Michel Brunet’s research while affiliated with Collège de France and other places

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Publications (205)


Spherical harmonics: a mathematical tool to quantify 3D shape without landmarks
  • Conference Paper
  • Full-text available

March 2019

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133 Reads

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Thibault Bienvenu

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Michel Brunet

Shape quantification generally requires the positioning of landmarks, either to measure distances and angles, or to compare Cartesian coordinates. However, the definition of homologous landmarks is sometimes very challenging, especially for smooth objects. Several methods have been proposed to circumvent this problem, such as sliding semi-landmarks. Here we present a method based on spherical harmonics, a generalization of elliptic Fourier analysis for 3D continuous surfaces. Our objective was to test whether spherical harmonics are an efficient tool to (1) quantify the 3D shape of an object and (2) compare 3D shapes between objects. We used the virtual endocranial surfaces of 72 primates representing 5 hominid species. The surfaces were first centred, aligned and scaled using Avizo software. Subsequent analyses were performed using SPHARM-MAT software. The first two steps, parametrization and expansion, corresponded to the computation of the spherical harmonic coefficients describing each specimen. The last step, registration, performed the alignment of the spherical representation of all the specimens, allowing inter-individual comparisons. Accurate surface reconstructions were obtained using a limited number of spherical harmonics, but artefacts tended to appear for small-scale shape deformations. The combination of several registration methods led to a reasonable alignment of all the surface reconstructions. Multivariate statistics on spherical harmonic coefficients discriminated all species, except within the genus Pan (chimpanzees). Though, interspecific differences were less clear than in analyses conducted on the coordinates of homologous landmarks, probably because the landmarks were mainly placed on the endocranial base, which is less homogenous than the smooth endocranial vault.

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3D shape quantification without landmark: Using spherical harmonics to compare brain endocast morphology within extant hominoids.

Brain evolution is a pivotal issue in paleoprimatology. However, quantitative comparisons of shape are difficult because the braincase is lacking locations for homologous landmarks. To cope with this problem, diverse landmark-free models of 3D surfaces exist, each having strengths and weaknesses. The aim of this study is to test wether a spherical harmonic-based model is relevant for description and comparisons of endocranial shapes across species. Here, we present the first spherical harmonic-based study of the morphology of primate brain endocasts. The comparative sample comprised 72 specimens representing 5 modern hominid species. After a virtual extraction from CT-scans, the endocasts were scaled, centered and aligned to a reference specimen. The subsequent computation process involved tree steps: parametrization, expansion and registration. Shape comparisons among species were performed using multivariate statistics on the final harmonic coefficients. A relatively low number of harmonics is sufficient for an accurate reconstruction of endocranial shape. Reconstruction artifacts and surface misalignment sometimes happen, that can be avoided by careful choices of computation parameters and registration method. Shape discrimination is statistically significant among species, except between chimpanzees and bonobos. Compared to analyses conducted on the same sample using fixed landmarks, species are less separated in the shape space, probably because the global endocranial morphology described by spherical harmonics is more homogenous across species than the endocranial base, where landmarks are concentrated. Our results highlight the benefits of spherical harmonics for shape quantification when potential landmarks are sparse. Methodological improvements still remain necessary.


Perspectives on the use of growth rate patterns in fossil ectotherm bones to characterise ancient continental environments: Case study in Late Neogene sites from northern Chad (Djurab)

June 2018

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87 Reads

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1 Citation

Journal of African Earth Sciences

We investigate the feasibility and potential relevance of studying growth patterns in the bones of fossil freshwater ectotherms with the aim of developing new markers for continental palaeoenvironments and climates. This prospective study is based on Late Neogene material from Chad. It thus provides preliminary results that interest the reconstruction of paleoenvironments in ancient hominid bearing sites and that also document paleoenvironmental changes in continental Africa along a critical time period for global change. We prepared a set of various fish bones and turtle plates from Chadian Mio-Pliocene fossiliferous areas. We were able to analyse growth rates recorded during the course of the life of the animals in about half of the fossils initially sampled for the study. The main conclusions are: 1) the absence of a relationship between the external aspect of the fossils and the preservation of the growth marks, which means that visible features are not helpful in primary sampling; 2) at least in the Neogene Chadian sites, cathodoluminescence does not help to reveal growth marks; 3) growth rate patterns observed in the section of the body of the fin spines in claroteids, latids and polypterids and in pelomedusoid plates seem to be informative about environmental control of animal growth; and 4) depending on the taxa, different environmental informations can be obtained.


