Showing posts with label fossil dogs. Show all posts
Showing posts with label fossil dogs. Show all posts

Wednesday, October 1, 2014

Paleodogs and the date of domestication

Top. A fox skull used to illustrated greatest patatal breadth 
and condylobasal length. Bottom. A bivariate plot from 
Morey (2014) of GPB (Greatest Palatal Breadth) by CL 
(Condylobasal Length) for three groups of modern or 
Holocene wolves, and one series of established prehistoric
dogs, post-dating 10,000 BP, from North America and Europe.
 The contours indicate the range of plotted scores for each 
group. Superimposed on this plot are the corresponding values 
for several putative Paleolithic dogs. Using CL as a guide, one 
can see that the putative Paleolithic dogs are wolf-sized, but 
have unusually broad palatal dimensions. A comparable plot is 
provided by Boudadi-Maligne and Escarguel (2014: 86, Fig. 5),
 based on the same variables and using a larger series of wolves. 
That plot includes the earliest of the putative Paleolithic dogs
 considered here (Goyet Cave, Razboinichya Cave, Predmostí), 
and shows the same basic result.
In a forth coming article Morey (2014) examines the evidence for paleodogs, dogs that are older than the fossil record has traditionally supported.

Archaeological evidence has, for a very long time placed the origin of the domestic dog between 15,000 to 12,000 YBP. But, recent works report fossil evidence suggesting a much earlier origin, dating to Paleolithic times and perhaps exceeding 100,000 years. With such studies as a backdrop, scenarios for more ancient dates for dog origins and domestication have been made and they exceed 30,000 YPB. Morey examines this evidence and suggests such studies exhibit conceptual and methodological flaws.

When a series of cases for putative Paleolithic dogs is assessed, the author finds convincing cases for such dogs are confined to about the past 15,000 years. Morey looks at the timing of reproduction and skull and tooth morphometrics and with two exceptions, finds the putative Paleolithic dogs fall within the range of established wolves. See the figure for an explanation. Thus, the morphometrics do not support the assessment of these canids as dogs.

He also discusses the age at first reproduction of wolves and dogs, noting it may have been almost two years for wild wolves; and noting captive wolves may breed much sooner. The point being that even first reproduction at two years old, the generational time translates into dozens of generations over a mere few hundred years. Combined with directional selection, the wolf/dog would change its morphology substantially in a very short time. So genetic isolation was likely not in place at first, resulting in some delay in the recognizable appearance of certain domestication traits. But, genetic isolation was never complete, since dogs and wolves continue to hybridize to a limited degree to the present day. Therefore, he concludes that allowing for modest delay in the appearance of domestication changes, 16,000-17,000 YBP is a reasonable estimate for the beginnings of sustained canid domestication.

The morphometric evidence is somewhat at odds with the genetic data. One study done in 1997 suggests dogs diverged from wolves somewhere between 100,000 to 30,000 YPB. A more recent (2013) study using mitochondrial genomes estimates 33,000 to 18,000 YBP, and a yet more recent study (2014) places the divergence date of wolves and dogs between 50,000 and 11,000, although the authors, suggest that a more recent date is probable.

Resolving the differences in the molecular studies with the morphometrics promises to be challenging and as several recent authors have suggested, the domestication of the dog is much more complex than previously imagined.


Citation
Morey, D. F. (2014). In Search of Paleolithic Dogs: A Quest with Mixed Results. Journal of Archaeological Science. 52:300-307.






Sunday, July 20, 2014

How long ago did the dog and wolf separate from their ancestor?


Dates for the most recent common ancestor (MRCA) for dogs and wolves are remarkable recent. When Stan Olsen (1983) wrote his classic work on domestic dog fossils (1983) he noted the oldest known remains were from Palegawra Cave in northeastern Iraq with an estimated age of 12 thousand years before present (YBP).

But subsequent evidence suggests that dogs split from wolves much latter than those fossils would imply. Deep in Chauvet cave, in France, Garcia (2005) found a track of footprints from a large canid associated with one of a child. Torch wipes made by this child were dated at about 26,000 YBP. Based on the short length of medial fingers in the footprints the canid track was interpreted as being made by a large dog.

Genetic data also suggests that the dogs originated prior to the often cited 15,000 YBP. Ostrander and Wayne (2005) report that mitochondrial DNA (mtDNA) sequence analysis shed some light on the location of dog domestication as well as the number of founding matralines. They found dog sequences in at least four distinct clades, suggesting a single origin event and at least three other origination or interbreeding events. They also found nucleotide diversity high, implying an origin date of 135 to 40 thousand YBP. And Ostrander and Wayne (2005) suggests dogs may have had a long prehistory when they were not phenotypically distinct from wolf progenitors. Therefore early dogs may not have been recognized as domesticated in the archaeological record prior to 15,000 YBP because of their physical similarity to gray wolves.

However, a group of morphologically distinct canids hypothesized to be early domesticated dogs have been identified by Germonpré et al., (2009, 2012). Seven complete large canid skulls and 26 skull fragments from the Gravettian Předmostí site in the Czech Republic were examined, three skulls were identified as European Palaeolithic dogs, characterized by short skulls, short snouts, wide palates and braincases, and even-sized carnassials. The presence of dogs at Předmostí supports the hypothesis that domestication of dogs began long before the Late Glacial. One of the skulls was identified as a Pleistocene wolf, three other skulls could not be assigned to a group. Furthermore, at Předmostí, several human modifications of the skulls and canines hint at a specific relationship between humans and large canids.

