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The mysticetes — baleen whales and their toothed ancestors — have a long evolutionary history that, despite many recent paleontological discoveries, remains highly debated. The description of a new mysticete from the latest Eocene of North America opens promising new research directions. [ABSTRACT FROM AUTHOR]

Extant baleen whales (Mysticeti) uniquely use keratinous baleen for filter-feeding and lack dentition, but the fossil record clearly shows that "toothed" baleen whales first appeared in the Late Eocene. 1 Globally, only two Eocene mysticetes have been found, and both are from the Southern Hemisphere: Mystacodon selenensis from Peru, 36.4 mega-annum (Ma) ago 1,2 and Llanocetus denticrenatus from Antarctica, 34.2 Ma ago. 3,4 Based on a partial skull from the lower part of the Lincoln Creek Formation in Washington State, USA, we describe the Northern Hemisphere's geochronologically earliest mysticete, Fucaia humilis sp. nov. Geology, biostratigraphy, and magnetostratigraphy places Fucaia humilis sp. nov. in the latest Eocene (ca. 34.5 Ma ago, near the Eocene/Oligocene transition at 33.9 Ma ago), approximately coeval with the oldest record of fossil kelps, also in the northeastern Pacific. 5 This observation leads to our hypothesis that the origin and development of a relatively stable, nutrient-rich kelp ecosystem 5,6 in the latest Eocene may have fostered the radiation of small-sized toothed mysticetes (Family Aetiocetidae) in the North Pacific basin, a stark contrast to the larger Llanocetidae (whether Mystacodon belongs to llanocetids or another independent clade remains unresolved) with the latest Eocene onset of the Antarctic Circumpolar Current in the Southern Hemisphere. 7,8,9 Our discovery suggests that disparate mechanisms and ecological scenarios may have nurtured contrasting early mysticete evolutionary histories in the Northern and Southern hemispheres. • A new fossil mysticete is described from Washington State, USA • This fossil represents the oldest known mysticete from the Northern Hemisphere • The small body size contrasts with larger coeval whales in the Southern Hemisphere • The coastal kelp ecosystem likely fostered the diversification of early whales Tsai et al. describe a new mysticete from the latest Eocene (dated at approximately 34.5 Ma) in Washington State, USA. This is the oldest known mysticete from the Northern Hemisphere, revealing a previously unknown early evolutionary history of whales and suggesting contrasting ecological settings for baleen whale evolution between two hemispheres. [ABSTRACT FROM AUTHOR]

The evolution of cetaceans (whales and dolphins) represents one of the most extreme adaptive transitions known, from terrestrial mammals to a highly specialized aquatic radiation that includes the largest animals alive today. Many anatomical shifts in this transition involve the feeding, respiratory, and sensory structures of the cranium, which we quantified with a high-density, three-dimensional geometric morphometric analysis of 201 living and extinct cetacean species spanning the entirety of their ∼50-million-year evolutionary history. Our analyses demonstrate that cetacean suborders occupy distinct areas of cranial morphospace, with extinct, transitional taxa bridging the gap between archaeocetes (stem whales) and modern mysticetes (baleen whales) and odontocetes (toothed whales). This diversity was obtained through three key periods of rapid evolution: first, the initial evolution of archaeocetes in the early to mid-Eocene produced the highest evolutionary rates seen in cetaceans, concentrated in the maxilla, frontal, premaxilla, and nasal; second, the late Eocene divergence of the mysticetes and odontocetes drives a second peak in rates, with high rates and disparity sustained through the Oligocene; and third, the diversification of odontocetes, particularly sperm whales, in the Miocene (∼18–10 Mya) propels a final peak in the tempo of cetacean morphological evolution. Archaeocetes show the fastest evolutionary rates but the lowest disparity. Odontocetes exhibit the highest disparity, while mysticetes evolve at the slowest pace, particularly in the Neogene. Diet and echolocation have the strongest influence on cranial morphology, with habitat, size, dentition, and feeding method also significant factors impacting shape, disparity, and the pace of cetacean cranial evolution. • Cetacean diversity was obtained through three key periods of rapid evolution • Highest evolutionary rates are seen during the initial evolution of stem whales • High evolutionary rates occur as neocetes diverge, and later as odontocetes diversify • Diet and echolocation have the strongest influence on cranial morphology Coombs et al. quantify morphology, disparity, and evolutionary rates in the cetacean cranium. Highest evolutionary rates are seen during the initial evolution of stem whales, followed by high rates at the divergence of neocetes and later the diversification of odontocetes. Diet and echolocation have the strongest influence on cranial morphology. [ABSTRACT FROM AUTHOR]

