Natural Endocast Research Articles

Fossil endocasts of two Pleistocene bovines (Bovidae, Mammalia) from the Upper Siwaliks of northern India

ABSTRACT Natural fossil endocasts are a direct source of information on palaeoneurology of extinct species and, in recent years, there has been a dramatic revival of interest in palaeoneurological investigations. Endocasts of bovines (family Bovidae), however, remain hitherto undescribed. Here we describe two well preserved natural endocasts of Pleistocene bovines from the Upper Siwalik deposits exposed near Panchkula (Haryana), in the vicinity of Chandigarh city, northern India. The two endocasts, referred here to cf. Bubalus platyceros and Bovini indet., are similar in gross morphology but differ significantly in several respects. Comparison with modern bovines reveals important similarities between the Siwalik endocasts and the brains of Bos taurus and Bubalus bubalis, especially in size of their cerebral hemispheres and placement of fissures. However, the Siwalik endocasts differ significantly in being less replete with gyri and sulci, suggesting that bovines have undergone an increase in complexity of their neuroanatomy during the later part of the Pleistocene. This study also supports the recently proposed hypothesis that mammalian taxa with relatively large brain size were more likely to survive the Pleistocene megafaunal extinctions.

Cephalic salt gland evolution in Mesozoic pelagic crocodylomorphs

Abstract Secondarily marine tetrapod lineages have independently evolved osmoregulatory adaptations for life in salt water but inferring physiological changes in extinct marine tetrapods is difficult. The Mesozoic crocodylomorph clade Thalattosuchia is unique in having both direct evidence from natural endocasts and several proposed osteological correlates for salt exocrine glands. Here, we investigate salt gland evolution in thalattosuchians by creating endocranial reconstructions from CT scans of eight taxa (one basal thalattosuchian, one teleosauroid, two basal metriorhynchoids and four metriorhynchids) and four outgroups (three extant crocodylians and the basal crocodyliform Protosuchus) to identify salt gland osteological correlates. All metriorhynchoids show dorsolateral nasal cavity expansions corresponding to the location of nasal salt glands in natural casts, but smaller expansions in teleosauroids correspond more with the cartilaginous nasal capsule. The different sizes of these expansions suggest the following evolutionary sequence: (1) plesiomorphically small glands present in semi-aquatic teleosauroids draining through the nasal vestibule; (2) moderately sized glands in the basalmost metriorhynchoid Pelagosaurus; and (3) hypertrophied glands in the clade comprising Eoneustes and metriorhynchids, with a pre-orbital fenestra providing a novel exit for salt drainage. The large gland size inferred from basal metriorhynchoids indicates advanced osmoregulation occurred while metriorhynchoids were semi-aquatic. This pattern does not precisely fit into current models of physiological evolution in marine tetrapods and suggests a unique sequence of changes as thalattosuchians transitioned from land to sea.

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

The natural endocast Museo di Geologia e Paleontologia of the Università degli Studi di Torino (MGPT)-PU 13873 is described and analyzed in order to interpret its taxonomic affinities and its potential significance on our understanding of cetacean brain evolution. The endocast is from the early Miocene of Piedmont (between ca. 19 and 16 million years ago), Northwestern Italy, and shows a number of plesiomorphic characters. These include: scarcely rounded cerebral hemispheres, cerebellum exposed in dorsal view with little superimposition by the cerebral hemispheres, short temporal lobe, and long sylvian fissure. The distance between the hypophysis and the rostral pons is particularly high, as it was determined by the calculus of the hypothalamus quotient, suggesting that the development of a deep interpeduncular fossa was not as advanced as in living odontocetes. The encephalization quotient (EQ) of MGPT-PU 13873 is ~1.81; therefore, this specimen shows an EQ in line with other fossil whales of the same geological age (early Miocene). Comparative analysis shows that there is a critical lack of data from the late Miocene and Pliocene that prevents us to fully understand the recent evolution of the EQ diversity in whales. Moreover, the past diversity of brain size and shape in mysticetes is virtually unknown. All these observations point to the need of additional efforts to uncover evolutionary patterns and processes on cetacean brain evolution.

