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The distinctive, branched thrombolite, Favosamaceria cooperi new group and form, is found widely in the Great Basin, USA, where it is restricted to the Late Cambrian Saukia trilobite Zone. This thrombolite is distinguished by a hedgerow, mazelike organization of ridges similar to garden walls (maceriae) in plan view, branching of ridges into daughter ridges and columns, the polymorphic nature of dark, 1–4 mm mesoclots, and the relative consistency of maceria width (approximately 1 cm). As a group, Favosamaceria is found elsewhere in Upper Cambrian strata of the Argentine Precordillera, Appalachians, and Upper Mississippi Valley, as well as in Lower Ordovician deposits of the Canadian Arctic and Newfoundland. The distribution of the group around Laurentia illustrates the use of microbialites in biogeographic studies.
The biostratigraphically important genus Hunnegraptus is recognized for the first time in the Marathon region, West Texas, based on restudy of the type material of Didymograptus novusBerry, 1960. The late Tremadoc Hunnegraptus Zone is the oldest unequivocally recognized graptolite zone in the Marathon region, underlain by faunas with nondiagnostic adelograptids. Hunnegraptus novus (Berry) shows a sicular bitheca, dichograptid stipes, and delayed first distal dichotomies as the most important rhabdosome characteristics. Hunnegraptus Zone faunas are more widely distributed in North America than previously realized and an immensely useful discovery for biostratigraphic correlation of this late Tremadoc time interval.
The growth of the food-gathering systems of Ordovician crinoids illustrates the solutions evolved to avoid or minimize problems of suspension feeding and maintenance. The column has low metabolic requirements and may even be self-sufficient; little or no food need be diverted from the crown to the column. The tissue that the food-gathering system supplies with food is all or mostly in the crown. The volume of tissue in the crown is isometric with its volume. Distal arm branches, ramules, or pinnules form throughout growth of most taxa. The number of arm branches is constant in hybocrinids and porocrinids. The length and number of plates in the food-gathering system show marked positive allometry relative to crown volume. Food grooves become wider in larger crinoids but growth rates vary greatly. Branch density declines in all species studied. The tubefoot spacing can be constant, increase, or decrease in larger crinoids. Food-gathering capacity is the number of food-catching tubefeet multiplied by the average food-groove width, and it is positively allometric in terms of crown volume. The food-gathering ratio (food-gathering capacity: crown volume) declines somewhat, remains the same, or increases slightly during growth. The food-gathering parameters are correlated with arm structure. Crinoids with pinnulate arms exhibit the highest food-gathering ratios, high values of tubefoot spacing and branch density, and narrow food grooves, and they catch small food particles with small and closely spaced tubefeet. The lowest food-gathering ratios are seen in crinoids with unbranched and nonpinnulate arms which possess low tubefoot spacings and branch densities and wide food grooves. On average these organisms ate larger food items collected by larger and more widely spaced tubefeet. Larger food-gathering ratios are associated with greater resistance to fluid flow through the arms and tubefeet. The allometry of the food-gathering systems of Ordovician crinoids suggests that their metabolic rates could be proportional to body mass0.75 as in many living animals and plants.
Two new species of conchostracans, Cyclestherioides wyomingensis and Prolynceus laneyensis, belonging to the Cyclestheriidae and Lynceidae, respectively, are described from the Eocene Laney Member of the Green River Formation of Wyoming, USA. These are the first Cenozoic fossil conchostracans to be formally reported from North America. Cyclestherioides wyomingensis has a close affinity to the extant Cyclestheria hislopi. The latter is a pan-tropical species, found between approximately 30°N and 35°S. Thus, Cyclestherioides may indicate that the Laney Member was deposited in a subtropical setting. The conchostracans and associated fauna of the Laney Member suggest that this member was deposited nearshore in a shallow lake. The concept of Cyclestherioides is emended and some fossil species referred to this genus are revised.
Thirty-one gastropod species and one type of isolated larval shell are described from a quarry near Ambatolafia in the Mahajanga Basin, northwestern Madagascar. The ammonite fauna indicates a lower Albian age of the fauna (Cleoniceras besairiei Zone). The taxonomic position of the species described earlier is reviewed, incorporating new data on shell structure and protoconch morphology. Twelve species and one genus are new, with four species described in open nomenclature. The oldest hitherto known representatives of Cocculina sensu lato, Iphitus, Conjectura, Entomope, Tomura, and possibly Vatopsis and Paladmete, are described. Nacre is documented in a species of Semisolarium, providing further evidence for the position of this genus within the Vetigastropoda. Eight of the species occur also in the Cretaceous of Europe or are tentatively assigned to European species. Three species have close relatives in the Aptian/Albian of Japan, one species may have relations to the Albian of Texas. The new genus is Mahajangina (family uncertain) for a species having a small, trochispiral teleoconch with spines on the periphery, and a conical, bicarinate larval shell. The new species are: Cirsocerithium collignoni, Zardinistylus betsibokaensis, Pommerozygia mahajangensis, Conjectura minuta, Buvignieria berwaldi, Mahajangina weitschati, Entomope crassilabrum, Paladmete? rasoarinoroae, Tomura ambatolafiensis, Carinathilda parviruga, Carinathilda bandeli, and Gymnothilda pagodoidea.
