Larisa A. Doguzhaeva

Characterization of Organics Consistent with β-Chitin Preserved in the Late Eocene Cuttlefish Mississaepia mississippiensis

Background Preservation of original organic components in fossils across geological time is controversial, but the potential such molecules have for elucidating evolutionary processes and phylogenetic relationships is invaluable. Chitin is one such molecule. Ancient chitin has been recovered from both terrestrial and marine arthropods, but prior to this study had not been recovered from fossil marine mollusks. Methodology/Principal Findings Organics consistent with β-chitin are recovered in cuttlebones of Mississaepia mississippiensis from the Late Eocene (34.36 million years ago) marine clays of Hinds County, Mississippi, USA. These organics were determined and characterized through comparisons with extant taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS), Field Emission Scanning Electron Microscopy (Hyperprobe), Fourier Transmission Infrared Spectroscopy (FTIR) and Immunohistochemistry (IHC). Conclusions/Significance Our study presents the first evidence for organics consistent with chitin from an ancient marine mollusk and discusses how these organics have been degraded over time. As mechanisms for their preservation, we propose that the inorganic/organic lamination of the cuttlebone, combined with a suboxic depositional environment with available free Fe2+ ions, inhibited microbial or enzymatic degradation.

Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna.

A new marine fossil assemblage from the Early Triassic shows unexpected phyletic diversity and functional complexity. In the wake of the end-Permian mass extinction, the Early Triassic (~251.9 to 247 million years ago) is portrayed as an environmentally unstable interval characterized by several biotic crises and heavily depauperate marine benthic ecosystems. We describe a new fossil assemblage—the Paris Biota—from the earliest Spathian (middle Olenekian, ~250.6 million years ago) of the Bear Lake area, southeastern Idaho, USA. This highly diversified assemblage documents a remarkably complex marine ecosystem including at least seven phyla and 20 distinct metazoan orders, along with algae. Most unexpectedly, it combines early Paleozoic and middle Mesozoic taxa previously unknown from the Triassic strata, among which are primitive Cambrian-Ordovician leptomitid sponges (a 200–million year Lazarus taxon) and gladius-bearing coleoid cephalopods, a poorly documented group before the Jurassic (~50 million years after the Early Triassic). Additionally, the crinoid and ophiuroid specimens show derived anatomical characters that were thought to have evolved much later. Unlike previous works that suggested a sluggish postcrisis recovery and a low diversity for the Early Triassic benthic organisms, the unexpected composition of this exceptional assemblage points toward an early and rapid post-Permian diversification for these clades. Overall, it illustrates a phylogenetically diverse, functionally complex, and trophically multileveled marine ecosystem, from primary producers up to top predators and potential scavengers. Hence, the Paris Biota highlights the key evolutionary position of Early Triassic fossil ecosystems in the transition from the Paleozoic to the Modern marine evolutionary fauna at the dawn of the Mesozoic era.

A Late Carboniferous Spirulid Coleoid from ahe Southern Mid-Continent (USA)

Ultrastructural study of a longiconic cephalopod, formerly described as Bactrites postremus (Miller, 1930; Mapes, 1979), reveals that the shell wall, consisting of two prismatic layers and lacking a nacreous layer, differs strongly from that of bactritoids. In the bactritoids, the shell wall after hatching is composed of the principal nacreous and thin outer prismatic layers, and only the embryonic shell, or bactritella, has a prismatic ultrastructure (Doguzhaeva, 1996a-c). Phragmocones possessing a marginal siphuncle and a prismatic shell wall are known in Recent Spirula and Cretaceous members of Spirulida: Groenlandibelus, Naefia and Adygeya (Doguzhaeva, 1996d). Ultrastructural comparison of the shell wall in so-called B. postremus and the four spirulid genera listed above supports the conclusion that the two distinctly separated prismatic layers of the shell wall represent the outer and inner plates sensu Appellof (1893), which were secreted as an internal shell. Thus, the form described as B. postremus cannot be assigned to Bactritoidea. It is redescribed as Shimanskya gen. nov. postremus (Miller, 1930), and is considered to be the earliest known member of the order Spirulida. On the basis of this form the family Shimanskyidae fam. nov. is established.

A Unique Late Eocene Coleoid Cephalopod Mississaepia from Mississippi, Usa: New Data on Cuttlebone Structure, and Their Phylogenetic Implications