Revised estimates of Taung’s brain size growth

Cranial capacity, a proxy for the volume of the brain and associated cranial contents, is an important yardstick used to compare early hominin species because increasing brain size is a key characteristic of our lineage. In 1925, Raymond Dart claimed that a natural endocast found at the Buxton Limeworks near Taung, South Africa (which he named Australopithecus africanus), showed signs of neural reorganisation, but its juvenile status complicated comparison to other hominoid species. In an attempt to put its brain size and reorganisation into a comparative context, subsequent researchers have tried to estimate Taung’s adult cranial capacity by comparison to coarse-grained hominoid growth data. In this study, we simulated brain growth in A. africanus using asymptotic growth models in known-age mountain gorillas, chimpanzees and modern humans, and show that, at just under 4 years old, Taung’s brain had already finished or nearly finished growing according to hominoid developmental schedules. Percentage-growth remaining estimates are lower here than in previous studies using cross-sectional ontogenetic samples of unknown chronological age. Our new adult estimates (between 404 cm3 and 430 cm3 overall and 405–406 cm3 for chimpanzee models) are smaller than previous estimates with a ‘starting’ cranial capacity of 404 cm3, supporting the hypothesis that Taung’s adult brain size would have fallen toward the lower end of the A. africanus range of variation and strengthening the case that Taung was female.
 Significance:
 
 This is one of several recent studies to show that brain growth is completed in African apes and humans earlier than previously appreciated.
 New adult cranial capacity estimates for Taung are lower than previous estimates, supporting the hypothesis that Taung was female.
 Cessation of brain growth in hominoids at earlier ages than previously reported suggests that adult cranial capacities for hominin juvenile specimens have been overestimated.
 
 Open data set:
 http://dx.doi.org/10.17632/wyfvwd4s22

The <italic>Australopithecus</italic> Taun child skull: A fossil that changed human evolution history

The <italic>Australopithecus</italic> Taun child skull: A fossil that changed human evolution history

Evolution of the modern human brain.

When compared to the brains of our closest living relatives, chimpanzees and bonobos, the brains of modern humans are larger and differently shaped. This chapter reviews what we know about the evolutionary history of these differences. We can make an educated guess about the size and shape of the brains of the hypothetical common ancestor of modern humans and chimpanzees/bonobos, but between ca. 8 million years ago and the present day evidence about the size and shape of the brain comes from either natural endocasts, which are literally brain-shaped rocks, or from individuals for which enough of the brain case is preserved to provide estimates of endocranial volume and/or the relative proportions of the different regions of the cerebral hemispheres and the cerebellum. The tempo and mode of brain size increase in the hominin clade has been the subject of spirited debate, but we suggest that some of this controversy is the combination of an overreliance on frequentist statistical tests and researchers addressing these issues at different taxonomic scales. The existence and significance of shape changes are also controversial topics, made more so by the dearth of reliable evidence.

Paleoneuroanatomy of the aetosaur Neoaetosauroides engaeus (Archosauria: Pseudosuchia) and its paleobiological implications among archosauriforms.

The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, we describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the inclination of the inner ear, could support the proposal for an animalivorous diet, instead of an herbivorous one as in most aetosaurs. The new information here obtained contributes to the knowledge of the neuroanatomical diversity of archosauriforms and more specifically among pseudosuchians and their paleobiological roles in the Triassic continental communities.

