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Identification of Shark Teeth (Elasmobranchii: Lamnidae) from a Historic Fishing Station on Smuttynose Island, Maine, Using Computed Tomography Imaging
Joshua K. Moyer, Nathan D. Hamilton, Robin Hadlock Seeley, Mark L. Riccio, and William E. Bemis

Northeastern Naturalist, Volume 22, Issue 3 (2015): 585–597

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Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 585 2015 NORTHEASTERN NATURALIST 22(3):585–597 Identification of Shark Teeth (Elasmobranchii: Lamnidae) from a Historic Fishing Station on Smuttynose Island, Maine, Using Computed Tomography Imaging Joshua K. Moyer1,*, Nathan D. Hamilton2, Robin Hadlock Seeley3, Mark L. Riccio4, and William E. Bemis1 Abstract - Two incomplete shark teeth were recovered during archaeological excavation of a historic fishing station on Smuttynose Island, ME. Specimens were identified to the species-level using non-destructive computed tomography (CT) imaging techniques. Their external and internal morphology is described and illustrated. Both teeth are from large sharks in the Order Lamniformes. The larger specimen is a developing tooth from the upper jaw of a Carcharodon carcharias (White Shark). The second specimen is a broken tooth from the lower jaw of a Lamna nasus (Porbeagle). The Smuttynose excavations provide an opportunity to examine faunal assemblages and the island’s historic 17th- through 19th-century fisheries. Criteria for identifying teeth of common pelagic sharks of the Western North Atlantic are offered, and the role of sharks in the historic Gulf of Maine fishery is discussed. Introduction Sharks (Chondrichthyes: Elasmobranchii) continually grow, shed, and replace their teeth (Applegate 1967, Peyer 1968). The teeth consist of an enameloid crown that covers dentine of different types in different groups of sharks. In an intact tooth, a root composed of osteodentine serves as the point of ligamentous attachment to the jaw (Fig. 1). Shark teeth preserve well as sub-fossil remains in archaeological sites. Because an individual shark may have as many as 100 functional teeth in its dentition at any given time, depending on species, archaeologists often recover shark teeth in sites associated with both maritime and inland communities (de Borhegyi 1961, Kozuch and Fitzgerald 1989, Handley 1996, Rick et al. 2002). Typically, single teeth are recovered because sharks can shed thousands of teeth over a lifetime and because the jaws are cartilaginous and do not preserve well (Cappetta 2012). To understand the presence and prevalence of a particular species of shark at a site, archaeologists must compare isolated and frequently incomplete teeth to descriptions of the morphology of whole teeth (Handley 1996), which can be challenging because most published descriptions are based on more complete material. Recent studies on the tissue arrangement and histology of shark teeth (Moyer et al. 2015) provide criteria for identification that can be applied to even incomplete teeth. 1Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853. 2Department of Geography and Anthropology, University of Southern Maine, Gorham, ME 04038. 3Shoals Marine Laboratory, Cornell University, Ithaca, NY 14853. 4Institute of Biotechnology, Cornell University, Ithaca, NY 14853. * Corresponding author - jkm228@cornell.edu. Manuscript Editor: Karsten Hartel Northeastern Naturalist 586 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 In some cases, shark teeth are found in archaeological sites not as byproducts of a society’s livelihood (i.e., fisheries) but as sought-after materials used to make ornaments or weapons with direct cultural significance (Drew et al. 2013, Leavesley 2007). In such instances, shark teeth offer insight to a community’s use of marine resources and the symbolism those resources take on. For the thorough analysis of such artifacts, it is necessary to identify the teeth to species. Identified teeth may be used to infer the symbolic importance of the artifact. For example, a tooth belonging to a large, predatory species may indicate that a collaborative effort or extensive planning was utilized to land such a large and potentially dangerous animal (Leavesley 2007). In the course of 5 seasons of archaeological excavations on the Isles of Shoals, two partial shark teeth were recovered on Smuttynose Island, 1 of 9 islands in the Isles of Shoals in the Gulf of Maine. Here, we demonstrate how nondestructive computed tomography (CT) imaging techniques and current fisheries data can be used to identify these specimens Field-Site Description The Isles of Shoals Archipelago consists of 9 rocky islands in the Gulf of Maine approximately 6 miles east of Rye, NH. The central islands—Appledore, Malaga, Smuttynose, Cedar, and Star—are shown in Figure 2. The islands straddle the borders of Maine and New Hampshire and were first utilized as hunting and fishing grounds by Native Americans during no fewer than 6 occupations spanning 6000 to 1000 B.P. (Robinson 2012). Figure. 