Glossary M - Z


M2 - Designation of the second true molar in the upper jaw of a mammal.

mammae (singular, mamma) - The glandular organs for secreting milk.

mastoid - Designating or pertaining to the mastoid bone (paired) or its process. This bone is bounded by the squamosal bone, the exoccipital bone, and the tympanic bone.

maxillary breadth - Width of skull from some designated place on the lateral face of the right maxillary bone (maxilla) to the corresponding place on the left maxillary bone; in shrews, across the ends of the zygomatic processes of the two maxillary bones.

maxillary toothrow - The row of teeth in one maxillary bone; in most mammals all the premolars and molars on one side of the upper jaw.

metabolic water - Water formed as an end product of cellular combustion of foodstuffs in an animal's body.

mesaxony"- Having the axis of the foot passing through the third digit (as opposed to paraxony, where the axis passes between digits III and IV). The adjectival form is mesaxonic.

metacarpal - Of or pertaining to a metacarpal bone. A bone of the hand or forefoot between the wrist and fingers; when all the digits are present, there are five more or less elongated metacarpal bones, one at the base of each digit.

metapodial - Term referring to the bones between the wrist or ankle and the digits. A general term when it's not necessary to specify whether the bones are metacarpals (those of the manus) or metatarsals (those of the pes).

microevolution. Evolution within species rather than at higher taxonomic levels. Some creationists have stretched the definition of microevolution far beyond any usage in biology, even to the point where all members of a taxonomic family might be considered the result of microevolution, and thus not "real" evolution.

molar - Of or pertaining to a molar tooth. One of the teeth behind the premolar teeth; a molar tooth is not preceded in embryological development by a deciduous (milk) tooth.

molarization - The phenomenon of one or more of the premolars becoming molariform (that is, becoming morphologically and functionally similar to molars).

molt (moult) - In a mammal, the act or process of shedding or casting off the hair, or outer layer of skin or horns; most mammals shed the hair once, twice, or three times annually. The cast off covering (obsolete). As a verb: to be shed (intransitive) or to shed (transitive).

monophyly - The case where all members of a taxon are descended from the same common ancestor. In strict monophyly (as used in cladistics), there also is the requirement that all descendents of that common ancestor be included in the taxon.

mutation. An inheritable change in the genetic material.

mya. The abbreviation for millions of years ago.

nasal - Of or pertaining to the nose, as a nasal bone (paired) on the dorsal surface of the skull at its anterior end. A nasal bone.

neoteny - Result of an evolutionary process wherein reproductive maturity has been retained at its normal timing while non-reproductive development (somatic development) has been slowed down to the point that it normally does not appear.

nocturnal - Active by night (opposed to diurnal).

nomenclature - A system of names; the rules governing the naming of taxa.

obligate taxonomic category - Any of the seven taxonomic ranks that are necessary to minimally classify a species.

occipitonasal length - Least distance between two vertical lines, one touching the posteriormost part of the skull above the foramen magnum (opening for the spinal cord) and the other touching the anteriormost part of the nasal bones or a nasal bone.

occlusal - Of or pertaining to the grinding or biting (occluding) surface of a tooth. The part of the tooth that meets the teeth of the complementary jaw.

oceanic island - An island that has never been connected to the mainland.

omnivorous - Diet consisting of significant amounts of both vegetal and animal material. Examples are humans, bears, and pigs.

opposable - Capable of being placed opposite something else; said of the first toe of an opossum in the sense that it can be placed opposite each of the other toes on that same foot.

orbit - The cavity in the skull in which the eye and its appendages are situated; the eye socket.

orthogenesis - A popular earlier theory that evolution acted to drive a phylogenetic line along a single pathway ("ortho" means straight) from simpler to more complex. Presumably this was due to some innate drive.

osseous - Composed of, or resembling, bone; bony. Osseous tissue is bony tissue.

overhairs - The longer hairs of the pelage of a mammal that project above the fur (shorter hairs).

oviparous - Egg-laying (as opposed to viviparous, live birth; or ovoviviparous, where the egg is retained until the embryo is mature enough to be born.

P3 - Designation of the third (next to last) premolar in the upper jaw of a mammal. Capital letters designate teeth in the upper jaw and lowercase letters designate teeth in the lower jaw.

palatal - Of or pertaining to the palate (as generally used, the bony roof of the mouth made up of two palatine bones, two maxillary bones, and two premaxillary bones).

secondary palate - The roof of the mouth, consisting of the structures that separate the mouth from the nasal cavity. The bony palate is composed of the premaxillae, maxillae, and palatines.

paleontology. The study of fossils (recognizable traces of past life).

parallel evolution. The situation wherein taxa have split from a common ancestor but, due to their similarity in genetic makeup and (usually) similar adaptive pressures, independently evolve similar structures (sensu lato).

parameter. An actual quantitative or qualitative value of a population. For example, the true mean value for some character of a population would be a parameter; the value of the population mean calculated from a sample of the population would not be (unless by chance it coincided with the true population mean). In regard to physics, a parameter may be defined as any of a set of physical properties whose values determine the characteristics or behavior of something.

