All living whales belong to one of two groups: baleen whales (Mysticeti), which filter tiny organisms from seawater using plates of keratin hanging from their upper jaws, and toothed whales (Odontoceti), which hunt individual prey and navigate with biological sonar. That split, rooted tens of millions of years in the past, shapes nearly everything about how each whale feeds, communicates, raises young, and interacts with the ocean around it. With roughly 90 recognized species and new ones still being described, the diversity within those two groups is far wider than most people realize.
Baleen Whales Versus Toothed Whales
The difference between the two suborders goes well beyond the presence or absence of teeth. Baleen whales have paired blowholes, symmetrical skulls, and no ribs connecting to the breastbone, while toothed whales have a single blowhole, asymmetrical skulls, and a skeletal structure that reflects a very different evolutionary trajectory.1Encyclopedia of Marine Mammals. Baleen Whales Baleen whales are generally larger and include the biggest animal ever to have lived, the blue whale. Toothed whales range from the massive sperm whale down to porpoises barely longer than a person is tall, and they include dolphins, beaked whales, and river dolphins.
Even the way they nurse their calves differs between the two groups. Baleen whale mothers tend to have short, intense lactation periods of about five to seven months, during which they eat little or nothing. Their milk is extraordinarily rich, often containing 30 to 50 percent fat. Toothed whale mothers, by contrast, nurse for one to three years, eating throughout, and produce more dilute milk with roughly 10 to 30 percent fat.2PubMed. Lactation in whales and dolphins: evidence of divergence between baleen- and toothed-species That pattern reflects a broader divide in life strategy: baleen whales pour energy into calves in a concentrated burst fueled by stored blubber, while toothed whales invest over a longer horizon.
How Baleen Whales Feed
Filter feeding sounds passive, but baleen whales have evolved some of the most energetically demanding feeding strategies in the animal kingdom. The rorquals, a family that includes blue, fin, humpback, and minke whales, are lunge feeders. They accelerate into dense patches of krill or small fish, open their enormous mouths, and engulf a volume of water that can exceed their own body mass. The mechanical cost is staggering: simulations suggest that in the largest blue whales, the metabolism during a single lunge can spike to nearly 50 times the resting metabolic rate of a land mammal of equal size, and oxygen demand overshoots maximum aerobic capacity by about 20 percent, requiring anaerobic metabolism and recovery time afterward.3PLoS ONE. Metabolic Expenditures of Lunge Feeding Rorquals Across Scale: Implications for the Evolution of Filter Feeding and the Limits to Maximum Body Size That oxygen ceiling may be one reason there is an upper size limit to these animals at all.4PubMed. Lunge Feeding in Rorqual Whales
Not all baleen whales lunge. Right whales and bowhead whales are skim feeders: they swim slowly with mouths open, letting water flow continuously through their baleen while trapping copepods and other tiny crustaceans. Gray whales are odder still. They roll onto their sides in shallow coastal waters and suction-feed along the seafloor, using paddle-shaped lower jaws to scoop up ghost shrimp and other burrowing invertebrates from the sediment.5PubMed. Kinematics of gray whale (Eschrichtius robustus) foraging on infaunal ghost shrimp (Neotrypaea californiensis) That benthic suction strategy carves out a feeding niche no other mysticete occupies. Gray whale feeding leaves visible pits on the ocean floor, sometimes acres of them, and those disturbed patches create habitat for other organisms that recolonize the churned sediment.
Feeding in cold water introduces its own engineering problem: heat loss through the mouth. Gray whales solve this with networks of countercurrent heat exchangers threaded throughout their massive tongues, converging into paired heat-conserving structures at the tongue base. Measurements from a live gray whale showed that, despite the tongue being far more vascularized and less insulated than the rest of the body, those heat exchangers keep oral heat loss manageable.6PubMed. Thermoregulation in the mouths of feeding gray whales
Echolocation and Sound Production in Toothed Whales
Toothed whales do not simply click and listen. Their sound production system drives air through nasal passages to vibrate specialized tissue, functioning much like a larynx does in land mammals or a syrinx in birds, but located in the nose rather than the throat. Research across porpoises, dolphins, and sperm whales has shown that these animals use distinct vocal registers: a vocal fry register for powerful, air-efficient echolocation clicks, and other registers for the whistles, burst-pulse sounds, and social calls that make up their communication repertoire.7PubMed. Toothed whales use distinct vocal registers for echolocation and communication This register-based system appears consistent across all major toothed whale lineages, suggesting it evolved early in the group’s history.
