An Isotopic and Morphometric Examination of Island Dogs (Canis familiaris): Comparing Dietary and Mobility Patterns in the Precolumbian Caribbean

In precolumbian insular Caribbean archaeological sites, domestic dog (Canis familiaris) remains have been recovered from varied contexts, such as formal burials, in refuse deposits, and as modified artifacts, indicating their complex and multifaceted role within indigenous societies. In this study, isotopic and morphometric analyses provide biochemical and morphological correlations to assess this differential treatment. We examined collagen values (n = 21) of carbon (δ13Cco) and nitrogen (δ15N), and enamel values (n = 81) of carbon (δ13Cen), oxygen (δ18Oen), and strontium (87Sr/86Sr) of dog remains from 16 precolumbian sites. Five comparative parameters were used to assess dietary variations between different groups: buried versus nonburied, local versus nonlocal, Greater versus Lesser Antilles, chronology, and modified versus unmodified remains. The only statistically significant difference in diets was between local and nonlocal dogs. Sufficient data were available to conduct isotopic mixing models using the FRUITS statistical program on four individuals for which depositional and morphological data were available. Results of dietary modeling indicate an unexpectedly heavy reliance on plant foods consistent with intentional feeding. This approach highlights the utility of combining isotope analysis, dietary models, morphometrics, and depositional context to provide comprehensive biographic overviews of individual animals.

C ross-culturally, dogs (Canis familiaris, Linnaeus 1758) are often valued members of societies, as expressed in the commonality of their inhumation, a practice rarely seen with other animals (Russell 2011). Within the precolumbian Caribbean, the role of dogs was that of a hunting aid, a companion, and potentially a food source (Grouard et al. 2013;Las Casas 1876[1561). Earlier studies on precolumbian Caribbean dogs assessed morphological differences (Grouard et al. 2013) and provided isotopic evidence of dietary and mobility patterns (Laffoon et al. 2015(Laffoon et al. , 2019. This article provides additional morphological data and is the most expansive investigation of Caribbean C. familiaris isotopic values conducted to date. Multi-isotopic analyses of precolumbian dogs in the insular Caribbean have primarily focused on enamel samples, with some collagen samples from El Flaco and El Carril in the Dominican Republic (Shev 2018) and from Punta Candelero in Puerto Rico (Pestle 2010). Laffoon and colleagues (2019) incorporated strontium ( 87 Sr/ 86 Sr) and carbon (δ 13 C) isotope values from El Flaco and El Cabo in the Dominican Republic and from Morel and Anse à la Gourde in Guadeloupe, demonstrating similarities between human and dog diet and mobility patterns at these sites. These human-dog linkages were previously reported globally in diverse archaeological contexts, leading to the proposition of a "canine surrogacy approach" in which dogs could be used as an isotopic surrogate for human remains (Guiry 2012).
An earlier study by Grouard and coauthors (2013) assessed the morphology of buried dogs from the region, indicating some differences in estimated withers heights (Grouard et al. 2013). These data suggest there may have been more than one variety of dog within the insular Caribbean. This notion may be supported by Las Casas, who reported the existence of two different breeds that may have received different treatment by humans (1876 [1561]). In our study, we assessed the withers heights of dogs from El Flaco and El Carril to determine whether there are correlations between morphology and differential treatment in the form of formal burials or dietary regimes.
We also compared C. familiaris isotope values from Puerto Rico, the Dominican Republic, Cuba, Saint-Martin, Guadeloupe, Barbados, and Grenada ( Figure 1; Supplemental Table 1) according to five criteria: local versus nonlocal, Early Ceramic (500 BC-AD 600) versus Late Ceramic Ages (AD 600-1500/1600), buried versus nonburied individuals, Greater versus Lesser Antillean, and modified (e.g., pendants) versus unmodified remains. Where applicable, published morphometric data permitted comparisons between, diet, localness, and morphology. Additionally, a dietary mixing model was applied to four buried dogs, providing a detailed biography of these individuals. Estimated withers heights provide morphological evidence for the existence of two native "breeds" of dogs; details regarding FRUITS mixing models are further addressed in the online supplement (Supplemental Text 1).
A total of 81 teeth and 24 bone collagen samples of C. familiaris were sourced from precolumbian sites throughout the Caribbean, including from a dog burial at El Flaco (Supplemental Table 1), and were analyzed by Shev (2018). Methods of stable isotope analysis, morphometric analysis, and FRUITS dietary mixing models are published extensively elsewhere and are presented online (Supplemental Text 1).

