Ambergrisichnus alleronae, Monaco & Baldanza & Bizzarri & Famiani & Lezzerini & Sciuto, 2014

Monaco, Paolo, Baldanza, Angela, Bizzarri, Roberto, Famiani, Federico, Lezzerini, Marco & Sciuto, Francesco, 2014, Ambergris cololites of Pleistocene sperm whales from central Italy and description of the new ichnogenus and ichnospecies Ambergrisichnus alleronae, Palaeontologia Electronica (29 A) 29, pp. 1-20 : 7-11

Ambergrisichnus alleronae igen. et isp. nov.

Figure 3.1-7

zoobank.org/ 862C00F-14BE-490E-9628-6115E88A7CFC

zoobank.org/ 5ECB7CBB-3D47-4EA7-8374-D5D2CCB2FF2B

Etymology. From the term ambergris (originally from Arabic ambar), indicating a solid substance usually associated with sperm whales ( Physeter macrocephalus Linnaeus, 1758 ) and less commonly with pygmy sperm whales. The species refers to the name of the village of Allerona, near Orvieto, in western Umbria, central Italy, were it was first found.

Material. Four specimens (one holotype and three paratypes).

Holotype. Specimen CT 01 ( Figure 3.3 ), (length 18 cm, width 20 cm), housed in Biosed Lab, Department of Physics and Geology, University of Perugia.

Paratypes. Specimens CT02 ( Figure 3.1, 3.7 ), CT03 ( Figure 3.2 ), and CT04 ( Figure 3.5-6 ), housed in Biosed Lab, Department of Physics and Geology, University of Perugia.

Type locality. Bargiano badlands, 2 km northeast from Allerona , in southwestern Umbria, 42°50′13″N, 11°58′22″E, in offshore marine clay deposits of the Chiani-Tevere sedimentary cycle, Chiani-Tevere unit .

Stratigraphic range. Early Pleistocene, Gelasian to Calabrian, about 1.95-1.55 Ma ( Baldanza et al., 2011; 2013)

Diagnosis. Ichnogenus: irregularly cylindrical permineralized structure, elongated or branched ( Figure 3.3 ), with apex showing convergent striae and strong tapering towards the tip. Dimensions varying from 20 to 40 cm (exceptionally up to 60 cm) in width, from 18 to 35 cm in length. Smooth or slightly rough outer surface ( Figure 3.1, 3.2, 3.7 ) showing compressional structures and irregular striae, with interposed oval to subspherical and/or compressed bulges (up to 7 cm wide and 9 cm long), emerging abruptly from the surface. Concentric helicoidally envelopment in cross section, converging towards a poorly cemented nucleus ( Figure 3.4, 3.6 ), with colour changes and locally exhibiting thin concentric bands.

Ichnospecies: as for the ichnogenus.

Description. The holotype of Ambergrisichnus alleronae isp. nov. (CT01, Figure 3.3 ) is an irregular cylinder, 18 cm long and 20 cm wide, with one apex showing convergent striae and strong tapering toward the tip, while the other apex is wider and includes two very short branches ( Figure 3.3 ). In cross section, the concentric envelopment, best visible on paratype 3 (CT04), converges towards a nucleus that is poorly cemented (a marly clay, Figure 3.4, 3.6 ). The external texture is smooth or slightly rough. In paratype 3, one apex has been cut to show the interior arrangement of rings and the helicoids; the helicoids, 10 to 40 cm thick, are well preserved, with colour changes and locally exhibit concentric bands. The outer surface of paratypes 1 and 2 ( Figure 3.1, 3.2, 3.7 ) show compressional structures and irregular striae, and between these structures there are some rognons (bulges: Clarke, 2006). The rognons, emerging abruptly from the outer surface, are oval to subspherical; they are up to 7 cm wide and 9 cm long, and compressed. The major change in colour is between striae and rognons, and similar features occur in modern and ancient cololites ( Hunt and Lucas, 2012a). The holotype represents the tip of a complex cololite hummock. About 30% of the terminal parts of outer sheaths of complex cololites exhibit comparable characteristics, although the shape can change (e.g., no branching). Morphological features of the holotype and the paratypes of A. alleronae igen. et isp. nov., such as striae, concentric bands, and rognons are recognized in many large masses (e.g., complex cololites), as well as in modern ambergris ( Clarke, 2006).

