Nicholas D. Pyenson

• Ph.D.
• Curator of Fossil Marine Mammals at Smithsonian Institution

Extremes in organismal size have broad interest in ecology and evolution because organismal size dictates many traits of an organism’s biology. There is particular fascination with identifying upper size extremes in the largest vertebrates, given the challenges and difficulties of measuring extant and extinct candidates for the largest animal of al...

The ecological state of the Persian or Arabian Gulf (hereafter ‘Gulf') is in sharp decline. Calls for comprehensive ecosystem-based management approaches and transboundary conservation have gone largely unanswered, despite mounting marine threats made worse by climate change. The region's long-standing political tensions add additional complexity,...

Whales are an extraordinary study group for questions about ecology and evolution because their combinations of extreme body sizes and unique foraging strategies are unparalleled among animals. From a terrestrial ancestry, whales evolved specialized oceanic foraging mechanisms that characterize the two main groups of living cetaceans: echolocation...

Desmostylus is an extinct marine mammal genus that belongs to Desmostylia, a clade of extinct herbivorous mammals. While desmostylian remains are widely reported from Paleogene and Neogene marine strata of the North Pacific Rim, occurrences of the genus Desmostylus are almost entirely limited to middle Miocene strata, with only a few early Miocene...

The hyoid apparatus is essential for underwater feeding in marine tetrapods, but it is unclear whether this complex has evolved as convergently as other traits, such as dentition or locomotion. Here we compare the ossified hyoid elements in ophthalmosaurid ichthyosaurs and odontocete cetaceans, two groups with an overall similar body shape, to unde...

Many marine mammal populations are recovering after long eras of exploitation.1,2 To what degree density-dependent body size declines in recovering species reflect a general response to increased resource competition is unknown. We examined skull size (as a proxy for body size), skull morphology, and foraging dynamics of the top marine predator, th...

Body size and feeding morphology influence how animals partition themselves within communities. We tested the relationships among sex, body size, skull morphology and foraging in sympatric otariids (eared seals) from the eastern North Pacific Ocean, the most diverse otariid community in the world. We recorded skull measurements and stable carbon (δ...

Marine tetrapods occupy important roles in modern marine ecosystems and often gather in large aggregations driven by patchy prey distribution,1,2 social or reproductive behaviors,3,4 or oceanographic factors.5 Here, we show that similar grouping behaviors evolved in an early marine tetrapod lineage, documented by dozens of specimens of the giant ic...

One of the largest and least documented populations of dugongs ( Dugong dugon ) resides in the coastal waters of the United Arab Emirates, and waters surrounding Saudi Arabia, Bahrain, and Qatar. The archaeological record of dugongs in the Gulf Region is abundant, but little is known about their fossil record in the region. Here we report an isolat...

Desmostylia is an extinct clade of marine mammals with two major sub-clades, Desmostylidae and Paleoparadoxiidae, known from Oligocene to Miocene strata of the North Pacific coastline. Within Paleoparadoxiidae, three genera have been identified: Archaeoparadoxia, Paleoparadoxia, and Neoparadoxia. The latter taxon is the geochronologically youngest...

Skeletal remains and historical accounts indicate that grey whales (Eschrichtius robustus) existed in the North Atlantic Ocean from the Pleistocene into the seventeenth century. Fossil and sub-fossil occurrences in this basin are rare, distributed from the east coast of the United States to Iceland and Europe. Here, we report an incomplete skeleton...

Today’s mysticetes filter-feed using baleen, a novel integumentary structure with no apparent homolog in any living mammal. The origins of filter-feeding and baleen can be informed by the fossil record, including rare instances of soft tissue preservation of baleen and also by potential osteological correlates of baleen. Lateral palatal foramina on...

Desmostylia is an extinct clade of marine mammals with two major sub-clades, Desmostylidae and Paleoparadoxiidae, known from Oligocene to Miocene strata of the North Paci c coastline. Within Paleoparadoxiidae, three genera have been identi ed: Archaeoparadoxia, Paleoparadoxia, and Neoparadoxia. The latter taxon is the geochronologically youngest pa...

Extinct megatooth sharks were globally distributed and contributed to ocean food chains that were potentially one to two steps longer than any food chain today.

A whale-sized ichthyosaur shows how fast these reptiles evolved

Baleen whales influence their ecosystems through immense prey consumption and nutrient recycling1–3. It is difficult to accurately gauge the magnitude of their current or historic ecosystem role without measuring feeding rates and prey consumed. To date, prey consumption of the largest species has been estimated using metabolic models3–9 based on e...

Living baleen whales (mysticetes) are bulk filter feeders that use keratinous baleen plates to filter food from prey laden water. Extant mysticetes are born entirely edentulous, though they possess tooth buds early in ontogeny, a trait inherited from toothed ancestors. The mandibles of extant baleen whales have neither teeth nor baleen; teeth are r...