fig. 1.-Tchadailurus adei n. gen., n. sp., TM 112-00-99, from Toros Menalla. Left maxilla with C-M1 in labial (A1), lingual (A2), and occlusal (A3) views; right hemimandible with c-m1 in lingual (B1), labial (B2), and occlusal (B3) views; fragmentary atlas in dorsal (D1) and ventral (D2) views. Scale bar: 10 mm. 
fig. 2.-Tchadailurus adei n. gen., n. sp., TM 112-00-99, from Toros Menalla. Fragment of left humerus in anterio view (A); subcomplete right ulna in lateral (B1), medial (B2), and anterior (B3) views; subcomplete left radius in medial view (C); proximal fragment of left scapula in lateral (D1) and proximal (D2) views; left scapholunar in proximal (E1), distal (E2), and posterior (E3) views; right pisiform in lateral view (F); articulated right Mc I and first phalanx of digit I in anterior view (G). Scale bar: 10 mm. 
fig. 3.-Tchadailurus adei n. gen., n. sp., TM 112-00-99, from Toros Menalla. Left metacarpals in dorsal view: Mc II (A), Mc III (B), Mc IV (C), and Mc V (D). Scale bar: 10 mm. 
fig. 4.-Tchadailurus adei n. gen., n. sp., TM 112-00-99, from Toros Menalla. Fragmentary right pelvis in lateral view (A); right astragalus in dorsal (B1) and ventral (B2) views; right calcaneus in medial (C1), dorsal (C2), and lateral (C3) views; left lateral cuneiform in medial (D1), lateral (D2), proximal (D3), and distal (D4) views. Scale bar: 10 mm. 
fig. 5.-Tchadailurus adei n. gen., n. sp., TM 112-00-99, from Toros Menalla. Metatarsals: right Mt II (A1) and Mt III (A2) in medial view; left Mt IV lateral view (A3) and subcomplete left Mt V in anterior view (A4). Dinofelis sp., TM 74-0106, from Toros Menalla: left upper canine in lateral (B1) and medial (B2) views. Scale bar: 10 mm. 
New sabre toothed Felidae (Carnivora, Mammalia) in the hominid-bearing sites of Toros Menalla (late Miocene, Chad)

February 2018

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957 Reads

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6 Citations

GEODIVERSITAS

The late Miocene fossil-bearing localities of Toros Menalla (Chad) have yielded a huge amount of vertebrate remains with, in particular, the hominid Sahelanthropus tchadensis Brunet et al., 2002. The order Carnivora is well represented in the fauna (with up to 23 species) and we describe here a new genus and species together with a species not previously recorded in the fauna. Both species belong to the saber-toothed felids. The new genus, size of a lynx, is known by jaws and several post-cranial bones. It displays in the upper canines, mandible and bones of the fore limb some features indicating machairodont affinities. The second genus, size of a leopard and well known in Africa, is only present through a characteristic upper canine. The presence of eight species of Felidae into 23 species of carnivorans is much rare into the Miocene carnivoran assemblages and is discussed in the conclusions. © Publications scientifiques du Muséum national d’Histoire naturelle, Paris, 2018.


First occurrence of a mawsoniid (Sarcopterygii: Actinistia), Mawsonia soba sp. nov., in pre-Aptian Cretaceous deposits from Cameroon

December 2017

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454 Reads

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9 Citations

Cretaceous Research

Coelacanth remains from the Lower Cretaceous (pre-Aptian) freshwater deposits of the Babouri Figuil Basin, Northern Cameroon are described as a new taxon Mawsonia soba sp. nov. based on two characters: four openings in the dentary for the branch of the trigeminal nerves and an extremely rugose and disorganized ornamentation of the bones. M. soba sp. nov. known by some three-dimensionally partially preserved specimens represents the first actinistian described from Cameroon. This discovery attests the presence of Mawsonia in the African counterpart of the continental pre-rift and rift environments where only Brazilian members were known so far. The fact that the Cameroonian coelacanth belongs to a new species suggest a certain endemism at least in this African basin.




New Data about Semicircular Canal Morphology and Locomotion in Modern Hominoids

May 2017

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85 Reads

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24 Citations

Journal of Anatomy

The labyrinth has two functional parts: the cochlea for audition and the vestibular system for equilibrioception. In the latter, the semicircular ducts and the otolithic organs are sensitive to rotational and linear accelerations of the head, respectively. The labyrinthine morphology influences perception accuracy, hence the adaptation to a specific locomotor pattern. The aim of this study is to determine the relationship between locomotion and semicircular canal morphology using geometric morphometrics, and to explain these links with existing functional models. The influence of factors other than functional constraints on labyrinthine morphology is discussed. The left bony labyrinth of 65 specimens was extracted virtually. Five extant hominoid species with various locomotion modes were sampled. A set of 13 landmarks was placed on the semicircular canals. After a Procrustes fit, their coordinates were analyzed using a principal component analysis. It was found that labyrinthine morphology is significantly distinct between species. More specifically, the differences involve a posterolateral projection of the lateral semicircular canal and the rotation of this canal relative to the vertical canals. This rotation occurs in the sagittal plane, which is consistent with previous studies based on traditional morphometrics. Among extant hominoids, the shape of the canals potentially discriminates species based on posture. This result could be used to reconstruct the locomotor pattern of fossil hominoids.