The killer whale (Orcinus orca) and false killer whale (Pseudorca crassidens) are the only extant cetaceans that hunt other marine mammals, with pods of the former routinely preying on baleen whales >10 m in length and the latter being known to take other delphinids. 1–3 Fossil evidence for the origins of this feeding behavior is wanting, although molecular phylogenies indicate that it evolved independently in the two lineages. 4 We describe a new extinct representative of the killer whale ecomorph, Rododelphis stamatiadisi , based on a partial skeleton from the Pleistocene of Rhodes (Greece). Five otoliths of the bathypelagic blue whiting Micromesistius poutassou are associated with the holotype, providing unexpected evidence of its last meal. The evolutionary relationships of R. stamatiadisi and the convergent evolution of killer whale-like features were explored through a broad-ranging phylogenetic analysis that recovered R. stamatiadisi as the closest relative of P. crassidens and O. orca as the only living representative of a once diverse clade. Within the clade of Orca and kin, key features implicated in extant killer whale feeding, such as body size, tooth size, and tooth count, evolved in a stepwise manner. The tooth wear in Rododelphis and an extinct species of Orcinus (O. citoniensis) are consistent with a fish-based diet, supporting an exaptative Pleistocene origin for marine mammal hunting in both lineages. If correct, predation by the ancestors of Pseudorca and Orca did not play a significant role in the evolution of baleen whale gigantism. [Display omitted] [Display omitted] • New fossil false killer whale, Rododelphis stamatiadisi , found on island of Rhodes • Discovered with fish remains as its last meal and unlikely that it fed on other dolphins • Killer whales are the sole survivors of a clade that flourished 4 million years ago • Tooth wear in fossil killer whales suggest preying on dolphins evolved recently Bianucci et al. investigate the origins of whales feeding on other marine mammals. They describe Rododelphis stamatiadisi , a fossil false killer whale from Greece, and the associated fish remains of its last meal. Tooth wear in Rododelphis and extinct species of orcas suggest fish-based diets, supporting marine mammal hunting as a recent innovation. [ABSTRACT FROM AUTHOR]

Separation of respiratory and digestive tracts in the mammalian pharynx is critical for survival. Food must be kept out of the respiratory tract, and air must be directed into the respiratory tract when breathing. 1 Cetaceans have the additional problem of feeding while underwater. Lunge-feeding baleen whales (rorquals) open the mouth while swimming at high speeds to engulf a volume of prey-laden water as large as their own body 2 and experience tremendous forces as water floods the mouth. How the respiratory tract is protected in the pharynx during engulfment and while swallowing a massive slurry of tiny living prey remains unknown, despite its importance to survival. By dissecting adult and fetal fin whales, we determined that a large musculo-fatty structure passively seals the oropharyngeal channel. This "oral plug" is not observed in other animals, and its position indicates it must be shifted to allow swallowing; it is a part of the soft palate and can only shift posteriorly and dorsally. Elevation of the oral plug allows food transfer to the pharynx and protects the upper airways from food entry. The laryngeal inlet in the floor of the pharynx is sealed by laryngeal cartilages, and the muscular laryngeal sac moves upward into the laryngeal cavity, completely occluding the airway. The pharynx is dedicated to the digestive tract during swallowing, with no connection between upper and lower airways. These adaptations to facilitate swallowing were a critical development in the evolution of large body size in these, the largest animals on earth. • The oropharyngeal inlet is protected by a musculo-fatty oral plug during lunge feeding • The default position of respiratory structures confers protection • The pharynx is entirely dedicated to the digestive tract during swallowing • The pharynx is optimized for use in respiratory and digestive capacities Adaptations of pharynx and larynx balance respiratory and digestive functions in rorqual whales. Gil et al. show an oral plug prevents water from entering the pharynx during lunge feeding. When swallowing, the larynx shifts from an intranarial breathing position to a ventral protective position and the laryngeal sac occludes the laryngeal cavity. [ABSTRACT FROM AUTHOR]

