Proceedings of the Iowa Academy of Science Volume 90 Number Article 6 1983 A Well-Preserved Ground Sloth (Megalonyx) Cranium from Turin, Monona County, Iowa H. Gregory McDonald Idaho State University Duane C. Anderson University of Iowa Let us know how access to this document benefits ouy Copyright ©1983 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation McDonald, H. Gregory and Anderson, Duane C. (1983) "A Well-Preserved Ground Sloth (Megalonyx) Cranium from Turin, Monona County, Iowa," Proceedings of the Iowa Academy of Science, 90(4), 134-140. Available at: https://scholarworks.uni.edu/pias/vol90/iss4/6 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact [email protected]. McDonald and Anderson: A Well-Preserved Ground Sloth (Megalonyx) Cranium from Turin, Mon Proc. Iowa Acad. Sci. 90(4): 134-140. 1983 A Well-Preserved Ground Sloth (Mega/onyx) Cranium from Turin, Monona County, Iowa H. GREGORY McDONALD 1 Idaho Museum of Natural History, Idaho State University, Pocatello, Idaho 83209 DUANE C. ANDERSON State Archaeologist, Univeristy of Iowa, Iowa City, Iowa 52242 A well-preserved cranium of a large Pleistocene ground sloth (Mega/onyx jeffersonii) is described in detail and compared with six other North American Mega/onyx crania. Although the morphology of the Iowa specimen compares favorably with all others, the descending flange of the zygomatic arch is unusual in that it is sharply deflected to the posterior. This suggests a more horizontal component to the masseter. Two new and six previous Iowa records of Mega/onyx in Iowa are reported or reexamined. INDEX DESCRIPTORS: Ground sloth, Xenarthra, Me[!,alonyx, Turin local fauna, Pleistocene, Monona Co., Iowa. In April, 1973, five amateur paleontologists uncovered a fragile a sizeable fauna! assemblage over the last 30 years. A study of the but nearly complete cranium of a large Pleistocene ground sloth Turin local fauna is currently in preparation by W. D. Frankforter and (Mega/onyx jeffersonii) in the gravel pit at Turin, Iowa (Fig. 1). The H. A. Semken. A partial fauna] list includes opossum, mastodon, specimen (Fig. 2) was carefully collected, transported to the Sanford mammoth, rabbit, pocket gopher, muskrat, giant beaver, beaver, Museum in Cherokee, and subsequently added to the museum's raccoon, bear, dire wolf, lion, muskox, and camel. collections (SM 21-73-Z). The junior author, then director of the The geological age of the Turin gravels is uncertain. Hay ( 1914) Sanford Museum, made a preliminary identification which was considers most of the gravels along the Missouri River to be Aftonian, confirmed by Holmes A. Semken, Department of Geology, Universi­ but Frankforter ( 1971) suggests late Kansan to early Illinoian age. ty of Iowa. The discovery received cohsiderable attention in the More recently, Semken (personal communication, Feb. 15, 1982) popular press (Des Moines Register, May 3, 1973) at that time. Casts of places the deposit late in the Pleistocene, noting that the fauna closely the specimen (SUI 38,929) were made at the University of Iowa resembles those of Rancho La Brean age. Museum of Natural History (Schrimper, 1973) and the original was returned to the Sanford Museum for display. This report describes the DESCRIPTION AND COMPARISON OF THE SKULL specimen and its geological context, and compares it with skulls of Mega/onyx from California, Idaho, Kansas, Mississippi, Oklahoma The skull (Fig. 2, Table 1) is incomplete, lacking the anterior and and Texas. palatal portion of the right maxilla and most of the left, except for the Records of Mega/onyx in the state are scanty and no new specimens base of the alveoli. No teeth are preserved and the cranium lacks both have been reported in the Iowa literature since Delevan ( 1926). Except the anterior tip of the right nasal and the right zygomatic arch. There for a few isolated teeth all previous discoveries have been post-cranial is some post-mortem abrasion of the left glenoid fossa and both material. The recovery of the Turin skull therefore is a ma1or occipital condyles but the rest of the skull, including muscle scars, is contribution to our knowledge of variation within the genus superbly preserved. The skull is of an old adult with all sutures Mega/onyx. obliterated except for the posterior portion of the temporo-parietal. Large clefts or fissures are present in the sagittal and supraoccipital crests, but these are not true sutures (discussed below). THE TURIN GRAVEL PIT The dorsal profile of the skull in lateral view (Fig. 2a) shows the nasal region to be lower than the level of the braincase. This The community of Turin is located in the Loess Hills landform configuration is similar to that seen in Leidy's Dickeson skull, ANSP region (Prior, 1973: 32-35) near the confluence