Once clicks are generated, they need to be aimed. That job falls to the melon, a fatty, lens-shaped organ in the forehead. The melon’s internal density varies in a structured gradient that focuses outgoing sound into a directional beam, much as a flashlight’s reflector concentrates light. The shape, size, and density topography of the melon differ between species, likely tuned to the specific frequencies and environments each species relies on.8Marine Mammal Science. Morphology of the odontocete melon and its implications for acoustic function A bottlenose dolphin hunting fish in murky shallows faces a different acoustic challenge than a sperm whale tracking squid a thousand meters down, and their melons reflect those differences.
Baleen Whale Sounds
Baleen whales produce sound in a fundamentally different way and at very different frequencies. They are the low-frequency specialists of the ocean. Blue and fin whales generate infrasonic calls, some below the threshold of human hearing, that can travel hundreds or even thousands of kilometers through seawater. Humpback whales take a different approach, producing complex, constantly changing songs that rank among the most elaborate acoustic displays in the animal kingdom.9The Journal of the Acoustical Society of America. Low-frequency signaling behavior in mysticete whales The functions of these calls are still debated, but they likely serve in mate attraction, territorial signaling, and long-range coordination between individuals spread across vast stretches of ocean.
Deep-Diving Physiology
Some toothed whales spend much of their lives in a world of crushing pressure, near-freezing temperatures, and zero light. Sperm whales routinely dive past a kilometer. Beaked whales hold the records, with some species reaching depths that would kill almost any other air-breathing animal. To survive, deep divers have evolved a suite of physiological tricks that genomic studies are only now beginning to unravel.
Comparative genomics across whale species has found that deeper divers tend to carry more oxygen-binding proteins in their blood and muscle, have thicker blubber for insulation and pressure resistance, and have proportionally smaller lungs relative to body mass, which limits the gas exchange that causes decompression sickness.10PubMed. Comparative Genomics Uncovers Molecular Adaptations for Cetacean Deep-Sea Diving Their myoglobin, the protein that stores oxygen in muscle, shows signs of positive selection with functional amino acid changes. And at the genetic level, deep divers appear to have reduced their capacity to produce uric acid under low-oxygen conditions, which may protect their cells from the oxidative stress of repeated oxygen deprivation and reperfusion.
A multi-omics study of the pygmy sperm whale, a smaller deep-diving species, added more detail: genes involved in breaking down glucose and fatty acids for energy have evolved rapidly in this lineage, and the animal’s heart tissue contains an increased proportion of a specialized type of cardiac muscle cell that may help maintain heart function during prolonged oxygen deprivation.11PubMed Central. Pygmy sperm whale multi-omics data reveal hypoxia adaptations in deep-diving cetaceans These are not single-gene adaptations but coordinated changes across energy metabolism, oxygen handling, and cardiac physiology.
Social Lives and Vocal Culture in Killer Whales
Killer whales are toothed whales and, taxonomically, dolphins. They offer the most thoroughly studied example of whale social complexity. Resident-type killer whales live in matrilines, family groups centered on a mother and her descendants, from which neither males nor females have been observed to permanently leave. Matrilines that associate at least half the time are grouped into pods, and pods that share part of their vocal repertoire form what researchers call acoustic clans.12Animal Behaviour. Cultural transmission within maternal lineages: vocal clans in resident killer whales in southern Alaska In southern Alaska, two acoustic clans were identified, each with a distinct mitochondrial DNA signature, suggesting that the vocal groupings reflect genuine lines of descent.
