DOCSLIB.ORG

Disconnecting Bones Within the Jaw‐Otic Network Modules Underlies

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Disconnecting Bones Within the Jaw‐Otic Network Modules Underlies Journal of Anatomy J. Anat. (2019) 235, pp15--33 doi: 10.1111/joa.12992 Disconnecting bones within the jaw-otic network modules underlies mammalian middle ear evolution Aitor Navarro-Dıaz,1 Borja Esteve-Altava2 and Diego Rasskin-Gutman1 1Paleobiology and Theoretical biology (Theoretical Biology), Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain 2Institute of Evolutionary Biology (UPF-CSIC), Department of Experimental and Health Sciences, University Pompeu Fabra, Barcelona, Spain Abstract The origin of the mammalian middle ear ossicles from the craniomandibular articulation of their synapsid ancestors is a key event in the evolution of vertebrates. The richness of the fossil record and the multitude of developmental studies have provided a stepwise reconstruction of this evolutionary innovation, highlighting the homology between the quadrate, articular, pre-articular and angular bones of early synapsids with the incus, malleus, gonial and ectotympanic bones of derived mammals, respectively. There are several aspects involved in this functional exaptation: (i) an increase of the masticatory musculature; (ii) the separation of the quadrate bone from the cranium; and (iii) the disconnection of the post-dentary bones from the dentary. Here, we compared the jaw-otic complex for 43 synapsid taxa using anatomical network analysis, showing that the disconnection of mandibular bones was a key step in the mammalian middle ear evolution, changing the skull anatomical modularity concomitant to the acquisition of new functions. Furthermore, our analysis allows the identification of three types of anatomical modules evolving through five evolutionary stages during the anatomical transformation of the jawbones into middle ear bones, with the ossification and degradation of Meckel’s cartilage in mammals as the key ontogenetic event leading the change of anatomical modularity. Key words: anatomical network analysis (AnNA); Meckel’s cartilage; modularity; synapsida. – Introduction (Watson, 1953; Hopson, 1966; Carroll, 1988, chapters 17 18; Rubidge & Sidor, 2001; Sidor, 2001, 2003; Luo, 2011; Han Several structures of the middle ear of mammals evolved et al., 2017; Luo et al., 2017) and recent advances in devel- from the lower jaw of basal synapsids through a series of opmental biology (Luo, 2011; Anthwal et al., 2013, 2017; anatomical changes that started about 315 million years Ramırez-Chaves et al., 2016; Urban et al., 2017). ago. The now extinct non-mammal synapsids had a lower The origin of the mammalian middle ear goes back to the jaw made of up to eight bones, which articulated to the mandibular and jaw joint arrangement of primitive synap- rest of the skull through the articular-quadrate jaw joint; sids. According to the Reichert–Gaupp theory, based on their only auditory bone was the stapes (Crompton & Par- comparative anatomy and development, the ectotympanic, ker, 1978; Sidor, 2003; Meng et al., 2011; Urban et al., gonial, malleus and incus bones of the ear in mammals are 2017). In contrast, modern mammals have a single jawbone, homologous to the angular, pre-articular, articular and the dentary, which articulates to the squamosal, and four quadrate bones of the jaw in reptiles (Rich et al., 2005; Luo, closely connected auditory bones: ectotympanic, malleus, 2011; Meng et al., 2011; Maier & Ruf, 2016; Han et al., incus and stapes. Many aspects of the origin and evolution 2017). At the same time, the evolutionary history of the of the mammalian middle ear are now better understood synapsid lower jaw suggests