1. General morphology of teeth of (A) Carcharodon carcharias (White Shark ) and (B) Lamna nasus (Porbeagle). Scale bar = 5 mm. Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 587 Figure. 2. Map of the central islands of the Isles of Shoals Archipelago showing locations, including the excavation site, for recovery of USM 9000 and USM 71. Bathymetry and place names based on NOAA ENCTM Chart US5NH02M (Portsmouth Harbor–Cape Neddick to Isles of Shoals). Inset shows general location of the Isles of Shoals Archipelago in the southern Gulf of Maine. Detailed view of the site is provided in Figure 3. Northeastern Naturalist 588 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 Figure. 3. Plan showing excavated test pits and units (red boxes) and adjacent historic and existing buildings on the southwest corner of Smuttynose Island. Locations of 2 recovered teeth and 3 vertebrae of lamniform sharks are indicated. Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 589 By 1623, Europeans had established a foothold on the Isles of Shoals (Nichols and Nichols 2008, Robinson 2012). Profitable seasonal fishing settlements developed on the islands, taking advantage of the abundance of Gadus morhua L. (Atlantic Cod), which was valued as a dried product in markets throughout southern Europe. Large quantities of Melanogrammus aeglefinus (L.) (Haddock) were also landed at the Isles of Shoals, but were primarily used as food locally and not as commonly shipped to European markets. Although Atlantic Cod, Haddock, and other gadid fishes were the most-common species targeted in the 17th to 19th centuries, they were not the only species landed in the Shoals Archipelago. For example, there is photographic evidence showing that into the late 19th century, large sharks, such as Prionace glauca (L.) (Blue Shark), were also caught and processed (Robinson 2012:114). In 1858, Boston doctor Henry Bowditch wrote to his wife describing “bodies of immense sharks that have been killed” and discarded from the beach in Haley’s Cove on Smuttynose Island (Robinson 2012). We have been able to find few other records of the sizes and species of sharks landed in or around the Isles of Shoals. The Isles of Shoals has been listed in the National Register of Historic Places since 1974 (Fig. 2). The excavation site is on Smuttynose Island and is located ad - jacent to several 18th- to 20th-century foundations and existing structures (Fig. 3), which are inventoried by the Maine Historic Preservation Commission (MHPC). MHPC numbers for some key features of the site are indicated in Figure 3, including ME 226-120, which is the site of a historic wharf, and ME 226-118, which is the site of a warehouse associated with fish processing. ME 226-114 is the foundation of the 19th-century Oceanic Hotel, and ME 226-117 is the foundation of the Hontvet House. ME 226-123 is the site of the Fish House. The Smuttynose excavations made from 2008 through 2013 sampled 68 m2 (indicated by red boxes in Fig. 3) of a site total of 2200 m2. The focus of the excavations was the low terrace landform directly adjacent to the protected Haley’s Cove. In this area of the site, deep (80–90 cm) stratified deposits from the 17th century were identified and excavated. Intensive fishing activities in the 17th century related to a fish-processing station there yielded large numbers of remains of Altantic Cod and Haddock as well as other marine vertebrates. Methods Institutional abbreviations In this report we use the following institutional abbreviations: AMNH = American Museum of Natural History, New York, NY; CUMV = Cornell University Museum of Vertebrates, Ithaca, NY; MCZ = Museum of Comparative Zoology, Harvard, Cambridge, MA; and USM = University of Southern Maine, Gorham, ME. Specimens recovered Two incomplete shark teeth were recovered (Fig. 4). The larger, USM 9000, was recovered in summer 2011. It has worn serrations on the medial and distal edges of the crown. The base of its enameloid crown is missing, as is the entire root (Fig. 4A; compare to intact tooth in Fig. 1). It was recovered from unit 153R20 (a unit is Northeastern Naturalist 590 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 1 m2) at level 3 (20–30 cm deep). This level is firmly dated in the 17th to early 18th century based on associated anthropogenic materials, including pipe stems, coins, and ceramics (Robinson 2012; these materials are cataloged at the University of Southern Maine). This part of the site is associated with the early fishing station and fish-processing area. The smaller of the two teeth, USM 71, was recovered in summer 2008 from test pit (TP) 2-4 (test pits are 50 cm2) at level 4 (40–50 cm deep) near the Haley House. This area of the site consists of fill taken from the beach in Haley’s Cove for reconstruction of a lawn in about 1870. USM 71 does not exhibit serrations on either edge of its crown. A small section of osteodentine associated with the root is present at the base of the crown, but most of the root is missing. Three isolated vertebrae from species of lamniform sharks yet to be determined (USM 8238, 13237.8, 13300) were also recovered in the Smuttynose excavation. These came from different units and were not associated with the 2 tooth specimens (Table 1, Fig. 3). Imaging methods We photographed the teeth using an Olympus DP70 digital camera and software with an Olympus SZX12 stereomicroscope. Teeth were scanned in an Xradia Versa XRM-500 nano-CT scanner in the Biotechnology Resource Center Multiscale Imaging Facility at Cornell University. USM 9000 was scanned at 33.6-μm resolution, and USM 71 was scanned at 17.4-μm resolution. Slice files represented by stacks of .tiff image files were generated via the scanner output. 