DOCSLIB.ORG

Mammals Fossil Evidence on Evolution of Inner Ear Cochlea In

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Mammals Fossil Evidence on Evolution of Inner Ear Cochlea In Downloaded from rspb.royalsocietypublishing.org on November 27, 2010 Fossil evidence on evolution of inner ear cochlea in Jurassic mammals Zhe-Xi Luo, Irina Ruf, Julia A. Schultz and Thomas Martin Proc. R. Soc. B 2011 278, 28-34 first published online 28 July 2010 doi: 10.1098/rspb.2010.1148 Supplementary data "Data Supplement" http://rspb.royalsocietypublishing.org/content/suppl/2010/07/26/rspb.2010.1148.DC1.h tml References This article cites 34 articles, 6 of which can be accessed free http://rspb.royalsocietypublishing.org/content/278/1702/28.full.html#ref-list-1 Subject collections Articles on similar topics can be found in the following collections palaeontology (134 articles) developmental biology (212 articles) evolution (2221 articles) Receive free email alerts when new articles cite this article - sign up in the box at the top Email alerting service right-hand corner of the article or click here To subscribe to Proc. R. Soc. B go to: http://rspb.royalsocietypublishing.org/subscriptions This journal is © 2011 The Royal Society Downloaded from rspb.royalsocietypublishing.org on November 27, 2010 Proc. R. Soc. B (2011) 278, 28–34 doi:10.1098/rspb.2010.1148 Published online 28 July 2010 Fossil evidence on evolution of inner ear cochlea in Jurassic mammals Zhe-Xi Luo1,2,*, Irina Ruf2, Julia A. Schultz2 and Thomas Martin2 1Section of Vertebrate Paleontology, Carnegie Museum of Natural History, Pittsburgh, PA 15213, USA 2Steinmann-Institut fu¨r Geologie, Mineralogie und Pala¨ontologie, Universita¨t Bonn, 53115 Bonn, Germany The coiled cochlea is a key evolutionary innovation of modern therian mammals. We report that the Late Jurassic mammal Dryolestes, a relative to modern therians, has derived bony characteristics of therian-like innervation, but its uncoiled cochlear canal is less derived than the coiled cochlea of modern therians. This suggests a therian-like innervation evolved before the fully coiled cochlea in phylogeny. The embry- ogenesis of the cochlear nerve and ganglion in the inner ear of mice is now known to be patterned by neurogenic genes, which we hypothesize to have influenced the formation of the auditory nerve and its ganglion in Jurassic therian evolution, as shown by their osteological correlates in Dryolestes, and by the similar base-to-apex progression in morphogenesis of the ganglion in mice, and in transformation of its canal in phylogeny. The cochlear innervation in Dryolestes is the precursory condition in the curve-to- coil transformation of the cochlea in mammalian phylogeny. This provides the timing of the evolution, and where along the phylogeny the morphogenetic genes were co-opted into patterning the cochlear innervation, and the full coiling of the cochlea in modern therians. Keywords: Mammalia; inner ear; evolution; Jurassic 1. INTRODUCTION stem taxon characterized by plesiomorphic dental fea- The snail-shaped cochlea with its hearing organ (Organ of tures, and a near relative to the modern marsupials and Corti) is a key evolutionary innovation in the inner ear of placentals. The fine inner ear structures are preserved in modern marsupial and placental mammals. Coiling of the a petrosal bone that houses the inner ear in the skull. cochlea is a major feature distinguishing the modern mar- Through the high-resolution micro-computer tomo- supials and placentals from all other mammals [1–5]. graphy (CT) scanning and comparative analysis, we The cochlea coils into a spiral to compact itself into a obtained new information on its morphological features smaller space in the skull for efficient innervation and that represent the evolutionarily ancestral condition of blood supply in marsupials and placentals [6,7]. extant therian mammals. This is relevant to the under- Elongation of the cochlea with more spiral turns is corre- standing of the evolution of the coiled cochlear canal and lated with increased resolution of