Head from Postglacial Marl in Cheboygan County, Michigan
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sz, t 3 [Reprinted from PAPERS OF TRE MICHIGAN ACADEMY OF SCIENCE, As, AND LETTERS, Vol. XXV, Dup. Published r94o] THE CRANIUM OF A FRESH-WATER SHEEPS- HEAD FROM POSTGLACIAL MARL IN CHEBOYGAN COUNTY, MICHIGAN CARL L. HUBBS HERE are fields of research in which even fragments of concrete T data are eagerly seized upon. This is especially true of subjects like zoogeography, in which conclusions can ordinarily be drawn only from circumstantial evidence. In recent attempts to trace the postglacial redispersal of fishes in North America (see especially Greene, 1935) the lack of purely objective data on the occurrence of fish species in given regions has been a particular deterrent to the drawing of precise conclusions. It is with much satisfaction, there- fore, that I am able to record with certainty the ancient, postglacial, occurrence of the fresh-water sheepshead, Aplodinotus grunniens Rafinesque, in the waters of Burt Lake, Michigan, or in one of its postglacial precursors. While digging a boat well at Burt Lake during the summer of 1937 Mr. J. H. Greenman uncovered a remarkably well preserved cranium of Aplodinotus (Pl. I). He specifies that the skull was found thirty feet from the water's edge and exactly six feet below the surface of the level ground (which here lies only a few feet above the lake level). It was under "about two feet of black muck or turf and about four feet of marl, right at the bottom of the marl where the marl bed lay on solid red clay." A coating of white marl remains in some of the cavities of the skull bones. In the unpublished soil survey of Cheboygan County, according to Lee R. Schoenmann (personal communication), the superficial "two feet of black muck or turf," which here overlies the marl, has been identified as a local area of Edwards muck associated with Granby sand. The location of the discovery is on Greenman Point, near the north end of the east shore of Burt Lake, in Section 14, T. 36 N., 293 294 Carl L. Hubbs R. 3W. (Burt Township), Cheboygan County, Michigan. By straight line the site lies thirteen miles inland from the Straits of Mackinac at Cheboygan. Burt Lake, a large body of water, is one of the main elements of the "Inland Waterway," which during most of post- glacial time constituted a strait connecting Lakes Michigan and Huron (Leverett and Taylor, 1915). As to the age of this semifossil fish skull, I have consulted a num- ber of scientists who are conversant with the region, including the glacial geologists Frank Leverett and George M. Stanley, the limnol- ogist P. S. Welch, and the land and economic survey expert Lee R. Schoenmann. All agree that the sheepshead in question must have lived in postglacial time, certainly many centuries ago. Without a specific field examination, however, no one is ready to correlate definitely the occurrence of the fish with any of the series of post- glacial lakes. Dr. Stanley suggests, however, that, because of the frequent finding of such marl and peat deposits of Nipissing age not far above present lake levels and the paucity of such materials in Algonquin deposits, a correlation with Lake Nipissing seems most plausible. The penetration of foramina in the bones by marl- preserved root or stem fibers makes it seem virtually certain that the skull was laid down in shallow water and, therefore, during neither of the high levels of Lake Algonquin. The occurrence of Aplodinotus grunniens in the Inland Waterway during postglacial time takes on added significance in view of the almost certain absence of the species in these waters at the present time. The sheepshead is an essentially southern species, as Barney (1926) has pointed out in detail. (I have taken it as far south as the Rio de la Pasi6n, a tributary of the Rio Usumacinta in El Peter', Guatemala.) It is rather common in southern Lake Michigan, in Lake Erie, and in Saginaw Bay of Lake Huron, and there is one published record for the mouth of the Au Sable River, which enters Lake Huron north of Saginaw Bay. Records of the commercial fish catch (made available by Dr. Ralph file of the United States Bureau of Fisheries) indicate an occasional straggling northward as far as the Beaver Islands in Lake Michigan, along the northern shores of Lake Huron in Michigan, and even into St. Martin Bay on the north 1 See Chart of Inland Route of Navigation, Michigan, from Cheboygan, to Little Traverse Bay, Including Petoskey and Harbor Springs, 1930 (War Depart- ment, Lake Charts, Cat. No. 66). A Sheepshead from Postglacial Marl 295 side of the Straits of Mackinac.' It is not surprising, therefore, to find proof of the penetration of the species into the location of Burt Lake, particularly at a time when the Inland Waterway was a broad, shallow, and probably turbid strait, providing conditions which would be favorable to the species. At present the sheepshead occurs even much farther north, in cool, shallow, and often turbid waters (Barney, 1926; Dymond and Hart, 1927). Its presumed use of the southern outlets of the glacial Great Lakes (Barney, 1926; Greene, 1935) is confirmed. The postglacial cranium of Aplodinotus grunniens (Pl. I), meas- uring 156 mm. from the tip of the vomer td the end of the supra- occipital crest, represents a rather large specimen of the species as compared with the usual size of present-day adults. The bones of the species found in Indian burials and middens prove, however, that vastly larger sizes were attained in prehistoric time. When this beautifully preserved skull is compared with that of a Recent specimen from Lake Erie, only slight differences are apparent (Pl. I). The greater thickening and the coarser sculpturing of the bones are attributable to the age of the postglacial individual (about twenty years, as determined from the winter lines on the membrane bones). Owing to the marked bilateral asymmetry of the post- glacial skull and of the variation shown by Recent skulls, differences in the foramina and in details of sculpturing probably lose all sig- nificance. The discoverer of the postglacial Aplodinotus cranium, Mr. J. H. Greenman, has very kindly deposited the specimen in the University of Michigan Museum of Zoology. We are grateful to Dr. Max M. Peet of Ann Arbor, a summer neighbor of Mr. Greenman, for recog- nizing the scientific value of the specimen and for bringing it to the Museum with information on the remarkable find. UNIVERSITY OF MICHIGAN 2 There is no evidence, however, to confirm the expectation of Barney (1926) that the species will be found to occur in Lake Superior. 3 A study of these remains has been in progress for some time. 296 Carl L. Hubbs LITERATURE CITED BARNEY, R. L. 1926. The Distribution of the Fresh-Water Sheepshead, Aplodinotus grunniens Rafinesque, in Respect to the Glacial History of North America. Ecology, 7: 351-364, figs. 1-3. DYMOND, JOHN R., AND HART, JOHN L. 1927. The Fishes of Lake Abitibi (Ontario) and Adjacent Waters. Publ. Ont. Fish. Res. Lab., No. 28: 1-19. GREENE, C. WILLARD. 1935. The Distribution of Wisconsin Fishes. Wisconsin Conservation Commission, Madison. 235 pp., 96 maps. LEVERETT, FRANK, AND TAYLOR, FRANK B. 1915. The Pleistocene of Indiana and Michigan and the History of the Great Lakes. U. S. Geol. Surv., Mon. 53 : 1-529, figs. 1-15, pls. 1-32. PLATE I CRANIA OF POSTGLACIAL AND RECENT SHEEPSHEAD Two crania are shown, each in posterior, dorsal, and lateral aspect. The larger, postglacial, skull is 156 mm. long from tip of vomer to end of supraoccipital crest. The smaller, Recent, cranium, 122 mm. long, was prepared from a Lake Erie specimen. Photographs, to the same scale, by F. W. Ouradnik .