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Tail

A tail is a flexible, elongated appendage extending from the posterior end of an animal's body, typically serving multiple adaptive functions such as balance, locomotion, and communication.^[1]^[2] In vertebrates, the tail consists primarily of caudal vertebrae—an extension of the spinal column—along with muscles, connective tissues, nerves, blood vessels, and an outer covering of skin, scales, fur, or feathers, but lacks internal organs.^[3]^[4] This structure varies widely across species, from the short, vestigial tails in humans (manifesting as the coccyx) to the long, prehensile tails in monkeys or the powerful, fin-like tails in fish and cetaceans.^[3]^[5] Tails have evolved diverse roles that enhance survival, including propulsion in swimming or jumping, counterbalancing during agile movements, and signaling during social interactions or mating displays.^[6]^[7] For instance, in many mammals, tails aid in thermoregulation by dispersing heat or providing insulation, while in some reptiles and amphibians, they can regenerate after loss for defense against predators.^[8]^[9] Birds often use tail feathers for steering in flight and courtship rituals, underscoring the tail's versatility as a multifunctional organ shaped by evolutionary pressures.^[5] Although not all animals possess tails—such as tailless apes or certain insects—the presence of this appendage remains a defining feature in much of the animal kingdom, influencing locomotion, behavior, and ecological niches.^[6]

Definition and Anatomy

Definition

In animals, a tail is defined as a post-anal extension of the body axis, extending posteriorly beyond the anus or cloaca.^[7] This structure is particularly prominent in vertebrates, where it typically consists of caudal vertebrae forming the primary skeletal support.^[10] The tail is distinguished from other appendages, such as limbs or antennae, by its embryonic origin from the tailbud—a specialized region of mesoderm and ectoderm at the posterior end of the embryo—rather than from lateral limb buds or anterior segmental structures.^[11] In vertebrates, this tailbud contributes to the formation of the notochord, somites, and neural tube specific to the tail region.^[12] Tails are present across various animal phyla, including chordates such as vertebrates (e.g., mammals, reptiles, and fish) and invertebrate lancelets, where the post-anal tail contains a notochord.^[12] In some arthropods, tail-like structures occur, such as the metasoma (tail) of scorpions or the abdominal tail fan of lobsters.^[13]^[14] In vertebrates, these tails generally include vertebrae and associated muscles as basic components.^[10]

Basic Structure

The tail, defined as a posterior extension of the vertebral column beyond the pelvis, exhibits a fundamental anatomical structure across vertebrates centered on the caudal vertebrae, which provide the primary skeletal support. These vertebrae are typically elongated and numerous, decreasing in size distally, and articulate via intervertebral discs or synovial joints to allow flexibility. In aquatic vertebrates like fish, the caudal vertebrae incorporate haemal arches, often termed chevrons, which form V-shaped structures on the ventral side to enclose and protect the major blood vessels (and notochord) while supporting the caudal fin.^[15]^[16] In terrestrial vertebrates, such as mammals and reptiles, the caudal vertebrae also feature haemal arches (chevrons) for similar protective roles, with the number varying widely—e.g., up to 50 in some lizards compared to 4 fused coccygeal vertebrae in humans.^[17] Muscular components form layered sheets around the caudal vertebrae, enabling movement and structural integrity. Key muscles include the intertransversarii, small paired muscles that span between adjacent transverse processes of the vertebrae, facilitating lateral flexion and stabilization of the tail. Additional musculature comprises longitudinal flexors (e.g., caudofemoralis) and extensors (e.g., longissimus caudae), which originate from the pelvic girdle and insert along the vertebral column, with their arrangement determining tail length and flexibility. Variations occur in prehensile tails, such as those in New World primates, where specialized tendons in the flexor musculature—often extrinsic tendons crossing multiple vertebral segments—enhance gripping capability by allowing precise control over tail curvature.^[18]^[19] The tail's external covering consists of skin and associated integumentary derivatives, which protect underlying tissues and vary by vertebrate group. In reptiles and fish, this includes keratinized scales for defense and hydrodynamic efficiency; in mammals, fur provides insulation; and in birds, feathers aid in aerodynamics. These coverings are anchored to the dermis, which interconnects with the muscular layer via connective tissue.^[20] Blood supply to the tail derives primarily from caudal arteries, branching from the internal iliac or median sacral arteries, forming a vascular network that parallels the vertebral column to nourish muscles and skin. Venous drainage occurs via accompanying caudal veins, often routing through renal portals in some species. Innervation stems from the coccygeal nerves, which extend from the spinal cord's caudal end, providing motor, sensory, and autonomic fibers; in many mammals, these nerves form after the spinal cord terminates, creating a structure akin to a cauda equina for distal tail control.^[21]^[22]^[23]