a trade-off between an thanks to the richness of the synapsids fossil record increase in the area of muscle attachment and a reduction of some mandibular bones to improve sound transmission (Hopson, 1966; Kermack et al., 1973; Fourie, 1974; Cromp- ton & Parker, 1978; Kemp, 1979, 2007; Carroll, 1988, pp. Correspondence 393–395; Wang et al., 2001; Sidor, 2003; Soares et al., 2011; Diego Rasskin-Gutman, Paleobiology and Theoretical Biology (Theo- retical Biology), Cavanilles Institute of Biodiversity and Evolutionary Ramırez-Chaves et al., 2016; Lautenschlager et al., 2017, Biology, University of Valencia, C/ Catedratico Jose Beltran n°2, 2018). During the Permian, synapsids evolved a new power- 46980 Paterna, Valencia, Spain. E: [email protected] ful adductor musculature attached to jawbones (Kemp, Accepted for publication 6 March 2019 1969, 1979; Reisz, 1972; Fourie, 1974; Crompton & Parker, Article published online 12 April 2019 1978). Such innovation enabled early synapsids to feed © 2019 Anatomical Society 16 Network modularity of the mammalian middle ear evolution, A. Navarro-Dıaz et al. larger preys and to increase their body mass (Watson, 1953; 2003; Kemp, 2007; Meng et al., 2011; Anthwal et al., 2013). Reisz, 1972; Carroll, 1988, pg. 363; Kammerer, 2011), leading The reduction in size and the cranial disconnection of this to an increase of the dentary surface that allowed the inser- bony chain increased its vibrational mobility and airborne tion of new-developed muscle fibers that changed biting sound sensitivity (Kermack et al., 1981; Laurin, 1998; Kemp, mechanisms (Carroll, 1988, p. 393; Lautenschlager et al., 2007; Luo, 2011; Meng et al., 2011). Mesozoic mammals 2017, 2018). evolved a new dentary-squamosal jaw joint (Hopson, 1966; After the Permian-Triassic and the Triassic-Jurassic mass Romer, 1970; Crompton & Parker, 1978; Luo & Crompton, extinction events, non-mammalian therapsids reduced their 1994; Kemp, 2007; Luo, 2011; Anthwal et al., 2013; Han body size (Hopson, 1966; Frobisch,€ 2007; Kemp, 2007; Sig- et al., 2017) and relocated the primitive quadrate-articular urdsen et al., 2012; Huttenlocker, 2014). The first small jaw joint to the middle ear after the novel ossification of an insectivorous mammaliaforms originated during the Triassic embryological mandibular element, the Meckel’s cartilage (Fourie, 1974; Carroll, 1988, pp. 401–402; Sidor, 2001) and (Wang et al., 2001; Meng et al., 2011; Urban et al., 2017). had a nocturnal lifestyle (Kermack et al., 1981; Luo, 2011; The loss of bones and the disconnections in the lower jaw Han et al., 2017). Living in the shadow of the large archo- (Sidor, 2001; Luo, 2011; Meng et al., 2011; Han et al., 2017; saurs that dominated this period, any anatomical changes Urban et al., 2017) produced novel patterns of anatomical on sensory organs that favored avoiding predation, as well organization in the jaw-otic complex. Authors recognize as detecting and capturing smaller prey, would have posed three distinct patterns of organization or configuration a selective advantage (Kermack et al., 1981; Luo, 2011; types in synapsids: (i) the mandibular middle ear type, with Urban et al., 2017). Triassic mammaliaforms had a fully reor- post-dentary bones attached to the dentary and a func- ganized musculoskeletal mandibular complex with some tional quadrate-articular jaw joint (Fig. 1A–D); (ii) the tran- jawbones having distinct new roles (Hopson, 1966; Kermack sitional mammalian middle ear type, with the middle ear et al., 1973; Kemp, 1979; Meng et al., 2011; Anthwal et al., bones indirectly connected to the mandible by a link to the 2013; Han et al., 2017; Lautenschlager et al., 2017, 2018). ossified Meckel’s cartilage (Fig. 1E); and (iii) the definitive