Summary: The early radiation of cetaceans coincides with the origin of their defining ecological and sensory differences []. Toothed whales (Odontoceti) evolved echolocation for hunting 36–34 million years ago, whereas baleen whales (Mysticeti) evolved filter feeding and do not echolocate []. Echolocation in toothed whales demands exceptional high-frequency hearing [], and both echolocation and ultrasonic hearing have also evolved independently in bats []. The motor protein Prestin that drives the electromotility of the outer hair cells (OHCs) is likely to be especially important in ultrasonic hearing, because it is the vibratory response of OHC to incoming sound waves that confers the enhanced sensitivity and selectivity of the mammalian auditory system []. Prestin underwent adaptive change early in mammal evolution [] and also shows sequence convergence between bats and dolphins [], as well as within bats []. Focusing on whales, we show for the first time that the extent of protein evolution in Prestin can be linked directly to the evolution of high-frequency hearing. Moreover, we find that independent cases of sequence convergence in mammals have involved numerous identical amino acid site replacements. Our findings shed new light on the importance of Prestin in the evolution of mammalian hearing. [ABSTRACT FROM AUTHOR]

Whales are now largely protected from direct harvest, leading to partial recoveries in many previously depleted species. 1 However, most populations remain far below their historical abundances and incidental human impacts, especially vessel strikes and entanglement in fishing gear, are increasingly recognized as key threats. 2 In addition, climate-driven changes to prey dynamics are impacting the seasonal foraging grounds of many baleen whales. 2 In many cases these impacts result directly in mortality. But it is less clear how widespread and increasing sub-lethal impacts are affecting life history, individual fitness, and population viability. We evaluated changes in body lengths of North Atlantic right whales (NARW) using aerial photogrammetry measurements collected from crewed aircraft and remotely operated drones over a 20-year period (Figure 1). NARW have been monitored consistently since the 1980s and have been declining in abundance since 2011 due primarily to deaths associated with entanglements in active fishing gear and vessel strikes. 3 High rates of sub-lethal injuries and individual-level information on age, size and observed entanglements make this an ideal population to evaluate the effects that these widespread stressors may have on individual fitness. We find that entanglements in fishing gear are associated with shorter whales, and that body lengths have been decreasing since 1981. Arrested growth may lead to reduced reproductive success 4,5 and increased probability of lethal gear entanglements. 6 These results show that sub-lethal stressors threaten the recoveries of vulnerable whale populations even in the absence of direct harvest. • Whales with severe entanglements in fishing gear are stunted • Whales whose mothers were entangled while nursing are stunted • Body lengths have been decreasing since 1981 • Cumulative impacts in addition to entanglements may contribute to stunted growth Stewart et al. examine trends in body lengths in endangered North Atlantic right whales using aerial photogrammetry. They show that whales that have experienced severe entanglements in fishing gear are shorter than whales with no documented entanglements, and that body lengths of right whales have been decreasing over the past four decades. [ABSTRACT FROM AUTHOR]

