Calcareous Concretions Research Articles

Taxonomy and distribution of species of Gastrocopta Wollaston 1878 (Mollusca: Gastropoda: Gastrocoptidae) from the Galápagos Islands (Ecuador)

ABSTRACTA revision of Gastrocopta from the Galápagos Islands (Ecuador) is made. Four new species from Pinzón, Santa Cruz and Floreana Islands are described; species previously known are redescribed and new locations are added. Gastrocopta (Gastrocopta) reibischi is revalidated through new records from Floreana, Isabela and San Bartolomé Islands. Shell shape and the number, morphology and disposition of the apertural barriers support the discrimination of the taxa. The species have cylindrical to pupoid shells; the number of apertural barriers – differentiated as lamellae, folds and nodulae – varies between 4 and 11, almost completely occluding the aperture in the more complex cases. These structures are: angular-parietal, infraparietal, supracolumellar, columellar, subcolumellar lamellae, and supernumerary, basal, infrapalatal, lower-palatal, interpalatal, upper-palatal and suprapalatal folds. In addition to this classic scheme, a supernumerary fold and a nodule are added. Calcareous concretions – pustulae – are found in several species, mainly located in the peristome. The aulacognathous jaw and radular dentition formulae of Gastrocopta (Gastrocopta) clausa and Gastrocopta (Gastrocopta) munita, are described and photographed for the first time.

Magnetic Anisotropy in Silurian Gas‐Bearing Shale Rocks From the Pomerania Region (Northern Poland)

AbstractAnalysis of anisotropy of magnetic susceptibility (AMS) and anhysteretic remanent magnetization (AARM) was conducted on unconventional gas‐bearing Silurian shale rocks from northern Poland. Samples of these rocks were collected from depths greater than 3,500 m from two drill cores. The aim was to investigate magnetic fabrics to verify current models of depositional conditions, current direction, and/or tectonic evolution. To obtain an in‐depth interpretation, rock magnetic studies, microscopic analyses, and graptolite orientation measurements were performed. The results indicate that the magnetic susceptibility is mainly governed by paramagnetic minerals (phyllosilicates) with a small contribution of ferromagnetic minerals, mostly magnetite. Typically, in the studied mudstones, the AMS and AARM fabrics are characterized by strong bedding‐parallel foliation, resulting mostly from compaction. The foliation is much weaker in the associated early‐diagenetic calcareous concretions. Although the mudstones are almost isotropic in the bedding plane, there is a slight tendency for grouping of magnetic lineation axes with an orientation of approximately NNW‐SSE. The corresponding orientation of the AMS lineation is preserved in the concretions, and the same trend also prevails in the preferred orientation of graptolites. Thus, we interpret this orientation to be related to paleocurrents. The observed directions show that during the Wenlock (Silurian) in the studied part of the Baltic Basin, the dominant currents had an orientation of circa NNW‐SSE along the margin of Baltica. Our results confirm that even in such fine‐grained sediments, in which there are no other unequivocal directional sedimentary indicators, paleocurrent directions can be determined by applying AMS and AARM methodology.

Geochemical Characterization of Exposed Black Shale Sediments of Matamuhari Anticline, Bangladesh

Matamuhari anticline is one of the largest anticline situated at Bandarban district of Bangladesh which is 60 km long and 20 km wide in the part of Bangladesh. Like other part of Bangladesh the whole sequence of exposed rocks of Matamuhari anticline is composed with Neogene sedimentary rocks of shale, sandstone, siltstone, silty shale, tabular and spheroidal calcareous concretions. Seven outcrop black shale samples were collected during February 2013 from the different parts of the anticline namely Boro Bari Jhiri, Ochir Jhiri and Tak Chara area were mineralogically and geochemically examined in order to better understand the depositional environment in the studied area. The major and trace elements were analyzed using XRF spectrometry. Two distinct lithofacies assemblages, mud and silty-clay are found in the collected sediments. The shales are predominated by quartz, kaolinite, chlorite, mica (muscovite and biotite), feldspar (both K-feldspar and plagioclase), and in addition to a variable ratio of vermiculite. Lithologial characteristics and geochemical data demonstrated that sediments are enriched with TOC contents ranging from 0.39 to 0.67 wt.% and shows distinctive correlation to concentration of TOC and particle size distribution. These shales are characterized by a low Mg and K as well as high Al and Fe contents. Studies also show that the values of MgO/Al2O3 and K2O/Al2O3 ratio ranges from 0.15 to 0.17 and 0.18 to 0.20 respectively. The relationship of log MgO/Al2O3 and log K2O/Al2O3 values reveals that all of the studied samples fell within the marine environment. Ni/Co ratio of the studied shale samples ranges from 2.84 to 3.88 (average 3.36). These low values of Ni/Co ratio suggest that the sediments were deposited under oxic conditions. However, the above observations suggest that the sediments of Matamuhari anticline area were deposited in a shallow marine environment under oxic conditions.

