Journal articles: 'Primitive mammal'

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Dellovade, Tammy L., Jean-Pierre Hardelin, Nadia Soussi-Yanicostas, Donald W. Pfaff, Marlene Schwanzel-Fukuda, and Christine Petit. "Anosmin-1 immunoreactivity during embryogenesis in a primitive eutherian mammal." Developmental Brain Research 140, no. 2 (2003): 157–67. http://dx.doi.org/10.1016/s0165-3806(02)00544-8.

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Cifelli, R. L. "A Primitive Higher Mammal from the Late Cretaceous of Southern Utah." Journal of Mammalogy 71, no. 3 (1990): 343–50. http://dx.doi.org/10.2307/1381944.

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Cifelli, Richard L., and Christian De Muizon. "Marsupial mammal from the Upper Cretaceous North Horn Formation, Central Utah." Journal of Paleontology 72, no. 3 (1998): 532–37. http://dx.doi.org/10.1017/s0022336000024306.

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Little is known of the non-dinosaurian fauna from the Cretaceous (Maastrichtian) part of the North Horn Formation, despite its biogeographic importance. Herein we describe a new marsupial mammal from the unit, founded on an exceptionally complete specimen of a juvenile individual, and present new information on the incisor region of early marsupials, based on comparison with complete specimens from the early Paleocene of Bolivia. Alphadon eatoni, new species, is the smallest Lancian species of the genus, and departs from a presumed marsupial morphotype in having the second lower incisor enlarged. The species is, however, primitive in lacking a “staggered” pattern to the incisor series and in having a labial mandibular foramen, and in these respects it differs from Paleocene and later marsupials. Poor representation of other taxa precludes meaningful comparison to most other North American Cretaceous marsupials, although Eodelphis, thought to be distantly related, also has an enlarged i2. Although Alphadon is characterized by many primitive features, the relative development of the incisors is not what would be predicted in a morphological antecedent to later Marsupialia.

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He, Jing, M. David Irwin, and YaPing Zhang. "Motilin and ghrelin gene experienced episodic evolution during primitive placental mammal evolution." Science China Life Sciences 53, no. 6 (2010): 677–82. http://dx.doi.org/10.1007/s11427-010-3105-6.

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Li, Jinling, Yuan Wang, Yuanqing Wang, and Chuankui Li. "A new family of primitive mammal from the Mesozoic of western Liaoning, China." Chinese Science Bulletin 46, no. 9 (2001): 782–85. http://dx.doi.org/10.1007/bf03187223.

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GHEERBRANT, EMMANUEL, MOHAMED IAROCHENE, MBAREK AMAGHZAZ, and BAÂDI BOUYA. "Early African hyaenodontid mammals and their bearing on the origin of the Creodonta." Geological Magazine 143, no. 4 (2006): 475–89. http://dx.doi.org/10.1017/s0016756806002032.

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We report a new proviverrine hyaenodontid creodont mammal, Boualitomus marocanensis, n.g., n.sp., from the earliest Eocene of Morocco, and provide new comments on Tinerhodon from the late Paleocene of Morocco. Aside from the autapomorphic loss of P/1, Boualitomus is characterized by a primitive morphology (e.g. M/3 subequal to M/2, short molar trigonid, narrow talonid, metaconid comparable to paraconid) which resembles most closely the proviverrine Prototomus. Boualitomus is more primitive than Prototomus, especially in its small size and the talonid of P/4 not being fully simplified, bearing at least two accessory cusps including a bulbous protostylid. These primitive features are remarkably reminiscent of Tinerhodon. The morphological relationship of Boualitomus and Tinerhodon supports the proviverrine affinity of the latter. Significant basal hyaenodontid synapomorphies of Boualitomus and Tinerhodon are the paraconid and paracristid development in M/1–3, anterior premolar morphology and occurrence of diastemata. Boualitomus and Tinerhodon throw new light upon the question of the origin of the Creodonta. Tinerhodon further fills the structural gap between Hyaenodontidae and primitive insectivore-like eutherians, and it provides additional data for the hypothesis of a didelphodontan origin for the Creodonta. The presence of cimolestids (as the stem-group of hyaenodontids) in the late Paleocene of Morocco, and the identification of Boualitomus and Tinerhodon as the most primitive and earliest known Hyaenodontidae, support an African origin of the family and its order.

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Jones, Matthew F., Qiang Li, Xijun Ni, and K. Christopher Beard. "The earliest Asian bats (Mammalia: Chiroptera) address major gaps in bat evolution." Biology Letters 17, no. 6 (2021): 20210185. http://dx.doi.org/10.1098/rsbl.2021.0185.

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Bats dispersed widely after evolving the capacity for powered flight, and fossil bats are known from the early Eocene of most continents. Until now, however, bats have been conspicuously absent from the early Eocene of mainland Asia. Here, we report two teeth from the Junggar Basin of northern Xinjiang, China belonging to the first known early Eocene bats from Asia, representing arguably the most plesiomorphic bat molars currently recognized. These teeth combine certain bat synapomorphies with primitive traits found in other placental mammals, thereby potentially illuminating dental evolution among stem bats. The Junggar Basin teeth suggest that the dentition of the stem chiropteran family Onychonycteridae is surprisingly derived, although their postcranial anatomy is more primitive than that of any other Eocene bats. Additional comparisons with stem bat families Icaronycteridae and Archaeonycteridae fail to identify unambiguous synapomorphies for the latter taxa, raising the possibility that neither is monophyletic as currently recognized. The presence of highly plesiomorphic bats in the early Eocene of central Asia suggests that this region was an important locus for the earliest, transitional phases of bat evolution, as has been demonstrated for other placental mammal orders including Lagomorpha and Rodentia.

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Gheerbrant, Emmanuel, and Humberto Astibia. "Addition to the Late Cretaceous Laño mammal faunule (Spain) and to the knowledge of European “Zhelestidae” (Lainodontinae nov.)." Bulletin de la Société Géologique de France 183, no. 6 (2012): 537–46. http://dx.doi.org/10.2113/gssgfbull.183.6.537.

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Abstract New mammal material from the Campano-Maastrichtian locality of Laño, Spanish Basque Country documents two new zhelestid eutherian species referred to the genus Lainodon. This material enlightens the upper molar pattern of the European zhelestids and confirms their originality and homogeneity. The European zhelestids are included in the new subfamily Lainodontinae, which is distinct and characterized by a mosaic of primitive and specialized features. The Lainodontinae clade adds to other endemic vertebrate taxa (among multituberculates, flightless birds, dinosaurs, and turtles) that typify the Late Cretaceous fauna of the European Archipelago. The material from Laño provides further evidence of a modest but significant lainodontine radiation known by five or six species belonging to two or three genera (Lainodon, Labes, ? Valentinella), which is currently restricted to western Europe, i.e. to the Ibero-Armorican Island. The plesiomorph features of the Lainodontinae (lower molar trigonid poorly compressed, upper molar without lingual cingulum) recall the earliest known zhelestids, and suggest an Asian origin from a Sheikhdzheilia-like stem lineage at the beginning of the Late Cretaceous. This dispersal event from Asia probably involved other vertebrate taxa, such as the multituberculate stem group of the kogaionid mammals and the hadrosaurid dinosaurs. The zhelestid subfamily Lainodontinae represents the most diverse and dominant taxon in the western European Late Cretaceous mammal fauna, which is eutherian-dominated, by contrast to the eastern European Late Cretaceous mammal fauna which is dominated by an original and at that time exclusive radiation of kogaionid multituberculates.

