Which Vertebrate Group?

9 The size, shape, and radiocarbon age of the Manasquan bone limit the range of possible vertebrates from which it could derive. These factors, together with its discovery location, suggest very strongly that it is a vertebra deriving from a large animal living on or near the now submerged part of the continental shelf at about the time of the last glacial maximum in North America. The recovery location and probable habitat place this large animal within 100–200 km of the southern terminus of the Laurentide ice sheet as mapped by Gallagher et al. (1989).

10 The extreme boreal conditions in which the progenitor of the Manasquan vertebra lived exclude reptiles and amphibians as the source of the bone. Fish have simple cylindrical or hourglass-shaped vertebrae lacking most of the morphological features of the Manasquan bone, and are not therefore the source of the specimen. The largest birds inhabiting such regions today – for example, eagles, auks, and geese – have vertebrae that are a small fraction of the size of the Manasquan bone. Thus, paleoclimate and vertebra size and shape exclude all vertebrate groups but mammals as the source of the bone.

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11 Although the specimen has undergone significant bone loss, it is sufficiently pristine to show that the pleurapophysis and neural crest do not contain articulations for ribs or pelvic bones. Thus, it is not a thoracic or pelvic vertebra, and it is too morphologically complex to be a caudal vertebra. Based on these considerations, we interpret the Manasquan specimen to represent a mammalian cervical vertebra (CV). The box-like shape evident in Fig. 2 excludes the atlas (CV1) and axis (CV2) vertebrae as they have axially flattened and prominently axially keeled shapes that function to provide strong articulation between the skull and neck. We infer from this that our specimen is one of the more posterior neck bones of a large, periglacial mammal.

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Which Mammal Group?

12 We first consider marine mammals. Figure 3a shows a narwhal cervical vertebra. It has a large, triangular neural canal, unlike the smaller, circular neural canal of the Manasquan bone evident in Fig. 2. In addition, the narwhal vertebra lacks the prominent zygapophyses of the Manasquan bone. Other cetaceans have similarly structured cervical vertebrae. These disparities indicate that the Manasquan bone is not that of a cetacean. A representative example of the cervical bones typical of each of the three families of pinnipeds is also shown in Fig. 3 (phocids in 3b, otariids in 3c, and odobenids in 3d). As illustrated in Fig. 3, pinnipeds have cervical vertebrae differing from the Manasquan bone in three essential features. Pinniped cervical vertebrae have large triangular neural canals; their zygapophyses are smaller and less pronounced than for the Manasquan vertebra; and their centra are elongated laterally rather than dorsoventrally. We conclude from these comparisons that the specimen in question is unlikely to have derived from a marine mammal.

13 The Late Pleistocene and early Holocene fossil record of northeastern North America provides a relatively limited range of possible terrestrial mammalian candidates for the Manasquan specimen: mastodon (Mammut americanum); wooly mammoth (Mammuthus primigenius); bears, particularly polar bear (Ursus maritimus); large periglacial bovids, especially musk oxen (Bootherium bombifrons; Ovibos moschata) and ice age bison (Bison latifrons); and larger periglacial cervids (caribou, elkmoose, and moose).

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14 Both Mammut and Mammuthus have axially compressed cervical vertebrae typical of proboscideans, rather than the box-like morphology of our specimen, and can thus be excluded. Additionally, in all but very young juveniles, the size of the cervical vertebrae in Mammut and Mammuthus are considerably larger than our specimen. Figures 4a and 4b show the fourth CV of a modern polar bear. It is considerably more gracile than our specimen, and has centra that are laterally elongated. This differs from the Manasquan vertebra in which the centra are dorsoventrally elongated (Figs. 2b, 2d). The other polar bear neck vertebrae are similarly structured, as are those of the other North American boreal bears, i.e., the arctic brown bear (Ursus arctos) and the grizzly bear (Ursus horribilis). These obvious disparities exclude bears as the source of our specimen. Figures. 4c and 4d show the fourth CV of a modern musk ox (Ovibos moschata). Like the Manasquan vertebra, the musk oxen specimen is robustly built and has a box-like overall shape. However, its zygapophyses are smaller and do not flare laterally to the extent seen in the Manasquan specimen. In addition, the musk oxen vertebra has centra that are laterally elongated. These differences eliminate this musk oxen species as the source of our bone. Because Bison latifrons has cervical vertebrae similar to those of Ovibos moschata (as do most large bovids), this species is also excluded. Elimination of these other mammalian candidates based on cervical-vertebra morphology indicates that the most likely source for the Manasquan specimen is a large cervid.