Withers Height
Withers height was estimated for dogs from El Flaco (n = 2) and was added to Grouard and coauthors' (2013) data (Supplemental Table 2).

Collagen Isotope Data
In total, 21 samples yielded high-quality collagen. An overlap in isotope values can be observed in all parameters of examination ( Figure 2a). Further details on sample conditions and results are provided in the online supplement (Supplemental Text 1).
Given the disparity in sample numbers between the two regions, we ran a t-test (critical t = 1.9939, p = 0.33867), which confirmed there was no significant difference in mean values.

Dietary Mixing Models
The results of the FRUITS modeling are presented in Figure 3b and Table 1 (see also Supplemental Text 1). They suggest that these dogs mainly consumed plants foods with modest amounts of C 4 plants (likely maize), possibly indicating intentional feeding. Of these, the two nonlocal dogs (FL FND2270 and MO FND2729) exhibited relatively higher proportions of marine protein consumption.

Discussion
We found overlapping mean values in four of the five comparative parameters. The values are similar to those of humans from the region, likely reflecting broad-spectrum diets comprised of C 3 plants supplemented with C 4 crops, as well as terrestrial and marine proteins (Laffoon et al. 2019;Pestle and Laffoon 2018). These data suggest that dogs are an effective isotopic surrogate in the precolumbian Caribbean. The only significant difference in mean δ 13 C values that we found is between nonlocals and locals. Of all samples (n = 49), 22.4% were deemed nonlocal. They likely either migrated alongside humans to new locations or were exchanged between different human groups. Similar mobility patterns have been suggested for Anse à la Gourde and Morel, where 30% of studied dogs were nonlocal (Laffoon et al. 2015(Laffoon et al. , 2019Plomp 2013).
Ethnographies of indigenous peoples from the South American lowlands provide insight into how dogs may have been treated in the past (see Koster 2009). The exchange of hunting dogs by renowned dog breeders such as the Waiwái of Guyana and Brazil (Howard 2001:248) may serve as a useful analogy. Ethnohistoric sources describe the use of dogs in Hispaniola as valued hunting aids, although it is possible that dogs were also a food source (Las Casas 1876[1561:341). However, given the sparse evidence of butchery or cooking, the consumption of dogs may have been restricted to times of food scarcity (Wing 2008). It is unlikely that dogs were traded as food; it is more probable that they were migratory companions or prized dogs exchanged between communities.
One nonlocal specimen from El Carril (FND 30) had an 87 Sr/ 86 Sr ratio (0.7090) denoting a likely coastal origin. This sample also had the most enriched δ 13 C en (−8.8‰) and δ 18 O en (−1.8‰) values of any dog from Hispaniola (Shev 2018). This individual likely subsisted on a diet rich in marine proteins, with higher oxygen values indicating natal origins in an arid, low-altitude, or coastal region (Wang et al. 2016). Two nonlocal dogs from Silver Sands in Barbados demonstrated similarly high δ 13 C en values (−8.8‰ and -8.6‰), whereas one exhibited an 87 Sr/ 86 Sr ratio (0.7075) suggesting possible natal origins from a nearby island.
According to the FRUITS modeling, two nonlocals (FL FND2270 and MO FND2729) consumed higher proportions of marine proteins, indicating that some individuals that were exchanged or migrated alongside humans were possibly "sea dogs" consuming foods such as pelagic fish.

Conclusion
Broad similarities and trends can be seen in the paleodietary and mobility signatures of dogs analyzed throughout the insular Caribbean, regardless of time period, burial context, and location. At a regional scale, geographic patterning of isotopic values of dogs appears to mirror that of humans for the most part. The most significant disparity in diet occurs between local and nonlocal dogs, which is statistically significant enough to merit consideration. Nonlocal dogs likely received different foods than did locals, perhaps reflecting differences in social value or spatially structured foodways between certain individuals. The findings from the dietary mixing model suggest that the two nonlocals had diets higher in marine protein than the two local dogs; however, more data are needed to accurately assess whether there is a broader correlation between mobility and enriched isotopic values.