Thereby, the enlarged dentary assumed all the masticatory mammalian middle ear type, with the middle ear bones muscular insertion in the new Mesozoic mammals, while fully disconnected from the dentary and isolated from par- the smaller post-dentary bones evolved an auditory role ticipating in any chewing action (Fig. 1F; Luo, 2011; Meng that improved sound transmission from the lower jaw to et al., 2011; Ramırez-Chaves et al., 2016; Anthwal et al., the inner ear through a bony chain between the angular, 2017; Han et al., 2017; Luo et al., 2017). These configura- articular, quadrate and stapes bones (Hopson, 1966; Ker- tions can also be seen as changes in the topological mack et al., 1973, 1981; Crompton & Parker, 1978; Sidor, arrangement of the ear bones throughout their evolution. Fig. 1 Representation of the lower jaw transition throughout the synapsid evolution. Notice the enlargement of the dentary bone, concomitant to the reduction of post-dentary bones until their disconnection as new mammalian middle ear bones. Lower jaws from (A) to (D) illustrate the mandibular middle ear type, with post-dentary bones fully attached to the dentary; the lower jaw arrangement of (E) illustrates the transitional mammalian middle ear type, with the ear bones indirectly connected to the dentary by the ossified Meckel’s cartilage; and (F) illustrates the defini- tive mammalian middle ear type, with the ear bones totally disconnected from the dentary bone. (A) Medial view of the lower jaw of the primitive synapsid Dimetrodon (modified from Sidor, 2003). (B) Medial view of the lower jaw of the gorgonopsian therapsid Aelurognathus (modified from Broom, 1913). (C) Medial view of the lower jaw of the cynognathian cynodont Diademodon (modified from Hopson, 1966). (D) Medial view of the lower jaw of the mammaliaform Morganucodon (modified from Kermack et al., 1973). (E) Medial view of the lower jaw of the eutriconodont mammal Yanoconodon (modified from Luo et al., 2007). (F) Lateral view of the lower jaw and middle ear bones of the marsupial mammal Mon- odelphis (Wible, 2003; Luo, 2011). Mandibles are not to scale. © 2019 Anatomical Society Network modularity of the mammalian middle ear evolution, A. Navarro-Dıaz
Load more

Recommended publications
  • Osteological Connections of the Petrosal Bone of the Extant Hippopotamidae Hippopotamus Amphibius and Choeropsis Liberiensis Maeva Orliac, Franck Guy, Renaud Lebrun
    Osteological connections of the petrosal bone of the extant Hippopotamidae Hippopotamus amphibius and Choeropsis liberiensis Maeva Orliac, Franck Guy, Renaud Lebrun To cite this version: Maeva Orliac, Franck Guy, Renaud Lebrun. Osteological connections of the petrosal bone of the extant Hippopotamidae Hippopotamus amphibius and Choeropsis liberiensis. MorphoMuseum, Association Palæovertebrata, 2014, 1 (1), pp.e1. 10.18563/m3.1.1.e1. hal-01902601 HAL Id: hal-01902601 https://hal.archives-ouvertes.fr/hal-01902601 Submitted on 26 Oct 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ANATOMY ATLAS Osteological connections of the petrosal bone of the extant Hippopotamidae Hippopotamus amphibius and Choeropsis liberiensis ORLIAC M.J*, GUY F.†, LEBRUN R.* * Laboratoire de Paléontologie, Institut des Sciences de l’Évolution de Montpellier (ISE-M, UMR 5554, CNRS, UM2, IRD), c.c. 064, Université Montpellier 2, place Eugène Bataillon, F-34095 Montpellier Cedex 05, France † Université de Poitiers - UFR SFA, iPHEP UMR CNRS 7262, Bât B35 - TSA 51106, 6 rue Michel brunet, 86073, Poitiers Cedex 9, France Abstract: This project presents the osteological connections of the petrosal bone of the extant Hippopotamidae Hippopotamus amphibius and Choeropsis liberiensis by a virtual osteological dissection of the ear region.