What makes this especially interesting is that killer whale dialects are not fixed. Tracking two matrilineal groups over more than a decade revealed that certain call types changed significantly over time, and the changes occurred in parallel in both groups, keeping the calls similar despite being made by different families. That pattern points to horizontal cultural transmission: the whales are learning modifications from each other, not just inheriting calls from their mothers.13Animal Behaviour. Dialect change in resident killer whales: implications for vocal learning and cultural transmission Vocal learning transmitted across family lines has major implications for how whale cultures evolve alongside their genes. The same pattern of stable kinship-based associations and shared dialects has been confirmed in the Northwest Pacific as well.14Mammalian Biology. The social organization of resident-type killer whales (Orcinus orca) in Avacha Gulf, Northwest Pacific, as revealed through association patterns and acoustic similarity
Humpback Whale Foraging Innovations
Humpback whales are baleen whales, but their foraging behavior shows a level of inventiveness more commonly associated with primates or corvids. Solitary humpbacks in Southeast Alaska manufacture bubble-nets: they dive beneath a school of krill and exhale controlled streams of bubbles that form ring-shaped structures, corralling the prey into a dense column before lunging upward through it. These nets are not random exhalations. Tag data and drone footage show that whales control the number of rings, the net diameter, the depth, and the spacing between individual bubbles, and the payoff is substantial. On average, feeding with a bubble-net increased prey intake per lunge about sevenfold compared to lunging without one.15PubMed Central. Solitary humpback whales manufacture bubble-nets as tools to increase prey intake
Bubble-netting is not the only trick. Humpbacks also use their unusually long pectoral fins to herd prey in at least three distinct ways: as a physical barrier blocking escape routes, as paddles generating water currents that push prey toward the mouth, and by flashing their light-colored ventral surface to alter the movement of light-sensitive prey.16PubMed Central. Pectoral herding: an innovative tactic for humpback whale foraging This behavioral plasticity may help humpbacks adapt when prey species shift due to changing ocean conditions.
The Narwhal’s Sensory Tusk
The narwhal is a mid-sized toothed whale that lives year-round in Arctic waters. Males, and occasionally females, grow a spiraling tusk that can exceed two meters in length. For centuries the tusk was assumed to be a weapon or a sexual display, and those functions may exist, but research has revealed something stranger: the tusk is a sensory organ. Ocean water enters through porous channels in the outer cementum layer, travels through millions of open tubules in the underlying dentin, and reaches nerve-rich pulp tissue that connects via the trigeminal nerve to the brain. When researchers alternated high-salt and fresh water solutions over the external tusk surface of a live narwhal, its heart rate changed significantly, confirming that the animal can detect chemical differences in the water through its tooth.17PubMed. Sensory ability in the narwhal tooth organ system No other mammalian tooth is known to work this way. The structural layering of the tusk, including a graded junction between the cementum and dentin that helps distribute mechanical stress, reflects a dual-purpose design: strong enough to withstand impacts, yet permeable enough to transmit environmental signals.18PubMed. The narwhal (Monodon monoceros) cementum-dentin junction: a functionally graded biointerphase
Species We Are Still Discovering
The idea that all whale species have already been catalogued is wrong. New species are still being identified, sometimes hiding in plain sight. A genetically distinct lineage of Bryde’s-like whale restricted to the northern Gulf of Mexico was recognized as a new species, now called Rice’s whale, after years of genetic and morphological work.19Marine Mammal Science. A new species of baleen whale (Balaenoptera) from the Gulf of Mexico, with a review of its geographic distribution With a population estimated at only a few dozen individuals, it may be the most critically endangered whale on Earth.
Beaked whales, which spend much of their time in deep water and rarely surface for long, are particularly rich in cryptic diversity. In the North Pacific, genetic analysis of what was assumed to be a single species of Baird’s beaked whale revealed a smaller, darker form whose mitochondrial DNA is more divergent from the known species than some fully recognized species are from each other.20Marine Mammal Science. Genetic structure of the beaked whale genus Berardius in the North Pacific, with genetic evidence for a new species In the Southern Hemisphere, genomic and morphological analysis confirmed a new beaked whale species, Mesoplodon eueu, that had been lumped with True’s beaked whale for over a century. The two lineages diverged roughly two million years ago and stopped exchanging genes entirely somewhere between 350,000 and 550,000 years ago.21PubMed Central. Speciation in the deep: genomics and morphology reveal a new species of beaked whale Mesoplodon eueu Given how difficult beaked whales are to observe alive, there are almost certainly more undescribed species out there.
What Whales Do for the Ocean
Whales are not just passengers in marine ecosystems. They actively reshape the nutrient landscape. When whales feed at depth and defecate near the surface, they move nitrogen, phosphorus, and trace elements from the deep ocean into the sunlit zone where phytoplankton can use them. This “whale pump” effect is measurable. In the Gulf of Maine, marine mammals are estimated to recycle roughly 23,000 metric tons of nitrogen per year into surface waters, more than all the rivers draining into the gulf combined.22PubMed Central. The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin Before commercial whaling reduced populations, the contribution was likely more than three times the atmospheric nitrogen input to those waters.