Summary Whales use baleen, a novel integumentary structure, to filter feed; filter feeding itself evolved at least five times in tetrapod history but demonstrably only once in mammals [ 1 ]. Living baleen whales (mysticetes) are born without teeth, but paleontological and embryological evidence demonstrate that they evolved from toothed ancestors that lacked baleen entirely [ 2 ]. The mechanisms driving the origin of filter feeding in tetrapods remain obscure. Here we report Maiabalaena nesbittae gen. et sp. nov., a new fossil whale from early Oligocene rocks of Washington State, USA, lacking evidence of both teeth and baleen. The holotype possesses a nearly complete skull with ear bones, both mandibles, and associated postcrania. Phylogenetic analysis shows Maiabalaena as crownward of all toothed mysticetes, demonstrating that tooth loss preceded the evolution of baleen. The functional transition from teeth to baleen in mysticetes has remained enigmatic because baleen decays rapidly and leaves osteological correlates with unclear homology; the oldest direct evidence for fossil baleen is ∼25 million years younger [ 3 ] than the oldest stem mysticetes (∼36 Ma). Previous hypotheses for the origin of baleen [ 4, 5 ] are inconsistent with the morphology and phylogenetic position of Maiabalaena. The absence of both teeth and baleen in Maiabalaena is consistent with recent evidence that the evolutionary loss of teeth and origin of baleen are decoupled evolutionary transformations, each with a separate morphological and genetic basis [ 2, 6 ]. Understanding these macroevolutionary patterns in baleen whales is akin to other macroevolutionary transformations in tetrapods such as scales to feathers in birds. Highlights • Maiabalaena nesbittae is 33 million year old fossil baleen whale from Oregon • Maiabalaena has neither teeth, nor baleen • Early whales lost teeth entirely before the evolutionary origin of baleen • Despite no teeth or baleen, these whales were effective suction feeders Peredo et al. report Maiabalaena nesbittae , a new genus and species of fossil whale that provides key evidence for the loss of teeth and origin of baleen. Maiabalaena had neither teeth nor baleen—it represents a surprising intermediate stage between modern filter-feeding whales and their toothed ancestors. Instead, Maiabalaena was a suction feeder. [ABSTRACT FROM AUTHOR]

Summary Baleen whales (Mysticeti) are the largest animals on Earth, thanks to their ability to filter huge volumes of small prey from seawater. Mysticetes appeared during the Late Eocene, but evidence of their early evolution remains both sparse and controversial [ 1, 2 ], with several models competing to explain the origin of baleen-based bulk feeding [ 3–6 ]. Here, we describe a virtually complete skull of Llanocetus denticrenatus , the second-oldest (ca. 34 Ma) mysticete known. The new material represents the same individual as the type and only specimen, a fragmentary mandible. Phylogenetic analysis groups Llanocetus with the oldest mysticete, Mystacodon selenensis [ 2 ], into the basal family Llanocetidae. Llanocetus is gigantic (body length ∼8 m) compared to other early mysticetes [ 7–9 ]. The broad rostrum has sharp, widely spaced teeth with marked dental abrasion and attrition, suggesting biting and occlusal shearing. As in extant mysticetes, the palate bears many sulci, commonly interpreted as osteological correlates of baleen [ 3 ]. Unexpectedly, these sulci converge on the upper alveoli, suggesting a peri-dental blood supply to well-developed gums, rather than to inter-alveolar racks of baleen. We interpret Llanocetus as a raptorial or suction feeder, revealing that whales evolved gigantism well before the emergence of filter feeding. Rather than driving the origin of mysticetes, baleen and filtering most likely only arose after an initial phase of suction-assisted raptorial feeding [ 2, 4, 5 ]. This scenario differs strikingly from that proposed for odontocetes, whose defining adaptation—echolocation—was present even in their earliest representatives [ 10 ]. [ABSTRACT FROM AUTHOR]

