A marginal excavation of the temporal skull region. It is not automatically homologous to a fully bounded temporal fenestra.

A temporal skull condition lacking the characteristic temporal openings. It can be ancestral or secondarily acquired, so its occurrence does not establish one exclusive lineage.

An eye is a sensory organ that gathers optical information and converts it into neural signals. In the vertebrate eye, the cornea and crystalline lens focus light toward the retina. Image formation, sensory transduction and later visual interpretation are related but distinct stages.

A fin is a projecting locomotor or stabilizing structure in an aquatic vertebrate. Median fins lie near the midline, while paired fins occur laterally. Shape, position and internal support affect thrust, steering and stability, so not every fin has the same mechanical role.

Skeletal tissues formed in a dermal association. The name distinguishes their developmental location from the internal cartilaginous skeleton; it does not imply that every component is external to the body.

Fluid within the membranous inner ear. Temperature-dependent fluid properties motivate biomechanical proxies for extinct-animal physiology.

An inner-ear structure involved in sensing angular motion. Its dimensions are influenced by body size, movement and fluid mechanics.

A nasal structure whose functions can include conditioning respiratory air or supporting olfactory tissue. Anatomical identification and function require care in fossils.

A bone projecting anteriorly from the pelvis in several mammalian lineages. Its presence in stem eutherians must be distinguished from the crown placental condition.

An embryonic cartilaginous component of the lower-jaw region. Its persistence or removal informs models of the evolutionary jaw–ear transition.

The skull and vertebral-axis skeleton, contrasted with the girdles and appendages of the appendicular skeleton.

The skeleton of appendages and their supporting girdles.

A respiratory organ exposing a vascular exchange surface to water.

A connective-tissue structure joining skeletal components and constraining motion at a joint.

A known amount of a reference substance added to a sample to support quantification and identify losses or instrumental variation. An isotope-labeled analogue can closely track the behavior of the analyte.

A full-scale range $V_{\mathrm{FS}}$ and allowed quantization step $\Delta$ require $b\ge \lceil {\log }_2(V_{\mathrm{FS}}/\Delta )\rceil$ bits. The ideal uniform-quantizer rms error is approximately $\Delta /\sqrt{12}$. Bandwidth determines the sampling-rate requirement, but does not by itself determine a bit depth.

A number-theoretic sieve processes many integers together by marking or updating those sharing a divisor, rather than testing each integer independently. The sieve of Eratosthenes marks composite multiples of successive prime numbers; related sieves accumulate a smallest prime factor, Euler's totient function, or Möbius function for every argument up to a bound. The useful structure is that the multiples of a fixed integer form an arithmetic progression, so one loop can update all affected entries in an array.

For example, initializing an array to true and then marking $2p,3p,\dots$ for each surviving prime number $p$ leaves precisely the prime numbers unmarked, apart from the separately excluded zero and one. Every composite number has a prime factor, which proves that every composite is eventually removed. Starting the marking at $p^2$ avoids work already performed by smaller prime numbers. Different sieves use different update rules and time complexity bounds; the name alone does not imply the complexity of the sieve of Eratosthenes.

Discarding a branch of a search tree after proving that no completion can satisfy the constraints or improve the current best solution. For minimization, a lower bound on every completion justifies pruning when it is at least the best value already found; this is the principle behind branch and bound.