Chapter 9: Hominin Origins: From Ape to Australopithecine

Question 1

missing links

Answer 1

a popular term referring to transitional fossils, which typically bear a combination of primitive and derived traits linking them with earlier and later forms within a clade

Question 2

speciose

Answer 2

literally, “full of species,” indicating a taxonomy consisting of many rather than fewer named species

Question 3

biological systematics

Answer 3

the formal science of classification and taxonomy, specifying a set of rules and guidelines for categorizing biological diversity and deriving phylogenies

Question 4

alpha taxonomy

Answer 4

the process of classifying organisms to genus and species, based on extensive data extracted from morphology, behaviour, DNA and so on. In the case of fossil species, detailed analyses of skeletal and dental morphology are essential elements in deriving the alpha taxonomy.

Question 5

holotype

Answer 5

the specimen that serves as the “name-bearer” of a fossil species and from which a description of the salient features of the taxon are obtained. It need not be the sole source of information for identifying a member of the taxon, nor does the holotype need to be a typical example

Question 6

sister taxon

Answer 6

in systematics, sister taxa are those forms that are related by virtue of a divergence event and that share a last common ancestor; panins and hominins are sister taxa, as are Australopithecus an Ardipithecus

Question 7

basal

Answer 7

a qualitative term distinguishing the earliest widely accepted hominins from those forms later assigned the genus Homo

Question 8

megadont

Answer 8

literally, large teeth; megadont hominins are characterized by expansion of the posterior teeth (i.e., premolars and molars)

Question 9

synchronic

Answer 9

at the same time; thus synchronic species coexist in time

Question 10

Neogene period

Answer 10

a geological time period comprising the Miocene and Pliocene epochs, associated with global climate change and diversification of a number of avian and mammal species, particularly open woodland and grassland forms

Question 11

aridification

Answer 11

a drying trend resulting from lower seasonal or annual precipitation levels

Question 12

mosaic habitats

Answer 12

areas characterized by a range of habitat types, from forest to grassland

Question 13

savannah hypothesis

Answer 13

the now discredited idea that the development of open savannah grassland created conditions leading to the evolution of hominins

Question 14

gallery forest

Answer 14

dense, canopied forest found along water courses such as rivers and lakeshores

Question 15

forest hypothesis

Answer 15

the suggestion that the hominin clade diverged from panins while still occupying a woodland/forest habitat, as suggested by paleoecological reconstruction of forest localities

Question 16

variability selection hypothesis

Answer 16

a model that suggests that the operating factor in hominin evolution was environmental disparity, rather than stability, which promoted adaptive flexibility in hominin traits, including locomotion, dental adaptations, and technology

Question 17

aligned sequence

Answer 17

in molecular genetics research, sequences of DNA (or RNA) derived from homologous sites within the genome are literally arranged or aligned to identify similarities and differences between two species, the latter resulting from, for example, point mutations, insertions, or deletions

Question 18

recurrent mutation

Answer 18

a mutation that tends to occur repeatedly at the same locus; a number of genetic disorders are maintained at high frequencies through recurrent mutation (e.g., Marfan syndrome in humans, leading to impaired collagen formation)

Question 19

genetic divergence

Answer 19

an estimate of the time since two genomes diverged, based on the number of differences observed and assuming a constant rate of mutation

Question 20

species divergence

Answer 20

an estimate of time since speciation; because genetic differences are constantly accumulating with in lineages, estimates of genetic divergence time will always be older than species divergence time

Question 21

alveoli

Answer 21

the bony sockets for teeth present in the upper and lower jaws

Question 22

assemblages

Answer 22

the collection of all remains of plants or animals from paleontological contexts

Question 23

foramen magnum

Answer 23

“large passage,” the foramen magnum is the largest hole in the cranium, through which the brain stem passes to become the spinal cord

Question 24

stem hominin

Answer 24

the progenitor of all later hominin species within a clade, arising from the last common ancestor

Question 25

proximal

Answer 25

in skeletal anatomy, a position closer to the midline of the body (e.g., the elbow is distal to the shoulder joint); in teeth, the term refers to the tooth surface facing the back of the mouth

Question 26

distal

Answer 26

in anatomy, a position farther from the midline of the body

Question 27

phalanx

Answer 27

one of a series of short bones that make up the fingers in the hand or the toes in the foot

Question 28

muscle markings

Answer 28

impressions on a bone surface that define the point of origin or insertion of a muscle; activities that build up muscles can also create more prominent muscle markings

Question 29

craniodental

Answer 29

a descriptive term referring to the hard tissues, bone, and teeth comprising the skull

Question 30

eurytopic

Answer 30

organisms that are able to live in diverse habitats and geographic ranges; the prefix “eury” means “broad, wide” and the affix “topic” refers to “place”

Question 31

gracile

Answer 31

small or slightly build; among australopithecines, refers to those species lacking the skeletal and dental features associated with the megadont adaptation

Question 32

robust

Answer 32

rugged or strongly built; several australopithecine species possess skeletal and dental features associated with large chewing muscles and crushing and grinding of hard foods

Question 33

percussive stone tools

Answer 33

implements fashioned by purposefully striking one stone against another to produce a cutting edge

Question 34

phyletic sequence

Answer 34

an unbroken lineage of ancestor-descendant species

Question 35

punctuated anagenesis

Answer 35

speciation has two tempos, slow and gradual (anagensis) or rapid followed by stasis (punctuated equilibrium); punctuated anagenesis combines these into a pattern of rapid change within a continually evolving lineage; the possibility of punctuated anagenesis is not universally held among evolutionary biologists

Question 36

mandibular symphsis

Answer 36

the midline of the lower jaw, where the left and right sides of the dental arcade meet

Question 37

orthognathic

Answer 37

“ortho” refers to vertical or flat, and “gnathic” to the jaws; thus, “orthognathic” means “flat face”

Question 38

breccia

Answer 38

a rock formation composed of stone fragments embedded within a fine-grained cement-like matrix

Question 39

prognathic

Answer 39

refers to the degree to which the lower face projects forward

Question 40

competitive exclusion

Answer 40

a phenomenon in which two species closely related in phenotype and ecology come into direct competition for resources. In these cases one species will either become extinct or adopt a new phenotype (morphology and/or behaviour), allowing it to exploit other resources.

Question 41

Liem’s Paradox

Answer 41

a model in biology that describes the apparent paradox between a specialized phenotype and a generalized behaviour; the paradox is resolved if the specialized phenotype does not restrict an organism from nonspecialized behaviours

Question 42

fallback foods

Answer 42

resources on which a species relies when its preferred, more easily acquired and processed foods are unavailable

Question 43

homoiology

Answer 43

similarities that occur among organisms by virtue of a bone’s ability to respond to existing mechanical forces; similar behaviours will reproduce such forces and thus the associated morphology, which may be confused with genetic relationships