While this has been controversial (see Crockford and Kuzmin, 2012), the evidence continues to mount supporting a much older origin of dogs. Druzhkova et al. (2013) provide molecular evidence that the 33,000-year old Pleistocene dog from Altai has a unique haplotype and the Altai dog is more closely related to modern dogs and prehistoric New World canids than it is to extant wolves.

In a forthcoming article in Quaternary International Pat Shipman of Pennsylvania State University asks the question, how do you kill 86 mammoths. The author examines a series of Eurasian archaeological sites formed between about 40 and 15 thousand years ago that feature unusually large numbers of mammoth remains with abundant artifacts and, often, mammoth bone dwellings. 

Since the late 19th century, archaeological sites dominated by mammoth remains have been a focus for research. How the bones of large numbers of mammoths, ranging from a minimum number of five individuals to hundreds of individuals, were deposited in one place remains an un-answered question. And, despite previous investigation, the cause of death of mammoths in these sites has remained controversial.

Two predominate hypotheses have been used to explain these megasites (a reference to the large number of mammoth remains): (1) the mammoths died natural deaths which were subsequently scavenged by humans; (2) or that specialized human hunting resulted in the deaths of the mammoths. Questions about collection and excavation techniques pose challenges for synthesizing the information, but the wealth of material has produced numerous published zooarchaeological analyses of the sites, including number of non-mammoth species represented, minimum numbers of mammoths at each site, mammoth age at death, and mammoth age profiles from individual sites.

All of these mammoth megasites are dated after the appearance of modern humans in Eurasia. These unusual sites are of interest given the obvious successes of the humans that made them. But, also because of the large number of individual mammoths and the scarcity of carnivore tooth marks and gnawing.  The evidence suggest the mammoth hunters had invented a new ability to retain and control the mammoth carcasses – protecting all of that valuable protein from scavengers.

Age profiles of mammoths at the megasites differ statistically at the p < 0.01 level from age profiles of African elephant populations that died of either attritional or catastrophic causes. However, age profiles from some mammoth sites exhibit a chain of linked resemblances with each other through time and space, again suggesting hunter behavioral and technological innovation.

The megasites Shipman analyzed are spread across most of the Eurasian continent and over a substantial time span. The introduction and spread of complex projectile weaponry by modern humans was probably important in producing the abrupt changes in assemblages associated with hominins that started about 45,000 YBP. Previous authors observed that reduced weight projectile weapons are a “niche-broadening technology” because they are easily carried, retain energy longer in flight, and they reduce the risk of injury when hunting dangerous animals or in combat when fighting other people. Thus early modern humans may have broaden their ecological niche. The reduced weight projectile weapons transforms the hunters from ambush predators (as Neanderthals were) to being long-distance hunters. Shipman also suggests a second advance which occurred during MIS 3 (marine isotope stage 3, which started 57,000 YBP) may have enhanced the advantages of reduced weight projectile weapon technology - a quasi-domesticated large canids willing to work cooperatively with humans.

Shipman (2014) hypothesize that this innovation may have been facilitated by an early attempt to domesticate dogs, as indicated by a group of genetically and morphologically distinct large canids which first appear in archaeological sites at about 32,000 YBP.

Thus at the moment it would appear that the MRCA of dogs and wolves is indeed much older than 15,000 YBP. It also appears that dogs, were co-operating with humans at least 32,000 YPB. But did humans domesticate the dog, or did dogs evolve from wolves all on their own?


Citations
Crockford, S. J., & Kuzmin, Y. V. (2012). Comments on Germonpré et al., Journal of Archaeological Science 36, 2009 “Fossil dogs and wolves from Palaeolithic sites in Belgium, the Ukraine and Russia: osteometry, ancient DNA and stable isotopes”, and Germonpré, Lázkičková-Galetová, and Sablin, Journal of Archaeological Science 39, 2012 “Palaeolithic dog skulls at the Gravettian Předmostí site, the Czech Republic”. Journal of Archaeological Science, 39(8), 2797-2801.

Druzhkova AS, Thalmann O, Trifonov VA, Leonard JA, Vorobieva NV, et al. (2013) Ancient DNA Analysis Affirms the Canid from Altai as a Primitive Dog. PLoS ONE 8(3): e57754. doi:10.1371/journal.pone.0057754.

Garcia, M.A., 2005. Ichnologie ge’ne’ rale de la grotte Chauvet. Bulletin de la Socie’ te’ pre’ historique francaise 102, 103–108.

Germonpré, M., Sablin, M. V., Stevens, R. E., Hedges, R. E., Hofreiter, M., Stiller, M., & Després, V. R. (2009). Fossil dogs and wolves from Palaeolithic sites in Belgium, the Ukraine and Russia: osteometry, ancient DNA and stable isotopes. Journal of Archaeological Science, 36: 473-490.

Germonpré, M., Lázničková-Galetová, M., & Sablin, M. V. (2012). Palaeolithic dog skulls at the Gravettian Předmostí site, the Czech Republic. Journal of Archaeological Science, 39(1), 184-202.

Kolosov, P. N. (2014). Primitive Mammoth Hunters and the Earliest Breed of Dog. Natural Resources, 2014.

Olsen, S. J. (1985). Origins of the domestic dog: the fossil record. University of Arizona Press, Tucson. 117 pp.

Ostrander, E. A., & Wayne, R. K. (2005). The canine genome. Genome research, 15(12), 1706-1716.

Shipman, P. (in press, 2014). How do you kill 86 mammoths? Taphonomic investigations of mammoth megasites. Quaternary International.