Study of the fish fossil Notelops brama from Araripe-Basin Brazil by Neutron Tomography

In the last decade, Neutron Tomography significantly gained importance as an analyzing tool to inspect samples of paleontological interest. In general, neutrons are able to provide new and complementary information when compared to the ones provided by X-rays imaging methods. Specifically, in the present paper, the Neutron Tomography equipment of the IPEN-CNEN/SP was successfully applied to investigate the internal structure of a fish fossil, embedded in a calcareous concretion. The resulting images, which will be presented, has revealed different contrast between several regions within the specimen enabling the differencing of osteological structures of the fossil, information about its state of conservation, degree of embedding, inclusions as well as regions within the concretion which could be related to humidity or to other substances and minerals containing hydrogen naturally added to the fossil. The technique is non-destructive and non-invasive allowing a close analysis of the specimen. Furthermore, the obtained images have demonstrated the feasibility of the equipment at IPEN-CNEN/SP for investigating this kind of sample.

Analysis of a Cretaceous (late Aptian) high-stress ecosystem: The Romualdo Formation of the Araripe Basin, northeastern Brazil

The Cretaceous (upper Aptian) Romualdo Formation of the Araripe Basin, northeastern Brazil, is a marine-influenced, predominantly fine-grained siliciclastic unit. In the eastern part of the basin, it corresponds to a depositional sequence composed of two transgressive-regressive cycles. Low-diversity benthic macrofaunas document high-stress conditions. Their palaeoecological and taphonomic analysis allows for the detailed reconstruction of the palaeoenvironments and of the temporal changes in the palaeoecosystem. The transgressive part of the lower cycle is a black shale with calcareous concretions that contain excellently preserved fishes and other vertebrates (the famous “Santana fossils”), but apart from abundant ostracods and rare decapod crustaceans, benthic faunal elements are very rare due to anoxic to dysoxic conditions. A low-diversity parautochthonous molluscan fauna of small bivalves and gastropods records fluctuating dysoxic conditions during early regression. Towards the top of the measured sections (late regression), thin gastropod shell beds become conspicuous. At the top of the sections decimetre-thick shell concentrations show signs of reworking and a greater marine influence (transgressive part of the upper cycle). The distribution pattern of three benthic associations and two assemblages is almost equally shaped by three environmental parameters: The low overall species diversity, small size of the fauna, and the lack of stenohaline elements suggest lowered and fluctuating salinity conditions. Fluctuating redox conditions with anoxia to dysoxia, identified especially in the lower parts of the succession, and substrate were the other two factors shaping the faunal distribution. The late Aptian sedimentary and faunal history of the eastern part of the basin indicates restricted marine influence, coupled with increasing freshwater input during phases of sea-level lowstand, and low-energy conditions offshore, which led to widespread anoxia, especially in the lower part of the formation. Thus, palaeoecological analyses are an excellent tool to disentangle the various environmental parameters that shaped the palaeoenvironments of the basin, to understand more closely its Fossil-Lagerstätten, and to corroborate and fine-tune the sequence stratigraphic framework.

Multimodal surface analyses of chemistry and structure of biominerals in rodent pineal gland concretions

Calcium carbonate and carbonate-hydroxyapatite are known to form inorganic components of crystals and calcareous concretions found in many non-skeletal tissues and structures including the pineal gland. We used advanced surface analyses techniques such as polarization microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), microfocus X-ray diffraction (XRD), transmission electron microscopy with selected area electron diffraction (TEM-SAED) to investigate samples extracted from rat pineal gland after irradiation with visible light for 12 h. Single-crystal X-ray diffraction showed that the concretions were largely amorphous with the presence of some nanocrystalline phases. High resolution TEM-SAED revealed the presence of iron oxide in the form of hematite. Spectroscopy data especially Raman spectroscopy revealed a mixed nature of these concretions, which corresponded reasonably with XPS, TEM and XRD. Overall the study confirms the presence of a mixed phase of calcium carbonates including calcite, aragonite and vaterite. We note that aragonite is not a common occurrence in vertebrates and recommend further investigation to rule out any link to pathology.