of the Maple and 12473, (Leidy, 1855:pl. 4) from Natchez, Mississippi. This feature Little Sioux rivers in the central portion of Monona County (Fig. 3). also is present in the type specimens of Mega/onyx brachycephalus from The town is built on Wisconsinan Loess. The loess overlies a Texas, M. milleri from California and M. hoiani from Oklahoma. In Sangamonian soil developed in Pre-Wisconsinan colluvium derived other skulls of Mega/onyx the nasal region is either at the same level or from both Pre-Wisconsinan till and Loveland Loess. The coiluvium in is dorsal to the braincase. Examination of a series of Mega/onyx skulls turn buries the gravels in which the Turin sloth skull was found (E. A. indicates that the formation of a "forehead" is related to the degree of Bettis, personal communication, May 3, 1982). Hay (1914) referred development of the sagittal crest. to the Turin locality as the Old Elliott pit. The temporal fossa qf the Mega/onyx skull is a well defined feature. The loess deposits at Turin are famous for the so-called Turin Man Its dorsal boundary is a parasagittal crest which extends along the discoveries which consist of four human skeletons of Archaic cultural interparietal suture from the supraoccipital anteriorly until it crosses affiliation (Frankforter and Agogino, 1959). The gravel ·pit, which is the frontoparietal suture. Just anterior to this suture, each parasagittal in the center of town, has been quarried intermittently for many years. crest diverges laterally to form a supra-orbital crest which terminates Frequent collecting trips to the site by the Sanford Museum and the at the post-orbital process. The posterior boundary of the temporal Northwest Chapter of the Iowa Archeological Society, have produced fossa is the parieto-occipital suture. In juvenile and some adult specimens the interparietal suture is closed and usually obliterated by 1 Present address: Vertebrate Paleontology Department, Royal Ontario Museum, the two parasagittal crests which remain separate. Even juveniles in Toronto, Canada M5S 2C6 which the other cranial sutures are open or at least visible have fused Published by UNI ScholarWorks, 1983 1 Proceedings of the Iowa Academy of Science, Vol. 90 [1983], No. 4, Art. 6 A WELL-PRESERVED GROUND SLOTH 135 Fig. l. Aerial view of the Turin gravel pit showing the approximate place (star) where the Mega/onyx skull was recovered in April, 1973. and barely visible interparieral and parieto-occipiral sutures. The and squamosal in the Turin specimen is only barely discernable. It is sagittal crest and its medial fissure is therefore a secondary feature indicated by a bulge on the lateral surface of the arch just ventral to the resulting from enlargement and joining of the parasagitral crests. It is frontal process of the jugal. There is a concavity in the same position the dorsal and medial growth of these crests which forms the fissure Or on the medial side. cleft seen in the Turin specimen. This fissure extends into the One of the unique features of the ground sloth zygomatic arch is the supraoccipiral crest as well (Fig. 2c). The formation of the fissure in large descending flange or process (Fig. 2a), a ventral continuation of the supraoccipiral crest is the result of a dorsal enlargement of the the base of the jugal. This descending flange is present only in two posterior edge of the parietal and the dorsal edge of the supraoccipital. other groups of mammals, g lyptodonts and entelodonts. The ventral In older animals the fissures between both crests eventually fi ll in, extension of the jugal affects the origin of the masseters and hence the forming a solid structure. Filling is underway in the anterior portion way the animal chewed. of the sagittal crest on the Turin specimen just before it bifurcates ro The morphology of the zygomatic arch of the Turin specimen is form the supraorbi cal crests. unusual compared to other specimens of Megalonyz. In nine of the ten The pattern of growth of the sagitral and supraoccipital crests after specimens of Megalonzx with preserved zygomatic arches, the de­ the initial closure of the sutures is not unique ro Mega/onyx. Davis scending flange slopes slightly posteriorly and rapers ro a round trip. ( 1964) described a similar occurrence in the giant panda, Ailuropoda. Additionall y, some specimens have an extra ridge on the posterior Like Mega/onyx, Ailuropoda is herbivorous. Whether or not this edge of the flange representing part of the muscle scar of the pattern occurs in carnivorous mammals with sagittal crests is not superficial masseter. In marked contrast to the nine other individuals, known. the Turin descending flange does not taper but is both blunt and In the earliest known sloths a gap exists between the jugal and the squared off.