formed by the fusion of five sacral vertebrae; the part of the vertebral column that forms the most dorsal part of the pelvic girdle, in between the os coxae.

sagittal crest

a protrusion made of bone at the joint between the parietal bones to which the temporalis muscles attach; common in many larger ape species and some fossil hominins.


a large, boat shaped carpal bone located in the proximal row that articulates distally with the lunate, trapezium, trapoezoid, capita and the capitate, and proximatlly with the radius.


[syn. shoulder blade] a flat triangular bone that articulates laterally with the proximal humerus.


a behavior that allows animals to incorporate meat into the diet, but one that relies on finding the carcasses of animals that died of natural causes or were killed by other predators, rather than engaging in active predation.


a process that studies the natural world and tests the accuracy of the results. Science's primary utility comes from its self-correcting nature, as erroneous ideas are discarded.

scientific law

a scientific statement or description of a fact that has been supported to be true by all available means of the scientific method. A scientific law explains behaviors or phenomena when specific conditions are applied.

scientific method

the process used by scientist to answer or clarify scientific inquiries. The process begins with the formation of a hypothesis based upon observation, followed by further systematic observations and experiments related to the phenomenon in question. These experiments and observations are conducted several times to establish whether the results are repeatable. The repeatable results are then used to support or disprove the initial hypothesis.

second cervical

[syn. axis] counting for the top, the second vertebra; allows for head movement via rotation of the atlas.

second lumbar

counting from the top, the second vertebra forming the lower back.

second rib

a true rib; counting from the top, the second rib that forms the rib cage.

second thoracic

counting from the top, the second vertebra forming the mid-back.


describes a region with low annual rainfall and predominantly short vegetation, such as shrubs and grasses.

seventh cervical

counting from the top, the seventh cervical vertebra that is transitional between the cervical and thoracic vertebrae.

seventh rib

a true rib; counting from the top, the seventh rib that forms the rib cage.

seventh thoracic

counting from the top, the seventh vertebra forming the mid-back.

sexual dimorphism

the condition in which the males and females of a particular species each have different forms of the same feature or characteristic (e.g., body size, canine size). In those primate species that display marked sexual body size dimorphism, the males are larger than the females. In some species, such as gorillas and orangutans, the males are twice as large as the females (i.e., a 2:1 difference in mass).

sexual selection

a form of natural selection where fitness is determined by an individual's ability to compete for mates.

shared derived character

a new trait common between evolutionary related groups or individuals.


refers to monkeys, apes, and humans.

sister group

a group that shares the same common ancestor with another.

sixth cervical

counting from the top, the sixth vertebra forming the neck.

sixth rib

a true rib; counting from the top, the sixth rib that forms the rib cage.

sixth thoracic

counting from the top, the six vertebra forming the mid-back.


the protective and supportive structure of an organism constructed of bone and cartilage.


the bony portions of the head, including the cranium and the mandible.


the evolution of a new species from an ancestral species; the foundation of macroevolution.


the basic unit of biodiversity. Individuals of a species are reproductively isolated, meaning that they cannot produce viable offspring with a mate of a different species. Taxonomic classification uses the binomial nomenclature: where the names of organisms start with a capitalized genus name (i.e., Homo for humans) and a specific epithet for the species name (i.e., sapiens for humans). Therefore, the proper species name for humans is Homo sapiens.


ankylosis specific to the vertebrae. Arthritic processes on the vertebral column

stabilizing selection

when the extreme variants are selected against, increasing the mean.


a period in which a species undergoes little to no morphological or behavioral changes; evolutionary stability.


a relative term used for bipedal hominins (those that travel on two legs) to describe features on the trunk that are closer to the head; the opposite of inferior. The term cranial is a synonym commonly used when referring to quadrupedal animals.


an extra element.


the idea that the top layer of sediments is younger than the sedimentarly layer below it.


rotary motion that moves the thumb from the medial position to a lateral position; the opposite of pronation.

suspensory behavior

a form of positional behavior in which the body of an organism is supported by their arms or legs holding on to a branch above them; the tail may also be used in suspensory posture.


a joint between two bones that are securely connected and are separated by fibrous tissue. The joints between most of the bones of the skull are sutures.


an object, behavioral act, or language that stands for something else and carries some codified meaning.

sympatric speciation

the evolution of a daughter species due to changes within a subset of the parent population; in this sense, the parent and daughter populations are not geographically isolated from one another.


when the home range of two different species overlaps.


a type of joint that is cartilaginous.


a shared primitive trait.


a shared derived trait.


'Infectious disease process caused by Treponema pallidum, can be visible in bone


the science of classification; the organization of organisms according to their evolutionary relationships.


'When a disease process affects the body as a whole