Cupressaceous Pollen Cones from the Early Cretaceous of Vancouver Island, British Columbia: Morinostrobus holbergensis gen. et sp. nov.

Premise of research. Four small pollen cones bearing pollen have been found attached to a leafy twig in a calcareous concretion from the Valanginian Apple Bay locality, northern Vancouver Island, B...

Tracking the Initial Diversification of Asterids: Anatomically Preserved Cornalean Fruits from the Early Coniacian (Late Cretaceous) of Western North America

Premise of research. The initial radiation of core eudicots (>70% angiosperm diversity) occurred during the Late Cretaceous (100.5–66 Ma). While there is strong fossil evidence for this diversification occurring throughout the Cenomanian (100.5–93.9 Ma) and Turonian (93.9–89.8 Ma), there are no unambiguous reports of the largest core eudicot clade, the asterids, from pre-Coniacian deposits (89.8–86.3 Ma). This study provides new insights into the early evolution of asterids by characterizing anatomically preserved fruits from the early Coniacian (∼89 Ma) of North America that represent three new taxa assignable to the earliest-diverging asterid order, Cornales.Methodology. Three fossil fruit types were identified within calcareous concretions from the Upper Cretaceous Eden Main locality on Vancouver Island, British Columbia. Specimens were prepared using the cellulose acetate peel technique.Pivotal results. These fruits have a thick-walled woody endocarp with germination valves, one apically attached seed...

Effects of substrata and environmental conditions on ecological succession on historic shipwrecks

An understanding of the interactions between biological, chemical and physical dynamics is especially important for the adequate conservation of the Underwater Cultural Heritage. However, while physical and chemical processes are relatively well-investigated, the biological communities associated with these habitats are poorly studied. We compared the sessile community developed on panels of different materials placed on two historical shipwrecks, the Fougueux and the Bucentaure, from the Battle of Trafalgar (October 1805). Six materials used at the construction of vessels at the 18th and 19th centuries were selected: copper, brass, cast iron, carbon steel, pine and oak. The sessile community developed on the panels was studied two and 15 months after their immersion at the water to determine the effects of materials and environmental conditions (sediments, waves, hydrodynamic conditions, temperature and salinity) on ecological succession and the possible implications at the conservation of historical shipwrecks. On the Fougueux, the environmental conditions more strongly influenced the biological succession than the material type, with pioneer colonisers dominating the communities in both sampling periods. On the Bucentaure, exposed to more stable environmental conditions, the sessile community showed differences between sampling periods and among materials at the end of the experiment. Under these more stable environmental conditions, the material type showed a higher influence on the sessile community. Species that produce calcareous concretions developed on metallic panels, but were absent on wood panels, where the shipworm Teredo navalis was more abundant. The relationship between environmental conditions, sessile organisms and material type can influence the conservation status of the archaeological sites.

Accounting for Calcareous Concretions in Calcic Vertisols Improves the Accuracy of Soil Hydraulic Property Estimations

Core Ideas Calcareous concretions (CCs) could maintain a considerable amount of water and the water content of CCs decreased with an increase in CC sizes. The addition of CCs to soils changed the WRC and the pore distribution of soils significantly. The available water content (AWC) of soil–CC mixtures decreased when the CC content increased. A linear equation, which included CC content and CC water content, was proposed to estimate the AWC of soils containing CCs accurately. The soil water retention curve (WRC) is one of the most important properties in soil hydraulic studies. Current studies normally focus on fine soils, ignoring the water‐holding capacity of coarse fragments (>2 mm) and their effects on soil available water content (AWC). Calcareous concretions (CC) are coarse inclusions distributed widely in soils around the world. This study was conducted to quantify the effects of the proportion and size of CCs on the soil WRC and AWC of a calcic vertisol. The WRCs of CCs were measured using the sand box and ceramic plate method, and the WRCs of fine soils and soil–CC mixtures of various sizes (2–5, 5–8, and 8–30) and proportions (5, 10, 15, and 30% on a total mass basis) of CC were determined with the centrifuge method. The WRCs were fitted with the van Genuchten equation. The results showed that CCs retained a considerable amount of water. The saturated water contents of CCs of 2‐ to 5‐, 5‐ to 8‐ and 8‐ to 30‐mm were 0.251, 0.220, and 0.196 cm3 cm–3, respectively. The addition of CCs changed the WRC and pore distribution of soils significantly. The AWC of soil–CC mixtures decreased with increasing CC content. A linear equation, which included the fraction of CCs and water content in CCs, was proposed to estimate the AWC of soils containing CCs accurately. Accounting for CCs in the calcic vertisol improved the accuracy of soil hydraulic property estimations.