2-D and 3-D digital reconstructions of each tooth were produced using OsirixTM Digital Imaging and Communication in Medicine (DICOM) software (version 4.0 64-bit edition; Rosset et al. 2004) on Apple Macintosh computers running OSX 10.8.5. In our 3-D reconstructions, tissue density is represented by color gradients, adjusted using standard and customized color look-up tables (CLUT). Dense tissues are represented by lighter shades (typically white or yellow in our reconstructions) and less-dense tissues by darker shades (typically red in our reconstructions). To view internal anatomy, we digitally dissected, or sectioned, 3-D reconstructions within OsirixTM. Results USM 9000 measures 23 mm wide x 31 mm high, indicating that it came from a large predatory shark. Both sides of the crown are serrated. Three-dimensional digital reconstructions of USM 9000 generated by CT scanning confirm that the Table 1. Lamniform shark remains recovered from Smuttynose Islan d. Test pit or Year Specimen number unit number Level (cm) recovered USM 71 (tooth) TP 2-4 40–50 2008 USM 8238 (unidentified lamniform vertebra) 99R89 20–30 2011 USM 9000 (tooth) 153R20 20–30 2011 USM 13237.8 (unidentified lamniform vertebra) 161R17 10–20 2013 USM 13300 (unidentified lamniform vertebra) 161R18 20–30 2013 Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 591 serrations are formed by folding of enameloid tissue and are not superficial damage or postmortem markings (Fig. 5A, B). Large predatory sharks common to the Gulf of Maine that have prominently serrated teeth include Carcharhinus obscurus Figure. 4. Light micrographs of tooth specimens: (A) labial view of the partial crown of USM 9000 and (B) labial view of the intact crown of USM 71. Scale bars = 1 cm. Figure. 5. CT generated models of USM 9000: (A) labial view of 3-D model rendered from CT scan of USM 9000, (B) lingual view of 3-D model rendered from CT scan of USM 9000, and (C) labial view of tooth, sectioned to show interior of crown. Scale bars = 1 cm. Figure. 6. CT generated models of USM 71: (A) labial view of 3-D model rendered from CT scan of USM 71, (B) lingual view of 3-D model rendered from CT scan of USM 71, and (C) lingual view of tooth sectioned to show interior of crown. Scale bars = 1 cm. Northeastern Naturalist 592 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 (Lesueur) (Dusky Shark), Carcharhinus longimanus (Poey) (Oceanic Whitetip Shark), Prionace gluaca (L.) (Blue Shark), and Carcharodon carcharias (L.) (White Shark). The Dusky Shark, Oceanic Whitetip Shark, and Blue Shark are carcharhinids, and their teeth have an orthodont histotype, meaning that a pulp cavity is retained in fully developed teeth. CT scanning and digital sectioning of USM 9000 reveals that it has an osteodont histotype, in which the crown lacks a pulp cavity and is filled by osteodentine (Fig. 5C). Osteodentine within the crown is of low density, indicating incomplete mineralization. The size, serrations, and histotype indicate that USM 9000 is the tooth of a White Shark. Enough of the tooth crown is intact in USM 9000 to be able to discern its lingual (facing inside the mouth) and labial (facing outside the mouth) surfaces. In teeth of Carcharodon, lingual tooth surfaces tend to be slightly convex. This is the case in USM 9000. We confirmed identification by comparison to museum specimens of Carcharodon carcharias MCZ 153575 and AMNH 53095 as well as several specimens in the Gordon Hubbell collection (Gainesville, FL). USM 71 is a partially intact tooth with a crown height of 14 mm. It lacks serrations. There is no indication of lateral cusplets in this specimen (for location of lateral cusplets in an intact tooth, see Fig. 1). USM 71 lacks pronounced inclination toward either its mesial or distal side. Such inclination is typical of the teeth of extant mako sharks, Isurus oxyrinchus Rafinesque (Shortfin Mako) and I. paucus Guitart (Longfin Mako), so the absence of inclination in USM 71 suggests that it is not from a species of Isurus. Also, mako shark teeth have a prominent cutting surface, known as the distal heel, that is not present in USM 71. CT scanning and digital reconstructions allow detailed study of the external morphology of the crown (Fig. 6A, B). Digital sectioning of USM 71 reveals an osteodont histotype (Fig. 6C). This rules out the possibility that it is from the lower jaw of a carcharhinid shark, which also often exhibit pointed, non-serrated tooth