sound frequencies the innervation of its hearing organ. [2,8]. The curved gradient of the coiled cochlear canal wall focuses acoustic energy towards the apex of the cochlea, the most sensitive region for the low-frequency 2. MATERIAL AND METHODS sound [9]. The key innovation in the fully coiled cochlea, The petrosal specimen (Guimarota Collection of Museo including its auditory innervation, is correlated with the Geolo´gico (Lisboa, Portugal), specimen number SGP earliest diversification of metatherians and eutherians in 6807) shows similar apomorphic features as the known pet- the Cretaceous, and has led to many spectacular func- rosal of the paurodontid Henkelotherium (Paurodontidae, tional adaptations in hearing in Cenozoic and living Dryolestoidea) [5,18]. The inner ear inside the petrosal marsupials and placentals [3,5,10–16]. However, evol- was observed by our high-resolution micro-CT scanning ution of this important ear structure cannot be fully and visualized by three-dimensional virtual endocasts from deciphered until the precursory condition of its main the CT data. characters can be mapped from the fossil record of The first scanning of X-ray CT was by the OMNI-X early therians, and their phylogenetic transformation Universal HD600 Scanner at the Center of Quantitative can be correlated with the morphogenesis patterned by Imaging (CQI), Pennsylvania State University, State Col- developmental genes. lege, Pennsylvania, USA. The images have a 1024 pixel Here, we report the discovery of the precursory struc- resolution and voxel size of 0.025 Â 0.025 Â 0.028891 mm. tures of the fully coiled cochlea of modern therians in the This scanning allowed us to initially identify this fossil. inner ear of the Late Jurassic mammal Dryolestes leiriensis The second scanning for greater morphological details was [17], a 150 Myr old fossil mammal in the cladotherian by scanner vjtomejx s (GE Sensing & Inspection Technol- clade, as defined by the common ancestor of ogies GmbH phoenixjx-ray) at the Steinmann-Institut fu¨r dryolestoids þ extant therians (e.g. [3]). Dryolestes is a Geologie, Mineralogie und Pala¨ontologie, Universita¨t Bonn, Germany. The images have a 1024 pixel resolution and a voxel size of 0.010158 Â 0.010158 Â 0.010158 mm. * Author for correspondence ([email protected]). To increase the resolution of the region of interest (cochlear Electronic supplementary material is available at http://dx.doi.org/10. canal), we used the software datosjx-reconstruction (GE 1098/rspb.2010.1148 or via http://rspb.royalsocietypublishing.org. Sensing & Inspection Technologies GmbH phoenixjx-ray) Received 28 May 2010 Accepted 6 July 2010 28 This journal is q 2010 The Royal Society Downloaded from rspb.royalsocietypublishing.org on November 27, 2010 Inner ear evolution of mammals Z.-X. Luo et al. 29 Table 1. Measurement of bony labyrinth structures of D. leiriensis (SGP 6807). (Endocast measurements from AVIZO 5.1 based on the second CT scanning in the scanner in Steinmann-Institut, Universita¨t Bonn. Scanned resolution 0.010158 mm; virtually half voxel size 0.005079 mm.) coiling along length estimated length (mm) cochlear canal 2708 3.3 primary bony lamina length 1.6 secondary bony lamina length 1.18 long diameter (mm) short diameter (mm) fenestra vestibuli 0.53 0.47 estimated diameter width (mm) height (mm) (width–height average mm) apical turn diameter 0.77 0.85 0.68 basal turn diameter 0.99 0.96 1.2 angle of basal turn to lateral 1458 semicircular canal semicircular canals width (mm) height (mm) arc radius lumen (inner curvature mm) diameter (mm) anterior 2.31 2.22 1.13 0.21 posterior 1.56 1.50 0.77 0.22 lateral 1.55 1.46 0.75 0.22 average radius 0.88 for virtually halving the voxel size (0.005079 mm) from the have gliding, flying, saltatorial or fully aquatic loco- raw dataset, which has further increased the resolution of motion. Dryolestes was either a generalized terrestrial, or fine structures (electronic supplementary material, figures a scansorial mammal, neither of which can be ruled out S2–S3). Virtual reconstructions of the petrosal