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Court, Nicholas, and Mohamed Mahboubi. "Reassessment of Lower Eocene Seggeurius amourensis: aspects of primitive dental morphology in the mammalian order Hyracoidea." Journal of Paleontology 67, no. 5 (1993): 889–93. http://dx.doi.org/10.1017/s002233600003715x.

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New lower dental material of the fossil hyracoid mammal, Seggeurius amourensis Crochet, 1986, from Eocene deposits of the Southern Atlas in Algeria, has prompted a reevaluation of the genus. The dentition as a whole is first described in detail, thus providing a more precise characterization of the genus than has hitherto been available. Peculiarities, particularly in upper molar morphology, are sufficient to uphold a generic distinction. However, based largely on lower molar morphology Seggeurius amourensis is transferred from the subfamily Geniohyinae to Saghatheriinae. In the upper molars, absence of a postmetacrista and the presence of a preprotocrista continuous with the parastyle are interpreted as primitive features in hyracoids. In the lower molars, extreme reduction of the paracristid and the presence of a mesoconid are also considered primitive for hyracoids. These features together with small size, bunodonty, low crown height, and very simple premolar morphology indicate that Seggeurius amourensis is the most primitive hyrax yet recovered.

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Abarca-Buis, RenéFernando, María Elena Contreras-Figueroa, David Garciadiego-Cázares, and Edgar Krötzsch. "Control of fibrosis by TGFβ signalling modulation promotes redifferentiation during limited regeneration of mouse ear." International Journal of Developmental Biology 64, no. 7-8-9 (2020): 423–32. http://dx.doi.org/10.1387/ijdb.190237ra.

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Transforming growth factor beta (TGF&beta;) signalling is involved in several aspects of regeneration in many organs and tissues of primitive vertebrates. It has been difficult to recognize the role of this signal in mammal regeneration due to the low ability of this animal class to reconstitute tissues. Nevertheless, ear-holes in middle-age female mice represent a model to study the limited epimorphic-like regeneration in mammals. Using this model, in this study we explored the possible participation of TGF&beta; signalling in mammal regeneration. Positive pSmad3 cells, as well as TGF&beta;1 and TGF&beta;3 isoforms, were detected during the redifferentiation phase in the blastema-like structure. Daily administration of the inhibitor of the TGF&beta; intracellular pathway, SB431542, during 7 days from the re-differentiation phase, resulted in a decreased level of pSmad3 accompanied by a transitory higher growth of the new tissue, larger cartilage nodules, and new muscle formation. These phenotypes were associated with a decrease in the number of &alpha;-SMA-positive cells and loose packing of collagen I. These results indicate that the modulation of the fibrosis mediated by TGF&beta; signalling contributes to enhancing the differentiation of cartilage and muscle during limited ear-hole regeneration.

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Chester, Stephen G. B., Jonathan I. Bloch, Doug M. Boyer, and William A. Clemens. "Oldest known euarchontan tarsals and affinities of Paleocene Purgatorius to Primates." Proceedings of the National Academy of Sciences 112, no. 5 (2015): 1487–92. http://dx.doi.org/10.1073/pnas.1421707112.

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Earliest Paleocene Purgatorius often is regarded as the geologically oldest primate, but it has been known only from fossilized dentitions since it was first described half a century ago. The dentition of Purgatorius is more primitive than those of all known living and fossil primates, leading some researchers to suggest that it lies near the ancestry of all other primates; however, others have questioned its affinities to primates or even to placental mammals. Here we report the first (to our knowledge) nondental remains (tarsal bones) attributed to Purgatorius from the same earliest Paleocene deposits that have yielded numerous fossil dentitions of this poorly known mammal. Three independent phylogenetic analyses that incorporate new data from these fossils support primate affinities of Purgatorius among euarchontan mammals (primates, treeshrews, and colugos). Astragali and calcanei attributed to Purgatorius indicate a mobile ankle typical of arboreal euarchontan mammals generally and of Paleocene and Eocene plesiadapiforms specifically and provide the earliest fossil evidence of arboreality in primates and other euarchontan mammals. Postcranial specializations for arboreality in the earliest primates likely played a key role in the evolutionary success of this mammalian radiation in the Paleocene.

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Prothero, Donald R., and Jessica Grenader. "A New Primitive Species of the Flat-Headed Peccary Platygonus (Tayassuidae, Artiodactyla, Mammalia) From the Late Miocene of the High Plains." Journal of Paleontology 86, no. 6 (2012): 1021–31. http://dx.doi.org/10.1666/12-050r.1.

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A new species of the Pliocene–Pleistocene flat-headed peccary, Platygonus pollenae, has been recovered latest Hemphillian (latest Miocene) localities from Nebraska, Kansas, Colorado, and Texas. It can be distinguished from other tayassuids by its distally rounded wing-like zygomatic process, and its subzygodont cheek teeth. In contrast to more derived species of Platygonus, it is much smaller in size, its molars are relatively more bunodont, the talon and talonid cusps are retained on the premolars of most individuals, and the mandibular symphysis lacks a median keel on the chin. In these characters, it is the earliest and the most primitive species of Platygonus known. It is more primitive than the typical Blancan species, or any of the species from the Pleistocene, and demonstrates the origin of this important Pleistocene mammal in the latest Miocene.

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Macfadden, Bruce J., and James L. Dobie. "Late Miocene three-toed horse Protohippus (Mammalia, Equidae) from southern Alabama." Journal of Paleontology 72, no. 1 (1998): 149–52. http://dx.doi.org/10.1017/s0022336000024082.

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Dental and postcranial remains of a donkey-sized, three-toed, primitive horse were collected from the “Undifferentiated Miocene” Ecor Rouge Sand (which underlies the widespread Citronelle Formation) from the Mauvilla site in southern Alabama. These fossils probably pertain to a single individual of Protohippus gidleyi Hulbert, 1988. This represents an exceedingly rare occurrence of a late Tertiary land mammal from the central Gulf Coastal Plain and allows comparisons with better-known, contemporaneous land-mammal assemblages from Florida. Based on the known biochronology of Protohippus gidleyi from other localities, and the stratigraphic position of the Mauvilla record, the age of: 1) the Ecor Rouge Sand is late Miocene (latest Clarendonian to early Hemphillian landmammal “age”), between 9.0 to 6.5 Ma; and 2) the overlying Citronelle Formation near its type locality in southern Alabama is therefore late Miocene or younger.