morphologies. The tooth is worn, and no root is present. USM 71 lacks the lateral cusplets found on either side of the long central cusp in intact teeth of Lamna nasus (Bonnaterre) (Porbeagle). A thick layer of enameloid tissue visible in the virtually sectioned tooth extends to the broken base of the crown (Fig. 6C). This is the position where the lateral cusplets would have been in life, so we interpret that the absence of cusps in USM 71 is due to postmortem wear. Comparison of USM 71 to a 2.6-m total length (TL) specimen of Porbeagle (CUMV 98002) suggests that it is a tooth from the lower jaw near the mandibular symphysis. We based this determination on the small indentation visible on the labial surface of USM 71 and the corresponding indentations present only on teeth of the lower jaw in CUMV 98002. The 3 vertebrae recovered from the Smuttynose excavations are positively identified as from lamniform sharks based on overall morphology but cannot be classified with certainty to species. Two of the 3 isolated vertebrae (USM 13237.8, 13300) were recovered from sites adjacent to the pit from which the White Shark tooth was recovered (Fig. 3, Table 1). There is no evidence that these vertebrae came from the same individual specimen. The third vertebra (USM 8238) was recovered from a pit excavated in the lawn (Table 1). Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 593 Discussion The identification of specimens USM 9000 as a tooth of White Shark and USM 71 as a tooth of Porbeagle agrees with the known ranges of both species (Bigelow and Schroeder 1948, 1953; Compagno 1984; Castro 2011; Ebert et al. 2013; Natanson and Skomal 2015; Skomal et al. 2012). White Shark is most abundant in New England during summer months (Curtis et al. 2014). Porbeagle and White Shark belong to the family Lamnidae, which includes a total of 5 extant species. While we cannot know for certain whether either of these teeth represent specimens caught in the 17th- or 18th-century fisheries, there is suggestive evidence that the White Shark tooth did not simply wash ashore on Smuttynose Island. First, the small beach (Fig. 3) is in an isolated cove. Second, the White Shark specimen is a developing tooth. Such teeth are more fragile than are fully formed teeth, and thus would not be expected to remain intact if transported by water any significant distance. Finally, the recovery location of this specimen was in an excavation near the site of the historic fishing station, above the level of the beach and in association with otoliths, vertebrae, and other evidence of the active fishi ng community. The width of the crown of White Shark tooth USM 9000 suggests that it most likely came from the upper jaw. Moyer et al. (2015) observed in developing teeth of the White Shark that osteodentine filling the inside of the crown is less dense than it is in fully developed teeth owing to the tissue’s incomplete mineralization. The lowdensity osteodentine core of USM 9000 suggests that this was a developing tooth rather than a functional tooth. Therefore, we can refine the identification of USM 9000 as a developing upper jaw tooth of a White Shark. By identifying its lingual and labial surfaces and measuring the height of the crown on its more complete side, we can estimate the minimum size of this shark. In particular, for the White Shark, Randall (1973) found a strong correlation between crown height of the largest upper jaw teeth and TL. Mollet et al. (1996) confirm a correlation between tooth size and TL in White Sharks. Based on Randall’s (1973) correlation, USM 9000 came from a shark ≥ 3 m TL, which would have weighed at least 200 kg. Using the method of Mollet et al. (1996) in which tooth height represents a percentage of TL, USM 9000 came from a shark of almost 4 m TL. If the root had been intact we could have made a more specific estimate of tooth position within the jaw, which would have yielded a more precise TL. Much larger specimens of Carcharodon are known including an authoritative record of 5.9 m TL for a specimen in the Gordon Hubbell collection. Still, assuming that this specimen represents an individual landed by the fishing community, by any measure, a 3- to 4-m White Shark would have been an impressive catch. The Porbeagle tooth, USM 71 bears a superficial resemblance to the worn crown of a tooth from the lower jaw of a Blue Shark. However, the osteodont histotype of USM 71, made visible by virtual sectioning of a digital reconstruction, allows us to rule out the possibility that it is from a Blue Shark. Based on our comparison of USM 71 to CUMV 98002 and regressions provided by Chavez et al. (2012), USM 71 came from a specimen of Porbeagle ≥ 2.6 m TL. Based on Castro (2011), we conclude this would have been a very large specimen of a Porbeagle for the Western Northeastern Naturalist 594 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 North Atlantic, although larger specimens are known from the Eastern North Atlantic. Figure 7 shows 2 intact lower jaw teeth in Porbeagle specimen CUMV 98002 and the location of characteristic lateral cusplets relative to the central cusp. Figure. 