Phytoliths indicate significant arboreal cover at Sahelanthropus type locality TM266 in northern Chad and a decrease in later sites

May 2017

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120 Reads

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38 Citations

Journal of Human Evolution

We analyzed phytolith and diatom remains preserved at 45 Miocene and Pliocene localities dated between 8 and 1 Ma in northern Chad (16–17°N). Some of these localities yielded cranial remains, lower jaws, and teeth of the hominin species Australopithecus bahrelghazali (∼3.6 Ma) and Sahelanthropus tchadensis (∼7 Ma). Of the 111 sediment samples analyzed, 41 yielded phytoliths, 20 yielded diatoms, and seven yielded both phytoliths and diatoms. Freshwater planktonic and tychoplanktonic diatom species, indicative of lacustrine conditions, are dominant (>91%) in the samples. The phytolith assemblages indicate an opening of the vegetation and a general trend toward an expansion of grass-dominated environments during the time spanning the two hominin occurrences in Chad. The phytoliths suggest the presence of a mosaic environment, including closed forest patches, palm groves, and mixed/grassland formations, between 7.5 and 7 Ma, the replacement by palm grove-like vegetation at approximately 6.5–5 Ma, and the presence of exclusive grass-dominated formations after 4.5 Ma. The type-locality of S. tchadensis (TM266) was likely similar to modern palm grove formations with an arboreal cover percentage ≥40%. The type locality of A. bahrelghazali (KT12) was a grass-dominated ecosystem (likely savanna) with an unrated percentage of arboreal cover. Furthermore, the grass phytolith data support the existence of a (recurrent) Sahelian-like dry climate in northern Chad since at least 8 Ma. Therefore the local closed vegetation formations in the Djurab region at 7.5–7 Ma were sustained by aquatic systems (such as lakes or related rivers, marshes) rather than by extensive annual precipitation.


Citations (73)


... The relationship between ectotherm's growth and isolated biotic and abiotic factors has been largely studied in multiple fields, for instance, developmental biology (Green & Fisher, 2004), ecology (e.g., Beckman et al., 1998;Rosenfeld et al., 2005), development of animal resources (Boeuf & Payan, 2001;Deane & Woo, 2009;Norberg et al., 2001), and paleontology or archaeology, to interpret the growth of animals as a paleoenvironmental proxy (Lapalus et al., 2018). Fossil growth patterns can aid in the evaluation of paleoenvironmental seasonal fluctuations, which are an important component of climate effects on past continental ecosystems (e.g., Tonkin et al., 2017;White & Hastings, 2020). ...

Reference:

Seasonality and growth in tropical freshwater ectotherm vertebrates: Results from 1-year experimentation in the African gray bichir, giraffe catfish, and the West African mud turtle
Perspectives on the use of growth rate patterns in fossil ectotherm bones to characterise ancient continental environments: Case study in Late Neogene sites from northern Chad (Djurab)
  • Citing Article
  • June 2018

Journal of African Earth Sciences

... iScience Article Chad, 7 Ma. 88 Bonis et al. 88 noticed the similarity of their new genus to Yoshi and stated that Tchadailurus is different from Yoshi in smaller size, proportionally higher canine, and longer diastema. In other aspects, this genus is much like Yoshi and unlike other metailurine, in having a high crowned P3, without an anterior accessory cusp and a transversely elongated M1. ...

New sabre toothed Felidae (Carnivora, Mammalia) in the hominid-bearing sites of Toros Menalla (late Miocene, Chad)

GEODIVERSITAS

... First discovered at the turn of the 20th century in the Early Cretaceous of Brazil [1], mawsoniid fossils were later found in various freshwater and euryhaline deposits in that country [2][3][4][5] and Uruguay [6,7]. Meanwhile, mawsoniid remains have been described from several Early to 'mid' Cretaceous localities in North Africa [8][9][10][11][12][13] and then in Central Africa [14,15]. ...