Which Cervid?

15 Among fossil cervids, features of the skull and antlers are most often used as criteria to distinguish fossil taxa. Such attributes are clearly not applicable in the present case. Instead, our study of the Manasquan specimen relies on morphological comparisons to cervical vertebrae of four large North American cervids: Alces alces (moose), Alces scotti (elkmoose), Rangifer tarandus (caribou), and Cervus canadensis (elk). Alces alces, Alces scotti, and Rangifer tarandus are boreal cervids known from the North American fossil record and thus are possible progenitors of the Manasquan specimen. Cervus canadensis makes a good comparative outgroup against which to evaluate the other species, and is included in our study for that reason. On paleoenvironmental grounds, however, Cervus canadensis is unlikely to be the source of the Manasquan vertebra in view of its modern non-boreal habitat preference. We exclude Alces latifrons and other large Eurasian boreal cervids (e.g., Megaloceros giganteus) from consideration because they are unknown in the New Jersey fossil record.

16 The cervid specimens we examined are listed in Table 1. For each specimen we measured CV3 through CV6. We excluded CV1, CV2 on morphological grounds as noted above. We also excluded the posteriormost cervical vertebra (C7) because, in the cervids we examined, C7 is transitional to the thoracic vertebrae. It is foreshortened axially, has prominent keels, and lacks the box shape of the Manasquan bone. Parameter measurement was done from digital images of single bones using Bersoft Image Measurement® software. Not all parameters could be measured in all bones examined due to break-related bone loss. Also, in the case of the NJSM elkmoose specimen (see Table 1), we were working with a restored, articulated skeleton so that parameters deriving from articulating bone surfaces, e.g., anterior and posterior centrum diameters, were difficult or impossible to obtain. Because of the small number of specimens sampled, rigorous statistical testing is not possible. All specimens we measured are large enough to have derived from adult animals, so we consider possible ontogenetic variation in bone morphology among sub-adult animals to be inconsequential to our analysis. Also, there is no known gender component to morphology among cervid cervical bones. Thus, differences discovered, if sufficiently robust, should have taxonomic significance.

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17 We focus here on the shape of cervid cervical vertebrae in dorsal view. Vertebral shape is defined as the ratio of vertebral length to vertebral width (see Fig. 5). Defining length and width as shown in Fig. 5 allows us to exclude the size and flaring of the zygapophyses in our consideration of bone shape. Vertebral shape in dorsal view for CV3 to CV6 of the animals listed in Table 1 is given in Fig. 6. We did not measure CV2, CV3, or CV7 for the reasons discussed above. Data for elk (squares) and moose (dots) are given in Fig. 6a. Each symbol represents the average shape ratio (L/W) for a specific vertebra. One standard deviation is shown by the vertical bars. All data points for moose fall within the dark gray area whereas all data points for elk fall within the light gray area. The separation of the two data sets is complete. This suggests that the shape of the cervical vertebrae of these two species is indeed different. Elk have neck bones elongated in the axial direction relative to moose. Fig. 6b shows data for elkmoose and caribou. Also plotted here are the elk and moose domains from Fig. 6a. The caribou data fall in the elk region. Elkmoose plot with moose. The dorsal length-width ratio for the Manasquan vertebra is 0.52. This is represented by the dashed line in Figs. 6a and 6b. It too falls in the moose domain along with the elk-moose data. It seems reasonable to conclude from Fig. 6 that the shape of the Manasquan vertebra in dorsal perspective is consistent with the view that the bone derives from a member of the genus Alces.