    [Show full text]
  • Recent Advances in Studies on Mesozoic and Paleogene Mammals in China
    Vol.24 No.2 2010 Paleomammalogy Recent Advances in Studies on Mesozoic and Paleogene Mammals in China WANG Yuanqing* and NI Xijun Institute of Vertebrate Paleontology and Paleoanthropology, CAS, Beijing 10004, China ike in other fields of paleontology, research in from the articular of the lower jaw and the quadrate of the paleomammalogy mainly falls into two aspects. cranium following the process of reduction and detachment LOne is related to the biological nature of fossil from the reptilian mandible, are new elements of the bony mammals, such as their systematics, origin, evolution, chain in the mammalian middle ear. The appearance of phylogenetic relationships, transformation of key features mammalian middle ear allows mammals to hear the sound and paleobiogeography, and the other is related to the of higher frequencies than reptiles do. Generally speaking, geological context, involving biostratigraphy, biochronology, a widely accepted hypothesis is that mammals originated faunal turnover and its relations to the global and regional from a certain extinct reptilian group. The formation and environmental changes. In the last decade, a number of development of the definitive mammalian middle ear well-preserved mammalian specimens were collected from (DMME) has thus become one of the key issues in the study different localities around the country. Such discoveries have of mammalian evolution and has drawn the attention from provided significant information for understanding the early many researchers for many years. evolution of mammals and reconstructing the phylogeny of Developmental biological studies have proven the early mammals. function of the Meckel’s cartilage and its relationship to Studies of Chinese Mesozoic mammals achieved the ear ossicles during the development of mammalian remarkable progress in the past several years.
    [Show full text]
  • The Ear in Mammal-Like Reptiles and Early Mammals
    Acta Palaeontologica Polonica Vol. 28, No. 1-2 pp, 147-158 Warszawa, 1983 Second Symposium on Mesozoic T erre stial Ecosystems, Jadwisin 1981 KENNETH A. KERMACK and FRANCES MUSSETT THE EAR IN MAMMAL-LIKE REPTILES AND EARLY MAMMALS KERMACK, K . A. a nd MUSS ETT, F.: The ear in mammal-like r eptiles an d early mammals. Acta Palaeont. P olonica , 28, 1-2, 147-158, 1983. Th e early m embers of the Theropsida lacked a tympanic membrane. In the later theropslds, the Therapsid a, a tym p an ic membrane develop ed from thc skin on the lateral side of th e lower jaw. The tympanum is not homologous In the Therapsida and ' t he Sauropslda. The ther apsid ea r w as a poor receiver of airborne sound, both In hi gh frequency r esp onse and In the r ange of frequencies encompassed. With the radiation of the Sauropsida in the Triassic the large therapsids became extinct, the small therap si ds evolv ed In to the mammal s and became nocturnal. High frequency hearin g w as essen tial for the nocturn al mode of life; quadrate and arttcutar became diss ociated from the jaw hinge to become the m ammali an au di tory ossi cles . I n the Theria the cochlea became coil ed. The spiral cochlea could n ot have existed until there w as a middle ear w ith the n ec essary h ig h f re q uency r esp onse. This m ay n ot have been until the Cretace ous.
    [Show full text]
  • The Skull O Neurocranium, Form and Function O Dermatocranium, Form
    Lesson 15 ◊ Lesson Outline: ♦ The Skull o Neurocranium, Form and Function o Dermatocranium, Form and Function o Splanchnocranium, Form and Function • Evolution and Design of Jaws • Fate of the Splanchnocranium ♦ Trends ◊ Objectives: At the end of this lesson, you should be able to: ♦ Describe the structure and function of the neurocranium ♦ Describe the structure and function of the dermatocranium ♦ Describe the origin of the splanchnocranium and discuss the various structures that have evolved from it. ♦ Describe the structure and function of the various structures that have been derived from the splanchnocranium ♦ Discuss various types of jaw suspension and the significance of the differences in each type ◊ References: ♦ Chapter: 9: 162-198 ◊ Reading for Next Lesson: ♦ Chapter: 9: 162-198 The Skull: From an anatomical perspective, the skull is composed of three parts based on the origins of the various components that make up the final product. These are the: Neurocranium (Chondocranium) Dermatocranium Splanchnocranium Each part is distinguished by its ontogenetic and phylogenetic origins although all three work together to produce the skull. The first two are considered part of the Cranial Skeleton. The latter is considered as a separate Visceral Skeleton in our textbook. Many other morphologists include the visceral skeleton as part of the cranial skeleton. This is a complex group of elements that are derived from the ancestral skeleton of the branchial arches and that ultimately gives rise to the jaws and the skeleton of the gill
    [Show full text]
  • Mesozoic: the Dark Age for Mammals!