Morphoarchitectural variation in South African fossil cercopithecoid endocasts

Despite the abundance of well-preserved crania and natural endocasts in the South African Plio-Pleistocene cercopithecoid record, which provide direct information relevant to the evolution of their endocranial characteristics, few studies have attempted to characterize patterns of external brain morphology in this highly successful primate Superfamily. The availability of non-destructive penetrating radiation imaging systems, together with recently developed computer-based analytical tools, allow for high resolution virtual imaging and modeling of the endocranial casts and thus disclose new perspectives in comparative paleoneurology. Here, we use X-ray microtomographic-based 3D virtual imaging and quantitative analyses to investigate the endocranial organization of 14 cercopithecoid specimens from the South African sites of Makapansgat, Sterkfontein, Swartkrans, and Taung. We present the first detailed comparative description of the external neuroanatomies that characterize these Plio-Pleistocene primates. Along with reconstruction of endocranial volumes, we combine a semi-automatic technique for extracting the neocortical sulcal pattern together with a landmark-free surface deformation method to investigate topographic differences in morphostructural organization. Besides providing and comparing for the first time endocranial volume estimates of extinct Plio-Pleistocene South African cercopithecoid taxa, we report additional information regarding the variation in the sulcal pattern of Theropithecus oswaldi subspecies, and notably of the central sulcus, and the neuroanatomical condition of the colobine taxon Cercopithecoides williamsi, suggested to be similar for some aspects to the papionin pattern, and discuss potential phylogenetic and taxonomic implications. Further research in virtual paleoneurology, applied to specimens from a wider geographic area, is needed to clarify the polarity, intensity, and timing of cortical surface evolution in cercopithecoid lineages.

First virtual endocasts of a fossil rodent: Ischyromys typus (Ischyromyidae, Oligocene) and brain evolution in rodents

ABSTRACTThe evolution of the brain in rodents has rarely been studied from the perspective of the fossil record. Here we describe the first virtual endocast of a fossil rodent, pertaining to Ischyromys typus (ROMV 1007; Orellan North American Land Mammal Age [NALMA], Nebraska), and form comparisons with partial and complete natural endocasts pertaining to the same genus, and with the virtual endocast of a closely related extant rodent (Sciurus carolinensis; AMNH 258346). These data allow us to formulate the first hypotheses informed by the fossil record concerning changes in brain size and shape through time in rodents, and to make comparisons with other euarchontoglirans, including Primates. Ischyromys exhibits several aspects of brain morphology that can be inferred to be primitive, in part based on their presence in plesiadapiform primates (e.g., exposed midbrain), although variation exists within the genus Ischyromys with respect to the visibility of the inferior colliculi. There is some evidence that neocorticalization occurred in rodents through time but to a lesser degree than in Primates. Arboreality might be linked to increases in the encephalization quotient and specializations related to vision in rodents, which contrasts with the situation in Primates. Finally, Oligocene rodents had smaller olfactory bulbs compared with plesiadapiform primates from the Eocene, meaning that olfaction might have been less critical in the early evolution of rodents. These results show that the evolution of the brain in mammals does not always follow the same evolutionary trajectories and demonstrates the importance of considering ecological factors when looking at brain size.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Bertrand, O. C., and M. T. Silcox. 2016. First virtual endocasts of a fossil rodent: Ischyromys typus (Ischyromyidae, Oligocene) and brain evolution in rodents. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1096275.

A lynx natural brain endocast from Ingarano (Southern Italy; Late Pleistocene): Taphonomic, Morphometric and Phylogenetic approaches

A natural brain endocast from the Late Pleistocene site of Ingarano (Apulia, Southern Italy) has been investigated in detail using CT scanning, image processing techniques and Geometric Morphometrics. Our analyses provide relevant information about the taxonomy and taphonomy of the specimen. The external morphology of the endocast was compared to those of the brains of living felids. This combination of techniques is commonly used in palaeoneurology for neuroanatomical and behavioural inferences and enables us to classify the fossil as the first reported natural brain endocast of a Late Pleistocene lynx. In addition, the investigation structure of the internal strctures of the natural endocast aloud us to reconstruct its taphonomic history. Download the complete issue.

Endocasts and brain evolution in Anthracotheriidae (Artiodactyla, Hippopotamoidea).