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Patočka, Jiří. "The Toxins of Cyanobacteria." Acta Medica (Hradec Kralove, Czech Republic) 44, no. 2 (2001): 69–75. http://dx.doi.org/10.14712/18059694.2019.87.

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Cyanobacteria, formerly called ”blue-green algae“, are simple, primitive photosynthetic microorganism wide occurrence in fresh, brackish and salt waters. Forty different genera ofCyanobacteriaare known and many of them are producers of potent toxins responsible for a wide array of human illnesses, aquatic mammal and bird morbidity and mortality, and extensive fish kills. These cyanotoxins act as neurotoxins or hepatotoxins and are structurally and functionally diverse, and many are derived from unique biosynthetic pathways. All known cyanotoxins and their chemical and toxicological characteristics are presented in this article.

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van, der, Slobodan Knezevic, and Ivan Stefanovic. "A mid-miocene age for the Slanci formation near Belgrade (Serbia), based on a record of the primitive antelope Eotragus cf. Clavatus from Visnjica." Annales g?ologiques de la Peninsule balkanique, no. 68 (2007): 53–59. http://dx.doi.org/10.2298/gabp0701053v.

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In a borhole at Veliko Selo near Belgrade in the Miocene lacustrine sediments Slanci, which are locally known as the Slanacka Serija, a mammal tooth was found. The age of these deposits is under discussion. The fossil is here described and attributed with a query to the primitive antelope Eotragus clavatus (GERVAIS, 1850), which is suggestive of a Early Serravallian ("upper Badenian") or Early Middle Miocene age for these deposits, whereas an Aquitalian or Eggenburgian ("Egerian" or "Eggenburgian") (Early Miocene) age can be ruled out.

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Reisz, Robert R., Diane Scott, and Jack van Bendegem. "Atlas–axis complex of Secodontosaurus, a sphenacodontid mammal-like reptile (Eupelycosauria: Synapsida) from the Lower Permian of Texas." Canadian Journal of Earth Sciences 29, no. 3 (1992): 596–600. http://dx.doi.org/10.1139/e92-051.

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The description of the atlas–axis complex of Secodontosaurus (an Early Permian synapsid) indicates that sphenacodontids share with primitive therapsids the derived feature of a tall atlantal pleurocentrum that extends to the ventral edge of the vertebral column. Although similar, the postcranial skeletons of Dimetrodon and Secodontosaurus can be differentiated by the distinct shape and size of the latter's axial neural spine and posterior zygapophysis.

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Marks, N. J., C. Shaw, D. W. Halton, and L. Thim. "The primary structure of pancreatic polypeptide from a primitive insectivorous mammal, the European hedgehog (Erinaceous europaeus)." Regulatory Peptides 47, no. 2 (1993): 179–85. http://dx.doi.org/10.1016/0167-0115(93)90422-5.

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Kondrashov, Peter E., and Spencer G. Lucas. "Nearly complete skeleton of Tetraclaenodon (Mammalia, Phenacodontidae) from the early Paleocene of New Mexico: morpho-functional analysis." Journal of Paleontology 86, no. 1 (2012): 25–43. http://dx.doi.org/10.1666/11-009.1.

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We describe the relatively complete skeleton of Tetraclaenodon undoubtedly associated with its dentition, from the Torrejonian interval of the Nacimiento Formation in the San Juan Basin, New Mexico. Tetraclaenodon is the most primitive and oldest genus of the family Phenacodontidae and is very important for assessing the phylogenetic relationships of the family. The newly described skeleton belonged to a lightly built terrestrial mammal that could use trees for shelter. The structure of the ulna, manus, femur, crus, and pes corresponds to that of a typical terrestrial mammal, while morphological features such as the low greater tubercle of the humerus, long deltopectoral crest, pronounced lateral supracondylar crest, and hemispherical capitulum indicate some scansorial adaptations of Tetraclaenodon. The postcranial skeleton of Tetraclaenodon does not exhibit the cursorial adaptations seen in later phenacodontids and early perissodactyls. Phylogenetic analysis did not recover monophyletic “Phenacodontidae”; instead, phenacodontids formed a series of sister taxa to the Altungulata clade. Tetraclaenodon is the basal-most member of the “Phenacodontidae” + Altungulata clade.

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Vizcaíano, Sergio F., and Gustavo J. Scillato-Yané. "An Eocene tardigrade (Mammalia, Xenarthra) from Seymour Island, West Antarctica." Antarctic Science 7, no. 4 (1995): 407–8. http://dx.doi.org/10.1017/s0954102095000563.

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Carlini et al. (1990) reported the presence of Xenarthra (Mammalia) from the Eocene deposits of Seymour Island, Antarctic Peninsula, based on an ungual phalanx from locality RV 8200. The locality, referred to informally as “mammal site” by Woodburne & Zinsmeister (1984), is located at 64°14′21″S, 56°39′44″W at an elevation of 45 m in the middle levels of the shallow marine La Meseta Formation (TELM 5 of Saddler 1988). Carlini et al. (1990) initially identified the phalanx as a megatherioid sloth (Order Tardigrada). Marenssi et al. (1994) revised its identification to ?Tardigrada or ?Vermilingua, by comparison with a primitive myrmecophagid (Order Vermilingua) from the Lower Miocene of Patagonia, whose ungual phalanges are indistinguishable from those of primitive sloths (Carlini et al. 1992). We report a fragmentary tooth of a member of the Tardigrada (Family incertue sedis) confirming the presence of this group in the Eocene of Antarctica.

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Ahnelt, Peter K., Jan Nora Hokoç, and Pal Röhlich. "Photoreceptors in a primitive mammal, the South American opossum, Didelphis marsupialis aurita: Characterization with anti-opsin immunolabeling." Visual Neuroscience 12, no. 5 (1995): 793–804. http://dx.doi.org/10.1017/s0952523800009366.

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AbstractThe retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.

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Boroviak, Thorsten, and Jennifer Nichols. "The birth of embryonic pluripotency." Philosophical Transactions of the Royal Society B: Biological Sciences 369, no. 1657 (2014): 20130541. http://dx.doi.org/10.1098/rstb.2013.0541.

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Formation of a eutherian mammal requires concurrent establishment of embryonic and extraembryonic lineages. The functions of the trophectoderm and primitive endoderm are to enable implantation in the maternal uterus, axis specification and delivery of nutrients. The pluripotent epiblast represents the founding cell population of the embryo proper, which is protected from ectopic and premature differentiation until it is required to respond to inductive cues to form the fetus. While positional information plays a major role in specifying the trophoblast lineage, segregation of primitive endoderm from epiblast depends upon gradual acquisition of transcriptional identity, directed but not initiated by fibroblast growth factor (FGF) signalling. Following early cleavage divisions and formation of the blastocyst, cells of the inner cell mass lose totipotency. Developing epiblast cells transiently attain the state of naive pluripotency and competence to self-renew in vitro as embryonic stem cells and in vivo by means of diapause. This property is lost after implantation as the epiblast epithelializes and becomes primed in preparation for gastrulation and subsequent organogenesis.