New collections rich in agnostoid trilobites were recovered from Lower Ordovician strata of the southern Montagne Noire, France. The faunas occur in the La Gardie/Val d'Homs, Saint–Chinian, La Maurerie, and Landeyran formations, coinciding with deposition in muddy outer-platform settings. Many previously described species are revised and their stratigraphic ranges emended. The studied agnostoids include Geragnostus cf. sidenbladhi (Linnarsson), G. aff. sidenbladhi, G. crassus Tjernvik, G. splendens (Holub), G. cf. explanatus Tjernvik, G. boutouryensis Howell, G. occitanus Howell, Geragnostus sp., Trinodus corpulentus Howell, Homagnostoides ferralsensis (Munier-Chalmas and Bergeron), Corrugatagnostus coulobresensis n. sp., Corrugatagnostus sp., Leiagnostus miqueli Sdzuy, and Leiagnostus sp. The record from the upper part of the Saint–Chinian Formation suggests a late Tremadocian age, whereas an early Arenigian age is indicated for the upper part of the La Maurerie Formation. Although the agnostoid record generally reinforces the peri-Gondwanan character of the Lower Ordovician shelly faunas from the Montagne Noire, some agnostoid species are independent of specific paleogeographic boundaries.
The family Emuellidae Pocock, 1970 was established for EmuellaPocock, 1970 and BalcoracaniaPocock, 1970 from the Lower Cambrian of South Australia. Based on their peculiar trunk tagmosis, emuellids have been interpreted as the sister group of all other trilobites with dorsal facial sutures, and classified as high as the ordinal level. Cladistic analysis with a range of exemplar taxa of the Olenellina and Redlichiina instead resolves the emuellids within the Redlichiina, with tagmosis into a prothorax and opisthothorax (“telosoma”) nonhomologous in olenellines and emuellids. A taxonomic revision of Australian species identifies Balcoracania flindersi as a junior subjective synonym of B. dailyi, whereas the two named species of Emuella are considered to be distinct. Balcoracania dailyi possesses up to 103 thoracic segments, the maximum number recorded in any trilobite.
Eight new species of lichid trilobites representing five genera in three subfamilies, from the Avalanche Lake area of the southern Mackenzie Mountains, Northwest Territories, Canada, are described. The subfamily Lichinae is represented by Dicranopeltis n. sp. and the subfamily Platylichinae by the early Llandovery Platylichas infimus n. sp. The subfamily Trochurinae is represented by six species belonging to four genera. These are Acanthopyge (Lobopyge) sp. (Wenlock), the earliest known species of the genus Acanthopyge and subgenus Acanthopyge (Lobopyge), A. (L.) pristina n. sp. from the Glyptograptus persculptus Zone in the latest Ordovician, Dicranogmus lepidus n. sp., D. wilsoni n. sp. (both Wenlock), Dicranogmus n. sp. (Llandovery), and Radiolichas guttatus n. sp. (Wenlock).
Exuviae comprising immature growth stages allow the tracing of morphological and morphogenetical features of the reduced-eyed phacopid species Plagiolaria poothaiiKobayashi and Hamada, 1968, from the Early Devonian of Satun Province, southern Thailand. Biometric and morphometric approaches have been used to characterize the shape changes. This is the fourth phacopid genus for which ontogenetic information is known. Ontogenetic features of this species are generally similar to those of Phacops and Weyerites. However, the ankylosis of the facial sutures occurs at the end of the meraspid period, later than in Phacops, and this is probably a derived character.
Calcareous horizons in the Qasr and Hammamiyat members (Lower Devonian, ?Pragian and lower Emsian) of the Jawf Formation, northwestern Saudi Arabia, yielded a rich assemblage of microremains from acanthodian, placoderm, chondrichthyan, and sarcopterygian vertebrates. The most abundant elements are scales from acanthodians Nostolepis spp., Milesacanthus ancestralis n. sp., Canadalepis? sp., and Gomphonchus? fromensis, scales and dermal bone fragments from acanthothoracid and ?rhenanid placoderms, and teeth from onychodontids. Rarer occurrences include ?chondrichthyan scales of several different morphotypes, and petalichthid and ?ptyctodontid placoderm elements. The Qasr Member assemblage shows a close resemblance to slightly older faunas from the Lochkovian of Brittany and Spain. The Hammamiyat Member microvertebrate fauna shows closest affinity with that of the stratigraphically lower Qasr Member, with similarities also to coeval faunas from southeastern Australia, late Emsian/Eifelian faunas from west-central Europe, and the Givetian Aztec Siltstone fauna from Antarctica.
The appendicular skeleton of the Lower Permian temnospondyl Eryops megacephalusCope, 1877, described and figured in detail, is similar to that of most temnospondyls, except that it is highly ossified. It displays terrestrial adaptations, including a reduced dermal pectoral girdle and comparatively large limbs, characterized by well-developed processes for muscle attachment. While many features that were previously unknown or uncommon among temnospondyls were identified, no apomorphies of the appendicular skeleton particular to Eryops were found. Some characteristics of the endochondral postcranial skeleton found in well-ossified temnospondyls, such as Eryops, are absent in less well ossified temnospondyls due to immaturity or paedomorphism. The effects of heterochronic processes on the morphology of the postcranial skeleton of temnospondyls and the implications for cladistics are discussed; the appendicular skeleton of Eryops is considered hypermorphic. Within the Temnospondyli, the Eryops appendicular skeleton is most similar to that of the Dissorophoidea, and most dissimilar to both the most plesiomorphic temnospondyls and the secondarily aquatic Mesozoic stereospondyls. The appendicular skeletons of well-ossified Late Permian and Mesozoic temnospondyls are not as robust as that of Eryops.
Surprisingly, Eryops, in common with other well-ossified temnospondyls, shares many derived features of the appendicular skeleton with seymouriamorphs and diadectomorphs. The presence of these previously unrecognized synapomorphies (relative to stem tetrapods and embolomeres) provides evidence for an alternative hypothesis of relationships of early tetrapods, suggesting that the Temnospondyli and seymouriamorphs plus diadectomorphs are sister taxa.