Early Whales Research Articles

3D models related to the publication: A heavyweight early whale pushes the boundaries of vertebrate morphology

3D models related to the publication: A heavyweight early whale pushes the boundaries of vertebrate morphology

A heavyweight early whale pushes the boundaries of vertebrate morphology.

The fossil record of cetaceans documents how terrestrial animals acquired extreme adaptations and transitioned to a fully aquatic lifestyle1,2. In whales, this is associated with a substantial increase in maximum body size. Although an elongate body was acquired early in cetacean evolution3, the maximum body mass of baleen whales reflects a recent diversification that culminated in the blue whale4. More generally, hitherto known gigantism among aquatic tetrapods evolved within pelagic, active swimmers. Here we describe Perucetus colossus-a basilosaurid whale from the middle Eocene epoch of Peru. It displays, to our knowledge, the highest degree of bone mass increase known to date, an adaptation associated with shallow diving5. The estimated skeletal mass of P. colossus exceeds that of any known mammal or aquatic vertebrate. We show that the bone structure specializations of aquatic mammals are reflected in the scaling of skeletal fraction (skeletal mass versus whole-body mass) across the entire disparity of amniotes. We use the skeletal fraction to estimate the body mass of P. colossus, which proves to be a contender for the title of heaviest animal on record. Cetacean peak body mass had already been reached around 30 million years before previously assumed, in a coastal context in which primary productivity was particularly high.

A new protocetid whale offers clues to biogeography and feeding ecology in early cetacean evolution.

Over about 10 million years, the ancestors of whales transformed from herbivorous, deer-like, terrestrial mammals into carnivorous and fully aquatic cetaceans. Protocetids are Eocene whales that represent a unique semiaquatic stage in that dramatic evolutionary transformation. Here, we report on a new medium-sized protocetid, Phiomicetus anubis gen. et sp. nov., consisting of a partial skeleton from the middle Eocene (Lutetian) of the Fayum Depression in Egypt. The new species differs from other protocetids in having large, elongated temporal fossae, anteriorly placed pterygoids, elongated parietals, an unfused mandibular symphysis that terminates at the level of P3, and a relatively enlarged I3. Unique features of the skull and mandible suggest a capacity for more efficient oral mechanical processing than the typical protocetid condition, thereby allowing for a strong raptorial feeding style. Phylogenetic analysis nests Phiomicetus within the paraphyletic Protocetidae, as the most basal protocetid known from Africa. Recovery of Phiomicetus from the same bed that yielded the remingtonocetid Rayanistes afer provides the first clear evidence for the co-occurrence of the basal cetacean families Remingtonocetidae and Protocetidae in Africa. The discovery of Phiomicetus further augments our understanding of the biogeography and feeding ecology of early whales.

What are the limits on whale ear bone size? Non-isometric scaling of the cetacean bulla.

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 dimensions of the bony auditory complex, in relation to body size, for both living and extinct cetaceans. We compared the dimensions of the tympanic bulla, a conch-shaped ear bone unique to cetaceans, with bizygomatic width—a proxy for cetacean body size. Our results demonstrate that cetacean ears scale non-isometrically with body size, with about 70% of variation explained by increases in bizygomatic width. Our results, which encompass the breadth of the whale fossil record, size diversity, and taxonomic distribution, suggest that functional auditory capacity is constrained by congruent factors related to cranial morphology, as opposed to allometrically scaling with body size.

Middle Eocene (Bartonian) vertebrate fauna from Bandah Formation, Jaisalmer Basin, Rajasthan, Western India

ABSTRACT A small vertebrate faunal assemblage of late Middle Eocene (Bartonian) age is described from the Bandah Formation, a shallow marine deposit in the Jaisalmer Basin of Rajasthan state, Western India. The Bandah assemblage comprises representatives of selachians (sharks, rays), crocodilians, turtles and archaeocete cetaceans (archaic whales). The mammalian component of this fauna, though represented by fragmentary specimens, allows identification of two archaeocete taxa for the first time from the Palaeogene of Rajasthan: an unnamed protocetid close to Babiacetus and an andrewsiphiine remingtonocetid (Kutchicetus sp.). Occurrence of Eocene cetaceans in the Jaisalmer Basin brings to light a new, potentially rich cetacean-yielding horizon in India, and has the potential to allow a better understanding of early whale evolution in the Indian subcontinent.

The role of desmosomes in the ear plug formation in the bowhead whale (Balaena mysticetus).

