Ontogeny of the Ammonoid Genus Dactylioceras from Northeastern Russia 2000 (original) (raw)
Phylogenetic relationships of the Dactyloa clade, based on molecular and morphological data
2010
The understanding of phylogenetic relationships within Anolis has seen great advances in the past ten years due to a significant number of phylogenetic studies based primarily on molecular data. Despite this large effort, there is still a large void of information regarding mainland species. According to recent phylogenies (Poe, 2004; Nicholson et al., 2005) mainland species belong to two non-nested clades: an unnamed clade (designated the M2 clade by Pinto et al. [2008]), which includes the deeply nested Central and South American species derived from Greater Antillean ancestors and Dactyloa (same as the latifrons series of Etheridge [1959] and the M1 clade of Pinto et al. [2008]), which represents one of the early branches in Anolis and includes species from Central and South America and the Lesser Antilles.
Polar Biology, 2013
In this paper, new data on larval and postlarval stages after newly collected and museum-deposited material of six Ammothea species is provided and compared with previously known information. Different developmental stages attached to the ovigerous legs of adult males for each species were found: four stages [protonymphon (Ptn), postlarval instar 1 (PL-1), postlarval instar 2 (PL-2), and postlarval instar 3 (PL-3)] for A. carolinensis; just one (Ptn) for A. clausi and A. minor; three stages (Ptn, PL-1, PL-2) for A. bicorniculata and A. spinosa; and other three (Ptn, PL-2, PL-3) for A. longispina. In the present contribution, the external morphology of each larval and postlarval instar is described, illustrated, and discussed. The larval and postlarval development of Ammothea bicorniculata, A. carolinensis, A. longispina, and A. spinosa is characterized by (1) the eggs hatch as a protonymphon larva; (2) the larvae and subsequent postlarval stages have yolk reserves and a relatively large size (0.5-0.85 mm in length for the protonymphon); (3) the postlarvae remain on the ovigerous legs of males during several moults; (4) the spinning spine is absent; and (5) the development of walking legs is sequential. The protonymphon larva of A. clausi and A. minor is the only stage on the ovigerous legs of males, and this stage is characterized by: (1) there is no yolk reserve and it has a relatively small size (0.22-0.3 mm in length); (2) the spinning spine is present; and (3) all larval appendages have a relatively large size.
The Genus Dalmasiceras (Ammonoidea) from the Berriasian of the Mountainous Crimea
A b stra c t— The genus Dalmasiceras from the Berriasian of the Mountainous Crimea is revised. Three new spe cies of this genus, D. tauricum, D. belbekense, and D. subtoucasi are described. The distribution of ammonites in the Kabanii Log Section (basin of the Belbek River) supports a correlation of the beds yielding Dalmasiceras in the M ountainous Crim ea to the D. dalmasi Subzone of the Berriasian stratotype.
On Frasnian ammonoids of the New Siberian Islands
Paleontological Journal, 2009
Ammonoids from the basal beds of the Nerpalakh Formation (Lower Frasnian) of Belkovsky Island (New Siberian Archipelago) are systematically studied. Taxonomically, the assemblage studied ( Manticoceras insulare sp. nov., Tornoceras typum (Sandberger, 1851), and T. contractum Glenister, 1958) is similar to the Early Frasnian ammonoid assemblage of South Timan, from which its is distinguished by the absence of the genera Timanites and Komioceras . The same beds contain conodonts of the Palmatolepis transitans Zone (= MN 4 Zone of the Montagne Noire standard succession), which allow the correlation of the beds studied with the Timanites keyserlingi and Komioceras stuckenbergi ammonoid zones of South Timan. The Early Frasnian ammonoids could supposedly have entered the region of the New Siberian Archipelago from the southwest at the time of a major transgression, which facilitated the distribution of the genera Manticoceras and Tornoceras . A new species of the genus Manticoceras is described.