A new family, Mississaepiidae, from the Sepia-Spirula branch of decabrachian coleoids (Cephalopoda), is erected on the basis of the following, recently revealed, morphological, ultrastructural and chemical traits of the cuttlebone in the late Eocene Mississaepia, formerly referred to Belosaepiidae: (i) septa are semi-transparent, largely chitinous (as opposed to all other recorded cephalopods having non-transparent aragonitic septa); (ii) septa have a thin lamello-fibrillar nacreous covering (Sepia lacks nacre altogether, Spirula has fully lamello-fibrillar nacreous septa, ectochochleate cephalopods have columnar nacre in septa); (iii) a siphonal tube is present in early ontogeny (similar to siphonal tube development of the Danian Ceratisepia, and as opposed to complete lack of siphonal tube in Sepia and siphonal tube development through its entire ontogeny in Spirula); (iv) the lamello-fibrillar nacreous ultrastructure of septal necks (similar to septal necks in Spirula); (v) a sub-hemispherical protoconch (as opposed to the spherical protoconchs of the Danian Ceratisepia and Recent Spirula); (vi) conotheca has ventro-lateral extension in early ontogenetic stages (as opposed to Sepia that has no ventro-lateral extention of the conotheca and to Spirula that retains fully-developed phragmocone throughout its entire ontogeny). Chitinous composition of septa in Mississaepia is deduced from (i) their visual similarity to the chitinous semi-transparent flange of Sepia, (ii) angular and rounded outlines and straight compressive failures of the partial septa and mural parts of septa similar to mechanically-damaged dry rigid chitinous flange of Sepia or a gladius of squid, and (iii) organics consistent with &bgr;-chitin preserved in the shell. The family Mississaepiidae may represent a unknown lineage of the Sepia-Spirula branch of coleoids, a conotheca lacking a nacreous layer being a common trait of the shell of this branch. However, Mississaepiidae is placed with reservation in Sepiida because of similarities between their gross shell morphology (a cuttlebone type of shell) and inorganic-organic composition. In Mississaepia, as in Sepia, the shell contains up to 6% of nitrogen by weight; phosphatised sheets within the dorsal shield may have been originally organic, like similar structures in Sepia; accumulations of pyrite in peripheral zones of aragonitic spherulites and in-between the spherulites of the dorsal shield may also indicate additional locations of organics in the shell of living animal.

Shell structures in Carboniferous bactritid-like coleoids (Cephalopoda) from South Central USA

Morphological features of the shell including internal structures of the phragmocones of three different bactritoid cephalopod taxa assigned to the Order Bactritida: Bactrites quadrilineatus, Ctenobactrites lesliensis (L. Carboniferous) and the Order Parabactritida: Rugobactrites jacksboroensis (U. Carboniferous) were studied. The material comes from South Central USA. The features examined include the conch shape, siphuncle shape and ultrastructure of the shell wall, septa, septal neck and the connecting ring. These traits were then compared with Shimanskya postremus from Upper Carboniferous of Texas, which has been originally referred to bactritids and later placed within the coleoids in the Order Spirulida. Based on similarities and differences observed, B. quadrilineatus and C. lesliensis are now also considered being coleoids similar to S. postremus; R. jacksboroensis remains placed in the Order Parabactritida.

Siphonal zone structure in the cuttlebone of Sepia officinalis

The evolutionary process through which the siphonal zone of the cuttlebone of Sepia replaced the tubular siphuncle seen in other shelled cephalopods is poorly understood. Recently, porous connecting stripes, interpreted as homologous to connecting rings of tubular siphuncles, were revealed in Sepia (Acanthosepion) cf. savignyi (Geobios, 45:13–17, 2012). New data on the siphonal zone structure are herein demonstrated through SEM testing of 16 beach-collected cuttlebones of Sepia officinalis from Vale do Lobo, southern Portugal. In examined cuttlebones, the organic connecting stripes are mineralized along their peripheries where they are attached to septa by inorganic–organic porous contacting ridges. The contacting ridges consist of globular crystalline units within an organic matrix; each globule is a stack of rounded alternating organic and mineralized microlaminas parallel to the septal surface; mineralized microlaminas contain carbonate microgranules. Porous connecting stripes together with the contacting ridges may serve as transport routes for the cameral liquid used in buoyancy regulation. The contacting ridges appear to reinforce contacts between the connecting stripes and septa, and may strengthen shell resistance to changing environments. Lamella–fibrillar nacre in septa is demonstrated in Sepia for the first time. Comparison of Sepia and Spirula reveals the common character of their phragmocones, the slit-like shape of the permeable zones between chambers and the siphuncle. Narrowing of the permeable zones may provide shell resistance to high hydrostatic pressure; however, the essentially dissimilar relative length of the permeable zones may results in different capabilities of two genera for buoyancy regulation. In Sepia, long narrow porous inorganic–organic permeable connecting stripes and contacting ridges may allow for rapid buoyancy regulation which would lead to environmental plasticity and higher species diversity.

The Additional External Shell Layers Indicative of “Endocochleate Experiments” in Some Ammonoids

The present chapter is a review on the aberrant shell wall structures of some ammonoids characterized by additional external layers. Secondary deposits of shell on the outside of the conchs of some ammonoid species suggest that the body exceeded the body chamber volume and the mantle coated the shell.