The external acoustic meatus (EAM) of most baleen whales accumulates cellular debris annually in the lumen as whales age, forming a lamellated ear plug. The bowhead whale ear plug is formed from annually molting lining of the EAM as the entire epithelium releases at the level of the stratum basale during the spring migration. Epithelial regeneration is mostly completed by the fall migration, remaining intact for 6-7 months before being torn off the following spring. Desmosomes are integral to cell-cell adhesion with connecting desmosomal cadherins desmoglein (dsg) and desmocollin (dsc). Paraffin sections of the oral cavity and EAM lining of spring and fall adult bowhead whales, as well as the EAM of spring-caught juvenile, were immunohistochemically examined for the presence of these cadherins. In all fall specimens, both cadherins occurred in all layers except the superficial keratinous layer of the oral cavity. In spring, three different conditions existed: (a) oral cavity of spring-caught adults had reduced cadherins, with superficial fissuring in its keratinized layer and vacuolation in the upper stratum spinosum; (b) EAM of juvenile spring-caught whales displayed fissuring with accompanying reduction of both cadherins in its superficial lining; and (c) EAM lining of spring-caught adults displayed deep fissures, reduced cadherins, and absence of dsc1 in the fissuring zone. These results suggest that shedding of skin layers in mammals, whether normal molting, pathological, or the result of injury and wound repair all revolve around desmosome function. The specific role, structure, and location of these two cadherins need to be further addressed.

Early evolution of the ossicular chain in Cetacea: into the middle ear gears of a semi-aquatic protocetid whale.

Modifications of the morphology and acoustic properties of the ossicular chain are among the major changes that accompanied the adaptation of Cetacea to the aquatic environment. Thus, data on the middle ear ossicles of early whales are crucial clues to understand the first steps of the emblematic terrestrial/aquatic transition that occurred in that group. Yet, the delicate nature and very small size of these bones make their preservation in the fossil record extremely rare. Due to the scarcity of available data, major questions remain concerning the sound transmission pathways in early non-fully aquatic whales. Virtual reconstruction of a partially complete ossicular chain of an Eocene protocetid whale documents for the first time the three ossicles of a semi-aquatic archaeocete. Contrary to previous hypotheses, these ossicles present different evolutionary patterns, showing that the ossicular chain does not act as a single morphological module. Functional analyses of the different middle ear units highlight a mosaic pattern of terrestrial and aquatic signatures. This integrative anatomical and functional study brings strong evidence that protocetids were adapted to their dual acoustic environment with efficient hearing in both air and water.

Reduction of olfactory and respiratory turbinates in the transition of whales from land to sea: the semiaquatic middle Eocene Aegyptocetus tarfa.

Ethmoturbinates, nasoturbinates, and maxilloturbinates are well developed in the narial tract of land-dwelling artiodactyls ancestral to whales, but these are greatly reduced or lost entirely in modern whales. Aegyptocetus tarfa is a semiaquatic protocetid from the middle Eocene of Egypt. Computed axial tomography scans of the skull show that A.tarfa retained all three sets of turbinates like a land mammal. It is intermediate between terrestrial artiodactyls and aquatic whales in reduction of the turbinates. Ethmoturbinates in A.tarfa have 26% of the surface area expected for an artiodactyl. These have an olfactory function and indicate that early whales retained a sense of smell in the transition from land to sea. Maxilloturbinates in A.tarfa have 6% of the surface area expected for an artiodactyl. These have a respiratory function and their markedly reduced size suggests that rapid inhalation and exhalation was already more important than warming and humidifying air, in contrast to extant land mammals. Finally, the maxilloturbinates of A.tarfa, although greatly reduced, still show some degree of similarity to those of artiodactyls, supporting the phylogenetic affinity of cetaceans and artiodactyls based on morphological and molecular evidence.

An Amphibious Whale from the Middle Eocene of Peru Reveals Early South Pacific Dispersal of Quadrupedal Cetaceans

Cetaceans originated in south Asia more than 50 million years ago (mya), from a small quadrupedal artiodactyl ancestor [1-3]. Amphibious whales gradually dispersed westward along North Africa and arrived in North America before 41.2 mya [4]. However, fossil evidence on when, through which pathway, and under which locomotion abilities these early whales reached the New World is fragmentary and contentious [5-7]. Peregocetus pacificus gen. et sp. nov. is a new protocetid cetacean discovered in middle Eocene (42.6 mya) marine deposits of coastal Peru, which constitutes the first indisputable quadrupedal whale record from the Pacific Ocean and the Southern Hemisphere. Preserving the mandibles and most of the postcranial skeleton, this unique four-limbed whale bore caudal vertebrae with bifurcated and anteroposteriorly expanded transverse processes, like those of beavers and otters, suggesting a significant contribution of the tail during swimming. The fore- and hind-limb proportions roughly similar to geologically older quadrupedal whales from India and Pakistan, the pelvis being firmly attached to the sacrum, an insertion fossa for the round ligament on the femur, and the retention of small hooves with a flat anteroventral tip at fingers and toes indicate that Peregocetus was still capable of standing and even walking on land. This new record from the southeastern Pacific demonstrates that early quadrupedal whales crossed the South Atlantic and nearly attained a circum-equatorial distribution with a combination of terrestrial and aquatic locomotion abilities less than 10 million years after their origin and probably before a northward dispersal toward higher North American latitudes. VIDEO ABSTRACT.