Functions

Locomotion and Balance

In aquatic environments, the tails of fish, particularly the caudal fin, serve as primary propulsors by generating thrust through oscillatory movements that create undulatory waves along the body. This mechanism propels the fish forward by accelerating water rearward, with the fin's shape and flexibility optimizing efficiency and speed; for instance, in species like tuna, a streamlined, crescent-shaped caudal fin minimizes drag while maximizing forward momentum.^[24]^[25] The active control over fin bending and area during these motions allows precise adjustment of propulsion force, enabling bursts of acceleration or sustained cruising.^[24] Among terrestrial mammals, tails contribute to propulsion and stability during specialized gaits, such as the pentapedal locomotion observed in kangaroos during slow hopping or walking. The kangaroo's muscular tail acts not only as a counterbalance to prevent forward pitching but also generates significant propulsive force—equivalent to that of a hindlimb—by pushing against the ground, enhancing stride length and energy efficiency in forward movement.^[26]^[27] This dual role transforms the tail into a dynamic fifth limb, conserving momentum during the airborne phase of hops and facilitating rapid directional changes without compromising speed.^[26] Tails also play crucial roles in balance mechanisms across diverse taxa, functioning as counterweights or aerodynamic stabilizers. In cats, the tail adjusts angular momentum during mid-air falls by counter-rotating opposite to the body's twist, aiding in righting reflexes and stable landing; electromyographic studies show coordinated tail muscle activation that fine-tunes equilibrium when the center of mass shifts.^[28]^[29] Similarly, in birds, the tail acts as a rudder during flight, providing yaw control by deflecting airflow to initiate turns and maintain stability, particularly at low speeds where wing adjustments alone are insufficient.^[30]^[31] Biomechanically, tails leverage principles of momentum conservation and torque generation to enhance jumping and maneuvering. In small mammals like kangaroo rats, the tail swings to redistribute angular momentum during evasive leaps, reorienting the body mid-jump for precise landings and predator avoidance, with the rate of change in the tail's angular momentum showing a strong correlation (R ≈ 0.60) to that of the body, significantly contributing to reorientation.^[32] This inertial appendage effect exploits the tail's mass distribution to create counter-torques, allowing efficient leverage without additional limb effort; in cheetahs, rapid tail swings during high-speed turns conserve linear momentum while redirecting the body axis through aerodynamic and inertial forces.^[33]^[34] Such adaptations underscore the tail's role in optimizing energy transfer and stability across dynamic locomotor demands.

Sensory and Defensive Roles

Tails in various animals serve critical sensory functions, enabling the detection of environmental cues essential for survival. In lizards, cutaneous sensilla on the tail act as multimodal sensory structures, primarily mechanoreceptors but also capable of chemoreception to perceive chemical signals from the surroundings, such as pheromones or prey scents.^[35] This sensory capability allows lizards to assess threats or resources without relying solely on head-based organs like the vomeronasal system. In weakly electric fish, such as those in the Gymnotiformes order, the tail plays a key role in active electroreception; by bending the tail, these fish modulate their electric organ discharge to enhance the resolution of electric images from nearby objects, aiding in prey detection and navigation in murky waters.^[36] Defensive roles of tails often involve adaptations for evasion or counterattack, prioritizing predator distraction or incapacitation over locomotion. Caudal autotomy in lizards exemplifies this, where specialized fracture planes in the tail's vertebrae and connective tissues allow voluntary detachment under predation pressure, enabling escape while the wriggling tail diverts the attacker's attention.^[37] The regenerated tail, though structurally different, restores much of this defensive utility. In scorpions, the tail's telson—a bulbous vesicle housing paired venom glands connected to a curved aculeus stinger—facilitates precise venom injection for subduing prey or deterring threats, with muscle contractions forcing toxin delivery through a narrow duct.^[38] Salamanders employ tail autotomy similarly for distraction, where the severed tail continues autonomous movement for several minutes, drawing predator focus and allowing the body to flee; experimental tests with predators like chickens demonstrated that detached tails were attacked in over 90% of encounters, confirming their effectiveness in reducing capture rates.^[39] Among insects, certain species evolve tail-like abdominal extensions or patterns mimicking heads—known as false head displays—to mislead predators; for instance, the spicebush swallowtail caterpillar (Papilio troilus) positions its enlarged, eye-spotted rear end upward to imitate a snake's head, prompting attacks on the non-vital tail region instead of the vulnerable anterior.^[40] Hairstreak butterflies (Lycaenidae) extend this strategy to hindwing tails adorned with antenna-like markings, deflecting strikes toward expendable structures.^[41] These adaptations highlight tails as versatile tools for sensory vigilance and defensive deception across taxa.

Reproduction and Communication

In male sharks and other chondrichthyan fishes, the tail region contributes to reproduction through specialized structures known as claspers, which are extensions of the pelvic fins used to transfer sperm during internal fertilization.^[42] These claspers, located near the base of the tail, insert into the female's cloaca to facilitate mating, ensuring efficient sperm delivery in aquatic environments.^[43] In many insect species, the tail serves as the site for an ovipositor, a specialized appendage that enables precise egg-laying into substrates such as plant tissues or soil.^[44] This structure, formed from modified abdominal segments at the posterior end, allows females to deposit eggs in protected locations, enhancing offspring survival by avoiding predation and environmental hazards.^[45] Peacocks (Pavo cristatus) employ elaborate tail displays during courtship, fanning and shaking their iridescent train feathers to attract females.^[46] These displays signal male quality through biomechanical efficiency and visual appeal, with females preferentially responding to males exhibiting vigorous tail shaking that highlights eyespot patterns.^[47] Tail movements in dogs (Canis familiaris) convey emotional states, with wagging patterns indicating positive or negative valence based on direction and amplitude.^[48] Rightward-biased wagging typically signals approach-oriented emotions like happiness or anticipation, while leftward wagging correlates with withdrawal-oriented states such as fear or aggression, influencing social interactions with conspecifics and humans. Certain rodents, such as the hispid cotton rat (Sigmodon hispidus), possess perineal scent glands located under the tail base that produce pheromones for chemical communication during social and reproductive contexts.^[49] These glands secrete volatile compounds that males deposit via tail dragging or direct contact, signaling dominance, territory, or mating readiness to females and rivals.^[50] In primates like rhesus macaques (Macaca mulatta), tail posture serves as a visual indicator of social hierarchy, with dominant individuals often carrying their tails in a raised or arched position to assert status during group interactions. Subordinate males, in contrast, adopt lowered or tucked tail carriages, which can reduce aggression and facilitate peaceful resolution of dominance disputes within troops.^[51]

