ramosa (Rominger) Dendroid, staghorn, 1 – 3 cm thick branches, thick-walled, corallites 1 – 2 mm wide, tabulae 1 mm apart (coral zone)
12) Favosites (Emmonsia) tuberosa Rominger Hemispherical to elongate nearly cylindrical, 3 mm pentagonal or hexagonal corallites surrounded by smaller triangular to quadrangular shaped, all with thin walls, short squamulae, wavy, closely set tabulae
13) Favosites (Emmonsia) undescribed species Flattened to hemispherical colonies, up to 1.5 meters across, 0.5 mm polygonal corallites, mural pores unknown, squamulae present (coral zone)
The following belong to the genus Favosites.
1) Favosites argus Hall Flattened to nearly hemispherical colonies, larger corallites 3 – 3.5 mm wide rounded, smaller corallites polygonal 1.6 – 2.2 mm wide, walls w/ 12 vertical low septal ridges w/ transverse grooves 0.5 – 1 mm apart (may resemble squamulae), tabulae complete, horizontal 0.5 – 1 mm apart (Beechwood and Boyle Limestone)
2) Favosites biloculi Hall Discoidal to hemispherical (also palmate & branching), apertures 2.5 – 3mm, polygonal, thin-walled, tabulate 0.5 – 1mm apart, can be other forms as well (coral zone)
3) Favosites clausus Rominger Bushy, irregularly branching, 1 – 1.5 cm wide, corallites in two sizes 1 and 0.5 mm wide (Beechwood Limestone)
4) Favosites clelandi Davis Discoidal to low hemispherical, corallites 1.5 – 2mm, polygonal, thin-walled, tabulate <0.2 mm apart (coral zone)
5) Favosites goldfussi d'Orbigny Hemispherical colonies up to 1 meter wide, hexagonal corallites 3 mm wide, tabulae variably spaced (up to 3 per mm) (coral zone)
6) Favosites hemisphericus var. cornutiformis Stewart Curved, club-shaped colonies, polygonal 1.6 – 2.5 mm corallites thin-walled, tabulate ~1 mm apart (coral zone)
7) Favosites hamiltoniae Hall Hemispherical colonies up to 30 cm across, polygonal 1 – 3 mm wide corallites, tabulae variably spaced 0.5 – 4 mm apart (Beechwood Limestone)
8) Favosites mundus Davis Low hemispherical, biscuit-shaped, larger corallites nearly round, averaging 1.6 mm wide, smaller polygonal 1.2 mm wide, thin-walled, tabulae closely set
9) Favosites patellatus Stumm Knee-cap shaped colony (flatter than F. turbinatus) radiating 1 – 1.5 mm wide polygonal corallites, thin-walled, tabulae ~1 mm apart
10) Favosites placentus Rominger Discoidal, flat with basal attachment, rounded to nearly polygonal corallites averaging 1 mm wide (vary from 0.5 – 1.3 mm), tabulae 0.5 mm apart (Beechwood Limestone)
11) Favosites pirum Davis Pear-shaped to nearly cylindrical or mushroom-shaped colonies, 1.6 – 1.8 mm wide polygonal corallites, thick-walled, tabulae 1 – 3 mm apart
12) Favosites quercus Davis Dendroid, 2 – 3 cm thick, corallites thin-walled, 1.9 – 2.3 mm wide, 1 mm apart (coral zone)
13) Favosites ramulosus Davis Dendroid, staghorn, 1 cm thick, thin-walled, 1 mm wide corallites, tabulae closely set (coral zone)
14) Favosites rotundituba Davis Discoidal colonies, 1 mm round corallites, smaller polygonal 0.5 – 0.7 mm wide (Beechwood Limestone)
15) Favosites turbinatus Billings Knee-cap to spherical colonies, skin-like surface on the lower surface, polygonal 1.6 – 2.5 mm corallites thin-walled, tabulate ~1 mm apart (Jeffersonville and Beechwood Limestone) Many species of Favosites are illustrated here.
Bibliography
Davis, W.J., 1887. Kentucky fossil corals, A monograph of the fossil corals of the Silurian and Devonian rocks of Kentucky, Part 2 (plates), Kentucky Geological survey, xiii pp., 139 pls.
Edwards, H.M. and Haime, J., 1851. Monographie des polypiers fossils des terrains palaeozoiques, Paris, Museum of Natural History Archives, vol. 5, 502 p, 20 pls.
Hall, J., 1876. Illustrations of Devonian fossils; Corals of the upper Helderberg and Hamilton groups, Albany, NY, Weed, Parsons and Co., p. 1 – 7, 43 pls.
Hill, D., 1981. Treastise on invertebrate paleontology, Part F, supplement: Coelenterata, University of Kansas Press and Geological Society of America, 762 p., 462 Figs.
Lamarck, J.B., 1816. Histoire naturelle des animaux sans vertebres, Paris, v. 2, p. 1- 568.
Rominger, C., 1876. Fossil corals, Geological Survey Michigan, v. 3, pt. 2, p. 1 – 159, Pls. 1 – 55.
Stumm, E.C., 1964. Silurian and Devonian corals of the Falls of the Ohio, Geological Society of America Memoir 93, 184 p., 80 pls.
Links to other pages on the Falls of the Ohio website related to this subject: Tabulate Coral List On-line Coral Brochure Fossil Pages
Created March 8, 2011, updated September 1, 2011.
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