7. Photograph of an anterior lower jaw tooth and replacement tooth of Lamna nasus (Porbeagle) specimen CUMV 98002. The forward-most tooth has worn lateral cusplets. The replacement tooth behind it has intact lateral cusplets. The dashed line represents approximate point of breakage in USM 71. Northeastern Naturalist Vol. 22, No. 3 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 595 In their earliest stages of development, shark teeth are composed of a hollow crown made only of enameloid (Moyer et al. 2015, Peyer 1968). Therefore, a hollow tooth crown might be recovered from an excavation. Sediment filling such a crown could cause it to resemble an osteodont tooth, but high-resolution CT scanning would allow easy determination of histotype, which provides essential clues for identification. The chronological integrity and breadth of the Smuttynose site offers a unique opportunity to learn about historic fisheries and fish processing (Hamilton et al. 2012, Robinson 2012). Sharks undoubtedly played a role in these fisheries, but based on the 2 shark teeth recovered so far, we can only speculate about this. For example, sharks may have been caught routinely, but because their teeth have value as curiosities, they may not have been discarded with other fish wastes. The location of the White Shark tooth (USM 9000) in levels associated with the 17th-century fishprocessing station suggests that it probably came from an animal that was processed there. The fact that it is a developing tooth supports this interpretation because an incomplete tooth is unlikely to have been a trade item (typically, if any part of a White Shark was retained for trade, then it was either an isolated, completely developed functional tooth or the entire jaw with its teeth intact). The Porbeagle tooth (USM 71) was found in a disturbed area and was probably introduced there as part of the lawn-reconstruction project in about 1870 (Fig. 3, Table 1). Material used for lawn reconstruction came from the beach in Haley’s Cove. It is possible that the Porbeagle tooth may have washed ashore in Haley’s Cove, but this seems unlikely because this is such a constricted beach with limited direct access to the open ocean. It is impossible to know how long the isolated Porbeagle tooth may have been in those beach materials before its relocation to the lawn site. Of the 3 isolated lamniform vertebrae, 2 were found adjacent to the White Shark tooth in an undisturbed area. The third vertebra is from a pit in the lawn, which, like the pit from which the Porbeagle tooth was recovered, may have been filled with material from the beach. Together, the presence of teeth and vertebrae in the Smuttynose excavations suggests that lamniforms were occasionally landed and processed. Preliminary analyses of otoliths and premaxillae reveal Atlantic Cod and Haddock as the primary fisheries resources landed and processed at Smuttynose Island in the 17th and 18th centuries (Hamilton et al. 2012). These historic fisheries used longlines and nets to catch gadid fishes much smaller than lamnid sharks. Historic fishing tackle recovered from the site (Robinson 2012) does not include sufficiently large hooks to effectively fish for such large species. Recovery and identification of teeth from large pelagic sharks from sites associated with the historic cod fishery is uncommon, but there are many records of Lamnidae and other members of Lamniformes from pre-contact sites in New England. For example, Handley (1996) summarized 13 sites in southern New England in which shark remains were found. Lamniform remains occurred in 11 of the 13 sites, and 9 of these were teeth and the other 2 were isolated lamniform vertebral centra. Handley (1996) did not provide photographs to support his proposed identifications to species level. In our experience, it can be difficult to identify shark Northeastern Naturalist 596 J.K. Moyer, N.D. Hamilton, R. Hadlock Seeley, M.L. Riccio, and W.E. Bemis 2015 Vol. 22, No. 3 teeth to the species level based only on external morphology. Another consideration is that there are overlapping common names for some species of sharks and many outdated generic names. For example, Handley (1996) refers to White Shark by the name Odontaspis taurus, a name that was once common in the literature but is no longer the valid name for the species. These reservations aside, it is intriguing that so many of the southern New England sites produced lamniform remains, and that teeth of the White Shark and Shortfin Mako are associated with pre-contact burial sites (Handley 1996), suggesting that they may have had ceremonial importance. Acknowledgments We thank Fred von Stein for assisting in CT scanning, Lisa Natanson for providing material for comparative studies, and Karsten Hartel and Andy Williston for access to specimens at the MCZ and sharing their thoughts on elasmobranchs of the Gulf of Maine. Gordon Hubbell kindly hosted J.K. Moyer for a visit to his collection in July 2013. 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