Tails Across Animal Groups

In Vertebrates

In vertebrates, tails exhibit diverse adaptations across major classes, reflecting evolutionary pressures for locomotion, stability, and environmental interaction. These structures typically consist of a series of caudal vertebrae extending from the vertebral column, often modified by surrounding musculature, fins, or feathers to fulfill specialized roles. While sharing a common axial origin, vertebrate tails diverge significantly in form and function among fish, amphibians, reptiles, birds, and mammals. In fish, the tail fin, or caudal fin, serves as the primary propulsor, with two main types distinguished by their asymmetry and hydrodynamic properties. Heterocercal tails, characteristic of primitive species such as sharks and sturgeons, feature an asymmetrical structure where the upper lobe is larger and extends from the upturned notochord, generating both thrust and upward lift to counteract the body's tendency to sink.^[52] In contrast, homocercal tails, prevalent in most bony fish like teleosts, are symmetrical with the vertebral column terminating at the fin's center, producing efficient forward propulsion through lateral oscillations while minimizing lift to maintain neutral buoyancy.^[53] This distinction arises developmentally from differential Hox gene expression, which patterns the notochord's extension and fin lobe growth.^[53] Amphibians demonstrate remarkable regenerative capabilities in their tails, particularly in urodele species like salamanders. When a tail is amputated, salamanders such as the axolotl (Ambystoma mexicanum) can fully regenerate the lost portion, including vertebrae, spinal cord, muscles, and skin, through the formation of a blastema—a mass of dedifferentiated cells that proliferates and redifferentiates into organized tissues.^[54] This process restores not only structural integrity but also functional components like sensory nerves, occurring repeatedly throughout the animal's life without scarring, unlike in higher vertebrates.^[55] Regeneration efficiency varies by species and age, with larval stages often achieving higher fidelity than adults.^[56] Reptiles exhibit tails adapted for grasping and support in arboreal habitats, as seen in chameleons. The prehensile tail of chameleons (family Chamaeleonidae) is a muscular, curling appendage with elongated caudal vertebrae and specialized musculature that enables it to grasp branches firmly, functioning as a fifth limb during locomotion and feeding.^[57] This adaptation features increased vertebral length and process area to accommodate robust flexor and extensor muscles, allowing precise control for anchoring in complex foliage without relying solely on limbs.^[58] Such tails enhance stability in three-dimensional environments, aiding balance during slow, deliberate movements.^[59] In birds, the tail is highly modified for aerodynamic control, with the pygostyle serving as a key skeletal fusion. The pygostyle forms by the coalescence of the terminal 5–6 caudal vertebrae into a single, triangular bone, providing a rigid anchor for tail feathers (rectrices) and associated muscles that manipulate the tail fan during flight.^[60] This structure supports steering, braking, and stabilization by adjusting feather spread and angle, with pygostyle morphology correlating to tail fan shape—such as forked or graduated—for species-specific flight demands.^[61] In diving birds, the pygostyle evolves an elongated form to streamline the tail against water resistance.^[60] Mammalian tails vary widely, from aquatic propulsion aids to manipulative tools. In cetaceans like whales, the tail culminates in horizontal flukes—broad, flattened lobes supported by fibrous connective tissue rather than vertebrae—driven by powerful caudal muscles to generate thrust through up-and-down oscillations perpendicular to the body axis.^[62] This design maximizes hydrodynamic efficiency in water, with fluke shape and size scaled to body mass for sustained swimming speeds.^[63] Among primates, prehensile tails have evolved independently in New World monkeys, such as spider monkeys (Ateles spp.), where the elongated, hairless tail tip acts as a grasping organ with tactile pads, facilitating suspension and object manipulation in arboreal settings.^[64] This trait enhances foraging reach and balance, originating from modifications in caudal vertebral flexibility and musculature.^[65]

In Invertebrates

Invertebrates lack a notochord or vertebral column, distinguishing their tail-like appendages from the endoskeletal tails of vertebrates, which provide internal support for elongation and flexibility.^[66] Instead, invertebrate analogs often rely on exoskeletal, segmented, or muscular structures for similar roles in locomotion, sensing, or defense. In arthropods, the telson serves as a prominent tail-like structure, particularly in scorpions, where it forms the terminal segment of the metasoma equipped with a venomous stinger for predation and defense.^[67] The telson consists of a bulbous vesicle housing venom glands and an aculeus, a curved tip that delivers the sting, with its original mechanical function aiding in prey capture before venom evolution.^[68] In insects, cerci function as paired sensory appendages at the abdominal tip, detecting air currents, vibrations, and wind to monitor environmental threats and facilitate escape responses.^[69] These cerci vary in form, from filiform in crickets for mechanoreception to pincer-like in earwigs for defense, emphasizing their role in sensory feedback rather than propulsion.^[70] Among mollusks, cephalopods exhibit tail-like features through fins and the siphon, adaptations of the foot that enable jet propulsion and maneuvering in aquatic environments. In squid, paired fins at the posterior mantle end act as stabilizers and propulsors, undulating to generate thrust similar to a vertebrate tail during cruising.^[71] The siphon, a muscular funnel derived from the foot, expels water for rapid escape, mimicking tail-driven swimming but powered by hydrostatic pressure.^[72] Larval stages of certain squid families, such as Chiroteuthidae, develop elongated tails supported by the gladius, an internal chitinous rod, which aids in buoyancy and dispersal before resorption in juveniles.^[73] Annelids, as segmented worms, utilize their posterior segments for burrowing and locomotion without a centralized tail, relying instead on peristaltic waves and setae for anchoring. In polychaetes, the pygidium—the terminal segment—bears cirri that stabilize the body during substrate penetration, facilitating burrow extension through fracture in soft sediments.^[74] These posterior structures contract to apply radial forces, enabling efficient progression in marine muds, as seen in early Cambrian fossils evidencing primitive burrowing behaviors.^[75] Unlike vertebrate tails, annelid segments lack rigid support, depending on coelomic fluid for hydrostatic leverage.

Human Tails

Embryological Development

During the gastrulation phase of human embryonic development, approximately in the third week post-fertilization, the tail bud emerges as a caudal extension of the primitive streak within the caudal eminence. This structure, composed of multipotent mesenchyme, facilitates the caudal extension of the body axis by generating key components such as the notochord, somites, and neural tube, which collectively form the foundational elements of the tail.^[76] The tail bud's formation involves the ingression of cells through the primitive streak, leading to the differentiation of paraxial mesoderm into somites that segment the future vertebral column, while the neural plate folds to create the caudal neural tube.^[77] In human embryos, somitogenesis proceeds at a rate of approximately one somite every 7 hours, contrasting with faster cycles in model organisms like mice, and supports the initial growth of a tail containing 10-12 caudal vertebrae by the fifth to sixth week.^[77] As development progresses into the fourth to eighth weeks (Carnegie stages 12-23), the embryonic tail reaches its maximum relative length before undergoing programmed regression. This process involves apoptosis of caudal tissues, resorption of the tail bud mesenchyme, and fusion of the distal vertebrae, resulting in the external disappearance of the tail by around 8 weeks of gestation. The remnant caudal vertebrae fuse to form the coccyx, a small triangular bone at the base of the spine serving as an attachment site for ligaments and muscles.^[78] Unlike in many other vertebrates where tails persist, human tail regression entails the complete loss of somites, notochord, and neural elements in the distal region, terminating axial elongation.^[77] Genetic regulation of tail development and regression is mediated by Hox genes, particularly the posterior paralogs (Hox9 through Hox13), which exhibit collinear expression along the anterior-posterior axis to control somite formation, vertebral identity, and the transition from trunk to tail structures. In human embryos, activation of these Hox genes in the tail bud correlates with the modulation of axial growth rates and the eventual cessation of elongation, influencing tail length in a conserved manner across vertebrate species. Additionally, a 2024 study identified an Alu element insertion in the genome of the hominoid ancestor that may have contributed to the evolutionary loss of tails in humans and apes.^[79]^[80] Disruptions in this genetic cascade or in regression mechanisms can lead to rare congenital anomalies, such as true human tails, which arise from incomplete resorption of the embryonic tail's distal end and may include vestigial vertebrae, neural tissue, or adipose-covered appendages protruding from the lumbosacral region.^[78] These true tails, distinct from pseudotails formed by shifted tissues, are extremely rare, with approximately 40-60 well-documented cases reported in the medical literature as of 2025 and often require surgical excision due to associated risks like spinal dysraphism.^[81]

Vestigial and Pseudotails

Human vestigial tails, also known as true tails, are rare congenital anomalies characterized by skin-covered protrusions extending from the lumbosacral region, containing adipose tissue, muscle, connective tissue, blood vessels, and nerve fibers.^[82] These structures arise as remnants of the embryonic tail bud and are typically benign, presenting at birth or shortly thereafter without functional purpose in humans.^[83] Surgical excision is the standard treatment, often performed in infancy to address cosmetic concerns and prevent potential complications such as infection or trauma.^[84] In contrast, pseudotails represent non-vestigial appendages that mimic true tails but result from underlying pathologies, such as spinal deformities, lipomas, teratomas, or prolongations of the coccygeal vertebrae.^[85] These are frequently associated with occult spinal dysraphism, including spina bifida occulta, which can lead to neurological deficits like neurogenic bladder or lower limb weakness if untreated.^[86] Unlike true tails, pseudotails require thorough preoperative imaging, such as MRI, to identify and address the associated spinal anomalies before removal.^[87] Reports of human tails date back to the 19th century, with early medical literature documenting cases as early as 1859, often sensationalized in popular accounts but analyzed pathologically in journals. A 1985 review identified 33 cases of true tails up to 1982, and subsequent reports have documented additional cases, with approximately 40-60 well-documented instances of true tails in the medical literature as of 2025, though underreporting due to social stigma may occur.^[88]^[87] Contemporary cases, such as those in newborns from diverse regions including Ethiopia and India, continue to highlight the anomaly’s rarity and the need for multidisciplinary evaluation.^[89] Surgical removal of both true and pseudotails is generally straightforward and low-risk when performed by pediatric surgeons or neurosurgeons, involving simple excision under general anesthesia with excellent cosmetic outcomes.^[90] However, ethical considerations arise, particularly for true tails, where removal is often elective for psychosocial reasons amid cultural stigma, raising questions about bodily autonomy and the medicalization of benign variations in children.^[81] For pseudotails, intervention is more urgent to mitigate neurological risks, but informed consent must emphasize the distinction from cosmetic procedures to avoid unnecessary surgeries.^[91]

Evolution and Development

Evolutionary Origins

The post-anal tail emerged as a key synapomorphy defining the phylum Chordata, alongside features such as the notochord, dorsal hollow nerve cord, pharyngeal slits, and endostyle, enabling efficient locomotion in early chordate ancestors through undulatory swimming.^[92] This structure, extending beyond the anus and containing segments of the notochord and nerve cord, first appeared in primitive chordates around 508 million years ago during the Cambrian period, facilitating propulsion in aquatic environments.^[93] Fossil evidence from the Burgess Shale, including the soft-bodied Pikaia gracilens, reveals a slender, eel-like body with chevron-shaped myomeres, supporting its interpretation as a basal chordate that used tail beating for swimming.^[94] Throughout vertebrate evolution, tails diversified through adaptive radiations, particularly during transitions from aquatic to terrestrial habitats in the Devonian period, where early tetrapods like Acanthostega retained finned tails for underwater propulsion while developing limbs for land.^[95] In Mesozoic archosaurs, tails underwent notable elaborations; for instance, early pterosaurs evolved long, stiff tails reinforced by elongated chevrons and possibly vaned structures for aerodynamic control and balance during flight initiation.^[96] Theropod dinosaurs, ancestral to birds, featured robust, muscular tails that provided counterbalance for bipedal locomotion and later stiffened into aerodynamic surfaces in maniraptoran lineages, enhancing agility before reduction.^[97] Conversely, tails were lost or reduced in certain lineages, reflecting adaptations to specific ecologies; in anurans (frogs), tadpoles possess functional tails for aquatic swimming, but adults resorb them during metamorphosis to support jumping on land, a trait linked to the evolution of the rigid urostyle.^[98] Similarly, hominoids including humans evolved tail loss, retaining only a vestigial coccyx, which coincided with shifts toward bipedalism and arboreal lifestyles in the Miocene.^[80] These patterns highlight tails' versatility, with losses in terrestrial specialists contrasting elaborations in aerial and aquatic forms, as seen in modern vertebrates like cetaceans.^[5]

Genetic and Developmental Mechanisms

The development of the vertebrate tail begins with the formation of the tail bud, a post-anal extension of the embryo that generates the posterior body axis, including the notochord, somites, and neural tube in the tail region.^[11] This structure arises through convergent extension and cell migration during gastrulation, where mesodermal progenitors ingress and elongate the axis.^[99] Key transcription factors orchestrate these processes, with T-box family genes playing a central role in specifying tail bud mesoderm and maintaining progenitor pools. T-box genes, such as Brachyury (T, or its zebrafish ortholog no tail [ntl]) and spadetail (spt, or Tbx16), are essential for tail bud formation and the differentiation of trunk and tail mesoderm, including the notochord and medial floor plate.^[100] In zebrafish embryos, ntl and spt mutants exhibit severe defects in posterior mesoderm formation, resulting in truncated tails due to impaired cell movements and failure to generate somites and ventral structures.^[100] These genes directly regulate targets like deltaD, a Notch ligand critical for initiating the segmentation clock in the tail bud presomitic mesoderm, ensuring oscillatory gene expression that patterns somites.^[101] Additionally, T-box factors promote neuromesodermal progenitor (NMP) maintenance in the tail bud, balancing differentiation into neural and mesodermal lineages through interactions with FGF and Wnt signaling pathways.^[102] Hox genes, particularly posterior paralogs (Hox9–13), exhibit collinear expression along the anterior-posterior axis and are crucial for tail vertebral identity and elongation dynamics.^[103] In chicken embryos, activation of these posterior Hox genes in the tail bud represses Wnt/β-catenin signaling via direct transcriptional inhibition of Wnt ligands and enhancers, which slows axial elongation and transitions the embryo from trunk to tail formation.^[79] This repression mechanism ensures timely termination of the body axis, as sustained Wnt activity would prolong elongation. Hox genes also specify regional vertebral morphology in the tail; for instance, Hox13 paralogs pattern the most posterior caudal vertebrae, influencing features like centrum shape and neural arch development.^[103] Mutations in Hoxb13, a posterior Hox gene, lead to overgrowth of the caudal spinal cord and abnormal tail vertebrae in mice, highlighting its role in limiting posterior expansion.^[104] Retinoic acid (RA) signaling integrates with Hox and T-box networks to modulate tail development, often acting as a posteriorizing cue that refines Hox expression gradients.^[102] In multi-omics studies of mouse tail buds, RA-responsive genes overlap with those regulating vertebral elongation, influencing differential growth rates between cervical and caudal regions through epigenetic modifications like histone acetylation.^[105] Collectively, these genetic mechanisms form a conserved gene regulatory network (GRN) across vertebrates, where T-box genes initiate tail bud competence, Hox clusters assign positional identity, and signaling modulators like Wnt and RA fine-tune growth and patterning to produce diverse tail morphologies.^[102]

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High aerodynamic lift from the tail reduces drag in gliding raptors
Feb 10, 2020 · Conventional aircraft tails act as rudders, elevators and stabilizers, providing moments about the centre of mass to initiate and maintain turns ...
[32]
How to Stick the Landing: Kangaroo Rats Use Their Tails to Reorient ...
Sep 21, 2021 · To examine the effect of tail motion on body re-orientation during a jump, we compared average rate of change in angular momentum. Rate of ...
[33]
Rapid turning at high-speed: Inspirations from the cheetah's tail
The mathematic model for a high-speed turn is derived and the model with a tail is shown to be more successful at rapid turns in simulation, and by rapidly ...<|control11|><|separator|>
[34]
Jointed tails enhance control of three-dimensional body rotation - PMC
Feb 5, 2025 · Tails used as inertial appendages induce body rotations of animals and robots—a phenomenon that is governed largely by the ratio of the body and ...
[35]
Cutaneous tactile sensitivity before and after tail loss and ...
Summary: Tactile sensitivity of the feet and tail in a species of lizard changes in response to tail loss and regeneration.
[36]
Electrolocation based on tail-bending movements in weakly electric ...
Jul 15, 2011 · Several studies have examined how electric fish identify objects with their electroreceptors and use electric images for electrolocation. It has ...
[37]
Unique Structural Features Facilitate Lizard Tail Autotomy - PubMed
Autotomy refers to the voluntary shedding of a body part; a renowned example is tail loss among lizards as a response to attempted predation.
[38]
Re-regeneration to reduce negative effects associated with tail loss ...
Dec 10, 2019 · Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective ...
[39]
The venom gland of the scorpion species Euscorpius mingrelicus ...
The telson, situated at the end of the metasoma, is a bulb-shaped structure that contains the venom glands and a sharp, curved stinger to deliver venom. The ...<|separator|>
[40]
Anti-Predator Effectiveness of Autotomized Tails of the Salamander ...
ABSTRACT: Seven chickens induced autotomy of 84.2% of Desmognathus ochrophaeus tails in the first 20 tests of each bird. The frequency of salamander tail ...<|separator|>
[41]
Meet the fakers of nature | BBC Earth
Named after English naturalist Henry Walter Bates, this is a form of mimicry in which a harmless species evolves to mimic the warning signs of a harmful species ...
[42]
Mimicry in the Wild | North Dakota Game and Fish
By doing this, they can trick predators into going for their tails rather their heads and avoid fatal attacks. Hairstreak butterflies also present this type of ...
[43]
Molecular development of chondrichthyan claspers and the ... - NIH
Apr 14, 2015 · Claspers in chondrichthyans are specialized elongations on the posterior side of male pelvic fins that are used for sperm transfer during ...
[44]
Shark Biology – Discover Fishes - Florida Museum of Natural History
Jun 2, 2025 · All sharks have internal fertilization. Then, the male inserts a clasper into the female's cloaca and releases sperm. Depending on species, ...Missing: roles | Show results with:roles
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Research Progress on Oviposition-Related Genes in Insects - NIH
Dec 25, 2020 · Most kinds of insects reproduce via oviposition, which includes the two stages of egg laying and egg hatching (Fig. 1). When a female finds ...
[46]
Oviposition Strategies in Beneficial Insects - PMC - NIH
Jul 25, 2018 · Oviposition strategies in beneficial insects involve chemical/physical cues, natural products, site selection, plant defenses, and egg laying ...
[47]
Biomechanics of the Peacock's Display: How Feather Structure and ...
Apr 27, 2016 · Courtship displays may serve as signals of the quality of motor performance, but little is known about the underlying biomechanics that ...
[48]
Peacocks maximize tail shimmer - Nature
May 4, 2016 · During their elaborate courtship displays, peacocks shake their iridescent tail feathers in an energetically efficient manner.
[49]
Left-right asymmetry and attractor-like dynamics of dog's tail ...
Aug 19, 2022 · Previous studies revealed that tail wagging was associated with a dog's inner state, related to the emotional state in humans, and conveyed ...
[50]
[PDF] Reproductive Correlates of a Perineal Gland in the Hispid Cotton Rat
During the breeding season, the adult male cotton rat possesses a large perineal gland (Fig. 1) located dorsal to the testes, under the tail, and just anterior ...
[51]
The Role of Pheromonal Responses in Rodent Behavior - NIH
Pheromones released from the whisker area of the rat significantly reduced resting time but increased sniffing, walking, and rearing. Reprinted from reference ...
[52]
Function of the Caudal Fin During Locomotion in Fishes
The sturgeon tail does not function according to the classical model of the heterocercal tail, and is hypothe- sized to generate reactive forces oriented near ...
[53]
Hox genes control homocercal caudal fin development and evolution
Jan 19, 2024 · Thus, the main difference between heterocercal and homocercal tails in development and evolution lies in the organization and extension of the ...
[54]
Salamanders: The molecular basis of tissue regeneration and its ...
Salamanders can regenerate a broad range of tissues, including limbs, parts of the brain and heart, and complex neural tissue, unlike humans.
[55]
The evolutionary origin and mechanism of chordate tail regeneration ...
Dec 18, 2024 · Salamanders such as the axolotl can regenerate their tail and re-establish segmented muscle and vertebrae (Vincent et al., 2015; Masselink et al ...
[56]
Tail regeneration at different ontogenetic stages of the tiger ...
Oct 13, 2023 · Contrary to lizards, salamanders can fully restore their tails, including the neural spine and components of the vertebral column. The axolotl ( ...INTRODUCTION · METHODS · DISCUSSION · CONCLUSION
[57]
Is variation in tail vertebral morphology linked to habitat ... - PubMed
The longer tails of prehensile species have more vertebrae as well as an increased length of the processes, likely providing a greater area for muscle ...
[58]
[PDF] Prehensile tail use chameleons - bioRxiv
Aug 24, 2020 · Chameleons are well-equipped for an arboreal lifestyle, having zygodactylous hands and feet as. 17 well as a fully prehensile tail.
[59]
[PDF] The Biology of Chameleons - ResearchGate
Mar 10, 2013 · This is particularly true in their highly prehensile tail, which they are able to curl tightly under their body. Various works have been done on ...<|separator|>
[60]
Coevolution of caudal skeleton and tail feathers in birds - PubMed
Aug 20, 2014 · Pygostyle shape is found to be a good predictor of tail fan shape (e.g., forked, graduated), supporting the hypothesis that the tail fan and the ...
[61]
[PDF] Coevolution of Caudal Skeleton and Tail Feathers in Birds
Aug 20, 2014 · For example, birds that forage underwater convergently evolve a characteristic pygostyle mor- phology, consisting of an elongate, straight shape.
[62]
Protein signaling and morphological development of the tail fluke in ...
Mar 17, 2024 · The tail flukes of cetaceans act as a single propulsor and control surface. ... Although biologists have a thorough understanding of the anatomy ...
[63]
Whale Evolution: Dispersal by Paddle or Fluke - ScienceDirect.com
Apr 22, 2019 · The most obvious adaptations in extant whales include a streamlined body, loss of hindlimbs, and the development of a large muscular tail with a fluke that ...
[64]
Prehensile Tail - Bezanson - Major Reference Works
Apr 16, 2017 · It appears that the prehensile tail has evolved twice in these neotropical primates, once in the common ancestor of the Atelidae (Alouatta, ...
[65]
[PDF] The Evolution of the Primate Prehensile Tail - Western OJS
The evolution of the primate prehensile tail is an example of an environmental effect: the arboreal habitat guided a pre-existing trait to take on alternative ...
[66]
34.4: Vertebrate Chordates - Biology LibreTexts
Dec 4, 2021 · Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column. The dorsal hollow nerve cord ...
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The coevolution between telson morphology and venom glands in ...
Oct 9, 2020 · Conclusions. The original function of the telson in scorpions was most certainly mechanical playing a major role in predation. In this case, ...
[68]
A Silurian ancestral scorpion with fossilised internal anatomy ...
Jan 16, 2020 · A telson bearing an expanded area for a poison vesicle and a stinger is an apomorphous condition for scorpions. The holotype of P. venator ...
[69]
Cercus - an overview | ScienceDirect Topics
The cercal system of insects is responsible for the detection and monitoring of wind currents on the body surface.
[70]
Cerci - Entomologists' glossary
Cerci perform a sensory function. The size of cerci varies between species with some having barely discernible cerci while others, like earwigs, having stout ...
[71]
the Fast Swimmers - Squids, Octopuses and Cuttlefish (Cephalopoda)
A squid's rear body is shaped like a torpedo. At its tail end there are two larger or smaller fins serving for locomotion and changing its direction. Mainly ...
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Functional Histology: The Tissues of Common Coleoid Cephalopods
Mar 8, 2019 · The siphon or funnel is a foot-derived muscular organ that projects from the margin of the mantle between the ventral mantle corners into a ...
[73]
'Tailed' cephalopods | Journal of Molluscan Studies - Oxford Academic
Feb 1, 2015 · For example, larval and early juvenile squid of the family Chiroteuthidae form a long tail that is supported from inside by the gladius. Narrow ...
[74]
Burrowing by small polychaetes – mechanics, behavior and muscle ...
Summary: Even very small polychaetes can extend burrows through muds by fracture; helical muscles may enable worms to apply larger radial forces,
[75]
A burrowing annelid from the early Cambrian - PMC - NIH
Oct 9, 2024 · This first report of an annelid worm from the Xiaoshiba biota provides the earliest known plausible evidence of burrowing behaviour in Annelida.
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Development of the human tail bud and splanchnic mesenchyme
Mar 11, 2013 · The tail bud generates the tailgut, blood vessels, coelom, notochord, somites and spinal cord in human embryo (O'Rahilly and Muller 1994).
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Spinal neural tube formation and tail development in human embryos
A somite is formed every 7 hr in human, compared with 2 hr in mice and a 5 hr 'segmentation clock' in human organoids. Termination of axial elongation occurs ...
[78]
A tale of two “tails:” A curiosity revisited - PMC - NIH
This regresses by fusion of vertebrae, leaving the vestigial coccyx. The embryonic tail disappears by the 8th week; persistence may lead to formation of a true ...
[79]
Hox genes control vertebrate body elongation by collinear Wnt ...
Feb 26, 2015 · We show that in the chicken embryo, activation of posterior Hox genes (paralogs 9–13) in the tail-bud correlates with the slowing down of axis elongation.
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A rare case of lumbosacrococcygeal mass in newborn: a human tail
Nov 27, 2020 · In 1998, Lu et al. [5] suggest that the presence of a human tail is an abnormality in embryonic development, rather than a regression in the ...
[81]
Human tail in a newborn - ScienceDirect.com
True tails, also known as vestigial tails, are appendages covered by skin, that contain connective, adipose, and striated muscle tissue, as well as blood ...
[82]
Spectrum of human tails: A report of six cases - PMC - PubMed Central
A “vestigial tail” describes a remnant of a structure found in embryonic life or in ancestral forms.[4] During the 5th to 6th week of intrauterine life, the ...
[83]
Experience with Human Tail and its Outcome
A true human tail is a benign vestigial caudal cutaneous structure composed of adipose, connective tissue, muscle, vessels and nerves.
[84]
Human tails and pseudotails - ScienceDirect.com
Pseudotails are varied lesions having in common a lumbosacral protrusion and a superficial resemblance to persistent vestigial tails. The most frequent cause of ...
[85]
Does this baby have a tail?: a case of congenital isolated perineal ...
A pseudo-tail is defined as a tail-like lesion in the lumbosacrococcygeal region that is not a true tail but one caused by disease. Perineal lipoma is one of ...
[86]
Vestigial human tail and occult spinal dysraphism: A case report
Dec 6, 2024 · According to Tubbs et al.,[ 15 ], any appendages caused by regression disturbance of the embryonic tail can be classified as a true human tail.Missing: incomplete | Show results with:incomplete<|control11|><|separator|>
[87]
Case Reports The human tail - ScienceDirect.com
In 1984, Dao and Netsky [1] reviewed 33 cases of human tails from descriptions in the literature between 1859 and 1982.
[88]
Human Tail: A Benign Condition Hidden Out of Social Stigma ... - NIH
There are only 40 cases of true human tails reported in literature, hence this condition warrants review.[1] This condition usually presents in newborns ...
[89]
Human Tail in an Ethiopian Newborn: A Clinicopathologic Case ...
A feature that is still present in embryonic life or ancestral forms is known as a "vestigial tail." A tail with 10-12 vertebrae is present in the human embryo ...Missing: literature | Show results with:literature<|control11|><|separator|>
[90]
Surgical Treatment of a Patient with Human Tail and Multiple ... - NIH
Oct 18, 2010 · The authors present a case of human tail occurring in a 9-month-old infant with multiple abnormalities of the spinal cord and spine.
[91]
The human tail: rare lesion with occult spinal dysraphism—a case ...
The human tail is an ill-defined, rare, fingerlike, midline, interesting anomaly and very difficult to classify as either a true (vestigial) tail or pseudotail ...
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Evolution and Development of the Chordates - Oxford Academic
Chordates evolved a unique body plan within deuterostomes and are considered to share five morphological characters, a muscular postanal tail, a notochord, a ...Missing: primary | Show results with:primary
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A new interpretation of Pikaia reveals the origins of the chordate ...
Jul 8, 2024 · Problematic Cambrian fossils that have been considered as candidate chordates include vetulicolians, Yunnanozoon, and the iconic Pikaia.
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The Middle Cambrian fossil Pikaia and the evolution of chordate ...
Jun 13, 2012 · Pikaia does not, therefore, fit entirely comfortably with modern chordates, suggesting that it is either divergent, if it is a chordate, or is a ...
[95]
Role of the Tail or Lack Thereof in the Evolution of Tetrapod Aquatic ...
The tail took on a non-propulsive role with the development of legged locomotion on land (Inger 1962), although the tail served as the origin for some muscles ...Diversity Of Tail... · Lunate Tail · Beyond The Tail
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New soft tissue data of pterosaur tail vane reveals sophisticated ...
Oct 8, 2024 · Early pterosaurs had long stiff tails with a mobile base that could shift their center of mass, potentially benefiting flight control. These ...Missing: Mesozoic | Show results with:Mesozoic
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Shake a Tail Feather: The Evolution of the Theropod Tail into a Stiff ...
May 15, 2013 · The evolutionary reduction in theropod tail length culminated in the CFL muscle being very small or absent in extant birds. This reduction of ...
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Ontogeny of the anuran urostyle and the developmental context of ...
Jan 27, 2020 · Our study points toward an explanation for the evolution of tail loss in anurans and the development of the urostyle: During the evolution ...
[99]
On the genetic basis of tail-loss evolution in humans and apes | Nature
Feb 28, 2024 · For primates in particular, the tail is adapted to a range of environments, with implications for the style of locomotion of the animal. The New ...Missing: posture hierarchy<|separator|>
[100]
Molecular mechanisms of embryonic tail development in the self ...
Dec 24, 2021 · Collectively, these data indicate that both noto and msgn1 have crucial roles in cell movement and deposition in the tail bud, and therefore ...
[101]
The zebrafish T-box genes no tail and spadetail are required for ...
Jul 15, 2002 · The Brachyury gene is expressed in the notochord and tail bud (Herrmann et al., 1990). Similar to their mouse Brachyury mutant counterparts, ...
[102]
Identification of direct T-box target genes in the developing zebrafish ...
We also find that deltaD is directly activated by T-box factors in the tail bud, where it has been implicated in starting the segmentation clock, suggesting ...Mrna Isolation And... · Results · Spt And Ntl Bind Similar...
[103]
Future Tail Tales: A Forward-Looking, Integrative Perspective on Tail ...
There are three key GRN components known to be involved in tail development across chordates: Homeobox (Hox) and T-box transcription factor genes, as well as ...
[104]
Hox genes and the evolution of vertebrate axial morphology
Feb 1, 1995 · The link between gene expression and vertebral morphology suggests that Hox genes may have played an important role in the evolution of specific ...
[105]
Hoxb13 mutations cause overgrowth of caudal spinal cordand tail ...
The 39 vertebrate Hox genes are involved in patterning numerous axes and subaxes in the developing mouse. Numerous functions of Hox genes have been identified ...Regular Article · Results · Hoxb13 Expression And Mutant...
[106]
A combination of transcriptomics and epigenomics identifies genes ...
Mar 26, 2025 · Overall, our multi-omics analyses yield new insights into the genetic modulation of vertebrate/mammalian tail development, as a basic data ...