A natural endocast of an early Miocene odontocete and its implications in cetacean brain evolution

Bisconti, Michelangelo; Damarco, Piero; Tartarelli, Giandonato; Pavia, Marco; Carnevale, Giorgio

doi:10.1002/cne.25015

Cited by 11 publications

(22 citation statements)

References 74 publications

(121 reference statements)

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“…5). Modern Cetacea are characterized by a very small and narrow vermis compared to the two voluminous, highly convoluted, cerebellar hemispheres (e.g., Ries and Langworthy 1937;Pilleri 1966a,b;Hanson et al 2013;Bisconti et al 2021). Regarding archaeocetes, little of the cerebellum is visible on cranial endocasts of basilosaurids as most of its surface is covered with a large rete mirabile (e.g., Breathnach 1955;Pilleri 1991;Geisler and Luo 1998;Uhen 2004), making it impossible to observe the relative size of the vermis accurately.…”

Section: Primitive Features Of the Brain Of Indohyus Indiraementioning

confidence: 99%

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

Orliac

Thewissen

2021

J Mammal Evol

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We present the first description of the endocranial cast of the small raoellid artiodactyl Indohyus indirae. Raoellidae are sister group to Cetacea and the new morphological observations allow for outlining some of the early steps of the evolutionary history of the cetacean brain. The combination of primitive artiodactyl features and typical cetacean characters is unique about the Indohyus endocast. The fact that it presents the symplesiomorphic brain pattern observed in earliest Artiodactyla indicates that the cetacean brain derives from a very simple, plesiomorphic brain, with simple neocortical folding pattern, widely exposed midbrain, and concurrent small neocortex expansion. On the other hand, the Indohyus endocast shows characters that also occur in early cetaceans. These include modifications of the olfactory tract with narrow, elongated olfactory bulbs and peduncles, accompanied by a posterior location of the braincase in the cranium. The derived endocranial cast features of Indohyus mainly reflect changes in cranial architecture and these are most probably associated with modifications of the masticatory apparatus and a shift in diet. Indohyus meninges were very thin like in most terrestrial artiodactyls and it had no extensive rostral or lateral retia mirabilia. It however shows a branching pattern of ramification of intraosseous blood sinuses above the cerebellum that might represent the initial development of the caudal venous rete mirabile that would have colonized the endocranial cavity later on, in early archaeocetes.

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Section: Primitive Features Of the Brain Of Indohyus Indiraementioning

confidence: 99%

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

Orliac

Thewissen

2021

J Mammal Evol

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“…Answering these questions is problematic because our knowledge of brain evolution in baleen whales is very limited. The fossil record provides only little help because only a few skull endocasts have been reported and only a handful of brain and endocast measurements are available for both extant and fossil species [Cozzi et al, 2017;Bisconti et al, 2021c;McCurry et al, 2021]. The lack of data is a major limiting factor that prevents the reconstruction of many aspects of the evolution of the mysticete brain.…”

Section: Introductionmentioning

confidence: 99%

“…Recent reviews showed a long gap in our knowledge about brain evolution between early-diverging, late Eocene, toothed mysticetes and the extant species with only a handful of data for the interval of around 35 million years that separates them [Boessenecker et al, 2017;Bisconti et al, 2021c;McCurry et al, 2021]. The evolutionary path linking the morphological patterns of the brain of the oldest mysticetes and the living species is scarcely known, and this prevents answering the above questions.…”

Section: Introductionmentioning

confidence: 99%

“…Evolution of morphology and size of the brain is better known in the sister group of the mysticetes (namely, the Odontoceti or toothed whales). Numerous measurements and descriptions of brains and endocasts are available that resulted from a considerable body of work by many authors [e.g., Boessenecker et al, 2017;Cozzi et al, 2017;Bisconti et al, 2021c;and literature therein]. In general, it is well established that Odontoceti include the four most encephalized mammals apart from man (i.e., Tur siops truncatus, Delphinus delphis, Lagenorhynchus obli quidens, and Sotalia fluviatilis) [Tartarelli and Bisconti, 2006]; however, a high encephalization is not a common feature in odontocete evolution.…”

Section: Introductionmentioning

confidence: 99%

“…From a morphological view, the brain of the living mysticetes is characterized by a wide exposure of the cerebellum posteriorly to the brain hemispheres and by a longer exposure of the thalamus ventrally [Bisconti et al, 2021c]. These characteristics represent ancestral states in that it is possible to observe the same characters in earlydiverging odontocetes and archaeocetes [Dart, 1923;Bisconti et al, 2021c].…”

Section: Introductionmentioning

confidence: 99%

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High Encephalization in a Fossil Rorqual Illuminates Baleen Whale Brain Evolution

et al. 2021

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Baleen whales are considered underencephalized mammals due to their reduced brain size with respect to their body size (encephalization quotient [EQ] << 1). Despite their low EQ, mysticetes exhibit complex behavioral patterns in terms of motor abilities, vocal repertoire, and cultural learning. Very scarce information is available about the morphological evolution of the brain in this group; this makes it difficult to investigate the historical changes in brain shape and size in order to relate the origin of the complex mysticete behavioral repertoire to the evolution of specific neural substrates. Here, the first description of the virtual endocast of a fossil balaenopterid species, <i>Marzanoptera tersillae</i> from the Italian Pliocene, reveals an EQ of around 3, which is exceptional for baleen whales. The endocast showed a morphologically different organization of the brain in this fossil whale as the cerebral hemispheres are anteroposteriorly shortened, the cerebellum lacks the posteromedial expansion of the cerebellar hemispheres, and the cerebellar vermis is unusually reduced. The comparative reductions of the cerebral and cerebellar hemispheres suggest that the motor behavior of <i>M. tersillae</i> probably was less sophisticated than that exhibited by the extant rorqual and humpback species. The presence of an EQ value in this fossil species that is around 10 times higher than that of extant mysticetes opens new questions about brain evolution and provides new, invaluable information about the evolutionary path of morphological and size change in the brain of baleen whales.

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Anatomical correlates and nomenclature of the chiropteran endocranial cast

Maugoust

Orliac

2023

The Anatomical Record

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Bats constitute a diverse group of mammals highly specialized toward active flight and ultrasound echolocation. These adaptations reflect on their morpho-anatomy and have been tentatively linked to brain morphology and volumetry. Despite their small size and delicateness, bat skulls and natural braincase casts have been preserved in the fossil record and allow for investigating brain evolutionary history and inferring paleobiology. Recent progresses in imaging techniques now allow for virtually extracting internal structures, assuming that the shape of internal cavity casts reflects soft organ morphology. Such a correspondence is not straightforward regarding the braincase cast ("endocast"), because meninges and vascular tissues surround the brain in living organisms and the resulting endocast morphology is a mosaic of the marks left by all these tissues. The hypothesis that the endocast reflects the brain in terms of both external shape and volume has drastic implications when addressing brain evolution, but has been little discussed. To date, a single work addressed the correspondences regarding brain and braincase in bats. Here, taking advantage of the advent of imaging techniques, we review the anatomical, neuroanatomical, and angiological literature and compare the available knowledge of bat's braincase anatomy to a sample of endocranial casts representing most modern bat families. Such comparison allows for proposing a Chiroptera-scale nomenclature for future descriptions and comparisons of bat endocasts. This also encourages further works to formally test what is hypothesized here.

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A natural endocast of an early Miocene odontocete and its implications in cetacean brain evolution

Cited by 11 publications

References 74 publications

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

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

High Encephalization in a Fossil Rorqual Illuminates Baleen Whale Brain Evolution

Anatomical correlates and nomenclature of the chiropteran endocranial cast

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