The Early Phylogenetic Diversification of Cornales: Permineralized Cornalean Fruits from the Campanian (Upper Cretaceous) of Western North America

Premise of research. Two permineralized fruits have been found within a single calcareous concretion from the Upper Cretaceous (upper Campanian) Spray Formation of Vancouver Island, British Columbia. These fossils provide additional evidence for the initial phylogenetic diversification of Cornales, the earliest diverging asterid lineage.Methodology. Specimens were prepared using the cellulose acetate peel technique.Pivotal results. A new cornalean species, Suciacarpa xiangae sp. nov., is characterized on the basis of a well-preserved fruit specimen. This fruit is represented by a large ovoid tetralocular sclerenchymatous endocarp. Locules are crescent shaped in transverse section and accompanied by short dorsal germination valves. Valves consist of small isodiametric sclereids as well as a large number of large secretory cavities. The septum and central axis are composed of transversely oriented and interwoven fibers and elongate sclereids. There is no major central vascular bundle; however, there are num...

EVIDENCE OF BACTERIAL DECAY AND EARLY DIAGENESIS IN A PARTIALLY ARTICULATED TETRAPOD FROM THE TRIASSIC CHAÑARES FORMATION

The vertebrate fauna from the lower Carnian Chanares Formation of Argentina is dominated by well-preserved small- and medium-bodied archosauriforms and therapsids. Here we report the discovery of a non-mammalian therapsid dicynodont (of greater than 20 cm skull length) that was found partially articulated within the floodplain deposit. Taphonomic analysis of this specimen reveals details of its paleobiology and taphonomic history, including the cause of death, exposure to predation and/or scavenging, subsequent subaerial decay, and final entombment. The specimen studied also allowed for the documentation of the activity of micro-organisms involved in decay processes during the biostratinomic stage (soft tissue decomposition on surface) and diagenetic stages (anaerobic decay). Our results indicate that despite bones being found in concretions the formation of calcareous concretions is not required for bone preservation. Consequently, this study highlights the role of volcanic ash in promoting bone preservation.

First Occurrence and Paleo-Ecological Implications of Insects (Orthoptera: Ensifera Gryllidae) in the Romualdo Member of the Santana Formation, Eo-Cretaceous of the Araripe Basin.

The Romualdo Member of the Santana Formation, a lithostatigraphic unit attributed to a marine intrusion, is famous for its preserved fossils in calcareous concretions, which stand out for their diversity and excellent preservation levels. This paper aims to record the first occurrence of the Class Insecta in the Romualdo Member of the Santana Formation of the Araripe Basin, as well as to describe and discuss the paleo-ecological implications of such finding. The first occurrence of the order Orthoptera (family Gryllidae) is presented for this unit. This new species is attributed to the genus Araripegryllus, that lasted throughout the deposition of the Crato Member, which is under the Romualdo Member. In reference to its statigraphic origin, the specimens was named Araripegryllus romualdoi sp. nov.

Anatomically preserved fossil cornalean fruits from the Upper Cretaceous of Hokkaido: Eydeia hokkaidoensis gen. et sp. nov.

The basal asterid clade Cornales radiated during the Late Cretaceous. However, our understanding of early evolutionary patterns and relationships remain obscure. New data from five permineralized fruits in calcareous concretions from the Upper Cretaceous (Coniacian-Santonian) Haborogawa Formation, Hokkaido, Japan provide anatomical details that aid our knowledge of the group. Specimens were studied from cellulose acetate peels, and three-dimensional reconstructions were rendered using AVIZO. Fruits are drupaceous, roughly pyriform, 2.9-4.3 mm in diameter, with a fleshy mesocarp, transition sclereids, and a stony endocarp of four to five locules, with the septa forming a cross or star-like pattern in transverse section, distinct germination valves, and one apically attached anatropous seed per locule. Vascular tissue occurs in zones between the mesocarp and exocarp, in two rows within the septa, and prominent seed bundles can be traced throughout the fruit sections. Seeds have a single integumentary layer of radially flattened square to rectangular cells and copious cellular endosperm. A fully formed, straight, cellular dicotyledonous embryo, with closely appressed, spathulate cotyledons, is present within each seed. The unique combination of characters shown by these fruits is found in Cornaceae, Curtisiaceae, and Davidiaceae and allows us to describe a new taxon of Cornales, Eydeia hokkaidoensis gen. et sp. nov., with many similarities to extant Davidia involucrata. These fossils underscore the phylogenetic diversification of Cornales that was underway during the Late Cretaceous and support the hypothesis that a Davidia-like fruit morphology is plesiomorphic within Cornales.