bone and because its postcranial skeleton is not preserved, except the inner ear bony labyrinth were completed by manual for a single humerus [22]. But the latter possibility of a segmentation function of the software AVIZO 5.1. Linear scansorial mammal is more likely by comparison to the measurements were from the inner ear bony labyrinth closely related dryolestoid Henkelotherium, which has endocast with Avizo (table 1). many scansorial skeletal features [18]. (b) Cochlear canal structure 3. DESCRIPTION AND COMPARISON The cochlear canal in Dryolestes is 3.3 mm long and partly (a) Vestibule and semicircular canals coiled through about 2708 or three-quarters of a complete On the three-dimensional virtual endocasts visualized turn, starting from the proximal entry point of the from the CT scanning, the vestibular part of the inner cochlear nerve (figures 1, 2 and table 1), according the ear shows a discernible separation between the utricle measurement landmarks suggested by West [8] (see also and the saccule of the vestibule (figure 1d–f ), the fenestra [5,23]). The canal is relatively straight and has a circular vestibuli (with a stapedial ratio of 1.2), which transmits cross section near the base. Its distal half-turn forms an sound into the inner ear, and the fenestra cochleae for arc around the distal point of the cochlear nerves and releasing the sound pressure (figure 1). The anterior, pos- has an oval cross section in the apical part. The curvature terior and lateral semicircular canals for the detection of of the cochlear canal corroborates previous observations motion and equilibrium function have their respective that the pre-tribosphenic mammals, such as Henkelother- arc radii at 1.13, 0.75 and 0.77 mm (figure 1: asc, lsc ium [ 5] and Vincelestes [24], have a consistent, and psc). The plane of the lateral semicircular plesiomorphic pattern of 2708 curvature of cochlea canal forms a 1458 angle to the axis through the basal (three-quarters of a turn).
Load more

Recommended publications
  • SUPPLEMENTARY INFORMATION: Tables, Figures and References
    Samuels et al. Evolution of the patellar sesamoid bone in mammals SUPPLEMENTARY INFORMATION: Tables, Figures and References Supplementary Table S1: Mammals$ Higher taxa Genus sp. Estimated. age of Patellar Comments# (partial) specimen, location state 0/1/2 (absent/ ‘patelloid’/ present) Sinoconodonta Sinoconodon Jurassic 0 Patellar groove absent, suggests no rigneyi (Kielan- patella Jaworowska, Cifelli & Luo, Sinoconodon is included on our 2004) phylogeny within tritylodontids. Morganucodonta Megazostrodon Late Triassic, southern 0 rudnerae (Jenkins Africa & Parrington, 1976) Morganucodonta Eozostrodon sp. Late Triassic, Wales 0 Asymmetric patellar groove, (Jenkins et al., specimens disarticulated so it is hard 1976) to assess the patella but appears absent Docodonta Castorocauda 164 Mya, mid-Jurassic, 0 Semi-aquatic adaptations lutrasimilis (Ji, China Luo, Yuan et al., 2006) Docodonta Agilodocodon 164 Mya, mid-Jurassic, 0 scansorius China (Meng, Ji, Zhang et al., 2015) Docodonta Docofossor 160 Mya 0 brachydactylus (Luo, Meng, Ji et al., 2015) Docodonta Haldanodon 150-155 Mya, Late 0 Shallow patellar groove exspectatus Jurassic, Portugal (Martin, 2005b) Australosphenida Asfaltomylos Mid-Jurassic, South ? Postcranial material absent patagonicus America (Martin, 2005a) Australosphenida Ornithorhynchus Extant 2 Platypus, genome sequenced Monotremata anatinus (Warren, Hillier, Marshall Graves et (Herzmark, 1938; al., 2008) Rowe, 1988) Samuels et al. Australosphenida Tachyglossus + Extant 2 Echidnas Monotremata Zaglossus spp. (Herzmark, 1938; Rowe, 1988) Mammaliaformes Fruitafossor 150 Mya, Late Jurassic, 0 Phylogenetic status uncertain indet. windscheffeli (Luo Colorado & Wible, 2005) Mammaliaformes Volaticotherium Late Jurassic/Early ? Hindlimb material incomplete indet. antiquus (Meng, Cretaceous Hu, Wang et al., 2006) Eutriconodonta Jeholodens 120-125 Mya, Early 0 Poorly developed patellar groove jenkinsi (Ji, Luo Cretaceous, China & Ji, 1999) Eutriconodonta Gobiconodon spp.
