Digital Cranial Endocast of Hyopsodus (Mammalia, “Condylarthra”): A Case of Paleogene Terrestrial Echolocation?

We here describe the endocranial cast of the Eocene archaic ungulate Hyopsodus lepidus AMNH 143783 (Bridgerian, North America) reconstructed from X-ray computed microtomography data. This represents the first complete cranial endocast known for Hyopsodontinae. The Hyopsodus endocast is compared to other known “condylarthran” endocasts, i. e. those of Pleuraspidotherium (Pleuraspidotheriidae), Arctocyon (Arctocyonidae), Meniscotherium (Meniscotheriidae), Phenacodus (Phenacodontidae), as well as to basal perissodactyls (Hyracotherium) and artiodactyls (Cebochoerus, Homacodon). Hyopsodus presents one of the highest encephalization quotients of archaic ungulates and shows an “advanced version” of the basal ungulate brain pattern, with a mosaic of archaic characters such as large olfactory bulbs, weak ventral expansion of the neopallium, and absence of neopallium fissuration, as well as more specialized ones such as the relative reduction of the cerebellum compared to cerebrum or the enlargement of the inferior colliculus. As in other archaic ungulates, Hyopsodus midbrain exposure is important, but it exhibits a dorsally protruding largely developed inferior colliculus, a feature unique among “Condylarthra”. A potential correlation between the development of the inferior colliculus in Hyopsodus and the use of terrestrial echolocation as observed in extant tenrecs and shrews is discussed. The detailed analysis of the overall morphology of the postcranial skeleton of Hyopsodus indicates a nimble, fast moving animal that likely lived in burrows. This would be compatible with terrestrial echolocation used by the animal to investigate subterranean habitat and/or to minimize predation during nocturnal exploration of the environment

The Endocranial Cast of Indohyus (Artiodactyla, Raoellidae): The Origin of the Cetacean Brain

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MorphoMuseuM : un journal scientifique pour la publication de spécimens virtuels

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MORPHOMUSEUM: AN ONLINE PLATFORM FOR PUBLICATION AND STORAGE OF VIRTUAL SPECIMENS

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Infrasonic and Ultrasonic Hearing Evolved after the Emergence of Modern Whales

International audienceMysticeti (baleen whales) and Odontoceti (toothed whales) today greatly differ in their hearing abilities: Mysticeti are presumed to be sensitive to infrasonic noises [1, 2, 3], whereas Odontoceti are sensitive to ultrasonic sounds [4, 5, 6]. Two competing hypotheses exist regarding the attainment of hearing abilities in modern whales: ancestral low-frequency sensitivity [7, 8, 9, 10, 11, 12, 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)

The inner ear morphology of the ‘condylarthran’ <i>Hyopsodus lepidus</i>

<div><p>We describe the bony labyrinth morphology of the Eocene ‘archaic ungulate’ <i>Hyopsodus</i><i>lepidus</i> (Bridgerian, North America) reconstructed from micro computed tomography scan data. Comparisons with the inner ear of the Eocene early diverging artiodactyl <i>Diacodexis</i> and perissodactyl <i>Xenicohippus</i> allow refining the picture of the ancestral inner ear morphology of Euungulates. These taxa are very close morphologically and mostly differ by slight differences in their semicircular canal angulations and profile. They all present a secondary crus and a low position of the plane of the lateral semicircular canal relative to the posterior semicircular canal. These two characters, considered as ancestral features for Theria, might be symplesiomorphies of Euungulata as well. <i>Hyopsodus</i> and <i>Xenicohippus</i> share characters also observed in other basal Equoidea, which would support the close relationship between these two taxa previously proposed in the literature. A functional study of the cochlea of <i>Hyopsodus lepidus</i> is also realised to discuss its putative ability of using terrestrial echolocation previously proposed in the literature. The morphology of the cochlea of <i>Hyopsodus lepidus</i> does not indicate a specialisation to sophisticated echolocation such as observed today in microchiropteran bats. However, its estimated audible range of frequencies (208 Hz to 76.8 KHz) would be compatible with terrestrial echolocation.</p></div

Endocranial Casts of Camelops hesternus and Palaeolama sp.: New Insights into the Recent History of the Camelid Brain

Endocranial casts are capable of capturing the general brain form in extinct mammals due to the high fidelity of the endocranial cavity and the brain in this clade. Camelids, the clade including extant camels, llamas, and alpacas, today display high levels of gyrification and brain complexity. The evolutionary history of the camelid brain has been described as involving unique neocortical growth dynamics which may have led to its current state. However, these inferences are based on their fossil endocast record from approximately ∼40 Mya (Eocene) to ∼11 Mya (Miocene), with a gap in this record for the last ∼10 million years. Here, we present the first descriptions of two camelid endocrania that document the recent history of the camelid brain: a new specimen of Palaeolama sp. from ∼1.2 Mya, and the plaster endocast of Camelops hesternus, a giant camelid from ∼44 to 11 Kya which possessed the largest brain (∼990 g) of all known camelids. We find that neocortical complexity evolved significantly between the Miocene and Pleistocene Epochs. Already ∼1.2 Mya the camelid brain presented morphologies previously known only in extant taxa, especially in the frontal and parietal regions, which may also be phylogenetic informative. The new fossil data indicate that during the Pleistocene, camelid brain dynamics experienced neocortical invagination into the sagittal sinus rather than evagination out of it, as observed in Eocene to Miocene taxa

Paleoneurology of Artiodactyla, an Overview of the Evolution of the Artiodactyl Brain

This chapter presents a detailed review of works published on Artiodactyla endocasts and provides a comprehensive examination of artiodactyl brain evolutionary history, including Cetacea, from the early Eocene (c.a. 45 Ma) onwards. Artiodactyl endocasts have been studied from the second half of the nineteenth century to the 1970s. These works on natural or artificial endocasts widely took place outside the frame of phylogenetic concerns. We compile the data available, including recent works using μCT-scan imagery techniques, and place them in a phylogenetic framework. We also provide new data regarding Paleogene representatives of North American extinct clades (Homacodon, Helohyus, Leptauchenia, Agriochoerus), endemic European clade (Mouillacitherium, Dichobune), and Suoidea (Palaeochoerus). The brain of modern artiodactyls is remarkable by the expansion and by the folding of the neopallium. Their brains are highly gyrencephalic and differ in their neocortical pattern. We highlight diversity of neopallium patterns of Artiodactyla and their convergent nature on the last 45 millions years and show that encephalization increases with time, but with different modes between terrestrial and fully aquatic taxa (i.e. Cetacea). Each clade shows a mosaic pattern of derived and plesiomorphic features that now has to be put in perspective with both the history and ecology of taxa

Small hyotheriine suids (Mammalia, Artiodactyla) from the late early Miocene of Turkey and a short overview of early Miocene small suoids in the Old World

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Endocast measurements for <i>Hyopsodus</i> (given in mm, and mm³ for endocast volume).

<p>R = right side of specimen; L = left side of specimen;</p><p>* = <i>H. paulus</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030000#pone.0030000-Gazin2" target="_blank">[35]</a>, pl. 1);</p><p>** = <i>H. miticulus</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030000#pone.0030000-Gazin2" target="_blank">[35]</a>, pl. 5).</p