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Which Moose?

18 If the bone is from a species of Alces, then we need to decide between Alces alces, Alces scotti, and Alces latifrons. The data in Fig. 6, however, do not give a clear indication as to which of these species the Manasquan bone belongs. Likewise, the ten other cervical bone metrics we tested are also indecisive, primarily because of the paucity of elkmoose data upon which to base comparisons with Alces alces. However, the North American fossil record for the Late Pleistocene and early Holocene provides information more useful than bone shape characteristics for discriminating between Alces species. Alces scotti is known only from North America. Alces latifrons is primarily a Eurasian species, although a Beringian population, apparently confined to a Wisconsinan age ice-free refugium, occurs in northern Canada and Alaska. Alces latifrons is, however, unknown in New Jersey. Beringian Alces latifrons predates Alces scotti in North America and is surmised by Azzaroli (1985) to be ancestral to Alces scotti. Thus, Alces latifrons can be excluded as the source of the Manasquan bone. Alces alces also is thought to have derived from Alces latifrons at about the same time as Alces scotti, but in Asia rather than North America (Kahlke 1990) and independently of the origin of Alces scotti. Only in the early Holocene did Alces alces move into North America (Kahlke 1990), including New Jersey. Once in North America, Alces alces very quickly replaced Alces scotti. Thus, the known record of Alces in North America, together with our radiocarbon date for the Manasquan bone of 23 530 ± 170 years BP, strongly suggests that the Manasquan bone is much too old to be identified with North American Alces alces. It is, however, consistent with the time range of Alces scotti as discussed by Churcher and Pinsof (1987) and Kahlke (1990). We suggest, therefore, that the Manasquan bone is most probably from Alces scotti.

Which Cervical Vertebra?

19 The four posterior-most cervical vertebrae of modern Alces alces show directed changes in several characteristics (see Fig. 7). For example, the height of the neural spine relative to the body of the bone increases posteriorly with position in the neck, i.e., from CV3 to CV6. Unfortunately this parameter is of little value in the present context because the neural spine has been lost from the Manasquan vertebra (see Fig. 2). However, two other patterns of variation, more useful in placing the Manasquan vertebra in the neck of the animal from which it came, are apparent in Fig. 7. The first of these relates to the shape of the pleurapophyses. CV3 has flattened, paddle-like vanes forming the distal ends of the pleurapophyses. In CV4, these vanes have developed strong flexures and have become broadly convex posteriorly. In CV5 the two main axes of the distal pleurapophysis have separated to form two distinct, but closely approximated processes. In CV6 these processes are widely separated forming a keel-like ventral process and a lateral transverse process. The second useful pattern of variation involves the transverse foramina on either side of the centrum. The transverse foramina increase markedly in size relative to bone size backward along the neck. CV3 has small transverse foramina positioned close to the centrum, while the more posterior vertebrae have larger foramina that extend laterally away from the centrum. These two patterns are present in all of the moose and elkmoose specimens that we examined and would thus appear to be species-wide characters.

20 Although the Manasquan vertebra has endured significant bone loss due to post-mortem abrasion, Fig. 2 indicates that one can still assess its status with regard to these two characters. In Fig. 2 the left pleurapophysis and the distal end of the right pleurapophysis are seen to be missing, but it is nevertheless clear that, on the right side of the bone, there is no indication that the pleurapophysis has bifurcated into two separate processes. The base of the right pleurapophysis is wide and robust, as is the case in CV3 and to a lesser extent in CV4, as illustrated in Fig. 7. Thus, we infer that the Manasquan bone is either a CV3 or CV4. The transverse foramina in the Manasquan bone support this view also. They are filled with sediment and encrusted material and thus partly hidden, but the outer rim of the left transverse foramen is visible in Fig. 2a (arrow). The foramen is small and close to the centrum. It is what one sees in CV3 in Fig. 7. In addition, the left side of the bone does not flare out around the foramen as in the case of CV4, but rather runs straight down to the pleurapophysis as in CV3. Thus, we conclude that the Manasquan bone is most likely to be a CV3.