    [Show full text]
  • Mammalian Fauna of the Late Jurassic Guimarota Ecosystem
    Asociación Paleontológica Argentina. Publicación Especial 7 ISSN 0328-347X VII International Symposium on Mesozoic Terrestrial Ecosystems: 123-126. Buenos Aires, 30-6-2001 MaMMalian fauna of the Late Jurassic Guimarota ecoSyStem Thomas MARTIN1 Abstract. The Late Jurassic (Kirnmeridgian) Guimarota loca lit y near Leiria in west-central Portugal has yielded more than 800 mammalian dentaries and partial skulls representing the largest sample of Late Jurassic mammals in the world. However, despite the enormous number of specimens collected, the mam- malian fauna appears somewhat depauperate. So far, only Multituberculata (several genera of Paulchoffatiidae; 28% of total number), Docodonta (Halda nadan exspectaius Kühne and Krusat; 24%), and Holotheria (48%) represented by Paurodontidae (Henkelatherium guimaratae Krebs and Drescheratherium acutum Krebs) and Dryolestidae (Dryalestes leiriensis Martín, Krebsoiherium Iusiianicum Martin, and Guimaroiodus inflatus Martin) have been detected. "Triconodonta" and Syrnmetrodonta, which are well represented at other Late Jurassic localities (e.g., Morrison Forrnation), are missing. To recover the rare mammalian taxa of the Guimarota ecosystem, a project was initiated to study the nearly 7000 isolated mammalian teeth that had been obtained by screenwashing. With a single exception, the same taxa are represented. Among the thousands of isolated teeth, however, 25 lower and 23 upper premolars and mo- lars of a tiny primitive Zatheria have been found, of which the lower molars closely resemble the "Porto Pinheiro molar". After sorting the isolated teeth, the mammalian fauna of the Guimarota ecosystem prob- ably is completely recorded. Apparently, the coastal swamp in the Lusitanian graben where the lignite formed represented a stressed environment not appropriate for some marnmalian groups.
    [Show full text]
  • Dual Origin of Tribosphenic Mammals
    articles Dual origin of tribosphenic mammals Zhe-Xi Luo*, Richard L. Cifelli² & Zo®a Kielan-Jaworowska³ *Section of Vertebrate Paleontology, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania 15213, USA ² Oklahoma Museum of Natural History, 2401 Chautauqua, Norman, Oklahoma 73072, USA ³ Institute of Paleobiology, Polish Academy of Sciences, ulica Twarda 51/55, PL-00-818 Warszawa, Poland ............................................................................................................................................................................................................................................................................ Marsupials, placentals and their close therian relatives possess complex (tribosphenic) molars that are capable of versatile occlusal functions. This functional complex is widely thought to be a key to the early diversi®cation and evolutionary success of extant therians and their close relatives (tribosphenidans). Long thought to have arisen on northern continents, tribosphenic mammals have recently been reported from southern landmasses. The great age and advanced morphology of these new mammals has led to the alternative suggestion of a Gondwanan origin for the group. Implicit in both biogeographic hypotheses is the assumption that tribosphenic molars evolved only once in mammalian evolutionary history. Phylogenetic and morphometric analyses including these newly discovered taxa suggest a different interpretation: that mammals with tribosphenic molars are not monophyletic. Tribosphenic
    [Show full text]
  • Mammal Disparity Decreases During the Cretaceous Angiosperm Radiation