Each year, the discovery of new shark species underscores how little we know about ocean biodiversity (1). This is alarming not only because human pressures threaten sharks more than other marine lineages (2) but also because their fossil record suggests that they were largely resilient to extinction in the past (3), with some extant species persis...

Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal kingdom. When and why this trait evolved remains controversial, with proposed drivers ranging from echolocation to foraging complexity and high-level sociality. This uncertainty partially reflects a lack of data on extinct baleen whales (mysticetes), whic...

Cetaceans (whales and dolphins) have some of the largest and most complex brains in the animal kingdom. When and why this trait evolved remains controversial, with proposed drivers ranging from echolocation to foraging complexity and high-level sociality. This uncertainty partially reflects a lack of data on extinct baleen whales (mysticetes), whic...

The history of cetaceans demonstrates dramatic macroevolutionary changes that have aided their transformation from terrestrial to obligate aquatic mammals. Their fossil record shows extensive anatomical modifications that facilitate life in a marine environment. To better understand the constraints on this transition, we examined the physical dimen...

Elephant seals ( Mirounga spp.) are the largest living pinnipeds, and the spatial scales of their ecology, with dives over 1 km in depth and foraging trips over 10,000 km long, are unrivalled by their near relatives. Here we report the discovery of an incomplete Holocene age Southern elephant seal ( M. leonina ) rostrum from Indiana, USA. The survi...

The fossil record of pinnipeds (seals, fur seals and walruses) is globally distributed, spanning from the late Oligocene to the Holocene. This record shows a complex evolutionary history that could not otherwise be inferred from their extant relatives, including multiple radiations and iterative ecomorphological specializations among different line...

Rorqual whales are among the most species rich group of baleen whales (or mysticetes) alive today, yet the monophyly of the traditional grouping (i.e., Balaenopteridae) remains unclear. Additionally, many fossil mysticetes putatively assigned to either Balaenopteridae or Balaenopteroidea may actually belong to stem lineages, although many of these...

Baleen whales (mysticetes) lack teeth as adults and instead filter feed using keratinous baleen plates. They do not echolocate with ultrasonic frequencies like toothed whales but are instead known for infrasonic acoustics. Both baleen and infrasonic hearing are separately considered key innovations linked to their gigantism, evolutionary success an...

Since the Permian, Earth’s aquatic ecosystems have been ecologically dominated by numerous lineages of predatory amniotes. Many of these groups evolved elevated ridges of enamel that run down the apical–basal axis of their teeth, referred to here as apicobasal ridges. This trait is commonly used as a taxonomic tool to identify fossil species and hi...

The evolutionary history of aquatic mammals reveals numerous evolutionary experiments in feeding phenotypes and performance in response to changing environmental conditions. In many respects, aquatic mammals have departed from using ancestral terrestrial feeding mechanisms and adopted novel ways of feeding that are influenced by both phylogeny and...

Why do cold-blooded and warm-blooded marine predators live in different parts of the world?

Toothed cetacean (Odontoceti) lineages in the Miocene and Pliocene evolved rostra that are proportionally more elongate than any other aquatic mammal or reptile, living or extinct. Their similarities in cranial proportions to billfish may suggest a convergent feeding style, where the rostrum is swept through the water to hit and stun prey. Here we...

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...

The fossil record of mammal dentition provides crucial insight into key ecological and functional transitions throughout mammalian evolutionary history. For cetaceans, both extant clades differ markedly from their stem ancestors; neither retains the differentiated dentition or the tribosphenic molars characteristic of Mammalia. We used quantitative...

Living baleen whales, or Mysticeti, lack teeth and instead feed using keratinous baleen plates to sieve prey-laden water. This feeding strategy is profoundly different from that of their toothed ancestors, which processed prey using the differentiated dentition characteristic of mammals. The fossil record of mysticetes reveals stem members that inc...

The evolution of cetaceans is one of the best examples of macroevolution documented from the fossil record. While ecological transitions dominate each phase of cetacean history, this context is rarely stated explicitly. The first major ecological phase involves a transition from riverine and deltaic environments to marine ones, concomitant with dra...

Many odontocete groups have developed enlarged facial crests, although these crests differ in topography, composition and function. The most elaborate crests occur in the South Asian river dolphin (Platanista gangetica), in which they rise dorsally as delicate, pneumatized wings anterior of the facial bones. Their position wrapping around the melon...

Supplementary Methods and Results: Phylogenetic Analysis, Model Performance, and Sampling Bias

Vertebrates have evolved to gigantic sizes repeatedly over the past 250 Myr, reaching their extreme in today's baleen whales (Mysticeti). Hypotheses for the evolution of exceptionally large size in mysticetes range from niche partitioning to predator avoidance, but there has been no quantitative examination of body size evolutionary dynamics in thi...