Anthracotheres are a fossil family of 'Suiformes' from the Old World, North and Central America. They are known from the middle Eocene to the late Pliocene, and are suggested to be the stem group of Hippopotamidae. Yet, their soft anatomy remains poorly known. In this study we describe the virtual endocast of the late Oligocene anthracothere Microbunodon minimum, reconstructed using microtomography, as well as the natural endocast of Merycopotamus medioximus from the late Miocene. These are the first anthracothere endocasts ever described. Particular attention is given to the relative proportions of the brain, the neocortex, the cerebellum and the olfactory bulbs. The 'backward shift' of the pituitary of M. minimum, and the possible presence of a K lobe in M. medioximus, is discussed. Previous statements that some endocranial characters were subject to convergence among mammals are also corroborated.

METRIORHYNCHIDAE (CROCODYLOMORPHA: THALATTOSUCHIA) FROM UPPER JURASSIC–LOWER CRETACEOUS OF NEUQUÉN BASIN (ARGENTINA), WITH COMMENTS ON THE NATURAL CASTS OF THE BRAIN

Fil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Division Paleontologia Vertebrados; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Cranial anatomy of the Duchesnean primate Rooneyia viejaensis: New insights from high resolution computed tomography

Rooneyia viejaensis is a North American Eocene primate of uncertain phylogenetic affinities. Although the external cranial anatomy of Rooneyia is well studied, various authors have suggested that Rooneyia is a stem haplorhine, stem strepsirrhine, stem tarsiiform, or stem anthropoid. Here we describe the internal cranial anatomy of the Rooneyia holotype based on micro-computed tomography and discuss the phylogenetic implications of this anatomy. Precise measurements of the natural endocast filling the braincase of the Rooneyia holotype reveal that the genus had a relative brain size comparable to some living callitrichines and strepsirrhines. Rooneyia was thus probably more encephalized than any other known omomyiform, adapiform, or plesiadapiform. Relative olfactory bulb size in Rooneyia was most comparable to some living strepsirrhines and the stem anthropoid Parapithecus. The nasal fossa of Rooneyia resembled that of living strepsirrhines in retaining an obliquely oriented nasolacrimal canal, four ethmoturbinals, and an olfactory recess separated from the nasopharyngeal meatus by a transverse lamina. The ear region of Rooneyia is characterized by large and complete canals for both the stapedial and promontory branches of the internal carotid artery. Rooneyia also retains a patent parotic fissure and thus had an extrabullar origin of the stapedius muscle. In most of these respects, Rooneyia exhibits the condition that is presumed to be primitive for crown primates and lacks a number of key crown haplorhine synapomorphies (e.g., a dorso-ventrally oriented nasolacrimal canal, loss of the olfactory recess, loss of ethmoturbinals 3–4, loss or extreme reduction of the stapedial canal due to involution of the stapedial artery). These data are consistent with the hypothesis that Rooneyia is an advanced stem primate or a basal crown primate but are inconsistent with prior suggestions that Rooneyia is a crown haplorhine.

Cranial anatomy and neuroanatomical features of a new specimen of Geosaurini (Crocodylomorpha: Metriorhynchidae) from west-central Argentina

Fossil records of Geosaurini taxa in South American margins of the Eastern Pacific are scarce. We describe a new specimen of Geosaurini found in sedimentites of the Vaca Muerta Formation (Substeueroceras koeneni Biozone, uppermost Tithonian–lowermost Berriasian) and referred it as Dakosaurus cf. D. andiniensis. The close stratigraphic association of this specimen with late Tithonian to early Berriasian ammonoids allows confirming with biostratigraphic accuracy that, up to date, the first known occurrence of the Geosaurini taxa in South America is in late Tithonian. The specimen consists of a partially preserved skull and a partially exposed natural endocast of the brain cavity. This work is the first detailed description of a natural endocast of a metriorhynchid. The conspicuous blood vessel fillings covering almost all the dorsal surface of the cerebral hemispheres suggest that the dural envelope of this region was thin and that the cerebral hemispheres filled most of the cavity. A large dorsal venous sinus that overlays the dorsal region of the hindbrain, a tube-like cavity connecting the cranioquadrate passage and an enlarged internal carotid canal, previously described for ‘Metriorhynchus’ cf. ‘M.’ westermanni and present in Dakosaurus cf. D. andiniensis, suggest that these features were more widely distributed within metriorhynchids.