    Mammal disparity decreases during the Cretaceous angiosperm radiation David M. Grossnickle1 and P. David Polly2 1Department of Geological Sciences, and 2Departments of Geological Sciences, Biology, and Anthropology, rspb.royalsocietypublishing.org Indiana University, Bloomington, IN 47405, USA Fossil discoveries over the past 30 years have radically transformed tra- ditional views of Mesozoic mammal evolution. In addition, recent research provides a more detailed account of the Cretaceous diversification of flower- Research ing plants. Here, we examine patterns of morphological disparity and functional morphology associated with diet in early mammals. Two ana- Cite this article: Grossnickle DM, Polly PD. lyses were performed: (i) an examination of diversity based on functional 2013 Mammal disparity decreases during dental type rather than higher-level taxonomy, and (ii) a morphometric analysis of jaws, which made use of modern analogues, to assess changes the Cretaceous angiosperm radiation. Proc R in mammalian morphological and dietary disparity. Results demonstrate a Soc B 280: 20132110. decline in diversity of molar types during the mid-Cretaceous as abundances http://dx.doi.org/10.1098/rspb.2013.2110 of triconodonts, symmetrodonts, docodonts and eupantotherians dimin- ished. Multituberculates experience a turnover in functional molar types during the mid-Cretaceous and a shift towards plant-dominated diets during the late Late Cretaceous. Although therians undergo a taxonomic Received: 13 August 2013 expansion coinciding with the angiosperm radiation, they display small Accepted: 12 September 2013 body sizes and a low level of morphological disparity, suggesting an evol- utionary shift favouring small insectivores. It is concluded that during the mid-Cretaceous, the period of rapid angiosperm radiation, mammals experi- enced both a decrease in morphological disparity and a functional shift in dietary morphology that were probably related to changing ecosystems.
    [Show full text]
  • Mammalia, Theria) Un Primitivo Mamífero Del Cretacico Inferior De La Cuenca Neuquina Rougier, Guillermo Walter 1993
    Tesis de Posgrado Vincelestes neuquenianus bonaparte (mammalia, theria) un primitivo mamífero del cretacico inferior de la cuenca neuquina Rougier, Guillermo Walter 1993 Tesis presentada para obtener el grado de Doctor en Ciencias Biológicas de la Universidad de Buenos Aires Este documento forma parte de la colección de tesis doctorales y de maestría de la Biblioteca Central Dr. Luis Federico Leloir, disponible en digital.bl.fcen.uba.ar. Su utilización debe ser acompañada por la cita bibliográfica con reconocimiento de la fuente. This document is part of the doctoral theses collection of the Central Library Dr. Luis Federico Leloir, available in digital.bl.fcen.uba.ar. It should be used accompanied by the corresponding citation acknowledging the source. Cita tipo APA: Rougier, Guillermo Walter. (1993). Vincelestes neuquenianus bonaparte (mammalia, theria) un primitivo mamífero del cretacico inferior de la cuenca neuquina. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. http://digital.bl.fcen.uba.ar/Download/Tesis/Tesis_2605_Rougier.pdf Cita tipo Chicago: Rougier, Guillermo Walter. "Vincelestes neuquenianus bonaparte (mammalia, theria) un primitivo mamífero del cretacico inferior de la cuenca neuquina". Tesis de Doctor. Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. 1993. http://digital.bl.fcen.uba.ar/Download/Tesis/Tesis_2605_Rougier.pdf Dirección: Biblioteca Central Dr. Luis F. Leloir, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires. Contacto: [email protected] Intendente Güiraldes 2160 - C1428EGA - Tel. (++54 +11) 4789-9293 UNIVERSIDAD NACIONAL DE BUENOS AIRES FACULTAD DE CIENCIAS EXACTAS Y NATURALES VINCELESTES NEUQUENIANUS BONAPARTE (MAMMAIJA, THERIA) UN PRIMITIVO MAMIFERO DEL CRETACICO INFERIOR DE LA CUENCA NEUQUINA.