A four-legged ancestor led the way for early whales dispersal

A four-legged ancestor led the way for early whales dispersal

Toothless whale fossil fills gap in filter-feeding evolution

Analysis of jawbones suggests early baleen whales used suction to vacuum up their prey. Analysis of jawbones suggests early baleen whales used suction to vacuum up their prey.

Fossil burrow assemblage, not mangrove roots: reinterpretation of the main whale-bearing layer in the late Eocene of Wadi Al-Hitan, Egypt

The UNESCO World Heritage Site of Wadi Al-Hitan near Fayum in the Western Desert of Egypt is well-known for its remarkable abundance and diversity of late Eocene marine fossils, especially well-preserved cetaceans and sirenians. However, the taphonomy of the early Priabonian whales and sea cows is still not fully understood. These marine mammals often occur on specific horizons in the Birket Qarun Formation, for example, on a distinctive firmground called the Camp White Layer (CWL). Vertical, rod-like structures in the CWL were previously interpreted as “mangrove pneumatophores,” which have influenced hypotheses about the habitat of early whales. Here, we reexamine the rod-like structures of the CWL and show that they do not represent mangrove rooting structures based on an analysis of their morphology and an extensive comparison with rooting structures of living mangroves. Instead, the morphology of the rod-like structures indicates that they are trace fossils representing five size classes of marine invertebrate burrows, including burrows of weakly umbonate clams and Ophiomorphidae. The complex overprinting of all burrows toward the top of the CWL indicates stratigraphic condensation caused by low overall rates of sedimentation on a marine flooding surface in the transgressive systems tract. The large number of whale carcasses, abundant invertebrate skeletal remains, logs, marine invertebrate-encrusted celestine crystals, and an extensive, diverse burrow network reflect a combination of environmental and temporal condensation. A peculiar feature of the CWL, celestine crystal aggregates and gastropod celestine pseudomorphs, indicate an evaporative phase that is difficult to reconcile with the current sequence stratigraphic framework.

Lumbar mobility in archaeocetes (Mammalia: Cetacea) and the evolution of aquatic locomotion in the earliest whales

Lumbar mobility in archaeocetes (Mammalia: Cetacea) and the evolution of aquatic locomotion in the earliest whales

Ancient whales did not filter feed with their teeth.

The origin of baleen whales (Mysticeti), the largest animals on Earth, is closely tied to their signature filter-feeding strategy. Unlike their modern relatives, archaic whales possessed a well-developed, heterodont adult dentition. How these teeth were used, and what role their function and subsequent loss played in the emergence of filter feeding, is an enduring mystery. In particular, it has been suggested that elaborate tooth crowns may have enabled stem mysticetes to filter with their postcanine teeth in a manner analogous to living crabeater and leopard seals, thereby facilitating the transition to baleen-assisted filtering. Here we show that the teeth of archaic mysticetes are as sharp as those of terrestrial carnivorans, raptorial pinnipeds and archaeocetes, and thus were capable of capturing and processing prey. By contrast, the postcanine teeth of leopard and crabeater seals are markedly blunter, and clearly unsuited to raptorial feeding. Our results suggest that mysticetes never passed through a tooth-based filtration phase, and that the use of teeth and baleen in early whales was not functionally connected. Continued selection for tooth sharpness in archaic mysticetes is best explained by a feeding strategy that included both biting and suction, similar to that of most living pinnipeds and, probably, early toothed whales (Odontoceti).

Evolution: Hearing and Feeding in Fossil Whales

The evolution of whales marks one of the major transitions in the history of mammals. Two new studies provide key insights into the evolution of hearing specializations and feeding strategies in early whales.

Infrasonic and Ultrasonic Hearing Evolved after the Emergence of Modern Whales

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 inmodern 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 akey 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 oftheir 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).

Singing whales generate high levels of particle motion: implications for acoustic communication and hearing?