Summary Many previous studies have shown that rorqual whales (Balaenopteridae), including the blue whale ( Balaenoptera musculus ), fin whale ( B. physalus ), sei whale ( B. borealis ), Bryde’s whale ( B. edeni ), minke whale ( B. acutorostrata ), and humpback whale ( Megaptera novaeangliae ), employ a strategy called lunge feeding to capture a large amount of krill and/or fish for nourishment [1] . Lunge feeding entails a high energetic cost due to the drag created by an open mouth at high speeds [1,2] . In the upper Gulf of Thailand, Bryde’s whales, which feed on small fish species [3] , predominantly anchovies, demonstrated a range of feeding behaviors such as oblique, vertical, and lateral lunging. Moreover, they displayed a novel head-lifting feeding behavior characterized by holding the vertical posture for several seconds with an open mouth at the water surface. This study describes the head-lifting feeding by Bryde’s whales, which is distinct from the typical lunge feeding of rorqual whales. Whales showing this behavior were observed on 58 occasions, involving 31 whales and including eight adult–calf pairs. Whales caught their prey using a series of coordinated movements: (i) lifting the head above the water with a closed mouth, (ii) opening the mouth until the lower jaw contacted the sea surface, which created a current of water flowing into the mouth, (iii) holding their position for several seconds, (iv) waiting for the prey to enter the mouth, and (v) closing the mouth and engulfing the prey underwater ( Figure 1 A–F, Movie S1 in Supplemental Information published with this article online). When a whale kept its upper jaw above the sea surface, many anchovies in the targeted shoal appeared to lose orientation and flowed passively into the mouth of the whale by the current created by the lower mandible breaking the surface of the water. We measured the duration of feeding events when the whales had a wide-open mouth mostly above the sea surface. The mean and maximum feeding durations were 14.5 ± 5.4 (SD; n = 58 events) and 32 s, respectively. Deployment of animal-borne data loggers yielded approximately 44 minutes of recordings from a single whale. The acceleration data showed that stroke rates, including tail beat and whole-body movements during feeding, were faster (approximately 0.7 s cycle) than during a cruising swim (approximately 3 s cycle) ( Figure 1 G). The swimming speed was lower than that in the stall speed (0.2 m s −1 ) of the device during the feeding phase, suggesting that thrust force was used to hold the head up and to stabilize body posture ( Figure 1 G). Stable positioning using the fluke and flipper was confirmed by video data for both the downward and upward direction of the whale ( Figure S1 ). According to the visual and behavioral data, we named the head-lifting feeding as ‘tread-water feeding’. Generally, all species of baleen whale, including rorqual whales, show active chasing and feeding, i.e., skimming, suction, and engulfing with lunging [1] . Tread-water feeding is considered passive feeding as compared with other feeding behaviors because the whales do not swim forward in pursuit of prey during the period from mouth opening to closing, and although they need thrust force to stabilize their posture, the head does not actively move. To the best of our knowledge, this discovery of tread-water feeding in Bryde’s whales represents the first report of passive feeding in baleen whales, which indicates their flexible capacity to modify their foraging strategy in relation to variable environments. [ABSTRACT FROM AUTHOR]

Summary As the largest known vertebrates of all time, mysticetes depend on keratinous sieves called baleen to capture enough small prey to sustain their enormous size [ 1 ]. The origins of baleen are controversial: one hypothesis suggests that teeth were lost during a suction-feeding stage of mysticete evolution and that baleen evolved thereafter [ 2–4 ], whereas another suggests that baleen evolved before teeth were lost [ 5 ]. Here we report a new species of toothed mysticete, Coronodon havensteini , from the Oligocene of South Carolina that is transitional between raptorial archaeocete whales and modern mysticetes. Although the morphology and wear on its anterior teeth indicate that it captured large prey, its broad, imbricated, multi-cusped lower molars frame narrow slots that were likely used for filter feeding. Coronodon havensteini is a basal, if not the most basal, mysticete, and our analysis suggests that it is representative of an initial stage of mysticete evolution in which teeth were functional analogs to baleen. In later lineages, the diastema between teeth increased—in some cases, markedly so [ 6 ]—and may mark a stage at which the balance of the oral fissure shifted from mostly teeth to mostly baleen. When placed in a phylogenetic context, our new taxon indicates that filter feeding was preceded by raptorial feeding and that suction feeding evolved separately within a clade removed from modern baleen whales. [ABSTRACT FROM AUTHOR]