The evolution of filter feeding in baleen whales (Mysticeti) facilitated a wide range of ecological diversity and extreme gigantism. The innovation of filter feeding evolved in a shift from a mineralized upper and lower dentition in stem mysticetes to keratinous baleen plates that hang only from the roof of the mouth in extant species, which are al...

Baleen whales, or mysticetes, include the largest vertebrates to have ever evolved. Their gigantism, evolutionary success, and ecological diversity have been linked to filter feeding. Mysticetes filter feed using elaborate keratinous baleen plates, which grow from the palate and allow them to strain large quantities of prey out of the water. While...

Ranging up to 15 m in length, the Triassic ichthyosaur Shonisaurus popularis was the first marine tetrapod to attain truly gigantic proportions. Shonisaurus is famous both for its size and for exceptional fossil concentrations found in the Upper Triassic (Carnian–Norian) Luning Formation in central Nevada. An assemblage of 6–9 skeletons concentrate...

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true wou...

The diversification of crown cetacean lineages (i.e., crown Odontoceti and crown Mysticeti) occurred throughout the Oligocene, but it remains an ongoing challenge to resolve the phylogenetic pattern of their origins, especially with respect to stem lineages. One extant monotypic lineage, Platanista gangetica (the Ganges and Indus river dolphin), is...

Referred specimens of Goedertius sp Photographs of undescribed platanistoid specimens housed in the Vertebrate Paleontology collections of the National Museum of Natural History, Smithsonian Institution, Washington D.C. All of the skulls are referred in this paper to the allodelphinid genus Goedertius. (A) USNM 335406, (B) USNM 335765, (C) USNM 314...

Character state descriptions Following Tanaka & Fordyce (2015a). Modifications new to this study are noted.

Morphology of the squamosal in platanistoids A homologous feature of the squamosal is observed in multiple platanistoid taxa: (A) Arktocara yakataga (USNM 214830), (B) Platanista gangetica (USNM 23456) and (C) USNM 214911, an undescribed platanistoid. This feature (highlighted in red), is a pointed lamina projected anteromedially from the anterior...

Matrix constructed in Mesquite for Odontoceti including Arktocara yakataga, .txt format 0, primitive state; 1, 2, 3, derived states; 0/1, a variable between 0 and 1; 1/2 a variable between 1 and 2; 1/3, a variable between 1 and 3; ?, missing character or taxon not coded for this character. Following Tanaka & Fordyce (2015a), with the removal of the...

Large consumers have ecological influence disproportionate to their abundance, although this influence in food webs depends directly on productivity. Evolutionary patterns at geologic timescales inform expectations about the relationship between consumers and productivity, but it is very difficult to track productivity through time with direct, qua...

The stratigraphy of the Bahía Inglesa Formation in the Caldera Basin west of Copiapó, (north-central Chile) is revised, based on hitherto unpublished stratigraphic sections and 87Sr/86Sr dating. The depositional environment varied from a rocky shoreline to the upper continental slope, with sea-level oscillations and tectonic movements causing numer...

Living sperm whales are represented by only three species (Physeter macrocephalus, Kogia breviceps and Kogia sima), but their fossil record provides evidence of an ecologically diverse array of different forms, including morphologies and body sizes without analog among living physeteroids. Here we provide a redescription of Ontocetus oxymycterus, a...

Phylogenetic tree with bootstrap values for Physeteroidea. (TIF)

Matrix constructed in Mesquite for Physeteroidea including Albicetus. 0, primitive state; 1, 2, 3, derived states; 0/1, a variable between 0 and 1; 1/2 a variable between 1 and 2; 1/3, a variable between 1 and 3;?, missing character or taxon not coded for this character. (TIF)

Specimens Observed. Fossil marine mammal specimens observed during the writing of this publication. (DOCX)

Measurement diagram. Diagram of measurements taken from the main rostral section and isolated upper rostral fragment from the holotype of Albicetus oxymycterus (USNM 10923). (TIF)

Character state descriptions. Following Velez-Juarbe et al. [25] (DOCX)

Table of condylobasal lengths of the Physeteroidea taxa. All approximated (~) measurements are estimates based on fragmentary material. For, Agorophius, Thalassocetus and Praekogia (denoted by *), estimated CBL were collected from cetacean genera of similar sizes (Simocetus for Agorophius, Kogia breviceps for Thalassocetus, and Praekogia for Nanoko...

Along the south-western coast of South America, three genera of fossil phocids (true seals) have been formally described from the late Neogene: Acrophoca and Piscophoca from Chile and Peru, and, more recently, Hadrokirus from Peru, which all represent medium- to large-sized phocids. Here, we report the discovery of Australophoca changorum gen. et s...

