Eric G Ekdale

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Verified

Eric verified their affiliation via an institutional email.

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• PhD
• Lecturer at San Diego State University

As fully aquatic mammals, hearing is arguably the most important sensory component of cetaceans. Increasingly, researchers have been harnessing computed tomography (CT) to investigate the details of the inner ear as they can provide clues to the hearing abilities of whales. We use microCT scans of a broad sampling of the ear bones (periotics) of pr...

Mysticetes (baleen whales) include the largest animals on Earth and are renowned for their songs and long-distance communication. Even so, the scope and origins of their hearing abilities remain poorly understood. Recent work on their sister clade, the toothed whales (odontocetes), has revealed notably convergent trends in the evolution of their in...

The transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bulk filtering batches of small prey using baleen ranks among the most dramatic evolutionary transformations in mammalian history. We review phylogenetic work on the homology of mysticete feeding structures from anatomical, ontogenetic, and genomic perspectives. Si...

Endothermy underpins the ecological dominance of mammals and birds in diverse environmental settings1,2. However, it is unclear when this crucial feature emerged during mammalian evolutionary history, as most of the fossil evidence is ambiguous3–17. Here we show that this key evolutionary transition can be investigated using the morphology of the e...

The transition in Mysticeti (Cetacea) from capture of individual prey using teeth to bulk filtering batches of small prey using baleen ranks among the most dramatic evolutionary transformations in mammalian history. We review phylogenetic work on the homology of mysticete feeding structures from anatomical, ontogenetic, and genomic perspectives. Si...

Endothermy (“warm-bloodedness”) underpins the ecological dominance of mammals and birds in diverse environmental settings1-3. However, it is unclear when this crucial feature emerged during mammalian evolutionary history, as most fossil evidence is ambiguous4-25. Here, we show that new information on this key evolutionary transition can be obtained...

Extant baleen whales (Mysticeti) have a deciduous foetal dentition, but are edentulous at birth. Fossils reveal that the earliest mysticetes possessed an adult dentition. Aetiocetids, a diverse clade of Oligocene toothed mysticetes, have a series of small palatal foramina and associated sulci medial to the postcanine dentition. The openings have be...

Computed tomography (CT) scanning is being increasingly employed in the study of natural history, particularly to investigate the internal anatomy of unique specimens in museum collections. Different techniques to enhance the contrast between tissues have been developed to improve the quality of the scans while preserving the integrity of these rar...

Caviomorphs, the ctenohystrican rodents endemic to the Neotropics, have a long evolutionary history during the Cenozoic, and is one of the more abundant mammalian groups with striking morphological disparity. Several living taxa have auditory regions adapted to hearing low-frequency sounds, yet almost nothing is known about the basicranium in fossi...

Caviomorphs, the ctenohystrican rodents endemic to the Neotropics, have a long evolutionary history during the Cenozoic, and is one of the more abundant mammalian groups with striking morphological disparity. Several living taxa have auditory regions adapted to hearing low-frequency sounds, yet almost nothing is known about the basicranium in fossi...

Extant baleen whales (Mysticeti) share a distinct suite of extreme and unique adaptations to perform bulk filter feeding, such as a long, arched skull, and mandible and the complete loss of adult dentition in favor of baleen plates. However, mysticetes still develop tooth germs during ontogeny. In the fossil record, multiple groups document the tra...

The inner ear of toothed whales (odontocetes) is known to have evolved particular shapes related to their abilities to echolocate and move under water. While the origin of these capacities is now more and more examined, thanks to new imaging techniques, little is still known about how informative inner ear shape could be to tackle phylogenetic issu...

The semicircular canal (SC) system of the inner ear detects head angular accelerations and is essential for navigation and spatial awareness in vertebrates. Because the bony labyrinth encloses the membranous labyrinth SCs, it can be used as a proxy for animal behavior. The bony labyrinth of dicynodonts, a clade of herbivorous non-mammalian synapsid...

Stereolitograph file of the MTA/ACL001 inner ear. (STL)

Linear measurements and respective summary statistics calculations. (XLSX)

Angular measurements and respective summary statistics calculations. (XLSX)

Extant mammal and Endothiodon SC minor and major axis measurements, eccentricity calculations, body mass estimates and linear regression calculations and respective statistics. (XLSX)

Stereolitograph file of the MTA/ACL003 inner ear. (STL)

History of Karoo vertebrate collection in Mozambique and AMNH6156 ascription to Endothiodon. The various important moments of Mozambican Karoo vertebrate paleontology are outlined starting 1949 with Domingos da Rocha to the 1980’s by Brigadas de Cartografia Geológica da Bacia carbonífera de Metangula. (DOCX)

Stereolitograph file of the MTA/ACL002 inner ear. (STL)

Several specimens of the complex trace fossil Hillichnus lobosensis have been recovered from the Middle Eocene Scripps Formation in San Diego County, California. These specimens represent the second undoubted occurrence of the ichnospecies. This report extends the geographic range of the ichnospecies from central to southern California, the stratig...

