Characteristics of Animals

Body Size

Sometimes we are able to determine the body size of animals from the bones. Most zooarchaeologists record the body size for bones from indeterminate animals such as indeterminate mammals as large (size of white-tailed deer or larger), medium to large, medium (e.g., size of coyote, dog, raccoon, or opossum), medium to small, small (e.g., size of a muskrat, squirrel, or eastern cottontail), and very small (size of mouse or shrew). Indeterminate bird fragments may be classified with the same gross categories with large being the size of a turkey or goose, medium the size of a duck, small the size of a robin, and very small the size of a small bird such as a sparrow.

These gross size categories may be helpful in determining the range of body sizes and which body parts were present among the remains. Bones that are difficult to identify (such as ribs) may only have been recorded as from large, medium, or small animals. For example, turkey ribs may only have been recorded as ribs from large birds. So the presence of ribs from large birds may indicate that ribs from turkey were present, but just not specifically identified. Determinations of the range of body sizes present at a site, should also consider flotation samples.  Bones from small-bodied animals are often better represented in flotation samples. 

We determine the body sizes of animals by comparing bones to skeletons of modern specimens of known body sizes. For fish bones identified to species, it is often possible to determine the standard length for the fish by comparing the fragment to elements from fish of known length in the comparative collection. We assign standard length estimates for identified fish species in 8-cm grouped categories (e.g., < 8 cm, >8 cm to <16 cm). The standard length is the length of the fish from the front-most part of the head to the junction of the body and tail. We use standard length rather than total length because tail lengths may vary within a species.  We rarely assign precise standard lengths for fish because the bones we study are often highly fragmented.

Some zooarchaeologists assign approximate weights for fish based on the standard length estimate. Standard lengths are recorded for all of the fish in our comparative collection and live weights are recorded for many of these fish. If you estimate the standard length, then you may also be able to estimate the weight.  We did not attempt to estimate weights for the fish recovered at Koster and Modoc, but we did estimate the standard lengths. 

The body sizes, kinds of fish, and their feeding behavior provide clues to how they might have been captured. For example, many of the fish bones recovered at Modoc and Koster are from small individuals. We think these small fish were more likely captured with nets and baskets than through hook and line fishing.


We identified the basipterygium from Modoc Rock Shelter (left side of image) as either smallmouth buffalo (Ictiobus bubalus) (center of image) or black buffalo (Ictiobus niger) (right side of image). Which of the two comparative specimen is the Modoc bone closer to in size?  Image taken by Bonnie Styles.

The bone on the left is a left basipterygium (a support for the paired fins on the sides of a fish) from a buffalo fish (Ictiobus) recovered at Modoc Rock Shelter. It was identified as either smallmouth buffalo (Ictiobus bubalus) or black buffalo (Ictiobus niger). The bone in the middle is a left basipterygium from a smallmouth buffalo in the comparative collection with a standard length of 46 cm. The bone on the right is from a black buffalo in the comparative collection with a standard length of 37.8 cm.  The bone from Modoc is closer in size to the middle specimen. We made a conservative size estimate that it falls in our sixth 8-cm grouped size class and had a standard length of 40-48 cm.    


We compared the channel catfish preopercle from Modoc to preopercles from channel catfish of known length in the comparative collection to figure out the length of the prehistoric fish. Image taken by Bonnie Styles.

A channel catfish (Ictalurus punctatus) preopercle fragment from Modoc is shown at the bottom of the image. The preopercles from a channel catfish from the comparative collection shown above are from a fish that had a standard length of 46 cm. The channel catfish bone from Modoc is from a larger individual than the comparative specimen.  It most closely matched an individual with a standard length of 50 cm so we estimated its length at 48-56 cm. The live weight for the catfish in the comparative collection with the standard length of 50 cm was recorded as 5 lbs.  Even though we did not estimate weights for our study, providing the standard lengths for Modoc and Koster fish allows other researchers to make weight estimates. 