    [Show full text]
  • The Miocene Mammal Necrolestes Demonstrates the Survival of a Mesozoic Nontherian Lineage Into the Late Cenozoic of South America
    The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America Guillermo W. Rougiera,b,1, John R. Wibleb, Robin M. D. Beckc, and Sebastian Apesteguíad,e aDepartment of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, KY 40202; bSection of Mammals, Carnegie Museum of Natural History, Pittsburgh, PA 15206; cSchool of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia; dCEBBAD–Fundación de Historia Natural ‘Félix de Azara’, Universidad Maimónides, 1405 Buenos Aires, Argentina; and eConsejo Nacional de Investigaciones Científicas y Técnicas de Argentina, C1033AAJ Buenos Aires, Argentina Edited by Richard L. Cifelli, University of Oklahoma, Norman, OK, and accepted by the Editorial Board October 18, 2012 (received for review July 27, 2012) The early Miocene mammal Necrolestes patagonensis from Pata- not referable to either Metatheria or Eutheria, but did not discuss gonia, Argentina, was described in 1891 as the only known extinct the evidence for this interpretation, nor did they identify the placental “insectivore” from South America (SA). Since then, and specific therian lineages they considered to be potential relatives despite the discovery of additional well-preserved material, the of Necrolestes. Starting in 2007, we oversaw additional prepara- systematic status of Necrolestes has remained in flux, with earlier tion of Necrolestes specimens that comprise the best-preserved studies leaning toward placental affinities and more recent ones material currently available, including skulls, jaws, and some iso- endorsing either therian or specifically metatherian relationships. We lated postcranial bones; as a result, many phylogenetically signif- have further prepared the best-preserved specimens of Necrolestes icant features have been revealed for the first time.
    [Show full text]
  • Morphological Evidence Supports Dryolestoid Affinities for the Living Australian Marsupial Mole Notoryctes
    Reviewing Manuscript Morphological Evidence supports Dryolestoid affinities for the living Australian Marsupial Mole Notoryctes Federico Agnolin, Nicolas Roberto Chimento Recent discoveries demonstrated that the southern continents were a cradle for the evolutionary radiation of dryolestoid mammals at the end of the Cretaceous. Moreover, it becomes evident that some of these early mammals surpassed the K/T boundary in South America, at least. Notoryctes is a poorly known living mammal, currently distributed in the s t deserts of central Australia. Due to its extreme modifications to fossoriality and peculiar n i anatomy, the phylogenetic relationships of this genus were debated in the past, but most r P recent authors agree in its marsupial affinities. A comparative survey of the anatomy of e Notoryctes reveals the poorly sustained marsupial affinities for the genus and striking r P plesiomorphies for a living mammal. Surprisingly, Notoryctes exhibits similarities with dryolestoids. Dryolestoids were a diverse and mainly mesozoic mammalian group phylogenetically nested between the egg-lying monotremes and derived therians. In particular, Notoryctes share a number of shared features with the extinct dryolestoid Necrolestes, from the Miocene of Patagonia. Both taxa conform a clade of burrowing and animalivorous dryolestoids that survived other members of their lineage probably due to their peculiar habits. Accordingly, Notoryctes constitutes a “living-fossil” from the supposedly extinct dryolestoid radiation, extending the biochron of the group more than 20 million years to the present day. The intermediate phylogenetic position of Notoryctes has the pivotal potential to shed light on crucial anatomical, physiological, ecological, and evolutionary topics in the deep transformation from egg-lying to placental mammals.