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Korth, William W., and Robert J. Emry. "Pipestoneomyidae, a new family of fossil rodents (Mammalia) from the Duchesnean (late middle Eocene, Bartonian) to Orellan (early Oligocene, Priabonian) of North America." Journal of Paleontology 87, no. 2 (2013): 289–96. http://dx.doi.org/10.1666/12-054r.1.

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Additional specimens of the problematical rodent Pipestoneomys Donahoe, 1956, have allowed for recognition of a new family, Pipestoneomyidae. A new genus and species of pipestoneomyid is recognized from the late middle Eocene (Duchesnean North American Land Mammal Age; Bartonian), Argorheomys septendrionalis, which is morphologically more primitive than Pipestoneomys and demonstrates that this new family has been distinct since the Duchesnean. The Pipestoneomyidae share a number of derived characters with the Geomorpha, especially the two-part inner layer of incisor enamel of the Eoymidae. The Pipestoneomyidae differ from the Eomyidae in lacking the basic “omega” pattern of the cheek teeth of the former, so are in the Eomyoidea as a distinct family.

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Csiki-Sava, Zoltán, Mátyás Vremir, Jin Meng, Stephen L. Brusatte, and Mark A. Norell. "Dome-headed, small-brained island mammal from the Late Cretaceous of Romania." Proceedings of the National Academy of Sciences 115, no. 19 (2018): 4857–62. http://dx.doi.org/10.1073/pnas.1801143115.

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The island effect is a well-known evolutionary phenomenon, in which island-dwelling species isolated in a resource-limited environment often modify their size, anatomy, and behaviors compared with mainland relatives. This has been well documented in modern and Cenozoic mammals, but it remains unclear whether older, more primitive Mesozoic mammals responded in similar ways to island habitats. We describe a reasonably complete and well-preserved skeleton of a kogaionid, an enigmatic radiation of Cretaceous island-dwelling multituberculate mammals previously represented by fragmentary fossils. This skeleton, from the latest Cretaceous of Romania, belongs to a previously unreported genus and species that possesses several aberrant features, including an autapomorphically domed skull and one of the smallest brains relative to body size of any advanced mammaliaform, which nonetheless retains enlarged olfactory bulbs and paraflocculi for sensory processing. Drawing on parallels with more recent island mammals, we interpret these unusual neurosensory features as related to the island effect. This indicates that the ability to adapt to insular environments developed early in mammalian history, before the advent of therian mammals, and mammals with insular-related modifications were key components of well-known dwarfed dinosaur faunas. Furthermore, the specimen suggests that brain size reduction, in association with heightened sensory acuity but without marked body size change, is a novel expression of the island effect in mammals.

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SAITO, Tsunemasa, John A. BARRON, and Masamichi SAKAMOTO. "An early late Oligocene age indicated by diatoms for a primitive desmostylian mammal Behemotops from eastern Hokkaido, Japan." Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences 64, no. 9 (1988): 269–73. http://dx.doi.org/10.2183/pjab.64.269.

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Tanaka, Yasukazu, Yoshinobu Elshi, and Bede Morris. "Splenic hemopoiesis of the platypus(Ornithorhynchus anatinus): Evidence of primary hemopoiesis in the spleen of a primitive mammal." American Journal of Anatomy 181, no. 4 (1988): 401–5. http://dx.doi.org/10.1002/aja.1001810408.

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Albert, Tatiani G., Nicola Schiel, and Antonio Souto. "The white-eared opossum failed to understand the parallel strings task: studying a primitive mammal under natural conditions." Animal Cognition 23, no. 5 (2020): 871–80. http://dx.doi.org/10.1007/s10071-020-01392-1.

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Deng, Tao, Xiaoming Wang, Mikael Fortelius, et al. "Out of Tibet: Pliocene Woolly Rhino Suggests High-Plateau Origin of Ice Age Megaherbivores." Science 333, no. 6047 (2011): 1285–88. http://dx.doi.org/10.1126/science.1206594.

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Ice Age megafauna have long been known to be associated with global cooling during the Pleistocene, and their adaptations to cold environments, such as large body size, long hair, and snow-sweeping structures, are best exemplified by the woolly mammoths and woolly rhinos. These traits were assumed to have evolved as a response to the ice sheet expansion. We report a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive woolly rhino. These new Tibetan fossils suggest that some megaherbivores first evolved in Tibet before the beginning of the Ice Age. The cold winters in high Tibet served as a habituation ground for the megaherbivores, which became preadapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe.

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Wiesgigl, Martina, and Joachim Clos. "Heat Shock Protein 90 Homeostasis Controls Stage Differentiation in Leishmania donovani." Molecular Biology of the Cell 12, no. 11 (2001): 3307–16. http://dx.doi.org/10.1091/mbc.12.11.3307.

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The differentiation of Leishmania parasites from the insect stage, the promastigote, toward the pathogenic mammalian stage, the amastigote, is triggered primarily by the rise in ambient temperature encountered during the insect-to-mammal transmission. We show here that inactivation of heat shock protein (Hsp) 90, with the use of the drugs geldanamycin or radicicol, mimics transmission and induces the differentiation from the promastigote to the amastigote stage. Geldanamycin also induces a growth arrest of cultured promastigotes that can be forestalled by overexpression of the cytoplasmic Hsp90. Moreover, we demonstrate that Hsp90 serves as a feedback inhibitor of the cellular heat shock response inLeishmania. Our results are consistent with Hsp90 homeostasis serving as cellular thermometer for these primitive eukaryotes, controlling both the heat shock response and morphological differentiation.

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Montellano-Ballesteros, Marisol, and Richard C. Fox. "A new tribotherian (Mammalia, Boreosphenida) from the late Santonian to early Campanian upper Milk River Formation, Alberta." Canadian Journal of Earth Sciences 52, no. 1 (2015): 77–83. http://dx.doi.org/10.1139/cjes-2014-0144.

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A new tribotherian mammal, Tirotherium aptum gen. et sp. nov., is described from the late Santonian to early Campanian upper Milk River Formation of Verdigris Coulee, southern Alberta, Canada. The new mammal is known only from isolated teeth, five upper and three lower molars. The upper molars represent two or possibly three pre-ultimate loci and are marked by reduction and loss of the stylar shelf anteriorly, loss of the stylocone, a paracone that is larger than the metacone, weakly developed conules, a low, small protocone, and specialized postvallum single-rank shear. The lower molars probably represent two pre-ultimate loci and are characterized by an anteriorly positioned paraconid, trenchant paracristid, small, posterolingual metaconid, a distal metacristid, broadly open trigonid angle, and a short, basined talonid in which the hypoconulid is closer to the entoconid than to the hypoconid. The molars of Tirotherium most closely resemble those of Picopsis Fox, 1980, a tribotherian that also occurs in the upper Milk River Formation, but the molars of Tirotherium are significantly larger than those of Picopsis. Nonetheless, Tirotherium aptum is best classified in the Picopsidae, a boreosphenidan family of tiny mammalian faunivores of uncertain relationships to other tribotherians, and displaying a unique mosaic of primitive and derived characters.