    Ed’s Simplified History of the Mammals Note progression from Pelycosaurs (1) to Therapsids and Cynodonts (2) in Triassic. Stem mammals appeared in Late Triassic and Early Jurassic (3). Relationships among the Middle Jurassic forms (4) are controversial (see handout). Therian clade, identified by the tribosphenic molar (5), emerged at the end of the Jurassic, Early Cretaceous. A slightly more detailed version… in case you like something that looks more slick From Pough et al. 2009. Vertebrate Life, 8th ed. Pelycosaurs Dominated the late Permian, gave rise to therapsids Therapsids Rapid radiation in late Permian, around 270 MYA Still “mammal-like reptiles” The mass extinction at the end of the Permian was the greatest loss of diversity ever with >80% of all known genera and about 90% of all species going extinct, both terrestrial and marine. Cynodonts Late Permian to mid Triassic Last remaining group of therapsids, survived mass extinction at the end of the Permian. Persisted well Only 1 lineage of into Triassic and developed cynodonts survived many features associated through the late Triassic, with mammals. and this group became ancestors of mammals. Mesozoic: the Dark Age for Mammals! multituberculate Morganucodon, one of the earliest mammals (What else was happening in the Late Triassic and Jurassic Hadrocodium that may have contributed to mammals becoming small and Most were very small with nocturnal?) conservative morphology ...but new fossil finds indicate more diversity than we thought Repenomanus Still, largest known mammal during Mesozic Most were shrew to is no larger than a mouse sized, for 125 woodchuck million years! Some Mesozoic events and mammals you should know 1.
    [Show full text]
  • Mammalogy Laboratory 1 - Mammalian Anatomy
    Mammalogy Laboratory 1 - Mammalian Anatomy I. The Goal. The goal of the lab is to teach you skeletal anatomy of mammals. We will emphasize the skull, because many of the taxonomically important characters are cranial characters. We will also demonstrate many of the differences that we’ve been discussing in lecture between mammals and other tetrapod groups. You will be responsible for all the structures in bold. The figure and key should be very helpful. In addition, be sure to check out the Animal Diversity Web at http://animaldiversity.ummz.umich.edu/chordata/mammalia.html. II. The Cranium - exemplified by a coyote (Canis latrans) skull. Two major regions of the skull may be recognized: the brain case and the rostrum. The brain case is the box of bone protecting the brain and the rostrum is the anterior region or the snout. The auditory bullae are associated with the brain case, and ventral to it; these house the middle and inner ears. The structure of the bullae varies greatly among mammals; this will be a useful taxonomic character. The dorsal portion of the cranium is composed of a series of paired bones the meet along the midline. The long slender nasal bones form the roof of the nasal passages. Posterior to these are the paired frontals, which extend down the sides of the cranium to form the orbit, or eye socket. The postorbital process is a projection of the frontal that marks the posterior margin of the orbit. In many mammals (a horse, for example) this process extends all the way to the zygomatic arch to form a postorbital bar.