For some animal species, there are mathematical relationships between the weight of the bone and the weight of meat associated with the bone in the living animal so you can weigh the bone, plug the weight into a formula, and determine the approximate weight of meat that was present for the animal. These kind of relationships between weight of the bone and weight of the meat associated with the bone are used to estimate the amount of meat represented for identified species. This technique allows zooarchaeologists to estimate the amount of meat represented by the total weight of bones for a species.  The article on allometry by Betsy Reitz and colleagues in the References at the end of the Clues from Bones section provides more information on this technique. In biology, allometry is the study of the relationship between part of an animal (in this case the bones) and another part of the animal (in this case the meat associated with the bone). 

Sometimes weights of animals such as deer are estimated based on average weights for that species.  For example, the estimated number of individual deer present at a site is multiplied times the average weight for deer.  These estimates are gross because they assume the whole animal was present and weights of living animals vary by sex, age, region, season, and even time period. 

The adult body size of some species, such as eastern cottontail rabbits (Sylvilagus floridanus) and fox squirrels (Sciurus niger), and gray squirrels (Sciurus carolinensis), varies from the eastern deciduous forest to the western prairie in contemporary times. In modern populations, the largest body size is present in the habitat to which the animal is best adapted. Zoologist Dr. James R. Purdue discovered temporal variation in the body sizes of these species in Archaic deposits at Rodger's Shelter and also at Graham Cave in Missouri. In these cases, the variation in body size is the result of environmental changes in habitat over time. The animals were largest during the times when the habitat was best suited to them. 


The epiphyses were not fused to the raccoon femur shaft from Modoc Rock Shelter (left side of image), but are fused to the raccoon femur from comparative collection (right side of image).  Which animal was fully grown and older in age? Image taken by Bonnie Styles.

Age of Animal

We sometimes are able to estimate and record the age of the animal. The level of precision depends on the kind of animal and body parts present. The body size of juvenile animals is smaller than for adult counterparts, so sometimes it is possible to link the body size to at least the gross maturity of the animal. For example, it is possible to identify a puppy versus a mature dog. It also possible to identify a fawn versus a mature deer based on body size. We know that the raccoon femur recovered at Modoc Rock Shelter shown on the left side of the image was from an immature animal because the epiphyses were not fused to the shaft. The raccoon bone from the comparative collection shown on the right side of the image is from a mature individual and has fully fused epiphyses.  


The distal epiphysis of the deer metacarpal from Modoc Rock Shelter is not fully fused.  The distal epiphysis for the deer metacarpal from the comparative collection is fully fused. If these deer were the same sex, which do you think was younger in age when it died? Image taken by Bonnie Styles.

For some species, such as white-tailed deer, we know the approximate age when epiphyses at the ends of certain bones fuse to the shaft. We compare the deer specimens from archaeological sites to published schedules for the fusion of epiphyses. In the deer metacarpal from Modoc Rock Shelter shown in the image, the distal epiphysis is partially fused to the shaft. The comparative specimen to the right shows a fully fused shaft.  A study of a modern sample of white-tailed deer in central Illinois by zoologist Dr. James R. Purdue indicated that this epiphysis was fused in 50% of the individuals at 20 months in females and 23 months in males and in all individuals by 29 months. So the deer represented at Modoc Rock Shelter was likely between about 20 months and 29 months old.


How could you determine the age of the white-tailed deer from Modoc Rock Shelter from its teeth (left side of image)? The comparative deer mandible at the center of the image is from an 18 month old deer. The comparative deer mandible at the top of the image is from a two year old deer. Image taken by Doug Carr.

One of the most common ways of aging animals is by examining tooth eruption and wear. Schedules of ages for eruption and wear of teeth for animals such as white-tailed deer have been developed and published by wildlife biologists. Look at the white-tailed deer mandible from Modoc Rock Shelter at the bottom of the image. The permanent second premolar is coming in and shows a little wear. The permanent first molar is fully erupted and shows wear. The teeth that would have been between these two teeth have fallen out and were not recovered. We compared this mandible to those from deer of known ages in the comparative collections. The mandible next to the archaeological specimen is from an 18 month old deer. For this deer, the permanent second premolar is not as fully erupted as in the archaeological specimen. The modern mandible at the top of the image is from a two year old deer. The permanent second premolar is fully erupted and the permanent first molar shows wear.  We estimated that the deer represented by the Modoc bone was between 18 months and two years old. 