parapatric. Geographic ranges that adjoin one another but do not overlap.

paraphyly - The case in cladistics where not all descendents of the common ancestor of a taxon are included within that taxon. For example, the class Reptilia as commonly used is paraphyletic in that it doesn't include birds and mammals but does include a common ancestor with birds and mammals.

parietal - Pertaining to or designating the parietal bone (paired) roofing the braincase. This bone is behind the frontal bone and in front of the occipital bones.

parsimony. Using the simplest explanation. In cladistics, the explanation that requires the fewest steps.

phenogram. A tree-like graph (dendrogram) summarizing the degree of similarity among taxa or other things being compared.

pectoral - pertaining to, or situated or occurring in or on, the chest.

pencil - Tuft of fur or hair, as a black pencil on the end of the tail of a mammal.

penicillate - Having a pencil, or tuft of longer hair (see above).

phalanx (plural, phalanges) - A bone, in a finger, distal to the metacarpus or a bone, in a toe, distal to the metatarsus.

phylogenetic line. - An ancestor-descendent line; the sequence of ancestral taxa leading from some point in the ancestry through time to a specific taxon. For example, our complete phylogenetic line would include all taxa that are in the ancestry of both apes and humans as well as all taxa ancestral to modern humans from the time the human line split from the ape line.

phylogenetic extinction. - The ending of a phylogenetic line.

phylogeny. - The relationships among a taxon and its ancestors (and often considered to include relationships with relatives not in the direct line of descent). A phylogeny, then, would list (or show diagrammatically) the ancestors in correct chronologic order.

pinna (plural, pinnae) - The projecting part of an ear.

placental mammals - Placental mammals consist of those mammals that form an efficient placenta between an embryo and its mother, resulting in a relatively long gestation period (the time spend within the mother's uterus). The non-placental mammals are the egg-laying mammals and the marsupials.

plantigrade - Walking on the entire sole of the foot, as in humans and bears.

plesiomorphic - A "primitive" character state; a character state doesn't differ from the ancestral state. Contrasted with apomorphic.

plesiomorphy. In cladistics, a non-derived character state that originated earlier in phylogeny than the nearest common ancestor (shared plesiomorphies are called symplesiomorphies).

polyphyly - In cladistics and evolutionary classification systems, a taxon that includes lower-level taxa that are not descended from the most recent common ancestor of the majority of the taxon members. For example, if the Mountain Lion were included in the family Canidae (dogs, wolves, foxes, etc.), the Canidae would be polyphyletic.

population. All the members of a species within a geographically defined area. When used without an adjective, it is a general, flexible term (e.g., the human population of El Paso/Juarez, the wolf population of North American, etc.). For restrictive uses, see deme and Mendelian Population.

postauricular - Situated behind the auricle (pinna) of the ear, as a postauricular patch (ordinarily referring to a patch of fur differing in color from surrounding fur).

postorbital - Situated behind the eye, as postorbital process of the frontal bone or postorbital process of the jugal bone.

premaxillary - Of or referring to the premaxilla, a bone (paired), in the mammalian skull bearing the incisor teeth of the upper jaw; the premaxilla is situated in front of the maxilla.

premolar - Designating or pertaining to one of the teeth (a maximum of 4 on each side of upper jaw and lower jaw of placental mammals, or 16 in all) in front of the true molars. When canine teeth are present, premolars are behind these teeth; premolars are preceded by deciduous teeth, and in the upper jaw are confined to the maxillary bone.

radioactive decay. Some kinds of isotopes emit radiation during nuclear events, changing into a different isotope of the same element or into a different chemical element. The change of one isotope or element into another is known as radioactive decay and proceeds at a characteristic rate for each isotope (the half-life).

rafting. Dispersal across bodies of water by riding on debris such as floating, tangled trees carried out to sea during floods.

reentrant angle - An infold of the enamel layer on the side, front, or back of a cheek-tooth, as in a molar of a muskrat or wood rat.

reproductive isolation. The inability of members of one population to breed with members of another population because of innate, genetic factors.

reversal - In terms of evolution, where a character state evolves back into an earlier character state. For example, if a tooth cusp were lost evolutionarily and then an identical-appearing cusp evolved in the same place at a later date, we would have a reversal.

rostrum - Of a mammalian skull, the part projecting in front of the orbits.

rut - The breeding period, as in deer.

sagittal crest - The ridge of bone at the juncture of the two parietal bones resulting from the coalescence of the temporal ridges; in old individuals of many species of mammals, the crest extends from the middle of the lambdoidal crest anteriorly onto the frontal bones and divides there into two temporal ridges, each of which extends anterolaterally on the posterior edge of the postorbital process of the frontal bone.

scrotum - An external sac enclosing the testes and associated structures in the males of most mammals.

sedimentary rocks. These are rocks formed from particles derived from larger rock bodies or cool-condition chemical precipitation. They include such rocks as limestones, shales, sandstones, siltstones, claystones, mudstones, gypsum, and salt deposits.