Relationships of †Codoichthys carnavalii Santos, 1994 (Teleostei, Clupeomorpha, †Ellimmichthyiformes) from the Late Aptian of São Luís-Grajaú Basin, NE Brazil.

†Codoichthys carnavalii is a clupeomorph fish only found in calcareous concretions of Codó Formation, State of Maranhão. It is known based on three specimens housed in the paleontological collection of the Museu de Ciências da Terra of Departamento Nacional da Produção Mineral, Rio de Janeiro. It was omitted in most of recent cladistic analyses about clupeomorphs. We revisited its anatomy furnishing new data and additional restorations. Furthermore we explored the relationships of †Codoichthys with the computer program TNT based on a matrix with 30 taxa and 60 unordered and unweight characters. Elops was used to root the tree. The strict consensus was obtained from three shortest trees (L=181; CI=0.387; RI=0.632). The monophyly of †Ellimmichthyiformes is supported by a sigmoid cleithrum and an uniquely derived predorsal scute series. Most of subgroups showed low support indices. †Sorbinichthyidae and †Horseshoeichthys appear in the most basal position, and not closely related to †Armigatus or †Diplomystus. A †Diplomystus clade is more advanced than †Armigatus and sister-group of remaining †ellimmichthyiforms. Within †Paraclupeidae, †Codoichthys is sister-group of remaining †paraclupeids (including †thorectichthyines and †paraclupeines). Within †Paraclupeinae, †Triplomystini includes a †Triplomystus clade, a sister group of †Rhombichthys plus †Tycheroichthys, and †Paraclupeini with †S. itapagipensis and all other †ellimmichthyiform taxa.

Huncalotis, an enigmatic new pectinoid genus (Bivalvia, Late Jurassic) from South America

The extensive outcrops of the Late Jurassic–Early Cretaceous Vaca Muerta Formation black shales and marls in the Neuquen Basin have yielded very few bivalves, and these are not well known. The material described here was collected in central Neuquen, from late Tithonian calcareous levels within the black shales, between beds with Substeueroceras sp. and with Argentiniceras noduliferum (Steuer). The material is referred to the new genus Huncalotis and to the new species H. millaini. The strongly inequivalve shells, the ligamental area with a triangular slightly prosocline resilifer, the right valve with ctenolium and a very deep byssal notch, and the lack of radial ornamentation make the shell of this new genus strikingly similar to the Triassic pectinid Pleuronectites. This resemblance may be due to either phylogenetic relationships or convergence. Obliquipecten peruanum Rivera from central Peru is tentatively referred to Huncalotis. The Neuquen specimens are found in two main preservation types. Most of the material occurs in shell pavements, with equally abundant right and left valves and wide size range, within “beef” or “sandwich concretions”. These specimens are commonly complete but disarticulated, and show radial fractures orientated at right angles to the shell margins. A few specimens were found on the outside of large calcareous concretions within black shales; these are often articulated, complete shells, which preserve the original convexity of the valves. In some cases these articulated shells seem to be associated with large ammonite shells, suggesting an epibyssate (possibly also pseudoplanktonic) lifestyle.