For domestic animals, such as dogs, veterinarians have developed similar schedules. The ages of animals provide information on hunting practices and the season of kill, which also tells us when people were living at the site.


The skulls of the adult minks from the comparative collection differ greatly in size.   The male (left side of image) is much larger than the female (right side of image). We also see this pattern for other mink body parts. Image taken by Bonnie Styles.

Sex of Animal

We may be able to determine the sex of the animal if there are remains present that provide clues. Sometimes there is sexual dimorphism between males and females of a species. For example there may be sexual differences in maximum adult body size, in the morphology of particular bones, or in the presence of special features such as antlers in male white-tailed deer and a tarsometatarsal spur in male turkeys. The mink (Neovison vison) skulls from the comparative collection show sexual dimorphism in adult body size. Adult male minks are much larger than adult females. It may be possible to sex some of the adult mink bones from a site based on this difference in body size. Other animals, such as wild turkey, show strong sexual dimorphism between adult males and adult females.  Although it should be possible to separate males and females based on adult body size of turkeys, we did not pursue these types of analyses for the Koster and Modoc sites.


This broken femur from a chicken bone from a historic archaeological site shows medullary bone in the marrow cavity.  Click on the image to make it larger so you can clearly see the medullary bone. What does medullary bone tell us about this chicken? Image taken by Bonnie Styles.

Bird bones provide an example of the presence of special, sex-related features. A special kind of bone is deposited in the marrow cavities of female egg-laying birds before and during egg-laying. This bone is called medullary bone. It stores calcium that is needed for the formation of the eggshells. Presence of medullary bone indicates that a bird is female. Medullary bone is sometimes visible in the marrow cavities of bird bones from archaeological sites. We noted the presence of medullary bone in some of the bird bones from Modoc Rock Shelter so we know those birds were females and that they were killed around the time of egg laying.

The bird bone in the image is a right femur with a modern break. It is from a domestic chicken (Gallus gallus) from a historic archaeological site in Springfield, Illinois. The break allows us to see into the marrow cavity. The marrow cavity on both halves of the bone shows medullary bone.


The more elongate threeridge shell on the left is from an Archaic Period layer (Horizon VIII) at the Koster site. The more rounded threeridge shell on the right is from a younger Archaic Period layer (Horizon VI) at the Koster site. A freshwater mussel is a bivalve. It has two shells. The shell on the left is from the left side of a mussel, and the shell on the right is from the right side of a mussel. Image taken by Bonnie Styles.


Zoologists may look for and record differences in the sizes and shapes of an animal species. Zoologist Frederick C. Hill recorded differences in the shell shape (based on measurements of length and height) for threeridge mussels (Amblema plicata) for the Koster site. The threeridge shells were more elongate in a particular layer (Horizon VIII) and more oval in the younger (Horizon VI) layer. Threeridge shells from both these layers are thick and show the inflated umbones (the beaklike projections of shell at the bottom of the image) characteristic of large river forms. He related the differences to temporal changes in the flow of the Illinois River. Measurements of mussels are not routinely taken by zooarchaeologists, but may provide interesting results.


The skull of the white-tailed deer from the Napoleon Hollow site (left side of image) shows evidence for an infected injury on its frontal bones (just above the scale in the image). The modern white-tailed deer skull from the comparative collection (right side of image) shows the normal, smooth condition of these bones. Images taken by Bonnie Styles.


Archaeozoologists sometimes discover pathological features on animal bones from archaeological sites.  The skull of the young male white-tailed deer from the Napoleon Hollow site (left side of image) preserves traces of an injury on its right and left frontal bones. This injury had become infected. The modern deer skull from the comparative collection (right side of image) shows the normal, smooth, flat surfaces of the frontal bones. You can see irregular raised areas of bone and evidence for cavities in the raised areas on the archaeological specimen. These features indicate that the infection was draining.

Retired veterinarian Dennis Lawler examined the Napoleon Hollow deer skull. Based on his experiences, he suggested that the infection was likely active at the time the deer was killed, but probably did not kill the deer. An Archaic Period hunter likely killed the deer. The infection may have made this deer an easy target.