sensu lato. In a broad sense. For example, when used with "morphology," sensu lato means morphology in a broad sense (including cellular, physiological, behavioral, etc., senses). "Sensu stricto" means in a strict sense; in the case of morphology, only the gross morphology.

sibling species - See cryptic species

speciation - Formation of a new species by splitting apart from the parent species, thus resulting in a multiplication of species (where there was one, there now are two). Not used by us where a single phylogenetic line changes to the degree that the later population has to be called by a different species name.

species - A taxonomic rank lying between the lower-level subspecies and the higher-level genus. There are various definitions, but in all it is a population-level term referring to individuals connected by some manner of genetic similarity. This similarity may be the reproductive, behavioral, or morphological, depending on the definition. The plural also is species.

species, biological. A group of interbreeding natural populations that is reproductively isolated from other such groups.

species, morphological. A group of populations whose members are morphologically similar and separated by a morphological gap from other such populations.

stereoscopic vision - Vision in which the field of vision of the two eyes overlaps, allowing three-dimensional vision.

subauricular spot - A spot, patch of hair, distinctively colored immediately below the ear.

subspecies. A subspecies is an aggregate of phenotypically similar populations of a species inhabiting a geographic subdivision of the range of that species and differing taxonomically from other populations of that species.

supraorbital process of frontal - The process of the frontal bone on the top rim of the orbit, as in a rabbit.

sympatric. Occurring together in the same geographic place.

systematics - The scientific study of the kinds and diversity of organisms and of any and all relationships among them.

tarsus - The ankle.

taxon - Any formally named taxonomic group of organisms. Thus Homo sapiens is a taxon; so is Mammalia. "Species" is not—it is a rank of the taxonomic hierarchy and does not denote a specific, named group of organisms. The plural of taxon is taxa.

temporal ridge (paired) - A curved, raised line on the side of the braincase marking the upper limit of attachment of the fascia of the temporal muscle. The temporal ridge is prominent on the parietal bone, frequently extends forward onto the frontal bone, and in some kinds of mammals extends backward onto the interparietal bone. When present, the sagittal crest is formed by the coalescence of the two temporal ridges.

terrestrial - Inhabiting the land, rather than the water, trees, or air.

tetrapod. The "four-footed" vertebrates: amphibians, reptiles, birds, and mammals. Includes forms that have secondarily lost limbs, such as snakes and caecilian amphibians.

tibia (plural, tibiae) - The inner and usually the larger of the two bones of the hind limb (leg) between the knee and the ankle.

torpid - Having lost most of the power of exertion; dormant. A ground squirrel is torpid when it is hibernating.

tragus - a flap of skin near the base of the external ear.

Diagram showing the tragus of bats
After Feldhamer et al. 1999.

tree-ring - See dendrochronology

tricolor - Having three colors. Said of hair on back of a mammal when the hair has three bands, each of a different color.

type locality - The place where a type specimen (the holotype) was obtained.

underfur - The short hair of a mammal; in temperate and boreal climates, the underfur ordinarily is denser, made up of more hairs, than the longer and coarser overhair.

underparts - The underneath (ventral) side of a mammal (not the back or sides), as of a woods mouse with white underparts.

ungulate - Hoof-bearing mammals, including the Artiodactyla and Perissodactyla, among others.

unicuspid - Mammalian teeth having a single (or single major) cusp. Used particularly for the single-cusped teeth posterior to the anterior incisors in shrews (marked "U" in the figure below), but may also be used for canines or other types of teeth with a single cusp.

Anterior skull of a shrew (Sorex) showing tooth types

upper parts - The top (dorsal) surface and all of the sides (not the belly, chest, or throat), as of a woods mouse with reddish-brown upper parts.

uropatagium - The interfemoral membrane of a bat; that is to say, the fold of skin that stretches from the hind legs to the tail.

vertical classification - A classification that divides a phylogenetic line from closely related lines even when early members of the two lines are very similar. E.g., the family Equidae (horses) includes as its earliest members species that are much more similar to early members of the families Tapiridae (tapirs) and Rhinocerotidae (rhinoceroses) than they are to later members of the Equidae.

Viviparity - The condition wherein the embryo is supplied nutrition and other support while in the uterus, followed by live birth. Usually defined as "giving live birth", but some animals merely retain eggs internally with little or no passage of materials between mother and embryo; this is oviviparity.

voucher specimen - Statements in the literature that are based on physical evidence need to be backed up by permanent preservation of that evidence. Materials preserved to vouch for the accuracy of such statements are understandably called "vouchers".

Wisconsin Age - The last age of the Pleistocene, running from about 120,000 to 10,000 BP.

zygapophysis - Paired vertebral processes that form connections between the vertebrae dorsal to the spinal canal. The articular surfaces of the anterior pair (prezygopophyses) slant upward and somewhat inward; those of the posterior pair (postzygopophyses) downward and outward.

zygomatic breadth - Greatest distance across zygomatic arches of cranium at right angles to the long axis of skull.

abdomen - The ventral part of the body between the thorax and the pelvis.


Last Update: 27 Jan 2008

Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso