A protuberance is any structure that bulges, projects, or sticks out from a surface, and they show up at every scale science can measure. The bumps on a humpback whale’s flipper improve lift by roughly 40%. The bony knob on the back of your skull appears to be growing larger in younger generations. Fungal cells build tiny dome-shaped structures that generate enough pressure to punch through a leaf. From the cellular to the planetary, protuberances solve problems, create them, and occasionally mystify the researchers who study them.
The Bumps on a Whale Flipper That Changed Engineering
Humpback whales are among the most acrobatic large animals on Earth, executing tight turns and rolls despite weighing up to 40 tons. Their flippers are unusually long for a whale, and along each flipper’s leading edge sit a row of rounded bumps called tubercles. Early anatomical work proposed that these protuberances function as lift-enhancing devices, helping maintain control of water flow over the flipper at steep angles of attack, which is the sort of sharp banking a whale needs when lunging at a school of fish.
1PubMed. Hydrodynamic design of the humpback whale flipperWind tunnel tests confirmed the idea in striking fashion. When researchers added tubercle-like bumps to a scale model of an idealized whale flipper, the stall angle increased by about 40%, lift went up, and drag went down.
2Physics of Fluids. Leading-edge tubercles delay stall on humpback whale (Megaptera novaeangliae) flippersStall is the moment when airflow (or water flow) separates from a wing’s surface and lift collapses. Delaying it by 40% is a dramatic improvement, and it immediately caught the attention of engineers working on wind turbines, where blades experience constantly shifting wind speeds and angles.
Researchers applying tubercle-inspired designs to horizontal-axis wind turbine blades found that the bumps gave blades roughly 27% better performance after stall, along with smoother, more stable output at varying wind speeds. In one simulation comparison using a small turbine model, tubercle-equipped blades showed about a 30% improvement in overall efficiency.
3Journal of Engineering Research and Reports. Design and Optimisation of Horizontal Axis Wind Turbine Blades Using Biomimicry of Whale TuberclesThe underlying mechanism is relatively intuitive: each bump channels air into the valleys between bumps, creating streamwise vortices that energize the boundary layer and keep it attached to the blade surface longer. It is one of the cleaner examples of biomimicry, a case where a biological protuberance that evolved over millions of years in ocean currents translates almost directly into better hardware on land.
The Bump on the Back of Your Skull
If you reach up and feel the base of your skull where it meets your neck, you can probably detect a small bony ridge. That is the external occipital protuberance, or EOP, a normal landmark of human anatomy where neck muscles and ligaments attach. In most people, it is unremarkable. But in some, the bump grows into a pronounced bony spur, sometimes large enough to be felt through the skin or even visible as a lump.
A study of over 1,200 skull radiographs found that about a third of participants had an enlarged EOP, defined as a protuberance exceeding a threshold size. Being male increased the likelihood by more than five times, and the researchers also found that greater forward head posture was a predictor.
4Scientific Reports. Prominent exostosis projecting from the occipital squama more substantial and prevalent in young adult than older age groupsWhat attracted media attention was the age pattern: the enlarged bumps were more common in younger adults than older ones, flipping the usual assumption that bony growths accumulate with age. A separate study confirmed this skew, finding that about a quarter of participants had an enlarged EOP, with males far more likely to have one, and nearly all cases occurring in people under 30.
5PubMed Central. The influence of age, biological sex, anthropometrics, and neck characteristics on external occipital protuberance sizeThe “phone bone” narrative, which blamed smartphone use for growing skull spurs in young people, was catchy but oversimplified. Forward head posture does seem to matter. Research on occipital spurs found that people with the growths had measurably worse forward head posture on imaging, and that certain angles of cervical spine alignment were strong predictors of having a spur.
6PubMed Central. The Association of Occipital Spur with Craniocervical Posture and Craniofacial MorphologyBut the connection to device use specifically, rather than to posture in general, remains unproven. Plenty of activities promote forward head posture, from reading books to hunching over a workbench.
The clinical relevance is sometimes real. A case report of a bony tubercle projecting from the EOP noted an 8 mm long exostosis that could cause occipital headaches, with particular risk during vertical neck movements in activities like tree climbing or volleyball.
7PubMed. Bony tubercle at external occipital protuberance and prominent ridgesIn patients with cervical spine disease, severe EOP enlargement shows a male-predominant pattern and has been linked to ossification of the nuchal ligament and cervical imbalance, suggesting it could serve as a marker for biomechanical problems in the spine.
8PubMed Central. Gender-specific patterns of external occipital protuberance hyperplasia: associations with nuchal ligament ossification and cervical sagittal imbalance in myelopathy patientsWhy Humans Have Chins
Modern humans are the only living primates with a chin, that forward-projecting shelf of bone at the bottom of the jaw. It is arguably the most debated protuberance in physical anthropology, because no one is entirely sure why it exists. Every other primate, and every earlier hominin species, lacks it.
The leading mechanical hypothesis is that the chin evolved to resist certain bending forces on the jaw during chewing. Finite element analysis shows that the presence of a chin lowers overall strain on the jaw during loading, and that a vertically oriented jaw without a chin experiences higher strain during a specific sideways-pulling force called wishboning.
9American Journal of Physical Anthropology. Why Do Humans Have Chins? Testing the Mechanical Significance of Modern Human Symphyseal Morphology With Finite Element AnalysisThis supports the idea that the relative importance of different chewing forces shaped the evolution of the modern human jaw.
But the story is not clean. An ontogenetic study tracking how chins develop as children grow found that increasing chin prominence did not come with increasing resistance to vertical bending. In other words, the chin gets more prominent as children age, but it does not seem to make the jaw structurally stronger in the most straightforward way you would expect if strength were the whole point.
10PubMed Central. The ontogeny of the chin: an analysis of allometric and biomechanical scalingAn alternative proposal sidesteps biomechanics entirely. One hypothesis argues that the chin evolved because bipedal humans, with their hands occupied carrying objects against their bodies, used the chin to clamp and stabilize items, freeing the hands for other tasks. The idea draws on observations of people from different cultures using their chins this way and connects it to the broader evolutionary trajectory of bipedalism and manual dexterity.
11Acta Zoologica. Chin up: A novel functional explanation for the evolution of the chinWhether this explanation gains traction remains to be seen. The chin remains a genuinely open question in human evolution, a bony protuberance whose purpose may involve some combination of jaw mechanics, facial development, and possibly functions no one has tested yet.
How Plants Build Prickles and Thorns
The spines and prickles on roses, cacti, and citrus trees are among the most familiar protuberances in everyday life, and they turn out to be more biologically interesting than they look. A common assumption has been that rose prickles are modified trichomes, the tiny hair-like structures that cover many plant surfaces. Detailed morphological work overturned this. Researchers showed that both glandular and non-glandular prickles in roses originate from multiple cells of the ground meristem beneath the outer skin of the stem, not from the outer layer itself. Prickles are therefore not enlarged hairs; they are a distinct type of outgrowth with a different developmental origin.
12PubMed Central. Morphological studies of rose prickles provide new insightsWhat controls whether a plant produces prickles or not? Genetic work in Sichuan pepper (Zanthoxylum armatum), a spiny shrub used in cooking, found that prickle formation involves a complex interplay of plant hormones and gene regulation. Prickly plants had higher levels of cytokinin and auxin and lower levels of other hormones compared to prickleless relatives. A suite of transcription factors, along with epigenetic modifications like DNA methylation and histone acetylation, appear to regulate whether prickle development switches on.
13PubMed. Comparative transcriptome analysis reveals hormone, transcriptional and epigenetic regulation involved in prickle formation in Zanthoxylum armatumOne of the more striking findings in this field is that prickles and chemical defenses appear to trade off against each other. In tropical soda apple (Solanum viarum), a prickleless mutant compensated for the loss of its physical protuberances by ramping up production of secondary metabolites like phenolics, flavonoids, and alkaloids in its skin tissues. The plant essentially swapped one defense strategy for another, suggesting that prickle development and chemical warfare draw on overlapping cellular resources.
14Scientific Reports. Transcriptome analysis provides insight into prickle development and its link to defense and secondary metabolism in Solanum viarum DunalSolar Prominences and Space Weather
In astrophysics, “protuberance” was historically the standard term for what are now called solar prominences: massive arcs and curtains of plasma that extend outward from the Sun’s surface, sometimes stretching hundreds of thousands of kilometers into space. Visible as bright loops during a total eclipse, these structures are suspended by magnetic fields and are far cooler and denser than the surrounding corona.
Computer simulations have reproduced how these structures form. In one approach, researchers built a magnetic flux rope in equilibrium, added a realistic atmosphere, then applied heating at the base. Plasma evaporated from the lower atmosphere, rose along the magnetic field lines, and condensed into fragmented, highly dynamic blobs and threads that continuously formed and reformed, with material constantly being replenished from below. A different simulation produced a prominence inside a helmet streamer through a runaway cooling instability, in which the prominence’s own weight dragged the magnetic field downward into a significantly distorted configuration.
15PubMed Central. Solar prominences: theory and models: Fleshing out the magnetic skeletonWhen prominences erupt, the consequences can be dramatic. A statistical study of prominence eruptions using microwave observations found that about 72% were clearly associated with coronal mass ejections, the massive bursts of solar wind that can disrupt satellites and power grids on Earth. The eruptions and the mass ejections appeared to start at roughly the same time, with a solar-cycle-dependent spatial relationship: during solar minimum, the mass ejection tended to be offset toward the equator relative to the eruption.
16The Astrophysical Journal. Prominence Eruptions and Coronal Mass Ejection: A Statistical Study Using Microwave ObservationsEruptive prominences are also more strongly linked to mass ejections than merely active ones, and the ejections they trigger tend to have visible cores in white-light imagery.
17The Astrophysical Journal. Active and Eruptive Prominences and Their Relationship to Coronal Mass EjectionsProminence eruptions are not limited to the Sun. Observations of M dwarf stars, the most common type of star in the galaxy, have captured simultaneous prominence eruptions and white-light flares, providing constraints on magnetic reconnection and mass ejection in low-mass stars. These events have implications for the space-weather environments of close-in exoplanets orbiting such stars.
18Astronomy & Astrophysics. A stellar prominence eruption associated with a white-light flare on an M dwarf observed simultaneously by LAMOST and TESSModeling suggests that Earth-like planets in the habitable zones of M dwarfs, which sit much closer to their stars than Earth does to the Sun, would experience continuous bombardment by coronal mass ejections. Combined with weak magnetic fields expected from tidal locking, such planets could have their protective magnetospheres compressed to within about a thousand kilometers of the surface, leaving their atmospheres vulnerable to erosion.
19PubMed. Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. I. CME impact on expected magnetospheres of Earth-like exoplanets in close-in habitable zonesCellular Protrusions and How Cells Move
At the microscopic scale, protuberances are how cells explore and move through their environment. Filopodia, thin finger-like projections that extend from the front edge of a moving cell, are built from bundles of actin filaments and act as sensory feelers. They probe the space ahead, make contact with surfaces or other cells, and help steer migration.
The mechanics are subtler than you might expect. Research tracking filopodia formation in real time found that actin filaments may not directly drive the protrusion outward. Instead, the cell membrane deforms first, and actin rushes in to stabilize the newly created space. Without that stabilization, efficient protrusion fails, but the filaments are playing a supporting role rather than acting as a battering ram.
20PubMed Central. Coordination of membrane and actin cytoskeleton dynamics during filopodia protrusionBundling proteins are essential for making this work. Individual actin filaments are too flimsy to push effectively. Fascin has long been recognized as the main cross-linking protein that bundles filaments into rigid rods inside filopodia, but research has shown that another protein, T-plastin, also plays a significant role in forming these protrusions.
21PubMed Central. Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and ContractionFungal Appressoria and the Pressure to Infect
Some of the most consequential protuberances in biology are invisible to the naked eye. When certain plant-pathogenic fungi land on a leaf, they germinate a spore tube that swells at its tip into a dome-shaped structure called an appressorium. This tiny protuberance is an infection tool, designed to generate enough mechanical force to physically rupture the plant’s outer cell wall.
22PubMed Central. Appressoria-Small but Incredibly Powerful Structures in Plant-Pathogen InteractionsIn the rice blast fungus Magnaporthe oryzae, one of the most destructive crop pathogens on Earth, the appressorium generates enormous internal pressure by rapidly synthesizing glycerol. A thick melanin layer on the inside of the cell wall prevents the glycerol from leaking out and provides structural rigidity. The accumulated pressure is enough to drive a narrow penetration peg through the tough cuticle of a rice leaf. For decades, melanin was assumed to be universally required for this trick. But work on a different fungus, Colletotrichum graminicola, which causes anthracnose in corn, showed that appressoria could still accumulate pressure and penetrate leaves even when melanin production was chemically blocked. Detailed measurements confirmed that melanin was not required for solute accumulation or turgor generation in that species.
23PubMed Central. Regulation of appressorium development in pathogenic fungiThe difference highlights a recurring theme with protuberances across biology: structures that look similar and serve the same function in different species do not always use the same underlying mechanism.
Horns, Frills, and Bony Armor in Animals
The most visually dramatic protuberances in the animal kingdom are skeletal: horns, antlers, ossicones (the fur-covered bumps on giraffes), and osteoderms (the bony plates embedded in the skin of armadillos and crocodilians). These structures are classified as extra-skeletal bones because they originate not from the skeleton itself but from tissues beneath the skin. During fetal development, the precursor cells arise in the subcutaneous layer, and ossification typically occurs after skeletal bone formation, sometimes depending on sexual maturity. Skin keratinization, which produces the horn sheath or velvet covering, proceeds alongside bone formation and may be regulated by androgens.
24PubMed. Formation, structure, and function of extra-skeletal bones in mammalsThe density gradients within these bony protuberances vary by species and by function. An antler tine that absorbs the shock of combat has a different internal architecture from an osteoderm that distributes the force of a predator’s bite. This structural variation is one reason paleontologists have long debated whether the elaborate horns and frills of ceratopsian dinosaurs were primarily for display, defense, or both. In Triceratops, analysis of cranial abnormalities across many specimens revealed healing fractures and reactive bone growth concentrated on the frill and around the horns, matching predictions from models of horn-to-horn combat. The pattern was not random and was most consistent with injuries inflicted by the horns of other Triceratops, suggesting that the protuberances served a real combat function alongside any role in visual signaling.
25PubMed Central. Evidence of Combat in TriceratopsSteep-Sided Domes on Venus
Even geology produces protuberances on a planetary scale. Radar mapping of Venus by the Magellan spacecraft revealed steep-sided volcanic domes, some exceeding 100 kilometers across and rising sharply above the surrounding plains. Their morphology puzzled geologists because they look nothing like the broad, gently sloping shield volcanoes built by low-viscosity basaltic lava, which is what Venus’s basalt-rich surface chemistry would predict.
Two competing models have been proposed. One suggests the domes formed from silicic magmas, produced when basaltic magma differentiated in a reservoir to create more viscous, evolved compositions. Eruptions of such magma through fissures of plausible width could build a dome comparable to large rhyolite flows on Earth. The second model proposes that the domes are basaltic foams: magma that became enriched with gas bubbles near the top of a reservoir, erupted with low viscosity during ascent, then stiffened dramatically at the surface as the bubbles expanded. The high bubble content would also explain the large volume of the domes relative to the amount of actual magma involved.
26Journal of Geophysical Research: Planets. Steep‐sided domes on Venus: Characteristics, geologic setting, and eruption conditions from Magellan dataNeither model has been definitively confirmed, in part because no lander has sampled a dome directly. But the structures remain among the most puzzling protuberances in the solar system, features that challenge assumptions about what volcanism looks like on a planet superficially similar to Earth.
Dental Cusps and How Teeth Get Their Shape
The bumps on your molars, the cusps that give teeth their chewing surfaces, are protuberances shaped by a developmental cascade that starts in the embryo. Each cusp forms at the site of an enamel knot, a specialized patch of cells in the developing tooth that acts as a signaling center. A new cusp can only form if its enamel knot is far enough from existing knots to escape their inhibitory signals. This spacing model predicts that tooth size and shape determine how many cusps and accessory features a tooth can develop.
One test of this model involves the Carabelli trait, a small extra cusp or ridge that sometimes appears on the inner surface of upper first molars. Researchers measured crown areas and distances between cusps in over 300 individuals and found that second molars, which are smaller and more triangular, have proportionally wider cusp spacing relative to their size, leaving less room for a Carabelli cusp to form. The presence and size of the Carabelli trait also covaried with other accessory cusps in complex ways, supporting the idea that the entire dentition develops and varies as a single interconnected system rather than tooth by tooth.
27PubMed. Metamerism, morphogenesis, and the expression of Carabelli and other dental traits in humansAnthropologists use these traits to trace population histories, because the frequencies of cusps like the Carabelli feature vary among human groups in ways that track ancestry and migration.