Remarks. The Allerona specimens differ from other similar large structures induced by diagenetic processes, because of the external shape and internal structures both of complex and simpler cololites. Although externally it may resemble vertebrate and invertebrate burrows ( Gaillard et al., 2013, Figures 6 and 8), or shafts of Tisoa siphonalis from the Early Jurassic (Pliensbachian) (van de Schootbrugge et al., 2010), A. alleronae differs significantly in important aspects. The internal arrangement of A. alleronae is helicoidal or concentric around a central nucleus (usually a dark grey clay core, Figure 3.6 ); this feature is lacking in most invertebrate burrows, as well as in the simple or columnar, abiotic carbonate concretion of Tisoa siphonalis . Moreover, a well-cemented series of concentric bands ( Figure 3.4-6 ), generally with oxidized reddish or yellowish crusts, is common in the specimens of A. alleronae ( Baldanza et al., 2013, Figures 3.1 and 3.2 ), and are very similar to those present in modern ambergris ( Figure 3.8 -9). In the holotype ( Figure 3.3 ) the external branched shape resembles some giant Thalassinoides in the Early Jurassic Calcari Grigi Formation of the Southern Alps ( Giannetti and Monaco, 2004), but in the latter specimens convergent striae and concentric rings are absent. In cross section, large Thalassinoides (type 4 of Giannetti and Monaco, 2004) shows a central large tunnel used by the crustacean for movements within the burrow. This feature is lacking in A. alleronae . The converging striae of A. alleronae are typical and never found in other fossil marine or freshwater cololites, although spiral bromalites are known and have been associated with primitive fish, for example freshwater sharks Orthacanthus (Shelton, 2013) . Striae are reported in other trace fossils such as the aestivation burrows of lungfish from the Eocene to Oligocene of south-eastern France ( Gaillard et al., 2013). Nevertheless, these striae are short and parallel, of the same width and regularly spaced, while striae of A. alleronae are convergent towards the apex and of irregular length ( Figure 3.3 ).

Discussion. The holotype of A. alleronae (CT01) is a portion of a large cololite formed as hummocks with many convolute tunnels, which has never been found in branched horizontal mazes of Thalassinoides ( Monaco, 2000; Monaco et al., 2007). Notably, the orientation of ambergris specimens, which is known only in two finds from the Southern Harvester floating factory obtained during the Antarctic whaling season of December 1953 (155 kg and 421 kg specimens), has the smaller end pointing towards the anus and the larger end pointing towards the stomach of the whale ( Clarke, 1954, 2006). Similarly, the end of each Allerona structure is tapered and exhibits wide and deep convergent striae, as in ambergris described by Clarke (2006). Subcircular lumps and protruding structures are common in the outer part of A. alleronae , just as in the rognons found in present-day ambergris ( Clarke, 1954, 2006, figure 4; Johnson, 2001; Perrin, 2005; Vogt, 2011). Clarke (2006) observed that the thinner end of each mass of ambergris may be tapered, or shaped like a thick bobbin protruding from the main mass, with a somewhat rounded terminus. The passive movement of the ambergris mass in the intestinal tract can produce such structures as large striae and compression of rognons as described in modern ambergris masses ( Clarke, 2006). Comparable features had not been reported in the paleontological and ichnological records, until the work of Baldanza et al. (2013). The findings of squid beaks within cololites ( Figure 5.1-4 ) further support the connection with Recent ambergris masses, wherein squid beaks are conspicuous.

Mineralogical Analyses

Baldanza et al. (2013) reported preliminary mineralogical data by FTIR analyses performed on the inner gray and outer red or yellow parts of cololites. The FTIR analysis showed a relatively low amount of aluminum silicates within the fossil structures, while the enclosing clay sediments showed a low content of CaCO 3 (<15%); the CaCO 3 in the cololites was interpreted as biogenecally precipitated due to local enrichment in organic matter ( Castanier et al., 1999; Douglas, 2005). Xray diffraction spectra of the new analysed samples are presented in Figure 6.1 . XRPD analysis shows that samples are essentially made up of dolomite, with minor amounts of quartz and phyllosilicates, and traces of calcite and plagioclases. Thermogravimetric analysis ( Figure 6.2 ) confirms the presence of volatile compounds related to the carbonate phases. Assuming that all the mass loss in the temperature range of 600-1000 °C may be attributed to carbon dioxide bound to dolomite, the amount of this carbonate phase ranges from 72% (sample 15) to 81% (sample 17) in weight.

A preliminary observation under the scanning electron microscope of the inner portions of cololites allowed us to identify a microcrystalline mosaic of rosette-shaped dolomite with mica (probably muscovite) crystals in the inner portion ( Figure 7.9 ), and scattered dolomite nanocrystals associated with spheres of probable bacterial origin ( Figure 7.10 ).

Microstructural Arrangement

The analysis in thin sections of different cololites has highlighted the pervasive presence of a micropeloidal matrix with microcrystals of dolomite, pyrite crystals, scattered benthic foraminifera, and other, and never observed peculiar structures. The micropeloids ( Figure 7.4-7 ) are very small, on an order of few microns, and might be the result of the original degraded microbial mat as indicated by Chafetz (1986). The distribution of pyrite crystals varies through the cololite bodies; the peripheral region of Ambergrisichnus alleronae (generally red or yellow-orange in colour) shows a much higher pyrite concentration (as small grains of 30-40 P m) than the interior region, where the pyrite formed framboids. The framboidal, from 50 to 100 P m, pyrite crystals ( Figure 7.3, 7.6, 7.8 ) occur as isolated or grouped ( Figure 7.8 ), and pyrite also infill microfossils (benthic foraminifera Bulimina and Bolivina ) ( Figure 7.5-6 ).