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Evens, T. M. S. "Twins are Birds and a Whale is a Fish, a Mammal, a Submarine: Revisiting 'Primitive Mentality' as a Question of Ontology." Social Analysis 56, no. 3 (2012): 1–11. http://dx.doi.org/10.3167/sa.2012.560301.

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Macfadden, Bruce J., Michael X. Kirby, Aldo Rincon, et al. "Extinct peccary “Cynorca” occidentale (Tayassuidae, Tayassuinae) from the Miocene of Panama and correlations to North America." Journal of Paleontology 84, no. 2 (2010): 288–98. http://dx.doi.org/10.1666/09-064r.1.

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Recently collected specimens of the extinct tayassuine peccary “Cynorca” occidentale (and another indeterminant tayassuid) are described from new excavations along the southern reaches of the Panama Canal. Fossil peccaries were previously unknown from Panama, and these new tayassuid specimens therefore add to the extinct mammalian biodiversity in this region. “Cynorca” occidentale occurs in situ in the Centenario Fauna (new name) from both the upper part of the Culebra Formation and overlying Cucaracha Formation, thus encompassing a stratigraphic interval that includes both of these formations and the previously described and more restricted Gaillard Cut Local Fauna. “Cynorca” occidentale is a primitive member of the clade that gives rise to modern tayassuines in the New World. Diagnostic characters for “C.” occidentale include a retained primitive M1, reduced M3, and shallow mandible, and this species is small relative to most other extinct and modern tayassuine peccaries. Based on the closest biostratigraphic comparisions (Maryland, Florida, Texas, and California), the presence of “C.” occidentale indicates an interval of uncertain duration within the early Hemingfordian (He1) to early Barstovian (Ba 1) land mammal ages (early to middle Miocene) for the Centenario Fauna, between about 19 and 14.8 million years ago. Based on what is known of the modern ecology of tayassuines and previous paleoecological interpretations for Panama, “C.” occidentale likely occupied a variety of environments, ranging from forested to open country habitat mosaics and fed on the diverse array of available plants.

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Frost, Shawn B., Garrett W. Milliken, Erik J. Plautz, R. Bruce Masterton, and Randolph J. Nudo. "Somatosensory and motor representations in cerebral cortex of a primitive mammal (Monodelphis domestica): A window into the early evolution of sensorimotor cortex." Journal of Comparative Neurology 421, no. 1 (2000): 29–51. http://dx.doi.org/10.1002/(sici)1096-9861(20000522)421:1<29::aid-cne3>3.0.co;2-9.

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Stumpf, Peter, Heinz K�nzle, and Ulrich Welsch. "Cutaneous eccrine glands of the foot pads of the small Madagascan tenrec ( Echinops telfairi, Insectivora, Tenrecidae): skin glands in a primitive mammal." Cell and Tissue Research 315, no. 1 (2004): 59–70. http://dx.doi.org/10.1007/s00441-003-0815-0.

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Prothero, Donald R., Brian L. Beatty, and Richard M. Stucky. "Simojovelhyus is a peccary, not a helohyid (Mammalia, Artiodactyla)." Journal of Paleontology 87, no. 5 (2013): 930–33. http://dx.doi.org/10.1666/12-084.

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Simojovelhyus pocitosense is based on a lower jaw fragment with three molars from the late Oligocene amber mine deposits near the village of Simojovel, Chiapas Province, Mexico. It is the oldest fossil mammal known from Central America. It was described by Ferrusquia-Villafranca in 2006 as a helohyid, a group of primitive artiodactyls known from the Bridgerian and Uintan (older than 49–42 Ma), yet it comes from early Arikareean deposits about 25–27 Ma, suggesting that it was a very late helohyid living more than 10 m.y. after their apparent Uintan extinction. We re-examined the specimen, and compared it to the large collection of recently described peccaries from the Chadronian (Perchoerus minor) and Orellan (Perchoerus nanus) and Bridgerian helohyids (Helohyus sp.). Once the range of variation of characters in helohyids and peccaries is accounted for, Simojovelhyus shows derived similarities to early peccaries, especially in the bunodont molars with inflated cusps and the configuration of cristids and accessory cuspulids, and none of the incipient lophodonty and primitive morphology seen in helohyids. In fact, the only real similarity other than symplesiomorphies between Simojovelhyus and helohyids is its small size, but it is close to the size range of the tiny Chadronian peccary P. minor. Thus, based on both derived tooth characters and its age, it is much more parsimonious to regard Simojovelhyus as a tiny Mexican peccary from the Arikareean, not a very late helohyid. This removes the anomalously late occurrence of helohyids from the mammalian fossil record, and forces a re-examination of our view of mammalian evolution in Central America.

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Temple, Jennifer L., Robert P. Millar, and Emilie F. Rissman. "An Evolutionarily Conserved Form of Gonadotropin-Releasing Hormone Coordinates Energy and Reproductive Behavior." Endocrinology 144, no. 1 (2003): 13–19. http://dx.doi.org/10.1210/en.2002-220883.

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Abstract GnRH is the master neuropeptide that coordinates and regulates reproduction in all vertebrates and in some nonvertebrate species. Sixteen forms of GnRH have been isolated in brain. In the vast majority of species, two or more forms occur in anatomically and developmental distinct neuronal populations. In mammalian brain, two GnRH forms, mammalian (GnRH-I) and chicken-II (GnRH-II), exist. The distribution and functions of GnRH-I have been well characterized and intensively studied. However, the function of GnRH-II, which is the most evolutionarily conserved form of GnRH, has been elusive. Here we demonstrate that in a primitive mammal, the musk shrew (Suncus murinus), GnRH-II activates mating behavior in nutritionally challenged females within a few minutes after administration. In addition GnRH-II immunoreactive cell numbers and fibers increase in food-restricted females. Furthermore, GnRH type II receptor immunoreactivity was detected in musk shrew brain in regions associated with mating behavior. Our results lead us to hypothesize that the role of the evolutionarily conserved GnRH-II peptide is to coordinate reproductive behavior as appropriate to the organism’s energetic condition.

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Wilkinson, Gerald S., Frieder Mayer, Gerald Kerth, and Barbara Petri. "Evolution of Repeated Sequence Arrays in the D-Loop Region of Bat Mitochondrial DNA." Genetics 146, no. 3 (1997): 1035–48. http://dx.doi.org/10.1093/genetics/146.3.1035.