Endocranial morphology of the extinct Antillean shrew Nesophontes (Lipotyphla: Nesophontidae) from natural and digital endocasts of Cuban taxa

Endocranial morphology of the extinct Antillean shrew Nesophontes (Lipotyphla: Nesophontidae) from natural and digital endocasts of Cuban taxa

New crania from Seymour Island (Antarctica) shed light on anatomy of Eocene penguins

Abstract Antarctic skulls attributable to fossil penguins are rare. Three new penguin crania from Antarctica are here described providing an insight into their feeding function. One of the specimens studied is largely a natural endocast, slightly damaged, and lacking preserved osteological details. Two other specimens are the best preserved fossil penguin crania from Antarctica, enabling the study of characters not observed so far. All of them come from the uppermost Submeseta Allomember of the La Meseta Formation (Eocene-?Oligocene), Seymour (Marambio) Island, Antarctic Peninsula. The results of the comparative studies suggest that Paleogene penguins were long−skulled birds, with strong nuchal crests and deep temporal fossae. The configuration of the nuchal crests, the temporal fossae, and the parasphenoidal processes, appears to indicate the presence of powerful muscles. The nasal gland sulcus devoid of a supraorbital edge is typical of piscivorous species.

The snout of Cricosaurus araucanensis : a case study in novel anatomy of the nasal region of metriorhynchids

Metriorhynchids are the only crocodyliforms adapted to pelagic marine life. Snout natural endocasts of the Tithonian (Late Jurassic) metriorhynchid Cricosaurus araucanensis indicated that skeletal changes defining the peculiar metriorhynchid body plan were coupled with changes of the soft cephalic anatomy such as the enlarged salt glands and restructuring of the paranasal sinus system. Seven new natural endocasts of the snout and a 3-D reconstruction of C. araucanensis are described. Data from these casts and the reconstruction are congruent, and they are combined into an accurate reconstruction that improves our knowledge of the pre-orbital anatomy. The olfactory tract, bulbs, olfactory nasal region and the anterior extension of the antorbital sinus within the maxilla are recognized. Osteological correlates of the salt gland body are also proposed. Palaeobiological inferences are erected based on the integration of natural endocasts and 3-D reconstruction data. It is proposed that C. araucanensis nasal salt glands were highly vascularized with a blood supply comparable with those of extant marine birds. Reduced olfactory bulbs and olfactory nasal region indicate that the aerial olfaction, differing from extant crocodilians, was not well developed.

Metopic suture of Taung ( Australopithecus africanus ) and its implications for hominin brain evolution

The type specimen for Australopithecus africanus (Taung) includes a natural endocast that reproduces most of the external morphology of the right cerebral hemisphere and a fragment of fossilized face that articulates with the endocast. Despite the fact that Taung died between 3 and 4 y of age, the endocast reproduces a small triangular-shaped remnant of the anterior fontanelle, from which a clear metopic suture (MS) courses rostrally along the midline [Hrdlička A (1925) Am J Phys Anthropol 8:379-392]. Here we describe and interpret this feature of Taung in light of comparative fossil and actualistic data on the timing of MS closure. In great apes, the MS normally fuses shortly after birth, such that unfused MS similar to Taung's are rare. In humans, however, MS fuses well after birth, and partially or unfused MS are frequent. In gracile fossil adult hominins that lived between ∼3.0 and 1.5 million y ago, MS are also relatively frequent, indicating that the modern human-like pattern of late MS fusion may have become adaptive during early hominin evolution. Selective pressures favoring delayed fusion might have resulted from three aspects of perinatal ontogeny: (i) the difficulty of giving birth to large-headed neonates through birth canals that were reconfigured for bipedalism (the "obstetric dilemma"), (ii) high early postnatal brain growth rates, and (iii) reorganization and expansion of the frontal neocortex. Overall, our data indicate that hominin brain evolution occurred within a complex network of fetopelvic constraints, which required modification of frontal neurocranial ossification patterns.