The morphology of the semicircular canal (SC) system is expected to be finely tuned with animal behavior. Using computed tomography data, we compiled a morphological dataset of dicynodont (n=18) and mammalian (n=54) bony labyrinths and found that dicynodonts have significantly higher eccentricity of the vertical SCs than mammals. Biomechanical mode...

Transformations of ear structures in the evolution of early mammals can be studied with the fossils of mammaliaforms. The middle ear is fully attached to the mandibles in mammaliaforms; however, in Mesozoic eutriconodont and spalacotherioid mammals, it is only connected to the mandible by an ossified Meckel’s cartilage, with the ectotympanic and ma...

Mammals hear across a greater range of auditory frequencies than other vertebrates, which was made possible through major modifications of sound transmission and processing pathways within the middle and inner ears. The first step in the evolution of the ear of mammals is a combination of the prootic and opisthotic bones to form a single petrosal b...

Marsupial mammal relatives (stem metatherians) from the Mesozoic Era (252–66 million years ago) are mostly known from isolated teeth and fragmentary jaws. Here we report on the first near-complete skull remains of a North American Late Cretaceous metatherian, the stagodontid Didelphodon vorax. Our phylogenetic analysis indicates that marsupials or...

Supplementary Figures, Supplementary Tables, Supplementary Notes and Supplementary References

Metatherian synapomorphies

Phylogenetic data matrix

The origin of baleen and filter feeding in mysticete cetaceans occurred sometime between approximately 34 and 24 million years ago and represents a major macroevolutionary shift in cetacean morphology (teeth to baleen) and ecology (raptorial to filter feeding). We explore this dramatic change in feeding strategy by employing a diversity of tools an...

Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high-frequency and ultrasonic sound vibrations and mysticetes to low-frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a po...

The inner ear of mammals consists of the cochlea, which is involved with the sense of hearing, and the vestibule and three semicircular canals, which are involved with the sense of balance. Although different regions of the inner ear contribute to different functions, the bony chambers and membranous ducts are morphologically continuous. The gross...

Information is scarce on gray whale (Eschrichtius robustus) anatomy and that of mysticetes in general. Dissection of the head of a neonatal gray whale revealed novel anatomical details of the eye, blowhole, incisive papilla with associated nasopalatine ducts, sensory hairs, and throat grooves. Compared to a similar sized right whale calf, the gray...

The gray whale (Eschrichtius robustus) is the sole living representative of the mysticete (baleen whale) family Eschrichtiidae. Previous anatomical work on gray whales has been limited owing, in part, to difficulties of specimen access. These contributions to the anatomy of the gray whale head based on dissection of a stranded specimen from norther...

Mysticetes have evolved a novel filter feeding apparatus-baleen-an epidermal keratinous tissue composed of keratin that grows as a serial arrangement of transverse cornified laminae from the right and left sides of the palate. The structure and function of baleen varies among extant mysticete clades and this variation likely can be viewed as adapta...

Little is known about the anatomy and musculature of the gray whale (Eschrichtius robustus), especially related to the anatomy of the tongue and hyoid region. The recovery of an extremely fresh head of a neonatal female gray whale provided an opportunity to conduct the first in-depth investigation of the musculoskeletal features of the tongue and h...

Retia mirabilia play broad roles in cetacean physiology, including thermoregulation during feeding and pressure regulations during diving. Vascular bundles of lingual retia are described within the base of the tongue of a neonatal female gray whale (Eschrichtius robustus). Each rete consists of a central artery surrounded by four to six smaller vei...

The origin of baleen in mysticetes heralded a major transition during cetacean evolution. Extant mysticetes are edentulous in adulthood, but rudimentary teeth develop in utero within open maxillary and mandibular alveolar grooves. The teeth are resorbed prenatally and the alveolar grooves close as baleen germ develops. Arteries supplying blood to h...

The specimen number for Eumetopias jubatus in Table S1 of the Supporting Information is incorrect. This specimen is not accessioned into a museum collection and thus does not have an associated specimen number. Specimen number TMM M-171 is associated with Equus caballus as identified correctly in the table.

The cetacean nose presents a unique suite of anatomical modifications. Key among these is posterior movement of the external nares from the tip of the rostrum to the top of the head. Concomitant with these anatomical changes are functional changes including the evolution of echolocation in odontocetes, and reduction of olfaction in Neoceti (crown o...