    [Show full text]
  • In Quest for a Phylogeny of Mesozoic Mammals
    In quest for a phylogeny of Mesozoic mammals ZHE−XI LUO, ZOFIA KIELAN−JAWOROWSKA, and RICHARD L. CIFELLI Luo, Z.−X., Kielan−Jaworowska, Z., and Cifelli, R.L. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47 (1): 1–78. We propose a phylogeny of all major groups of Mesozoic mammals based on phylogenetic analyses of 46 taxa and 275 osteological and dental characters, using parsimony methods (Swofford 2000). Mammalia sensu lato (Mammaliaformes of some authors) are monophyletic. Within mammals, Sinoconodon is the most primitive taxon. Sinoconodon, morganu− codontids, docodonts, and Hadrocodium lie outside the mammalian crown group (crown therians + Monotremata) and are, successively, more closely related to the crown group. Within the mammalian crown group, we recognize a funda− mental division into australosphenidan (Gondwana) and boreosphenidan (Laurasia) clades, possibly with vicariant geo− graphic distributions during the Jurassic and Early Cretaceous. We provide additional derived characters supporting these two ancient clades, and we present two evolutionary hypotheses as to how the molars of early monotremes could have evolved. We consider two alternative placements of allotherians (haramiyids + multituberculates). The first, supported by strict consensus of most parsimonious trees, suggests that multituberculates (but not other alllotherians) are closely re− lated to a clade including spalacotheriids + crown therians (Trechnotheria as redefined herein). Alternatively, allotherians can be placed outside the mammalian crown group by a constrained search that reflects the traditional emphasis on the uniqueness of the multituberculate dentition. Given our dataset, these alternative topologies differ in tree−length by only ~0.6% of the total tree length; statistical tests show that these positions do not differ significantly from one another.
    [Show full text]
  • Postcranial Anatomy of Haldanodon Exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and Its Bearing for Mammalian Evolution
    Blackwell Science, LtdOxford, UKZOJZoological Journal of the Linnean Society0024-4082The Lin- nean Society of London, 2005? 2005 1452 219248 Original Article Postcranium of Haldanodont. martin Zoological Journal of the Linnean Society, 2005, 145, 219–248. With 16 figures Postcranial anatomy of Haldanodon exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and its bearing for mammalian evolution THOMAS MARTIN* Forschungsinstitut Senckenberg, Senckenberganlage 25, 60325 Frankfurt am Main, Germany Received October 2004; accepted for publication March 2005 The postcranium of the Late Jurassic docodont Haldanodon exspectatus Kühne & Krusat, 1972 is represented by a partial skeleton and isolated bones of other individuals from the Late Jurassic (Kimmeridgian) of the Guimarota coal mine in Portugal. Haldanodon exhibits adaptations for a fossorial lifestyle such as stout and short limb bones and humeri with greatly expanded distal joints and strong deltopectoral crests. Short first and second phalanges and moderately curved and laterally compressed terminal phalanges with lateral grooves suggest that Haldanodon was a scratch-digger. The dorso-ventrally elongated, triangular scapula has a convex transverse profile with strongly lat- erally reflected anterior and posterior scapula margins, enclosing a deep trough-like ‘infraspinous fossa’. A supra- spinous fossa is not developed. The saddle-shaped glenoid facet is mainly formed by the coracoid and orientated antero-ventrally indicating a sprawling gait. No epiphyses were detected and the wide size range of humerus and femur possibly indicate a lifelong growth. Haldanodon is more derived than Morganucodon by complete reduction of the procoracoid, absence of the procoracoid foramen, and a peg-like coracoid. It shares with monotremes a postscapular fossa that is absent in Morganucodon.
    [Show full text]
  • Doctoral Thesis
    IX. Conclusions - Implications for Locomotion Henkelotherium guimarotae had already evolved a number of the typical therian postcranial characters, such as a scapula with a supraspinous fossa and a distinct femoral neck. These "modern" features had already evolved before the Late Jurassic and thus are more ancient than has generally been assumed so far. A modern pectoral girdle is also known in some other Mesozoic mammals, e.g. in the Early Cretaceous eutherian Eomaia scansoria (Ji et al. 2002), in Jeholodens jenkinsi (Ji et al. 1999), a Early Cretaceous Chinese “triconodont”, and also in Cretaceous “triconodonts” from North America (Jenkins and Crompton 1983). However, Henkelotherium also retained certain primitive characters present in other Mesozoic mammals, e.g., distinct condyles at the distal end of the humerus. This mosaic of primitive and derived postcranial features of Henkelotherium demonstrates the intermediate evolutionary position of this species between archaic mammals (e.g., Morganucodon, Jenkins and Parrington 1976) and the modern therian mammals. A most significant morphological character of Henkelotherium is its small body size (Fig. 34) (head-body-length about 65 - 70 mm). As a consequence of small body size, Recent species with similar dimensions are frequently confronted with surface irregularities and a pronounced three-dimensionally constructed habitat that require a certain amount of climbing (Jenkins 1974). In the perspective of a small mammal, the forest floor, the trees and all the interconnecting 112 secondary growth and the undergrowth are a ragged network of locomotor surfaces (Jenkins 1974). For a generalized small mammal the perception of such a habitat is an irregular three-dimensional space, independent of the nature and inclination of the surfaces.