Summary Mysticeti (baleen whales) and Odontoceti (toothed whales) today greatly differ in their hearing abilities: Mysticeti are presumed to be sensitive to infrasonic noises [ 1–3 ], whereas Odontoceti are sensitive to ultrasonic sounds [ 4–6 ]. Two competing hypotheses exist regarding the attainment of hearing abilities in modern whales: ancestral low-frequency sensitivity [ 7–13 ] or ancestral high-frequency sensitivity [ 14, 15 ]. The significance of these evolutionary scenarios is limited by the undersampling of both early-diverging cetaceans (archaeocetes) and terrestrial hoofed relatives of cetaceans (non-cetacean artiodactyls). Here, we document for the first time the bony labyrinth, the hollow cavity housing the hearing organ, of two species of protocetid whales from Lutetian deposits (ca. 46–43 Ma) of Kpogamé, Togo. These archaeocete cetaceans, which are transitional between terrestrial and aquatic forms, prove to be a key for determining the hearing abilities of early whales. We propose a new evolutionary picture for the early stages of this history, based on qualitative and quantitative studies of the cochlear morphology of an unparalleled sample of extant and extinct land artiodactyls and cetaceans. Contrary to the hypothesis that archaeocetes have been more sensitive to high-frequency sounds than their terrestrial ancestors [ 15 ], we demonstrate that early cetaceans presented a cochlear functional pattern close to that of their terrestrial relatives, and that specialization for infrasonic or ultrasonic hearing in Mysticeti or Odontoceti, respectively, instead only occurred in fully aquatic whales, after the emergence of Neoceti (Mysticeti+Odontoceti). [ABSTRACT FROM AUTHOR]

Summary Although combined molecular and morphological analyses point to a late middle Eocene (38–39 million years ago) origin for the clade Neoceti (Odontoceti, echolocating toothed whales plus Mysticeti, baleen whales, and relatives), the oldest known mysticete fossil dates from the latest Eocene (about 34 million years ago) of Antarctica [ 1, 2 ]. Considering that the latter is not the most stemward mysticete in recent phylogenies and that Oligocene toothed mysticetes display a broad morphological disparity most likely corresponding to contrasted ecological niches, the origin of mysticetes from a basilosaurid ancestor and its drivers are currently poorly understood [ 1, 3–8 ]. Based on an articulated cetacean skeleton from the early late Eocene (Priabonian, around 36.4 million years ago) of the Pisco Basin, Peru, we describe a new archaic tooth-bearing mysticete, Mystacodon selenensis gen. et sp. nov. Being the geologically oldest neocete (crown group cetacean) and the earliest mysticete to branch off described so far, the new taxon is interpreted as morphologically intermediate between basilosaurids and later toothed mysticetes, providing thus crucial information about the anatomy of the skull, forelimb, and innominate at these critical initial stages of mysticete evolution. Major changes in the morphology of the oral apparatus (including tooth wear) and flipper compared to basilosaurids suggest that suction and possibly benthic feeding represented key, early ecological traits accompanying the emergence of modern filter-feeding baleen whales’ ancestors. [ABSTRACT FROM AUTHOR]

Summary Rorqual whales (Balaenopteridae) are among the largest vertebrates that have ever lived and include blue ( Balaenoptera musculus ) and fin ( Balaenoptera physalus ) whales. Rorquals differ from other baleen whales (Mysticeti) in possessing longitudinal furrows or grooves in the ventral skin that extend from the mouth to the umbilicus. This ventral grooved blubber directly relates to their intermittent lunge feeding strategy, which is unique among vertebrates and was potentially an evolutionary innovation that led to gigantism in this lineage [1] . This strategy involves the rorqual whale rapidly engulfing a huge volume of prey-laden water and then concentrating the prey by more slowly expelling the water through baleen plates ( Figure 1 A). The volume of water engulfed during a lunge can exceed the volume of the whale itself [2] . During engulfment, the whale accelerates, opens its jaw until it is almost perpendicular to the rostrum, and then the highly compliant floor of the oral cavity is inflated by the incoming water [3] . The floor of the oral cavity expands by inversion of the tongue and ballooning of the adjacent floor of the mouth into the cavum ventrale , an immense fascial pocket between the body wall and overlying blubber layer that reaches as far back as the umbilicus. The ventral grooved blubber in fin whales expands by an estimated 162% in the circumferential direction and 38% longitudinally [4] . In fin whales, multiple lunges can occur during a single dive, and the average time between lunges is just over forty seconds [3] . Here, we show that nerves in the floor of the oral cavity of fin whales are highly extensible. [ABSTRACT FROM AUTHOR]