Intraspecific variability through ontogeny in early ammonoids
Paleobiology, 2013
Mollusks in general and ammonoids in particular are known to display a sometimes profound morphological intraspecific variability of their shell. Although this phenomenon is of greatest importance, it has rarely been investigated and quantified. It is especially crucial for taxonomy and incidentally for biodiversity analyses to account for it, because otherwise, the number of described species might exceed that of actual species within any group. Early ammonoids (Early Devonian, Paleozoic) typically suffer from this bias. For instance, most specimens from the same layer and the same region (e.g., theErbenocerasbeds of the Moroccan eastern Anti-Atlas studied here) differ morphologically from each other. Depending on the importance given to certain morphological characters, therefore, one could create a new species for almost every specimen. In this study, we measured nearly 100 such specimens from a restricted stratigraphic interval and quantified their intraspecific variability. The...
Paleontological Research, 2010
Based on materials from the Krasnoyarka Formation in the Naiba area in south Sakhalin, Russia, taphonomic histories of a large Campanian ammonoid, Canadoceras kossmati Matsumoto, 1954, were closely investigated. Large Canadoceras shells exceeding 30 cm in diameter are usually embedded horizontally and solitarily in muddy sandstone. A thin, lenticular calcareous concretion envelopes the shell (= envelope concretion). Their body chambers are mostly lost. The inner whorls comprising the center of the umbilicus completely disappear without exception, and only two or three outer whorls are preserved. The body and air chambers are somewhat compressed by compaction and are filled with sediments. Phycosiphon burrows are common not only in open body chambers but also in inner air chambers, which were originally closed. These observations suggest that the thin-shelled inner whorls and organic-rich siphuncular tubes degraded before final burial of the shell, and sediment infilling to the inside of the chambers followed. The early loss of inner whorls and siphuncular tubes gave rise to "draft-through currents." The continuous supply of oxygen and nutrients by the draft-through currents supported the Phycosiphon producers in the inner air chambers. Compared with other calcareous concretions containing intact fossils, values of minus-cement porosity (MCP) remain relatively low (63-74%) and vary by areas even in the same envelope concretion. This indicates that the envelope concretions were cemented under a progressive increase of compaction during the later diagenetic stage. The formation of the envelope concretion appears to be a long-term phenomenon. Various events at different stages have been overprinted in a single large ammonoid fossil.
Stratigraphy and Geological Correlation, 2017
⎯The species Cadochamoussetia aff. subpatruus (Nik.), Cadochamoussetia surensis (Nik.), and Cadoceras cf. simulans Spath are found for the first time in the lower reaches of the Anabar River. The first two species are characteristic of the Lower Callovian Cadochamoussetia subpatruus Subzone of Central Russia, which is equivalent to the Siberian Cadochamoussetia tschernyschewi Zone. Species of the genus Cadochamoussetia, found for the first time in the Arctic, are described. Shells of Siberian representatives of Cadochamoussetia are distinguished from the typical East European species by their larger umbilicus, which is similar to that of the ancestral genus Cadoceras. It is suggested that the Siberian taxa belong to the oldest representatives of this genus, which appeared in the early Callovian Arctic seas and later migrated to seas of Central Europe and England.
Paleontological Research, 2006
Ontogenetic shell development of the Turonian desmoceratine ammonoid Tragodesmoceroides subcostatus is examined based on more than 200 specimens collected by detailed biostratigraphic survey in the Tappu and Saku areas, Hokkaido, Japan. After the ammonitella stage, the mode of ribbing on the shell surface becomes coarser with growth. The shell surface ornament changes from stage 1 (almost smooth) to stage 3 (coarse ribbing) via stage 2 (weak ribbing). Stage 1 is subdivided into an earlier substage 1a with desmoceratid-type constrictions and a subsequent substage 1b without constrictions. Appearance order of these four ornament stages and substages seems to be ontogenetically fixed in the present species. Other characters, such as ammonitella and early shell shape and whorl geometry are also stable. On the other hand, the shifting-timing from stages 1 to 2 and from stages 2 to 3 changes chronologically, i.e., it becomes ontogenetically earlier in upward sequence. In the Lower and Middle Turonian, the adult or subadult shells still remain stage 1 or 2. In contrast the strongly ribbed holotype and paratypes showing stage 3 are regarded as the Upper Turonian peramorphic endmembers of the single biospecies T. subcostatus. Taking these features into consideration, T. subcostatus should be taxonomically revised.