Baleen whales add another nutrient pathway through their long-distance migrations. By feeding in productive high-latitude waters and then traveling to tropical or subtropical breeding grounds, they physically carry nutrients across ecosystem boundaries in their bodies, releasing them through feces, urine, and other excretions in regions that are otherwise nutrient-poor.23PubMed Central. Migrating baleen whales transport high-latitude nutrients to tropical and subtropical ecosystems Ecosystem modeling in the Nordic and Barents Seas found that while the annual effect of whale-derived nutrients on primary production is modest overall, the impact can reach up to 10 percent in offshore areas during summer stratification, when the water column is layered and nutrients from depth cannot mix upward on their own.24PubMed Central. Impact of baleen whales on ocean primary production across space and time
Whale Falls and the Deep-Sea Afterlife
When a large whale dies and sinks to the deep seafloor, its carcass becomes an island of abundance in an otherwise food-starved environment. These whale falls pass through overlapping stages of community succession. First, mobile scavengers like hagfish and sleeper sharks strip the soft tissue. Then smaller invertebrates colonize the remains. Finally, in a stage that can last decades, specialized bacteria break down the lipid-rich bones and generate hydrogen sulfide, supporting chemosynthetic communities related to those found at hydrothermal vents and cold seeps. Whale falls harbor many species found nowhere else, including bone-eating worms and specialized snails, and molecular evidence suggests the carcasses have served as evolutionary stepping stones, helping organisms adapted to chemical energy sources disperse across the deep ocean.25PubMed. Whale-fall ecosystems: recent insights into ecology, paleoecology, and evolution
Conservation Threats Across the Group
The threats facing whales are not distributed evenly. North Atlantic right whales remain critically endangered largely because of vessel strikes and entanglement in commercial fishing gear, a combination that has kept their population at a few hundred despite decades of protection. Entanglement can be immediately fatal or can drag on for months, with the animal slowly weakening under the weight and constriction of ropes. Western Arctic bowhead whales, by contrast, have been recovering steadily, in part because their habitat overlaps less with dense shipping lanes and fishing operations.26Marine Policy. Implications of Arctic industrial growth and strategies to mitigate future vessel and fishing gear impacts on bowhead whales Bowhead whales were heavily exploited during commercial whaling between the sixteenth and twentieth centuries, eroding what had been roughly 11,000 years of population stability.27PubMed. Four centuries of commercial whaling eroded 11,000 years of population stability in bowhead whales
Even in remote areas, human activity is encroaching. In the Beagle Channel at the southern tip of South America, bycatch in king crab fisheries and collisions with vessel traffic have become more frequent in recent years, driven partly by recovering whale populations moving back into waters they once inhabited and partly by increasing marine industrial activity.28Marine Policy. Anthropogenic activities and emerging threats to large whales in the Beagle Channel It is an ironic pattern: as conservation efforts succeed and whale numbers rise, the animals increasingly encounter the infrastructure of a busier ocean.
Whale Brains and the Question of Complexity
Whales have large brains, but brain size alone says little. What has drawn neuroscientists’ attention is the presence of von Economo neurons, a distinctive spindle-shaped cell type found in specific brain regions. In humans and great apes, these cells cluster in the anterior cingulate cortex and anterior insula, areas linked to social cognition and emotional processing. They have been found in humpback whales, fin whales, and the largest toothed whales in the same cortical regions and the same layer of tissue.29PubMed. Structure of the cerebral cortex of the humpback whale, Megaptera novaeangliae (Cetacea, Mysticeti, Balaenopteridae) That looks like a remarkable parallel with primate brains, but the picture is more complicated. A broader survey found von Economo neurons in cows, sheep, deer, horses, and pigs as well, with species-specific differences in density and distribution. Their repeated appearance in distantly related mammals likely represents convergent evolution rather than a marker of any particular cognitive threshold.30PubMed. An analysis of von Economo neurons in the cerebral cortex of cetaceans, artiodactyls, and perissodactyls
One thing genomics has confirmed is that whales lost most of their taste receptors long ago. Both baleen and toothed whales carry broken copies of the genes for sweet, umami, bitter, and sour taste, while only the genes for sensing saltiness remain functional.31Genome Biology and Evolution. Massive Losses of Taste Receptor Genes in Toothed and Baleen Whales Since most whale species swallow prey whole, there was presumably little evolutionary pressure to maintain fine taste discrimination. It is a quiet reminder that whales, for all their complexity, have streamlined themselves in ways that would surprise anyone who imagines them as simply larger versions of the land mammals they descended from.