This is Mazon Monday post #306.  What’s your favorite Mazon Creek fossil?  Tell us at  email:esconi.info@gmail.com.

---

Drevotella proteana is believed to be a hydrozoan. It lived during the Pennsylvanian Period. Fossils of this soft-bodied animal are known only from the Mazon Creek fossil deposit, where exceptional preservation allows such delicate organisms to be recorded. Hydrozoans are cnidarians and include jelly-like forms within the subphylum Medusozoa.

Drevotella proteana was formally described by Matthew Nitecki and Eugene Richardson, Jr. in the paper “A New Hydrozoan From the Pennsylvanian of Illinois,” published in Fieldiana: Geology.

Abstract

Drevotella proteana, a new genus and species of colonial hydrozoan, is described from the Middle Pennsylvanian Francis Creek Shale of the Mazon Creek area of northeastern Illinois. It is represented by numerous specimens preserved in ironstone concretions in which the large, irregularly branched colonies appear as flattened impressions visible by virtue of color contrast.

Diagnosis. — Arborescent sessile colonies a few centimeters in height; shape and size of colony variable; one or more erect or prostrate, irregularly divided stems of variable length and thickness; branching racemose; hydranths broad and rounded, terminal on branches.

Description. — Almost all colonies are arborescent, with dichotomous or irregular branching. Irregularities of branching may be exaggerated by post-mortem deformation. Both prostrate stolons and erect stems (hydrocauli) are probably present. The stems are thick, and bear rather widely-spaced hydranths and hydranth-bearing branches.

Growth is apparently “monopodial,” and perhaps “hydrorhizal” as well (Hyman, 1940, p. 403). Bases are poorly preserved. In some specimens there is an ill-defined area (fig. lb) that may represent a basal expansion deriving from a mat or tangle of stolons. This may be similar to the attachment structure of the modern fresh-water to brackish-water thecate hydroid Cordylophora (Kinne, 1956).

Branches arising from the stems are simple or profusely divided. A medial structure observable in some branches (fig. la) may represent a colonial gastrovascular cavity, and while it is possible that Figure la shows a hydrocaulus encased in stolons (Hyman, 1940, fig. 116B) the appearance makes this seem unlikely. Rather, from the relative thickness of the inner core and the thinness of the external layer, this could represent a thin perisarc or periderm surrounding the coenosarc (body tissues) inside.

No surface detail is observable; if there was a chitinous periderm, it was only lightly sclerotized. The swellings at the ends of the finest branches probably represent hydranths, the expanded terminal portions of polyps. Some of the hydranths may be adnate on the major stems (fig. 2b). Tentacles have not been observed.

…

Acknowledgements

We are grateful to Prof. Donald P. Abbott of Stanford University for his critical reading of the manuscript, and to Messrs. Corliss Ingels and James Turnbull and Mrs. Ted Piecko, who allowed examination of their specimens.

Drevotella proteana can be found on page 7 of Jack Wittry’s “The Fossil Fauna of Mazon Creek“.

Drevotella proteana is a soft-bodied hydroid which closely resembles present day hydroids. Specimens appear to represent complete colonies or appreciable portions of colonies. However, little but the gross form is preserved as flattened color markings, rather than impressions, on the inside of the concretion.

Further examination will reveal a thick stem with irregular branches, sometimes widely spaced. Tentacles have not been observed. Most bases or attachment structures are poorly preserved or missing and may have been separated from the colony at the time of burial. However, some specimens of D. proteana have been found attached to bivalves, indicating that the shells were used as supporting bases. (See Associations, page 169.)

The “Richardson’s Guide to the Fossil Fauna of Mazon Creek” includes a short description of Drevotella proteana in chapter 6 “Cnidaria” by Steven D. Sroka.

Class Hydrozoa
Drevotella proteana Nitecki and Richardson, 1972
Figure 6.11

Drevotella are benthic treelike sessile colonies of varying size (maximum height approximately 10 cm) and shape with two or more main stems of varying thickness. Stems show irregular dichotomous branching with smaller branches along their lengths. Swellings exist at the ends of the finest branches and probably represent hydranths (Nitecki and Richardson, 1972). The hydranths are broad and rounded compared to their stalks. Several specimens of D. proteana have been found attached to bi-valves (Aviculopecten mazonensis and a myalinid), indicating that the shells were used as a supporting base. Nitecki and Richardson (1972) judged Drevotella to be a fossil hydrozoan.

Specimens

From “A New Hydrozoan From the Pennsylvanian of Illinois“

Figure 1

Figure 2

Figure 3

From “The Fossil Fauna of Mazon Creek” by Jack Wittry. The specimen on the left is from Jim Fairchild, while the one on the right is PE 36822