Chapter 9: Hominin Origins: From Ape to Australopithecine Flashcards
missing links
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
speciose
literally, “full of species,” indicating a taxonomy consisting of many rather than fewer named species
biological systematics
the formal science of classification and taxonomy, specifying a set of rules and guidelines for categorizing biological diversity and deriving phylogenies
alpha taxonomy
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.
holotype
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
sister taxon
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
basal
a qualitative term distinguishing the earliest widely accepted hominins from those forms later assigned the genus Homo
megadont
literally, large teeth; megadont hominins are characterized by expansion of the posterior teeth (i.e., premolars and molars)
synchronic
at the same time; thus synchronic species coexist in time
Neogene period
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
aridification
a drying trend resulting from lower seasonal or annual precipitation levels
mosaic habitats
areas characterized by a range of habitat types, from forest to grassland
savannah hypothesis
the now discredited idea that the development of open savannah grassland created conditions leading to the evolution of hominins
gallery forest
dense, canopied forest found along water courses such as rivers and lakeshores
forest hypothesis
the suggestion that the hominin clade diverged from panins while still occupying a woodland/forest habitat, as suggested by paleoecological reconstruction of forest localities
variability selection hypothesis
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
aligned sequence
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
recurrent mutation
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)
genetic divergence
an estimate of the time since two genomes diverged, based on the number of differences observed and assuming a constant rate of mutation
species divergence
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
alveoli
the bony sockets for teeth present in the upper and lower jaws
assemblages
the collection of all remains of plants or animals from paleontological contexts
foramen magnum
“large passage,” the foramen magnum is the largest hole in the cranium, through which the brain stem passes to become the spinal cord
stem hominin
the progenitor of all later hominin species within a clade, arising from the last common ancestor
proximal
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
distal
in anatomy, a position farther from the midline of the body
phalanx
one of a series of short bones that make up the fingers in the hand or the toes in the foot
muscle markings
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
craniodental
a descriptive term referring to the hard tissues, bone, and teeth comprising the skull
eurytopic
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”
gracile
small or slightly build; among australopithecines, refers to those species lacking the skeletal and dental features associated with the megadont adaptation
robust
rugged or strongly built; several australopithecine species possess skeletal and dental features associated with large chewing muscles and crushing and grinding of hard foods
percussive stone tools
implements fashioned by purposefully striking one stone against another to produce a cutting edge
phyletic sequence
an unbroken lineage of ancestor-descendant species
punctuated anagenesis
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
mandibular symphsis
the midline of the lower jaw, where the left and right sides of the dental arcade meet
orthognathic
“ortho” refers to vertical or flat, and “gnathic” to the jaws; thus, “orthognathic” means “flat face”
breccia
a rock formation composed of stone fragments embedded within a fine-grained cement-like matrix
prognathic
refers to the degree to which the lower face projects forward
competitive exclusion
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.
Liem’s Paradox
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
fallback foods
resources on which a species relies when its preferred, more easily acquired and processed foods are unavailable
homoiology
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