    [Show full text]
  • 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]
  • Science Journals
    RESEARCH | REPORT PALEONTOLOGY the hyoid apparatus in monotremes and placen- tals, and in a modified condition in marsupials (for details, see the supplementary materials) New Jurassic mammaliaform (16–18). Based on the distinctly mammal-like morphol- sheds light on early evolution ogy of the hyoid elements of Microdocodon,we can now identify hyoid elements of several other mammaliaforms (16)(figs.S4toS9).TheJurassic of mammal-like hyoid bones haramiyidan Vilevolodon has preserved basihyal 1,2 3 4 and ceratohyal bones (fig. S6 and movie S2) (19). Chang-Fu Zhou *, Bhart-Anjan S. Bhullar *, April I. Neander , The Cretaceous eutriconodontan Yanoconodon 5† 4† Thomas Martin , Zhe-Xi Luo also has preserved hyoid elements (fig. S6) (20). Computed tomography (CT) scanning has re- We report a new Jurassic docodontan mammaliaform found in China that is preserved vealed the basihyal, thyrohyals, ceratohyals, and with the hyoid bones. Its basihyal, ceratohyal, epihyal, and thyrohyal bones have mobile epihyals of the trechnotherian Maotherium and joints and are arranged in a saddle-shaped configuration, as in the mobile linkage the multituberculate Sinobaatar of the Cretaceous of the hyoid apparatus of extant mammals. These are fundamentally different from (figs. S7 and S8 and movie S2) (16). Addition- the simple hyoid rods of nonmammaliaform cynodonts, which were likely associated ally, Sinobaatar has preserved stylohyal bones with a wide, nonmuscularized throat, as seen in extant reptiles. The hyoid apparatus (fig. S7), which is similar to the Cretaceous multi- provides a framework for the larynx and for the constricted, muscularized esophagus, tuberculate Kryptobaatar (21). We interpret this crucial for transport and powered swallowing of the masticated food and liquid in extant to mean that multituberculates have an integro- Downloaded from mammals.
    [Show full text]
  • Mammalogy Lecture 2 - Origin of Mammals I
    Mammalogy Lecture 2 - Origin of Mammals I. There are three major living (extant) groups of mammals A. Monotremes - egg laying mammals B. Metatherians - marsupial mammals C. Eutherians - Placental mammals These are related by the following evolutionary tree or phylogeny Monotremes Metatherians (Marsupials) Eutherians (Placentals) Node - Divergence Event Branch - Common Ancestor Marsupials and placentals share an ancestor not shared by monotremes. II. A. In order to understand the origin of mammals, we have to look farther back, into the Paleozoic (350 MYA), and look at relationships among the tetrapod vertebrates. So we’ll start by going deeper in time, and work our way back up to this level in the phylogeny. Amp hibians Mamm als Tur tles Squ amates Crocodylians Dino1 Birds Dino 2 Synaps ida Stem Rep tiles - Captor hino mo rp hs Am n ion Trans ition to land We can mark evolutionary changes along this phylogeny; the evolution of limbs, the evolution of the amnion, etc. It’s this lineage labeled Synapsida that we’ll examine in order to understand the origin of mammals. We need to understand the situation just prior to this in the “stem reptiles,” the ancestors to mammals, birds, turtles, and other reptiles. Captorhinomorphs. B. In the Carboniferous, ca. 350 MYBP, the captorhinomorphs evolved, and the synapsid lineage diverged from the stem reptiles 30 MY later 320 MYA, and it’s this lineage that will eventually lead the modern mammals. Synapsid - “together arch” describes a skull condition that is unique to this lineage. The word “synapsid” is also used to refer to the group of organisms that exhibit this condition.
    [Show full text]
  • Jaw Roll and Jaw Yaw in Early Mammals
    Matters arising Reply to: Jaw roll and jaw yaw in early mammals https://doi.org/10.1038/s41586-020-2364-z Bhart-Anjan S. Bhullar1,2,6 ✉, Armita R. Manafzadeh3,6, Juri A. Miyamae1,2, Eva A. Hoffman4, Elizabeth L. Brainerd3, Catherine Musinsky5 & Alfred W. Crompton5 Published online: 17 June 2020 Check for updates REPLYING TO D. M. Grossnickle Nature (2020) In the accompanying Comment1, Grossnickle disputes our conclusion2 identification1,11 of the ancestral cladotherian talonid surface with the that roll-dominated processing is ancestral for therian mammals on the therian hypoflexid alone. It is true that the primitive talonid favoured basis of the following assertions: that the surface of the therian talonid shearing, whereas the therian basin allowed grinding. However, it has basin (Fig. 1a–i) is not homologous to the ancestral cladotherian talo- previously been observed that mediolateral motion from jaw roll would nid heel; that the inflected angle in marsupials suggests secondarily have increased the efficiency of both kinds of processing4, which exist increased jaw roll; that the rotational grinding stroke as we describe as points on a continuum rather than a dichotomy. it might be a passive movement; that the cladotherian angular pro- With regard to the so-called inflection of the marsupial angle, this cess (Fig. 1j–s) increases mechanical advantage for yaw instead of for phenomenon has previously been found12 to be little more than an roll; and that the angular process of yaw-processing mammals has elaboration of a ventral bony lamina known as the pterygoid shelf in expanded instead of vanished. stem therians.