The evolution of hearing in cetaceans is a matter of current interest given that odontocetes (toothed whales) are sensitive to high frequency sounds and mysticetes (baleen whales) are sensitive to low and potentially infrasonic noises. Earlier diverging stem cetaceans (archaeocetes) were hypothesized to have had either low or high frequency sensiti...

Variation is a naturally occurring phenomenon that is observable at all levels of morphology, from anatomical variations of DNA molecules to gross variations between whole organisms. The structure of the otic region is no exception. The present paper documents the broad morphological diversity exhibited by the inner ear region of placental mammals...

Ancestral character state reconstructions for ancestral nodes in text Figure 2. Letters in the first column refer to node labels in text Figure 2. Ancestral states reconstructed in Mesquite [94]. Definitions of characters: LSC Entry, entry of the posterior limb of the lateral semicircular canal into the secondary common crus, posterior ampulla, or...

Taxa examined and scanning parameters. a Definitions of parameters are as follows: FR, field of reconstruction refers to the dimensions of an individual CT slice, expressed in millimeters; Pixel, interpixel spacing, or vertical and horizontal dimensions of an individual pixel, expressed in millimeters, and calculated as FR/Size; Size, number of pix...

Additional information, imagery, and sources of data selected specimens. Further imagery is available at http://morphobank.org/index.php/Projects/ProjectOverview/project_id/833. Institutional abrreviations listed in Table S1. (PDF)

Three most parsimonious trees recovered from phylogenetic analysis of 48 petrotympanic characters. Major difference between topologies lies with Eschrichtius robusts and Megaptera novaeangliae (in bold). (TIFF)

Measurements (mm) of tympani bulla of balaenid and neobalaenid species. (PDF)

Measurements (mm) of tympanic bulla of balaenopterid and eschrichtiid species. (PDF)

Petrosal measurements (mm) among mysticetes and reated taxa. (PDF)

Dichotomous key for identifying extant species of mysticetes using the petrotympanic complex. (PDF)

Six most parsimonious trees recovered from phylogenetic analysis of petrotympanic characters excluding #45 (location of hiatus Fallopii). (TIFF)

List of extant mysticetes studied (institutional abbreviations in text). (PDF)

Tympanic bulla anterior lobe measurements (mm) among mysticetes. (PDF)

Tympanic bulla conical process measurements (mm) among mysticetes. (PDF)

Data matrix of petrotrympanic characters scored for extant mysticetes used in phylogeneti analyses. Matrix can be downloaded from project page associated with this manuscript at MorphoBank (www.morphobank.org). (PDF)

Phylogenetic characters derived from the petrotympanic complex of extant mysticetes. Further information can be found on the project page associated with this study at MorphoBank (www.morphobank.org). (PDF)

Background: Anatomical comparisons of the ear region of baleen whales (Mysticeti) are provided through detailed osteological descriptions and high-resolution photographs of the petrotympanic complex (tympanic bulla and petrosal bone) of all extant species of mysticete cetaceans. Salient morphological features are illustrated and identified, includ...

The morphology of the labyrinth of zhelestids, a group of eutherian mammals from the Late Cretaceous, agrees with that of other extinct eutherians, including Kulbeckia kulbecke, Ukhaatherium gobiensis, and Zalambdalestes lechei. Features of the labyrinth of zhelestids include a cochlea with one and a half turns and a secondary common crus, which ar...

A large sample of isolated elephantimorph petrosal bones was recovered from Pleistocene deposits in Friesenhahn Cave, Bexar County, Texas. Morphology of the middle and inner ear of the elephantimorphs is described and variation within the sample is identified. Observed variations occur in the stapedial ratio, morphology of the aquaeductus Fallopii,...

Ontogeny, or the development of an individual from conception to death, is a major source of variation in vertebrate morphology. All anatomical systems are affected by ontogeny, and knowledge of the ontogenetic history of these systems is important to understand when formulating biological interpretations of evolutionary history and physiology. The...

Sulestes karakshi Nessov, 1985b (= Deltatheroides kizylkumensis Nessov, 199374. Nessov , L. A. 1993 . [New Mesozoic mammals of Middle Asia and Kazakhstan and comments about evolution of theriofaunas of Cretaceous coastal plains of Asia] . Trudy Zoologicheskogo Instituta RAN , 249 : 105 – 133 . [In Russian] View all references = Marsasia aenigma Nes...

The morphological diversity of the external and internal surfaces of the petrosal bone, which contains the structures of the inner ear, across a broad range of therian mammals is documented, and patterns of variation across taxa are identified. One pattern of variation is the result of ontogenetic changes in the ear region, as described for the ext...