    [Show full text]
  • Supplemental Data
    Supplementary Information Diversity Data The Paleobiology Database [1] was used as the principal source for taxonomic ranges of the early mammalian genera. Much of the data in the Paleobiology Database came from Kielan- Jaworowska et al. [2], Lofgren [3], Clemens [4], Archibald [5], Hartman [6], Fox [7], Eaton and Cifelli [8], Montellano [9], Pearson et al. [10], and Lillegraven and McKenna [11]. Dental Functional Types For our purposes, triconodont refers to a molar with three primary cusps in a linear or obtuse- angled arrangement, such as in eutriconodontans, amphilestids, and morganucodontans. Symmetrodont molars are those with three primary cusps in a triangular arrangement and no talonid. Tribosphenic molars have dual-function trigonids and talonids such as in true tribosphenic eutherians, metatherians, and stem boreosphenidans, as well as pseudo-tribosphenic australosphenidans. Upper molars of plagiaulacoid multituberculates possess two rows of cusps and upper molars of cimolodont multituberculates have three rows, although the two dental types are also distinguished by number of incisors and premolars [2]. See Kielan-Jaworowska et al. [2] for descriptions of gondwanatherians, haramiyids, eupantotherians, and docodonts. One of the most contentious assignments for dental functional type involves the triconodonts (in the most general usage of the term) (see [71]). It should be noted, however, that even if alternative dental functional types were chosen for triconodont genera (e.g., if amphilestids were included with symmetrodonts instead of triconodontans), the overall diversity patterns of tribosphenic mammals and multituberculates relative to other dental types in the Cretaceous (the main focus of this portion of the study) would not be altered (figure 1).
    [Show full text]
  • HARPER-DISSERTATION-2019.Pdf
    CRANIODENTAL ADAPTATION AND HOMOPLASY IN EARLY MAMMALS by Anthony Maxwell Harper A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor of Philosophy Baltimore, Maryland September, 2019 Abstract For the first two-thirds of their over 180-million-year history, mammals left a sparse fossil record. Often the only direct evidence of these early forms are small and unassociated craniodental fragments. Despite these limitations, the three chapters of this thesis support the effectiveness of this type of material for estimating the functional and autecological capacities in Mesozoic mammals, through high resolution imaging and morphometric analysis of the molariform dentition. Each of the three chapters is a self-contained study addressing separate topics relating to the evolution of dental and petrosal morphology. The common thread between all sections is that variation in craniodental structure among Mesozoic lineages is greater than would be expected based only on the disparity seen among extant small mammals. This is a result of both the more “modern” dynamics of dental evolution in more Mesozoic mammalian lineages than historically appreciated (Chapters 1 and 3), and the more “primitive” morphology of the inner ear, even in groups very closely related to extant crown therians (Chapter 2). In both cases, the craniodental morphologies described are outside the range of variation seen in extant species. Chapter 1 describes several new specimens from the herbivorous stem-therian mammal Reigitherium, from the Late Cretaceous of Patagonia. These newly available specimens demonstrate that the herbivorous molar morphology seen in Reigitherium is ii derived from the more plesiomorphic tuberculosectorial pattern seen in the South American endemic group Meridiolestida.
    [Show full text]