Underwater human activities and anthropogenic noise in our oceans may be a major source of habitat degradation for marine life. This issue was highlighted by the opening of the United States Eastern Seaboard for seismic oil and gas exploration in 2014, which generated massive media coverage and widespread concern that seismic surveys could kill or...

In contrast to dominant mode of ecological transition in the evolution of marine mammals, different lineages of toothed whales (Odontoceti) have repeatedly invaded freshwater ecosystems during the Cenozoic era. The so-called 'river dolphins' are now recognized as independent lineages that converged on similar morphological specializations (e.g., lo...

Whales are important model systems for understanding the physiological and ecological consequences of extreme body size. However, whales are also some of the most difficult animals to study because their large size precludes experimental studies under controlled conditions. Here we review a wide range of morphological studies that enable greater in...

Fossil remains of Cetacea are known globally from nearshore marine sediments along continental coastlines, but they are poorly known from volcanic oceanic island archipelagos. Here we report Pleistocene fossil cetacean material from late Neogene and Quaternary age outcrops on the Santa Maria Island of the Azores island archipelago in the North Atla...

The genus Mirounga is the largest living member of the Phocidae family (true seals) and includes two species: M. angustirostris and M. leonina. These species exhibit a noticeable antitropical distribution in the Northern and Southern hemispheres, respectively. The evolutionary history of elephant seals, especially in regard to establishing this ant...

Many top consumers in today's oceans are marine tetrapods, a collection of lineages independently derived from terrestrial ancestors. The fossil record illuminates their transitions from land to sea, yet these initial invasions account for a small proportion of their evolutionary history. We review the history of marine invasions that drove major c...

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 groo...

Whales receive underwater sounds through a fundamentally different mechanism than their close terrestrial relatives. Instead of hearing through the ear canal, cetaceans hear through specialized fatty tissues leading to an evolutionarily novel feature: an acoustic funnel located anterior to the tympanic aperture. We traced the ontogenetic developmen...

"River dolphins" are a paraphyletic group of toothed whales (Odontoceti) that represent independent secondary invasions of freshwater habitats. Different "river dolphin" lineages display suites of convergent morphological specializations that commonly reflect adaptations to riverine and freshwater environments, such as longirostry, reduced orbits,...

Marine mammal mass strandings have occurred for millions of years, but their origins defy singular explanations. Beyond human causes, mass strandings have been attributed to herding behaviour, large-scale oceanographic fronts and harmful algal blooms (HABs). Because algal toxins cause organ failure in marine mammals, HABs are the most common mass s...

Muscle serves a wide variety of mechanical functions during animal feeding and locomotion, but the performance of this tissue is limited by how far it can be extended. In rorqual whales, feeding and locomotion are integrated in a dynamic process called lunge-feeding where an enormous volume of prey-laden water is engulfed into a capacious ventral o...

Rorqual whales (crown Balaenopteridae) are unique among aquatic vertebrates in their ability to lunge feed. During a single lunge, rorquals rapidly engulf a large volume of prey-laden water at high speed, which they then filter to capture suspended prey. Engulfment biomechanics are mostly governed by the coordinated opening and closing of the mandi...

Cetacean evolution represents one of the best-documented transitions from land to sea, and paleontological evidence in particular has made this evolutionary transformation a textbook case of macroevolution. However, the transition from land to sea represents only the first third of cetacean evolution, during the Eocene; over 30 million years of the...

A bstract Marine tetrapods have evolved different sensory solutions to meet the ecological challenges of foraging at depth. It has been proposed that pinipeds, like ichthyosaurs, evolved large eyeballs for such demands. Here, we test this hypothesis using morphological and diving data from a comprehensive data set ( n = 54 species; 435 individual s...

Modern pinnipeds distributed along the coasts of continental South America consist almost entirely of otariids (sea lions and fur seals). In contrast, phocids (true seals) are present only on the southernmost extreme of Chile. This recent biogeographic pattern is consistent with the zooarchaeological record (∼8—2 ka), but it is incompatible with th...

Toothed whales (crown Odontoceti) are unique among mammals in their ability to echolocate underwater, using specialized tissue structures. The melon, a structure composed of fat and connective tissue, is an important component in the production of an echolocation beam; it is known to focus high frequency, short duration echolocation clicks. Here, w...

Top ocean predators have evolved multiple solutions to the challenges of feeding in the water. At the largest scale, rorqual whales (Balaenopteridae) engulf and filter prey-laden water by lunge feeding, a strategy that is unique among vertebrates. Lunge feeding is facilitated by several morphological specializations, including bilaterally separate...

Here we describe Bohaskaia monodontoides, a new taxon of beluga-like odontocete cetacean from the early Pliocene Yorktown Formation of Virginia and North Carolina. Among odontocetes, Bohaskaia shares key characteristics of the rostrum and face with belugas (Delphinapterus leucas), narwhals (Monodon monoceros), and Denebola brachycephala from the la...