Sexual dimorphism in the Bathonian morphoceratid ammonite Polysphinctites tenuiplicatus

Asphinctites tenuiplicatus [M] and Polysphinctites secundus [m] from the Asphinctites tenuiplicatus Zone (Early Bathonian), are usually considered as a sexual dimorphic pair, although authors describe them as separate species. We used statistical methods to test the sexual dimorphic correspondence between those morphospecies, based on a rather large sample of well-preserved macro- and microconchs derived from a single horizon of calcareous concretions in the Polish Jura. Our results indicate that both dimorphs or sexes have identical ontogeny up to a critical diameter, from which they diverge towards the characteristic morphology and sculpture of each dimorph. Thus, both dimorphs are described as a single species: Polysphinctites tenuiplicatus [M and m]. After review of the several nominal species usually assigned to the genera Asphinctites and Polysphinctites throughout their stratigraphic and biogeographic range in the Early Bathonian of the Tethys, it is concluded that they actually correspond to only two species of a single lineage. The corresponding name for the lineage should be Polysphinctites (= Asphinctites as a junior synonym).

Submandibular Salivary Sialolith: A Case Report with Review of Literature

Sialolithiasis is a condition characterized by the obstruction of a salivary gland or its excretory duct due to the formation of calcareous concretions, resulting in salivary ectasia and subsequent dilatation of the salivary gland. The majority of sialoliths occurs in the submandibular gland or its duct and is a common cause of acute and chronic infections. Majority of salivary stones are less symptomatic or cause minimal discomfort but the larger stones may interfere with the flow of saliva and cause pain and swelling. Sialoliths are calcified organic matter that is formed within the secretory system of the major salivary glands. Salivary gland calculi account for the most common disease of the salivary glands, and may range from tiny particles to several centimeters in length. This case report describes a patient presenting with submandibular gland sialolith

Dinosaur trackways from the Upper Cretaceous Oldman and Dinosaur Park formations (Belly River Group) of southern Alberta, Canada, reveal novel ichnofossil preservation style

Dinosaur tracksites recently discovered in exposures of the Belly River Group in the Milk River Natural Area (MRNA) and Dinosaur Provincial Park (DPP) of southern Alberta represent a novel type of ichnofossils. The tracks, all referable to hadrosaurs, occur as sideritic or calcareous concretions protruding above fine-grained deposits and are here termed concretionary tracks. Detailed sedimentological, petrographic, and geochemical analyses reveal that, although the MRNA and DPP tracks are of different mineralogical compositions (calcium carbonate versus siderite, respectively), they display similar internal structures (microscopic convoluted laminations) and occur in depositional settings indicative of wet paleoenvironments, where the ground was soft and water saturated. These characteristics suggest that concretionary tracks are footprint casts that formed as groundwater rich in dissolved carbonates flooded depressions left in the soft substrate. As the ponded water evaporated, minerals began to precipitate and mix with clastic material transported into the depressions, settling as finely laminated mud within the tracks and filling them either completely or partially. The geochemical composition of the precipitate would depend on the prevalent groundwater conditions (e.g., pH, dissolved carbonate and sulphate concrentrations). Cementation of the tracks occurred relatively soon after burial (<100 years), possibly in response to microbial activity and saturation by mineral-rich groundwater, and modern erosion exposed the concretionary tracks by removing the softer host unit. Recognition of this novel type of ichnofossils suggests dinosaur tracks may be more common than previously thought. Unfortunately, concretionary tracks tend to break apart rapidly when the encasing and underlying substrate erodes away, altering their diagnostic shape and rendering them indistinguishable from nonichnogenic concretions. As such, concretionary tracks may be transient ichnofossils in the badlands, explaining why they are rarely recognized.

The morphology of the pineal gland of the yellow-toothed cavy (Galea Spixii Wagler, 1831) and red-rumped agouti (Dasyprocta leporina linnaeus, 1758).

The pineal gland is an endocrine gland found in all mammals. This article describes the morphology of this important gland in two species of Caviideae, namely the yellow-toothed cavy and the red-rumped agouti. Ten adult animals of the two species used in current analysis were retrieved from the Center for the Multiplication of Wild Animals (CEMAS/UFERSA) and euthanized. The glands were removed and photographed in situ and ex situ. They were fixed in a paraformaldehyde solution 4% or glutaraldehyde 2.5% solution and submitted to routine histological techniques respectively for light and scanning electron microscopy. Macroscopically, the pineal gland with its elongated structure may be found between the cerebral hemispheres facing the rostral colliculi. Microscopically, pinealocytes and some glia cells were predominant. Contrastingly, to the cavy's pineal gland, a capsule covered the organ in the agouti, with the emission of incomplete septa to the interior, which divided it into two lobules. Light and scanning electron microscopes failed to show calcareous concretions in the pineal gland. Based on the topography of the cavy's and agouti's pineal gland, it may be classified as supra-callosum and ABC type.