    [Show full text]
  • A New Spalacotheriid Symmetrodont from the Early Cretaceous of Northeastern China
    PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3475, 20 pp., 5 ®gures, 1 table May 11, 2005 A New Spalacotheriid Symmetrodont from the Early Cretaceous of Northeastern China YAO-MING HU,1 RICHARD C. FOX,2 YUAN-QING WANG,3 AND CHUAN-KUI LI4 ABSTRACT Symmetrodonts are Mesozoic mammals having lower molars with nearly symmetrical tri- gonids but lacking talonids. They appear to be stem members of the mammalian clade that led to extant tribosphenic mammals, but the fossil record of symmetrodonts is poor. Here we report a new genus and species of an acute-angled spalacotheriid symmetrodont, Heishanlestes changi, n.gen. and n.sp., represented by well-preserved lower jaws with teeth from the Early Cretaceous of northeastern China. The new mammal has four tightly spaced premolars and three morphological groups of lower molars, in which the ®rst molar has an obtuse trigonid angle and the last two molars have a large neomorphic cusp in the center of the trigonid, a feature not seen in other mammals. Heishanlestes appears to be a specialized member of the spalacotheriid subfamily, Spalacolestinae, which is otherwise only known from North America. The animal probably used the premolars to crush its prey before shearing it with the molars. 1 Division of Paleontology, American Museum of Natural History; Institute of Vertebrate Paleontology and Paleo- anthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China; Biology Program, Graduate School and City College of New York, City University of New York ([email protected]).
    [Show full text]
  • Jaw Suspension
    JAW SUSPENSION Jaw suspension means attachment of the lower jaw with the upper jaw or the skull for efficient biting and chewing. There are different ways in which these attachments are attained depending upon the modifications in visceral arches in vertebrates. AMPHISTYLIC In primitive elasmobranchs there is no modification of visceral arches and they are made of cartilage. Pterygoqadrate makes the upper jaw and meckel’s cartilage makes lower jaw and they are highly flexible. Hyoid arch is also unchanged. Lower jaw is attached to both pterygoqadrate and hyoid arch and hence it is called amphistylic. AUTODIASTYLIC Upper jaw is attached with the skull and lower jaw is directly attached to the upper jaw. The second arch is a branchial arch and does not take part in jaw suspension. HYOSTYLIC In modern sharks, lower jaw is attached to pterygoquadrate which is in turn attached to hyomandibular cartilage of the 2nd arch. It is the hyoid arch which braces the jaw by ligament attachment and hence it is called hyostylic. HYOSTYLIC (=METHYSTYLIC) In bony fishes pterygoquadrate is broken into epipterygoid, metapterygoid and quadrate, which become part of the skull. Meckel’s cartilage is modified as articular bone of the lower jaw, through which the lower jaw articulates with quadrate and then with symplectic bone of the hyoid arch to the skull. This is a modified hyostylic jaw suspension that is more advanced. AUTOSTYLIC (=AUTOSYSTYLIC) Pterygoquadrate is modified to form epipterygoid and quadrate, the latter braces the lower jaw with the skull. Hyomandibular of the second arch transforms into columella bone of the middle ear cavity and hence not available for jaw suspension.
    [Show full text]