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Analysis of mitochondrial DNA control region sequences from 41 species of bats representing 11 families revealed that repeated sequence arrays near the tRNA-Pro gene are present in all vespertilionine bats. Across 18 species tandem repeats varied in size from 78 to 85 bp and contained two to nine repeats. Heteroplasmy ranged from 15% to 63%. Fewer repeats among heteroplasmic than homoplasmic individuals in a species with up to nine repeats indicates selection may act against long arrays. A lower limit of two repeats and more repeats among heteroplasmic than homoplasmic individuals in two species with few repeats suggests length mutations are biased. Significant regressions of heteroplasmy, θ and π, on repeat number further suggest that repeat duplication rate increases with repeat number. Comparison of vespertilionine bat consensus repeats to mammal control region sequences revealed that tandem repeats of similar size, sequence and number also occur in shrews, cats and bighorn sheep. The presence of two conserved protein-binding sequences in all repeat units indicates that convergent evolution has occurred by duplication of functional units. We speculate that D-loop region tandem repeats may provide signal redundancy and a primitive repair mechanism in the event of somatic mutations to these binding sites.

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Allen, K. M., and R. C. Tinsley. "The diet and gastrodermal ultrastructure of polystomatid monogeneans infecting chelonians." Parasitology 98, no. 2 (1989): 265–73. http://dx.doi.org/10.1017/s0031182000062181.

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SUMMARYAll polyopisthocotylean monogeneans previously studied, including representatives of the Polystomatidae infecting anuran amphibians, feed on host blood. However, the present analysis of species of Polystomoides, Polystomoidella and Neopolystoma, polystomatids which infect chelonian reptiles, has shown that this group has diverged nutritionally from related parasites. Histochemical tests failed to demonstrate haemoglobin in the gut caeca, and X-ray microanalysis confirmed the absence of haematin (or high concentrations of bound iron) in the gastrodermis. The chelonian poly-stomatids (and also the single monogenean which infects a mammal, Oculotrema hippopotami) feed on epithelial cells and mucus, the diet typical of monopisthocotyleans. Transmission electron microscopy revealed the same gastrodermal architecture in representatives of Polystomoides from Africa, N. America and S.E. Asia. The organization of the caecal epithelium conforms with that of blood-feeding polyopisthocotyleans, with two components: lamellated cells responsible for intracellular digestion interspersed with elements of a non-lamellated connecting syncytium. In other polyopistho-cotyleans, the syncytium probably has a skeletal, supportive role, related to the problems of intracellular accumulation of haematin, but in polystomatids infecting chelonians the syncytium is extremely reduced and its presence probably reflects an ancestry amongst blood-feeding relatives. The utilization of the presumably more primitive monogenean diet of epithelial cells and mucus by chelonian polystomatids may be related to the scarcity of superficial blood vessels in their oral and urinary bladder habitats.

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Bastos, Ana Carolina Fortes, and Lílian Paglarelli Bergqvist. "A postura locomotora de Protolipterna ellipsodontoides Cifelli, 1983 (Mammalia: Litopterna: Protolipternidae) da Bacia de São José de Itaboraí, Rio de Janeiro (Paleoceno superior)." Anuário do Instituto de Geociências 30, no. 1 (2007): 58–66. http://dx.doi.org/10.11137/2007_1_58-66.

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The Litopterna is a group of endemic South America ungulates that lived from Late Paleocene (Itaboraiense) to Late Pleistocene (Lujanense). The order is divided in two large groups based on dental features: the Bunolipterna, in which the Protolipternidae is placed, is composed by taxa with primitive bunodont teeth; and the Lopholipterna, grouping taxa with derived lophodont teeth. In both the postcranial morphology is derived and uniform since the early forms. The Itaborai Basin, located at São José district, Itaboraí city, Rio de Janeiro state, is filled with different kinds of limestones, cut vertically by fissure fill deposits, where most of the fossils were collected. Protolipterna ellipsodontoides was described in 1983 based on dental features, but later postcranial bones were associated to this species. The main goal of this article is to infer the foot posture of P. ellipsodontoides. The material studied consists of femora, astragali, calcanea and metatarsals III, comprising 165 bones. All fossils were deposited in the fossil mammal collection of Departamento Nacional da Produção Mineral, in Rio de Janeiro state, Brasil. The methodology employed consisted of 15 linear and curvilinear measurements, which were submitted to a multivariate analysis (Principal Component Analysis -PCA and Discriminant Function Analysis -DFA). The results suggested a digitigrade posture to P. ellipsodontoides. Other morphological features of the skeleton, associated with a digitigrades posture, are suggestive of a cursorial locomotion, but with probable saltatory habits.

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Gingerich, Philip D., and Henri Cappetta. "A new archaeocete and other marine mammals (Cetacea and Sirenia) from lower middle Eocene phosphate deposits of Togo." Journal of Paleontology 88, no. 1 (2014): 109–29. http://dx.doi.org/10.1666/13-040.

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Lutetian lower middle Eocene phosphate deposits of Kpogamé-Hahotoé in Togo yield new information about whales and sea cows in West Africa. Most specimens are individual teeth and bones, collected as isolated elements, but some appear to have been associated. Most are conservatively interpreted to represent a new 300–400 kg protocetid archaeocete, Togocetus traversei. This genus and species is distinctly primitive for a protocetid in retaining a relatively small mandibular canal in the dentary and retaining a salient metaconid on the lower first molar (M1), but it is derived relative to earlier archaeocetes in having large, dense, osteosclerotic tympanic bullae. Mandibular canal size and large dense bullae are not as tightly linked in terms of function in hearing as previously thought. Postcranially Togocetus traversei had many characteristics found in other semiaquatic protocetids: a relatively long neck, mobile shoulder, digitigrade manus, large pelvis, well-developed hind limbs, and feet specialized for swimming. Loss of a fovea on the head of the femur indicates loss of the teres ligament stabilizing the hip, which is a derived specialization consistent with life in water. Protocetid specimens distinctly smaller and larger than those of Togocetus traversei indicate the presence of at least three protocetids at Kpogamé. Sirenian vertebral and rib pieces indicate the presence of a protosirenid and a dugongid. Finally, a vertebral centrum and piece of humerus appear to represent a large land mammal. A diverse fauna of archaic whales and early sirenians inhabited the western margin of Africa and the eastern Atlantic Ocean as early as 46–44 million years before present, showing that both cetaceans and sirenians were widely distributed geographically by this time.

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40

Silcox, Mary T., Gregg F. Gunnell, and Jonathan I. Bloch. "Cranial anatomy of Microsyops annectens (Microsyopidae, Euarchonta, Mammalia) from the middle Eocene of Northwestern Wyoming." Journal of Paleontology 94, no. 5 (2020): 979–1006. http://dx.doi.org/10.1017/jpa.2020.24.