A large number of dolomite crystals of different size ( Figure 7.4-6, 7.8 ) is scattered in the matrix and in some cases, the micrometric crystals constitute the matrix of cololites ( Figure 7.6 ). Other particular types of structures, such as long chains of pyrite spherules ( Figure 7.1, 7.3 ) and elliptical bodies with central pyrite crystals ( Figure 7.4 ), are identifiable into cololites and could be comparable with structures produced by filamentous large sulphur bacteria like Beggiatoa and Thioploca . Beggiatoa ( Figure 7.2 , free-living specimens) is a candidate for a source because of its morphology, represented as a single free-living filament with sulfur inclusions (Salman et al., 2011). Other discoid pyritized structures (ranging in diameter from 0.5 to 2.0 cm), were commonly found close to the cololites and near the whale skeletal remains ( Figure 7.11 -13). Several discs are circular, with a rough surface, undulate margins, and an umbonate to convex central area. From a microbiological point of view, they are comparable to colonies or structured communities of bacteria ( Branda et al., 2001; Kearns et al., 2005; Granek and Magwene, 2010). Observation under the scanning electron microscope, indeed, revealed a rough surface formed by microspheres of pyrite, attributable to original bacterial bodies. The only known comparable structures are the “discs of pyrite in coal” described by Southam et al. (2001) as an example of fossilized bacterial colonies.

Figures

FIGURE 3. Simpler cololites (intestinelite group) from Bargiano section. 1., 7. Typical irregular elongated mass (CT02), produced by different helicoidal swirls, Bargiano section, in lateral view (1) and backside view (7). Arrows indicate the occurrence of longitudinal striae. 2. Mass (CT03) with bulges (rognons). 3. Holotype of Ambergrisichnus alleronae (CT01), showing converging striae in the left apex (arrow) and enlargement at the other apex. 4. Characteristic helicoidal arrangement and rings with different colours (CT04). 5-6. Side view (5) and front view (6) of rings (CT04), (modified after Baldanza et al., 2013). 8-9. Modern examples of ambergris masses with concentric rings and changes in colour, comparable to study specimens (arrow in 8 indicates a squid beak).

FIGURE 4. Complex cololites (intestinelite group), Bargiano section. 1., 4. Hummock-like cololite (n 8 in Figure 2.2), 50 cm high and 80 cm wide, with a concave, irregular center and outer sub-circular to elliptical tunnels (1). Disaggregated portions (4) reveal both striae and concentric structure. 2. Hummock-like cololite (n 12 in Figure 2.2) formed by an accumulation of irregular, elongated slabs. 3. Complex hummock-like structure (n 15 in Figure 2.2) with irregular, meandering tunnels disposed at various levels. 5. Isolated linear cololite (n 25 in Figure 2.2), 20 cm in diameter, partially emerging from clay deposits. 6. Irregular, 60 cm long linear cololite (n 11 in Figure 2.2), showing spiral coiling at the right side.

FIGURE 5. Squid beaks from structure n 8 (Figure 2.2). Part of a lower beak (1) and longitudinal section of a beak (2), emerging from the rough surface of rock sample. 3-4. Microscopic features of squid beaks inside cololites (structure n 12, Figure 2.2). Crystals and framboids of pyrite (4), scattered into the micropeloidal matrix with dolomite microcrystals are also visible (1 and 4 are modified after Baldanza et al., 2013).

FIGURE 6. XRPD patterns (1) and mass changes in thermogravimetric analysis (2) of five cololite samples. Numbers of samples correspond to the structure of provenance (Figure 2.2).

FIGURE 7. 1, 3-8. Transmitted light photomicrographs of petrographic thin sections of the Bargiano cololites. 1. Interior of cololite (structure n 12) showing a micropeloidal matrix crossed by long chains of pyrite microgranules. 2. Beggiatoa specimens, sulphur large bacteria, single free-living filament with sulphur inclusion. 3. Detail of fossil Beggiatoa-like filaments from structure n 12. 4. Subspherical, red-brownish micromasses of pyrite (or sulphur), surrounded by a grey “halo” that inglobates all. To note the micropeloidal matrix. This structure may be comparable with large Thioploca cells. 5-7. Benthic foraminifera, partially and/or totally filled by bacteria-induced microcrystals of pyrite. 8. Pyrite framboids from structure n. 12. 9-10. SEM images of cololite internal fragments.The both surfaces are fresh, no acid attack was made. 9. Rosette structures made of dolomite microcrystals, and scattered single spherical cells referable to bacteria. In the centre, mica crystals with typical shape. 10. Dolomite crystals with well-developed orthorhombic shape (at central right), sparse spherical cells of bacteria, and a quartz crystal. Dolomite crystals (left) are aggregated to form a compact mass. 11-13. Bacteria-induced pyritization (sun-like pyrite discs). 11. Stereomicrophotograph of a large pyrite disc (about 1.5 cm in diameter). 12. SEM image of disc surface (particular), showing a large amount of spherical cells, progressively smaller form center to periphery. This arrangement is associated to bacteria colonies. 13. Small pyrite disc, yellow/orange, with elliptical to dumb bell shaped bacteria bodies arranged in a short chain.