An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods

Background The Subclass Coleoidea (Class Cephalopoda) accommodates the diverse present-day internally shelled cephalopod mollusks (Spirula, Sepia and octopuses, squids, Vampyroteuthis) and also extinct internally shelled cephalopods. Recent Spirula represents a unique coleoid retaining shell structures, a narrow marginal siphuncle and globular protoconch that signify the ancestry of the subclass Coleoidea from the Paleozoic subclass Bactritoidea. This hypothesis has been recently supported by newly recorded diverse bactritoid-like coleoids from the Carboniferous of the USA, but prior to this study no fossil cephalopod indicative of an endochochleate branch with an origin independent from subclass Bactritoidea has been reported. Methodology/Principal findings Two orthoconic conchs were recovered from the Early Eocene of Seymour Island at the tip of the Antarctic Peninsula, Antarctica. They have loosely mineralized organic-rich chitin-compatible microlaminated shell walls and broadly expanded central siphuncles. The morphological, ultrustructural and chemical data were determined and characterized through comparisons with extant and extinct taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS). Conclusions/Significance Our study presents the first evidence for an evolutionary lineage of internally shelled cephalopods with independent origin from Bactritoidea/Coleoidea, indicating convergent evolution with the subclass Coleoidea. A new subclass Paracoleoidea Doguzhaeva n. subcl. is established for accommodation of orthoconic cephalopods with the internal shell associated with a broadly expanded central siphuncle. Antarcticerida Doguzhaeva n. ord., Antarcticeratidae Doguzhaeva n. fam., Antarcticeras nordenskjoeldi Doguzhaeva n. gen., n. sp. are described within the subclass Paracoleoidea. The analysis of organic-rich shell preservation of A. nordenskjoeldi by use of SEM/EDS techniques revealed fossilization of hyposeptal cameral soft tissues. This suggests that a depositional environment favoring soft-tissue preservation was the factor enabling conservation of the weakly mineralized shell of A. nordenskjoeldi.

The Body Chamber Length Variations and Muscle and Mantle Attachments in Ammonoids

The varying body chamber lengths and the different attachment of muscles and mantle to conch wall belong to the major adaptations to their diverse modes of locomotion. Therefore, these traits are indirect indicators of different life styles. The sparse record of ammonoid body chamber lengths and attachment marks has impeded the understanding of this aspect of ammonoid paleobiology. The examination of body chamber length revealed that the decrease of the ammonitella body chamber lengths shows is the long-term trend characterizing the evolutionary development of the Goniatitida–Prolecanitida–Ceratitida–Phylloceratida branch of the Ammonoidea. The analysis of the body chamber lengths and the attachment marks leads to conclusion that a precondition for the jet-powered swimming of ammonoids is less than one whorl body chamber length and the position of the attachment marks in sites from where the cephalic retractor and funnel retractor muscles would be able to extend straight across to the head and to the funnel. This is the case of goniatitids and ammonitids possessing moved forward large ventrolateral muscle marks; jet-powered swimming is highly probable for them. None of the universal small dorsal, umbilical and ventral marks may be left in the attachment sites of the cephalic retractor and funnel retractor muscles. In the hook-shaped terminal body chambers of heteromorph ammonoids, like Audouliceras, the long tongue-like umbilical marks perhaps indicate the moved forward strong umbilical muscles adapted for regular change of the mantle cavity volume for sucking and filtering seawater. This suggests that such ammonoids fed on fine plankton or suspended organic rich substance. Their irregular coiled spiral shells, best suited to floating and perhaps vertical (diurnal) migrations, support the view above. The fossilized mantle so far described in the ceratitid ammonoid Austrotrachyceras has a laminated structure fibrous seen in internally shelled Jurassic belemnotheutis and Loligosaepia.

A new late Carboniferous coleoid from Oklahoma, USA: implications for the early evolutionary history of the subclass Coleoidea (Cephalopoda)

Abstract. The limited record of the bactritoid-like coleoid cephalopods is here expanded due to discovery of a late Carboniferous (Moscovian) orthocone comprising a phragmocone and a body chamber with a proostracum-like structure, a sheath-like rostrum, an ink sac, and a muscular mantle preserved on top of the conch. The specimen comes from the Wewoka Formation in the vicinity of the city of Okmulgee, Oklahoma, which previously yielded an orthocone indicative of an evolutionary branch of the Carboniferous cephalopods described as the order Donovaniconida Doguzhaeva, Mapes, and Mutvei, 2007a within the subclass Coleoidea Bather, 1888. Here, we describe from that site a bactritoid-like coleoid, Oklaconus okmulgeensis n. gen. n. sp. in Oklaconidae n. fam. A broad lateral lobe of the suture line and a compressed conch with a narrowed dorsal side and a broadly rounded ventral side distinguish this genus from Donovaniconus Doguzhaeva, Mapes, and Mutvei, 2002b. The muscular mantle is preserved as a dense sheet-like structure, with a crisscross pattern and a globular-lamellar ultrastructure. Recent knowledge on the early to late Carboniferous coleoids is discussed. Carboniferous coleoids show a high morphological plasticity with a capacity for being altered to create the diverse combinations of ‘bactritoid’ and ‘coleoid’ structures. This could be the principle evolutionary driver of their radiation in the late Carboniferous.