We included the faunal database for the Archaic Period occupations at the Napoleon Hollow site in tDAR. This site is located along the Illinois River in Pike County, Illinois. The location of the site is shown on the map of our study area. You can see this map in the What is Zooarchaeology or the About the Project sections.

Other pathologies that we noted on Archaic Period animal bones from sites in our study area include healed fractures and arthritis.

Season of Death

Most zooarchaeologists attempt to record any information that might reveal the season when an animal was killed. This information is critical to understanding when an ancient camp was occupied. Season of kill may be determined through age estimates for young individuals based on tooth eruption and wear, body size, fusion of epiphyses, or other aging criteria. The techniques are useful when the seasonal schedule of births is known, such as for white-tailed deer. For example, the peak season of births for modern white-tailed deer in Illinois is June.  A deer mandible from an archaeological site from an individual that was 6 months old represents a deer that was likely killed around November or December. 

Other seasonally restricted occurrences, such as the growth, development, and shedding of antler for white-tailed deer also provide indications of the season of kill. In Illinois today, anlter growth begins in April and continues through June. The antlers become hard by September. A deer frontal skull from which antler was attached or shed provides a better indicator of season of kill than a piece of shed antler.  Deer shed their antlers each year, and they could be picked up by humans at a later date or saved for later use. Historically most white-tailed deer in Illinois shed their antlers from about mid-January through early April.  However, we have to remember that climate was different in the past so the timing may have been a little different. 


Mallard ducks (Anas platyrhynchos) overwinter in Illinois today in areas where open water persists. During the Archaic Period, they would have been most abundant during the spring and fall migrations. The timing of  the migrations would have varied with the climate. The image of a female (front) and male mallard (back) is taken from Wikimedia Commons. 

Presence of migratory animals at sites may provide evidence of the season when they were procured. For example, large quantities of migratory waterfowl at an Illinois archaeological site may indicate hunting in the spring and/or fall. Presence of relatively high numbers of ducks in late Middle Archaic deposits at Koster provides evidence for human occupation of the camps during the spring and/or fall migrations. The timing of migrations may have varied through time. For example, the spring migration may have been a little later and the fall migration may have been a little earlier in the Early Holocene when it was cooler and moister than today.

Sometimes seasonality is based on the presence of bones of small, juvenile fish called fingerlings from species where the season of spawning and growth rates are known. For example, bowfin (Amia calva) spawn in April and May, channel catfish (Ictalurus punctatus) spawn in May, and bigmouth buffalo (Ictiobus cyprinellus) fish spawn in April, so presence of fingerling size fish of these species at an Illinois archaeological site could indicate summer exploitation. However, the precise timing of spawning may have varied some in the past. 

Some zooarchaeologists examine annual growth lines (called annuli) on elements such as fish scales and freshwater mussel shells to see if they can determine season of death. Zoologist Dr. Frederick Hill examined the annuli on freshwater drum (Aplodinotus grunniens) scales from the Koster site. There are many factors that influence the growth of scales, and false annuli are possible. Also many scales from archaeological sites are broken. However, scales from young fish that preserve the last annuli and any growth that followed it provide the best evidence of season of death. Dr. Hill concluded that thee of the drum scales from Horizon VI (late Middle Archaic) represented fish that died in May, June, and July.  Two additional scales from Horizon VI were from fish that were killed between July and April.   Two scales from Horizon VIII (middle Middle Archaic) drum were from fish that were killed in the summer (June or July and July or August).  

dog-wolf skulls

The Archaic Period domestic dog skull from the Koster site (left side of image) is much smaller than the modern gray wolf skull from the comparative collection (right side of image).The image of the dog skull was taken by Claire Martin, and the image on the wolf skull was taken by Bonnie Styles.

Domestication, Management, and Special Uses of Animals

Presence of domestic animals suggest a different interaction than that with wild animals. Because domestication of animals often includes selection for desirable attributes, morphological changes may be apparent. The body proportions of early domestic dogs in the Midwestern United States differ from those of their wild ancestors (gray wolves, Canis lupus). Dog skeletons from the Koster and Modoc sites show that adult dogs are smaller in stature than gray wolves and other wild canids such as coyotes (Canis latrans) of equivalent age and sex.

dog-wolf mandibles

The left and right mandibles of the domestic dog from the Koster site (left side of image) are much smaller than the fused mandibles from a modern gray wolf in the comparative collection (right side of image). Images of dog mandibles were taken by Claire Martin, and the image of the fused wolf mandible was taken by Bonnie Styles.