Endocasts of Microsyops (Microsyopidae, Primates) and the evolution of the brain in primitive primates

We describe a virtual endocast produced from ultra high resolution X-ray computed tomography (CT) data for the microsyopid, Microsyops annectens (middle Eocene, Wyoming). It is the most complete and least distorted endocast known for a plesiadapiform primate and because of the relatively basal position of Microsyopidae, has particular importance to reconstructing primitive characteristics for Primates. Cranial capacity is estimated at 5.9 cm 3, yielding encephalization quotients (EQ) of 0.26–0.39 (Jerison’s equation) and 0.32–0.52 (Eisenberg’s equation), depending on the body mass estimate. Even the lowest EQ estimate for M. annectens is higher than that for Plesiadapis cookei, while the range of estimates overlaps with that of Ignacius graybullianus and with the lower end of the range of estimates for fossil euprimates. As in other plesiadapiforms, the olfactory bulbs of M. annectens are large. The cerebrum does not extend onto the cerebellum or form a ventrally protruding temporal lobe with a clear temporal pole, suggesting less development of the visual sense and a greater emphasis on olfaction than in euprimates. Contrasts between the virtual endocast of M. annectens, and both a natural endocast of the same species and a partial endocast from the earlier-occurring Microsyops sp., cf. Microsyops elegans, suggest that the coverage of the caudal colliculi by the cerebrum evolved within the Microsyops lineage. This implies that microsyopids expanded their cerebra and perhaps evolved an improved visual sense independent of euprimates. With a growing body of data on the morphology of the brain in primitive primates, it is becoming clear that many of the characteristics of the brain common to euprimates evolved after the divergence of stem primates from other euarchontans and likely in parallel in different lineages. These new data suggest a different model for the ancestors of euprimates than has been assumed based on the anatomy of the brain in visually specialized diurnal tree shrews.

Description of a digital cranial endocast of Bathygenys reevesi (Merycoidodontidae; Oreodontoidea) and implications for apomorphy-based diagnosis of isolated, natural endocasts

ABSTRACT Relatively few studies of cranial endocasts document intraspecific variation. Here, discrete morphological and morphometric variation from a sample of more than 150 natural cranial endocasts from a single Eocene locality, Reeves Bonebed (hereafter ‘RBB’) from West Texas are documented. The first description of a digital endocast of an oreodont, Bathygenys reevesi, is given to provide comparative data for other oreodont endocasts. The RBB endocasts were originally assigned to B. reevesi, but virtually none has diagnostic craniodental material still attached, and isolated endocasts of other cetartiodactyl species are known from this locality. Consequently, an attempt was made to identify apomorphies on the RBB sample to diagnose specimens to the lowest possible taxonomic level. The RBB endocasts were diagnosed as oreodonts based on the presence of large, rounded casts of the tuberculum olfactorium, but no specimen can be diagnosed to a particular species. The range for most linear measurements for the RBB sample overlapped with measures from multiple species of oreodonts from RBB. A coefficient of variation analysis of linear measurements suggests that the RBB sample represents more than one species. Therefore, endocasts from RBB that lack associated craniodental material cannot be definitively assigned to a species, and the original assumption that all are B. reevesi is not supported. This illustrates the necessity of applying apomorphy-based identifications for isolated specimens, including endocasts. In addition, this study reveals some gaps in data from cetartiodactyl brains, which need to be filled for future studies on brain evolution in this clade.