Acoustic signals are fundamental to animal communication, and cetaceans are often considered bioacoustic specialists. Nearly all studies of their acoustic communication focus on sound pressure measurements, overlooking the particle motion components of their communication signals. Here we characterized the levels of acoustic particle velocity (and pressure) of song produced by humpback whales. We demonstrate that whales generate acoustic fields that include significant particle velocity components that are detectable over relatively long distances sufficient to play a role in acoustic communication. We show that these signals attenuate predictably in a manner similar to pressure and that direct particle velocity measurements can provide bearings to singing whales. Whales could potentially use such information to determine the distance of signalling animals. Additionally, the vibratory nature of particle velocity may stimulate bone conduction, a hearing modality found in other low-frequency specialized mammals, offering a parsimonious mechanism of acoustic energy transduction into the massive ossicles of whale ears. With substantial concerns regarding the effects of increasing anthropogenic ocean noise and major uncertainties surrounding mysticete hearing, these results highlight both an unexplored pathway that may be available for whale acoustic communication and the need to better understand the biological role of acoustic particle motion.

The walking whales: from land to water in eight million years

1. A Wasted Dig Fossils and War A Whale Ear 2. Fish, Mammal, or Dinosaur? The King Lizard of Cape Cod Basilosaurid Whales* Basilosaurids and Evolution 3. A Whale with Legs The Black and White Hills A Walking Whale 4. Learning to Swim Meeting the Killer Whale From Dog-Paddle to Torpedo Ambulocetid Whales* Ambulocetus and Evolution 5. When the Mountains Grew The High Himalayas Kidnapping in the Hills Indian Whales 6. Passage to India Stranded in Delhi Whales in the Desert A 150-Pound Skull 7. A Trip to the Beach The Outer Banks A Fossilized Coast 8. The Otter Whale The Whale with No Hands Remingtonocetid Whales* Building a Beast out of Bones 9. The Ocean Is a Desert Forensic Paleontology Drinking and Peeing Fossilized Drinking Behavior Walking with Ambulocetus 10. The Skeleton Puzzle If Looks Could Kill How Many Bones Make a Skeleton? Finding Whales' Sisters 11. The River Whales Hearing in Whales Pakicetid Whales* September 11, 2001 12. Whales Conquer the World A Molecular SINE The Black Whale Protocetid Whales* Protocetids and History 13. From Embryos to Evolution A Dolphin with Legs The Marine Park at Taiji Shedding Limbs Whaling in Taiji 14. Before Whales The Widow's Fossils The Ancestors of Whales Indohyus* A Trust for Fossils 15. The Way Forward The Big Question Tooth Development Baleen as Teeth Notes Index *These six headings summarize the biology of the six fossil groups that form the transition between whales and their terrestrial ancestors. Their relationships to each other and to the living families of cetaceans (whales, dolphins, and porpoises) are given in figure 66.

Characterization of lipids in adipose depots associated with minke and fin whale ears: Comparison with “acoustic fats” of toothed whales

Characterization of lipids in adipose depots associated with minke and fin whale ears: Comparison with “acoustic fats” of toothed whales

Return to the sea: the life and evolutionary times of marine mammals

Preface Acknowledgments 1. Marine Mammals Major Groups of Marine Mammals Discovering, Naming, and Classifying Marine Mammals Reconstructing the Hierarchy of Marine Mammals Adaptations and Exaptations What Is a Species and How Do New Species Form? Where Do They Live and Why Are They Where They Are? 2. Past Diversity in Time and Space,Paleoclimates, and Paleoecology Fossils and Taphonomy The Discovery of the First Fossil Marine Mammal (a Whale) The Importance of Fossils How Do We Know the Age of a Fossil? How Do We Know Where Marine Mammals Were? Marine Mammal Diversity and Communities Through Time What Led Marine Mammals Back to the Sea? 3. Pinniped Diversity, Evolution, and Adaptations The Earliest Pinnipeds: Webbed Feet or Flippers? Crown Pinnipeds Desmatophocids: Extinct Phocid Relatives Evolutionary Trends Structural and Functional Innovations and Adaptations Mating and Social Systems, Reproduction, and Life History 4. Cetartiodactylan Diversity, Evolution, and Adaptations Early Whales Had Legs! Crown Cetacea (Neoceti) Evolutionary Trends Structural and Functional Innovations and Adaptations Mating and Social Systems, Reproduction, and Life History 5. Diversity, Evolution, and Adaptations of Sirenians and Other Marine Mammals Walking Sea Cows! Crown Sirenia Evolutionary Trends Structural and Functional Innovations and Adaptations Mating and Social Systems, Reproduction and Life History Desmostylians Aquatic Sloths Marine Otters Polar Bears 6. Ecology and Conservation What Marine Mammals Eat and What Eats Them Interactions Between Human and Marine Mammals: Lessons Learned Extinction: The Rule, Not the Exception Glossary Further Reading and Online Sources Illustration Credits Index