Many zooarchaeologists have argued that the teeth on the mandibles of early domestic dogs are more crowded than noted for wolves or coyotes.  Zooarchaeologists linked this crowding to the reduction in the length of the snout with domestication. However, research published in September 2017 in the Journal of Archaeological Science documented high levels of tooth crowding for ancient and modern wolves.

This finding suggests that tooth crowding cannot be used to separate dogs and wolves and that tooth crowding is not a reliable indicator of early domestication. Genetics research of modern and ancient wolves, coyotes, and domestic dogs reveals a complex history of origins and interactions among these species.  The DNA research is more reliable for the separation of domestic and wild animals and documentation of interbreeding. We will discuss the domestic dogs from Modoc and Koster more in the Human Use of Animals section. 

A faunal assemblage at a site may provide clues about human attempts to manage animal populations. Management of populations could include practices such as improving the habitat for a particular species and not hunting females during the reproductive season to ensure the growth of the population. Attempts to demonstrate management often include assessment of the numbers, ages, and sexes of the animals in the assemblage.

Some zooarchaeologists have suggested that turkeys (Meleagris gallopavo) may have been managed in the Eastern United States. There is evidence that turkeys were managed or domesticated in the Mesoamerica by 2,300 years ago and in the Southwestern United States by 2,200 years ago.  Dr. Tanya Peres of our research team and Kelly Ledford have argued that late prehistoric Mississippian Period people in the Southeastern United States may have managed turkeys around 1,000 years ago. Turkeys are sexually dimorphic. The males are much larger than the females. Peres and Kelly reported that both female and male turkey remains were found in assemblages based on a rigorous study of measurements of the bones. The numbers of males present was equal to or greater than the numbers of females. Based on the absence of medullary bone in females, there is no evidence that females were taken during the egg-laying period. Perhaps hunters avoided taking females during this time to ensure the growth of the population. Dr. Peres and Ledford argue this pattern could represent management of turkeys for feathers and meat or perhaps a greater focus on the hunting of large adult males. The Mississippian Period sites are much younger than our Archaic Period sites. However, these researchers are recording measurements for turkey bones from Archaic Period sites to explore if there is any evidence for management.

The faunal assemblages from Modoc and Koster include turkey bones. Modoc may also include turkey egg shell. However, the egg shells do not provide definitive evidence for presence of captive birds. Archaic Period people may have collected turkey eggs from nests in the wild.  Zooarchaeologists did not attempt to separate the turkey bones from Modoc and Koster into those from males and females. We currently have no evidence suggesting that turkeys were being managed by Archaic peoples in the Illinois area. 

We will discuss evidence for Archaic Period management of freshwater gastropods in the mid-south in the Human Use of Animals section.

Zooarchaeologists look for other evidence of special interactions with animals. Special uses of bones and shells and burial of animal remains in special contexts are suggestive of a different relationship. The burials of dogs at Modoc and Koster are examples of special contexts. An unusual cache of numerous Canada Goose (Branta canadensis) wing bones and some Sandhill Crane (Grus canadensis) leg bones in a feature at Modoc is an example of special use and special context. We will discuss these occurrences in the Human Use of Animals section. 

Habitat and Migratory History 

Elements in bones and shells from archaeological sites provide information on animal diets, habitats, and even their migratory patterns. Some zooarchaeologists take small samples from bones and shells to extract and study isotopes (different atomic forms) of elements such as carbon, oxygen, and strontium. Paleontologist Dr. Chris Widga collected samples from individual layers of enamel in bison teeth. He analyzed the strontium isotopes preserved in these layers. The sediments in different geographic regions have different istotopic signatures of strontium, which are absorbed by and also present in the grasses and other plants living in the area. The strontium from the plants the bison ate is deposited in layers in the bison teeth. The different strontium signatures in the layers of a tooth allowed Dr. Widga to track how far bison were moving across the landscape in his study area in the eastern Great Plains.