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AbstractThe Microsyopidae are extinct mammals from the late Paleocene–late Eocene of North America and the late Paleocene of Europe. While results from phylogenetic analyses support euarchontan affinities, specific relationships of microsyopids to other plesiadapiforms (plausible stem primates), Euprimates (crown primates), Scandentia (treeshrews), and Dermoptera (colugos) are unresolved. An exceptionally well-preserved cranium of Microsyops annectens includes a basicranium that is generally primitive relative to that of other extinct and extant euarchontans in having: (1) a transpromontorial groove for an unreduced internal carotid artery (ICA) entering the middle ear posteromedially; (2) grooves (not tubes) on the promontorium, marking the course for both stapedial and promontorial branches of the ICA; (3) a foramen faciale that opens into the middle ear cavity, with the facial nerve exiting through a stylomastoid foramen primitivum; and (4) unexpanded caudal and rostral tympanic processes of the petrosal. The absence of any preserved bullar elements in the middle ear contrasts with that of other plesiadapiforms for which the region has been recovered, all of which have evidence of an ossified bulla. Microsyops lacks many of the specialized cranial characteristics of crown scandentians and dermopterans. The basicranial anatomy of microsyopids does not provide evidence in support of a clear link to any of the extant euarchontans, and suggests that the primitive morphology of this region in Euarchonta was little differentiated from that observed in the primitive placental mammals.

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Kingsley, Paul D., Jeffrey Malik, Katherine A. Fantauzzo, and James Palis. "Yolk sac–derived primitive erythroblasts enucleate during mammalian embryogenesis." Blood 104, no. 1 (2004): 19–25. http://dx.doi.org/10.1182/blood-2003-12-4162.

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Abstract The enucleated definitive erythrocytes of mammals are unique in the animal kingdom. The observation that yolk sac–derived primitive erythroid cells in mammals circulate as nucleated cells has led to the conjecture that they are related to the red cells of fish, amphibians, and birds that remain nucleated throughout their life span. In mice, primitive red cells express both embryonic and adult hemoglobins, whereas definitive erythroblasts accumulate only adult hemoglobins. We investigated the terminal differentiation of murine primitive red cells with use of antibodies raised to embryonic βH1-globin. Primitive erythroblasts progressively enucleate between embryonic days 12.5 and 16.5, generating mature primitive erythrocytes that are similar in size to their nucleated counterparts. These enucleated primitive erythrocytes circulate as late as 5 days after birth. The enucleation of primitive red cells in the mouse embryo has not previously been well recognized because it coincides with the emergence of exponentially expanding numbers of definitive erythrocytes from the fetal liver. Our studies establish a new paradigm in the understanding of primitive erythropoiesis and support the concept that primitive erythropoiesis in mice shares many similarities with definitive erythropoiesis of mammals.

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Frost, Shawn B., and R. Bruce Masterton. "Hearing in primitive mammals: Monodelphis domestica and Marmosa elegans." Hearing Research 76, no. 1-2 (1994): 67–72. http://dx.doi.org/10.1016/0378-5955(94)90088-4.

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Baron, Margaret H., Joan Isern, and Stuart T. Fraser. "The embryonic origins of erythropoiesis in mammals." Blood 119, no. 21 (2012): 4828–37. http://dx.doi.org/10.1182/blood-2012-01-153486.

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Abstract Erythroid (red blood) cells are the first cell type to be specified in the postimplantation mammalian embryo and serve highly specialized, essential functions throughout gestation and postnatal life. The existence of 2 developmentally and morphologically distinct erythroid lineages, primitive (embryonic) and definitive (adult), was described for the mammalian embryo more than a century ago. Cells of the primitive erythroid lineage support the transition from rapidly growing embryo to fetus, whereas definitive erythrocytes function during the transition from fetal life to birth and continue to be crucial for a variety of normal physiologic processes. Over the past few years, it has become apparent that the ontogeny and maturation of these lineages are more complex than previously appreciated. In this review, we highlight some common and distinguishing features of the red blood cell lineages and summarize advances in our understanding of how these cells develop and differentiate throughout mammalian ontogeny.

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Gaudin, Timothy J., and William D. Turnbull. "The stapedial morphology of the Xenarthra and its implications for higher-level mammalian relationships." Paleontological Society Special Publications 6 (1992): 107. http://dx.doi.org/10.1017/s2475262200006675.

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The mammalian order Xenarthra (including the living Neotropical armadillos, anteaters, and tree sloths) has figured importantly in recent hypotheses of interordinal relationships among eutherian mammals. It has been suggested that the group shares a common ancestry both with the extant Old World order Pholidota (i.e. the pangolins or scaly-anteaters) and the extinct North American group Palaeanodonta. Furthermore, these three groups have been linked together into a monophyletic Cohort Edentata, which has been hypothesized to represent the sister-group to all other eutherians. This placement of edentates relative to the remainder of Eutheria has been supported in part by a purported difference in the morphology of the stapes in the two groups- edentates possessing a primitive, imperforate/columelliform morphology, other placentals a derived, perforate/stirrup-shaped morphology.A recent study of stapedial morphology among mammals by Novacek and Wyss (1986) suggests that within the Xenarthra itself a perforate stapes is found among armadillos, but that the pilosa in particular (the clade including anteaters and sloths) and the order as a whole are characterized primitively by an imperforate stapes. Our studies of the xenarthran ear region (Patterson et al., in press) have uncovered new ontogenetic and paleontological evidence which contradict the findings of Novacek and Wyss. Among adults of the two extant tree sloth genera, the stapes lacks a stapedial foramen. However, in both genera, this adult imperforate morphology is derived from a perforated juvenile stapes. Novacek and Wyss ignored fossil species in their consideration of the xenarthran stapes. It has long been known that extinct ground sloths of the family Mylodontidae possessed a large stapedial foramen. Unfortunately, until now no stapes were known from the remaining ground sloth families, the Megatheriidae and the Megalonychidae. We have uncovered a complete left stapes of an early Miocene megatheriid ground sloth Eucholoeops ingens. This stapes possesses a well-developed stapedial foramen. We believe that this new paleontological evidence, combined with our information on the ontogeny of the stapes in the living genera, clearly indicates that a perforate stapes is primitive for sloths. Moreover, when we plot distributions of stapedial morphologies of both living and fossil edentates onto a phylogeny of the Edentata, we can demonstrate that the a large stapedial foramen is primitive for the Xenarthra as a whole, and probably for the entire Cohort Edentata. Such a distribution makes it unlikely that stapedial morphology can be used to separate edentates from other eutherian mammals.

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Jovells-Vaqué, Sílvia, Montserrrat Ginestí, and Isaac Casanovas-Vilar. "Cricetidae (Rodentia, Mammalia) from the early Miocene site of els Casots (Vallès-Penedès Basin, Catalonia)." Fossil Imprint 73, no. 1-2 (2017): 141–54. http://dx.doi.org/10.2478/if-2017-0007.

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Abstract Els Casots is an extremely rich early Miocene site located in the Vallès-Penedès Basin (Catalonia, Spain) that has provided both micro- and macrovertebrates. However, the small mammals have been poorly studied. In this work we describe the cricetid fauna from els Casots and provide further insights into the chronology of the site. The cricetids are very common and include the species Megacricetodon primitivus and Democricetodon hispanicus. A second, larger-sized Democricetodon species is also represented by just one molar. The presence of M. primitivus together with the eomyid Ligerimys ellipticus indicates a correlation to zone MN 4 and to the local zone C of the Calatayud-Montalbán Basin (Aragón, east-central Spain), the type area of the Aragonian mammal age. This is further supported by the presence of two different Democricetodon species. A correlation to the local subzones of that area is attempted, but unfortunately the cricetid succession is not the same in both basins. However, the fact that L. ellipticus is the only eomyid species present at els Casots would indicate that this site is somewhat younger than other MN 4 localities from the Vallès-Penedès, where this species coexists with its ancestor Ligerimys florancei.

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Williams, Terrie M. "The evolution of cost efficient swimming in marine mammals: limits to energetic optimization." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 354, no. 1380 (1999): 193–201. http://dx.doi.org/10.1098/rstb.1999.0371.

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Mammals re–entered the oceans less than 60 million years ago. The transition from a terrestrial to an aquatic lifestyle required extreme morphological and behavioural modifications concomitant with fundamentally different locomotor mechanisms for moving on land and through water. Energetic transport costs typically reflect such different locomotor modes, but can not be discerned from the fossil record. In this study the energetic challenges associated with changing from terrestrial to aquatic locomotion in primitive marine mammals are examined by comparing the transport, maintenance and locomotor costs of extant mammals varying in degree of aquatic specialization. The results indicate that running and swimming specialists have converged on an energetic optimum for locomotion. An allometric expression, COT TOT = 7.79 mass −0.29 ( r 2 = 0.83, n = 6 species), describes the total cost of transport in J kg −1 m −1 for swimming marine mammals ranging in size from 21 kg to 15,000 kg. This relation is indistinguishable from that describing total transport costs in running mammals. In contrast, the transitional lifestyle of semi–aquatic mammals, similar to that of ancestral marine mammals, incurs costs that are 2.4–5.1 times higher than locomotor specialists. These patterns suggest that primitive marine mammals confronted an energetic hurdle before returning to costs reminiscent of their terrestrial ancestry, and may have reached an evolutionary limit for energetic optimization during swimming.

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Amador, Lucila I., Nancy B. Simmons, and Norberto P. Giannini. "Aerodynamic reconstruction of the primitive fossil bat Onychonycteris finneyi (Mammalia: Chiroptera)." Biology Letters 15, no. 3 (2019): 20180857. http://dx.doi.org/10.1098/rsbl.2018.0857.

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Bats are the only mammals capable of powered flight. One of the oldest bats known from a complete skeleton is Onychonycteris finneyi from the Early Eocene (Green River Formation, Wyoming, 52.5 Ma). Estimated to weigh approximately 40 g, Onychonycteris exhibits the most primitive combination of characters thus far known for bats. Here, we reconstructed the aerofoil of the two known specimens, calculated basic aerodynamic variables and compared them with those of extant bats and gliding mammals. Onychonycteris appears in the edges of the morphospace for bats, underscoring the primitive conformation of its flight apparatus. Low aerodynamic efficiency is inferred for this extinct species as compared to any extant bat. When we estimated aerofoil variables in a model of Onychonycteris excluding the handwing, it closely approached the morphospace of extant gliding mammals. Addition of a handwing to the model lacking this structure results in a 2.3-fold increase in aspect ratio and a 28% decrease in wing loading, thus greatly enhancing aerodynamics. In the context of these models, the rapid evolution of the chiropteran handwing via genetically mediated developmental changes appears to have been a key transformation in the hypothesized transition from gliding to flapping in early bats.

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McGrath, Kathleen E., Paul D. Kingsley, Anne D. Koniski, Rebecca L. Porter, Timothy P. Bushnell, and James Palis. "Enucleation of primitive erythroid cells generates a transient population of “pyrenocytes” in the mammalian fetus." Blood 111, no. 4 (2008): 2409–17. http://dx.doi.org/10.1182/blood-2007-08-107581.

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Enucleation is the hallmark of erythropoiesis in mammals. Previously, we determined that yolk sac–derived primitive erythroblasts mature in the bloodstream and enucleate between embryonic day (E)14.5 and E16.5 of mouse gestation. While definitive erythroblasts enucleate by nuclear extrusion, generating reticulocytes and small, nucleated cells with a thin rim of cytoplasm (“pyrenocytes”), it is unclear by what mechanism primitive erythroblasts enucleate. Immunohistochemical examination of fetal blood revealed primitive pyrenocytes that were confirmed by multispectral imaging flow cytometry to constitute a distinct, transient cell population. The frequency of primitive erythroblasts was higher in the liver than the bloodstream, suggesting that they enucleate in the liver, a possibility supported by their proximity to liver macrophages and the isolation of erythroblast islands containing primitive erythroblasts. Furthermore, primitive erythroblasts can reconstitute erythroblast islands in vitro by attaching to fetal liver–derived macrophages, an association mediated in part by α4 integrin. Late-stage primitive erythroblasts fail to enucleate in vitro unless cocultured with macrophage cells. Our studies indicate that primitive erythroblasts enucleate by nuclear extrusion to generate erythrocytes and pyrenocytes and suggest this occurs in the fetal liver in association with macrophages. Continued studies comparing primitive and definitive erythropoiesis will lead to an improved understanding of terminal erythroid maturation.

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Ameghino, Florentio. "1. On the Primitive Type of the Plexodont Molars of Mammals." Proceedings of the Zoological Society of London 67, no. 3 (2009): 555–71. http://dx.doi.org/10.1111/j.1469-7998.1899.tb06874.x.

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Robinson, Stephen R. "Relationships between Müller cells and neurons in a primitive tetrapod, the Australian lungfish." Visual Neuroscience 14, no. 4 (1997): 795–800. http://dx.doi.org/10.1017/s0952523800012748.

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AbstractWe recently proposed a model of cytogenesis which assumes that primitive ancestral mammals and premammalian vertebrates had a retinal composition that consisted of about seven neurons per Müller cell, comprising 1–2 cone photoreceptors, 1–2 rod photoreceptors, 2–3 bipolar cells, 1–2 amacrine cells, less than 1 ganglion cell, and less than 1 horizontal cell (Reichenbach & Robinson, 1995). The Australian lungfish (Neoceratodus forsten) closely resembles the lobe-finned ancestors of land vertebrates, and has an extremely plesiomorphic nervous system. The present study, therefore, has examined the relative frequencies of retinal neurons and Müller cells (identified by immunolabelling for glutamine synthetase) in the lungfish retina. It was found that for each Müller cell there is an average of 1.9 cone photoreceptors, 1.7 rod photoreceptors, 3.1 amacrine/bipolar/horizontal cells, and 0.6 ganglion cells; amounting to a ratio of 7.3 neurons per Müller cell. These results support our conjecture that the sequence of cytogenesis in mammals is constrained by a developmental program that predates the evolution of mammals. The study also provides the first detailed morphological descriptions of lungfish Müller cells and their relationship with adjacent neurons. It was found that individual Müller cells in lungfish have a volume (more than 12,000 μm3) that is an order of magnitude higher than in mammals, yet the proportion of total retinal volume occupied by these cells (20%) is very similar.

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Journal articles on the topic 'Primitive mammal'

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