First occurrence of a mawsoniid (Sarcopterygii: Actinistia), Mawsonia soba sp. nov., in pre-Aptian Cretaceous deposits from Cameroon
  • Citing Article
  • December 2017

Cretaceous Research

... The relative unimportance of the foramen magnum position (character 41, uninformative) is somewhat surprising given its intermediate and that it is continually implicated in bipedal transitions (Brunet et al., 2002;Zollikofer et al., 2005;Russo and Kirk, 2013), though its relationship with positional behavior has been questioned (Neaux et al., 2017). Interestingly, when looking at all OTUs, the value for foramen magnum position is in the third quartile of values (suggestive of its potential to be informative), but when we recalculated values solely for Pan + hominin, the foramen magnum position's is in the lowest quartile. ...

Relationship between foramen magnum position and locomotion in extant and extinct hominoids
  • Citing Article
  • September 2017

Journal of Human Evolution

... As such, peripheral vestibular system morphology needs to be attuned for effective detection of behaviorally-induced head motion 9-13 , while positional behaviors require adequate gaze stabilization and motor coordination, both depending on accurate head motion detection 14 . In this context, morphological differences in specific regions of the peripheral vestibular system (e.g., semicircular canal radius of curvature, semicircular canal orientation) have been studied to assess evolutionary shifts in the locomotor repertoire of primates [15][16][17][18][19][20] , as well as to understand mammalian positional behavior more broadly [21][22][23][24] . ...

New Data about Semicircular Canal Morphology and Locomotion in Modern Hominoids
  • Citing Article
  • May 2017

Journal of Anatomy

... This was undoubtedly also true of the past, with the added complications that our palaeo-proxies record information about ancient environments at different spatial and temporal scales [56,92,93] and that environments of the past may not necessarily have present-day analogues [94,95]. It is therefore unsurprising that, for example, the environments of S. tchadensis at Toros-Menalla have been characterized by phytolith analysis as a forest-palm grove mosaic with woodlands [96], while the faunal evidence [97,98] points to a more grass-dominated landscape. The earliest putative hominins and Australopithecus anamensis are both characterized by isotopically ape-like diets (C 3 plants, presumably fruit and leaves) [99] and forelimb morphology suggesting significant arboreality [82], so more recent models locate hominin origins in the context of relatively wooded environments (e.g. ...

Phytoliths indicate significant arboreal cover at Sahelanthropus type locality TM266 in northern Chad and a decrease in later sites
  • Citing Article
  • May 2017

Journal of Human Evolution

... The location of the Ngwa Basin in a slope of Mount Bambouto suggests that the later is the main sediment provider of the Ngwa depression. A few studies have been dealt with Ngwa Basin (Capponi 1945;Kenfack et al. 2011;Benammi et al. 2017;Bessong et al. 2017), however, the sediment provenance and facies analyses are still lacking and the new obtained data indicate that the sedimentary and volcanic facies are more diversified. In this work, we provide the detailed lithostratigraphic column and a new evidence for alternation between sedimentary and volcanic processes in the Ngwa Basin. ...

Preliminary Magnetostratigraphic and Isotopic Dating of the Ngwa Formation (Dschang Western Cameroon)

Journal of Geology & Geophysics

... We obtained data from the literature 40,44,50,122,[128][129][130][131][132][133][134][135][136] to represent two more traits relevant to functional diversity and ecometrics: hypsodonty and longitudinal loph count. Together these traits illustrate a species' dentition and dietary adaptations. ...

New hippotragini (Bovidae, Mammalia) from the Late Miocene of Toros-Menalla (Chad)
  • Citing Article
  • March 2008

... According to Toteu et al. (2004), the Lake Chad Basin is located in the Central African zone of the "Pan-African Mobile Zone". It is characterized by the deposition of sedimentary platform as a result of regressions and transgressions in a lacustrine environment (Mathieu, 1978;Massuel, 2001;Schuster et al., 2005, Moussa et al., 2016. Lake Chad is located at the junction of the Saharan desert and the savannah. ...

Lake Chad sedimentation and environments during the late Miocene and Pliocene : new evidence from mineralogy and chemistry of the Bol core sediments

... Thus, given the difficulties of inferring the characteristic morphology of a taxon with a relatively meager fossil record (Smith, 2005), and the fact that the nature and relationships of S. tchadensis rely on morphological evidence from a distorted cranium, or from a virtually reconstructed version of that cranium, any additional information, especially from anatomical regions not sampled in the existing hypodigm, has the potential to help clarify the evolutionary relationships of S. tchadensis. Specifically, the current hypodigm of S. tchadensis does not include any postcranial remains that might be informative about the posture and locomotion of S. tchadensis (Brunet et al., , 2004Brunet and Jaeger, 2017). The purpose of this contribution is to introduce the first postcranial evidence of S. tchadensis. ...

De l’origine des anthropoïdes à l’émergence de la famille humaine

Comptes Rendus Palevol