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Fig. 10 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 10. Contours of all the ellesmeroceratid nautiloid conchs (interpreted below as Ruthenoceras elongatum Korde, 1949) from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia, superimposed on the most complete specimen ZPAL N. IV/4 (Fig. 5A).

Fig. 9 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 9. Apical parts of ellesmeroceratid nautiloid conchs (interpreted below as Ruthenoceras elongatum Korde, 1949) from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia. A, B. ZPAL N. IV/11 and 117, respectively; conchs with low expansion rate rate in lateral (A1, B1) and dorsal (A2, B2) views. C–E. ZPAL N. IV/103, 18, and 114, respectively; conchs with high expansion rate rate in lateral (C1, D, E2), ventral (C2), and dorsal (E1) views.

Fig. 6 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 6. Suture lines of ellesmeroceratid nautiloids from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia. A–H. ZPAL N. IV/109, 111, 10, 27, 56, 51, 48, and 9, respectively. Scale bars 2 mm.

Fig. 1 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 1. Loose block No. 1 of a stromatolitic limestone with abundant nautiloid conchs of the Ust-kut Formation (latest Furongian or earliest Tremadocian) found on the left bank of the Angara River at the former village Pashino. A. The block partially exploited for fossils. B. Stromatolite columns with empty cavities and a laminar cover above. C. A piece of the rock with exposed nautiloids. D. Polished rock surface (note similarity of the specimen in the middle to the holotype of Ruthenoceras elongatum Korde, 1949). E. Naturally abraded upper surface of the stromatolite columns.

Fig. 12 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 12. Relationships between the basic conch geometry aspects of ellesmeroceratid nautiloids from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia. A. With an increase of septum depth its obliquity increases even stronger but the correlation is rather loose. B. If non-linear correspondence to ontogeny of these phragmocone aspects is ignored, the pattern of variability appears roughly unimodal. C–E. Also the distribution of indices of the living chamber elongation, septum inclination and depth does not reveal any multimodality. The regression lines in A and B are intuitive (drawn by hand and not computed) because only one dimension (aperture height) is measurable in smallest conchs.

Fig. 11 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 11. Ontogenetic change of conch geometry aspects of ellesmeroceratid nautiloids from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia. Aperture height is used as a measure of an individual age. A–C. Characters with linear growth pattern. D–G. Characters with non-linear growth pattern. The regression lines are intuitive (drawn by hand and not computed) because only one dimension (aperture height) is measurable in smallest conchs.

Fig. 7 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 7. Medial sections of ellesmeroceratid nautiloids interpreted below as Ruthenoceras elongatum Korde, 1949, from sample Ang-4, block No. 1, probably latest Furongian Ust-kut Formation found at Pashino on the Angara River, Siberia, Russia. A, B. Mature phragmocones with moderately oblique septa, ZPAL N. IV/14 and 15, respectively. C. Almost complete juvenile phragmocone ZPAL N. IV/92 showing extend of diaphragms in the siphuncle. D–G. Apical parts of phragmocones (not strictly medial sections), ZPAL N. IV/115, 118, 121, and 125, respectively. H. Mature phragmocone ZPAL N. IV/16 with extremely oblique septa. I. Straight part of the phragmocone ZPAL N. IV/17 with oblique diaphragms. Wet ground surfaces (A1, B, C1, D–G, H1, I) and acetate peels (A2, C2, H2).

Fig. 2 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 2. Exposure of the source strata for the blocks with nautiloids found a few kilometers upstream the Angara River. A. Transition from the Ust-kut to Iya Formation. B. Top of the limestone succession of the Ust-kut Formation. C. Columnar stromatolite and limestone of the Ust-kut Formation. D. Field sketch of the section showing position of conodont samples and probable correspondence between the strata exposed and the loose blocks.

Fig. 3 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 3. Conodonts from the probably latest Furongian Ust-kut Formation from the exposure at Pashino on the Angara River, Siberia, Russia, samples Ang-4, block No. 1 (A–E; Fig. 1) and Ang-1, topmost limestone layer (F–N; Fig. 2B). A, K–N. Utahconus(?) eurypterus (Abaimova, 1971), ZPAL N. IV/163, 168, 169, 170, and 172, respectively. B–J. Laurentoscandodus triangularis (Furnish, 1938), ZPAL N. IV/165, 166, 167, 173, 174, 175, 177, and 176, respectively; in posterior views, except for medial view in L1 and occlusals view in M1 and N2. Tentative identification of elements locations indicated S, S0, M, P.

Fig. 4 in Variability of conch morphology in a cephalopod species from the Cambrian to Ordovician transition strata of Siberia

Fig. 4. Benthic bellerophontid and monoplacophoran molluscs from the probably latest Furongian Ust-kut Formation from the exposure at Pashino on the Angara River, Siberia, Russia; samples Ang-4, block No. 1 (A, B, D) and Ang-1, topmost limestone bed (C, E–I). A, B. Sinuitopsis sp. nov., ZPAL N. IV/154 and 155, in external (A1, B1) and lateral (A2, B2) views. C. Bellerophontid gen. et sp. nov. ZPAL N. IV/156, in lateral (C1) and external (C2) views. D. Hypseloconid ZPAL N. IV/157, in anterior (D1) and lateral (D2) views. E. Monoplacophoran? ZPAL N. IV/158, in dorsal (E1) and lateral (E2) views. F–I. Phosphatised conchs of juvenile individuals probably representing the same species as that on C; ZPAL NIV/162, 161, 160, and 159, respectively, in lateral (F1, H, and I) and apertural (F2, G) views.

Fig. 10 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 10. Model showing the shell orientation (φ) attained during neutral buoyancy for Maorites seymourianus models. White circle, center of buoyancy; asterisk, center of mass.

Fig. 9. A in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 9. A. Comparison of the model geometry for Maorites seymourianus defined by the Equation 3, and the closest logarithmic spiral (dotted line) found for these data (radius r = 88.97e-0.12Θ, determination coefficient R2 = 0.988). B. Close up of the initial whorls showing the slow increase in growth rate at the beginning of the ontogeny. The arrows indicate the differences in growth between the polynomial curve (solid arrows) and the logarithmic curve (dashed arrows).

Fig. 7 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 7. The final simplified model of the conch of Maorites seymourianus. A. External elements of the conch in lateral view, the smooth areas emulate rectiradiate constrictions; the phragmocone in dark gray, the body chamber in grey. B. Internal elements within the phragmocone; the siphuncle in black, the septa in grey.

Fig. 3 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 3. Example of the alignment process using only two specimens. Here it is graphed the radius against the angle showing the curves that describe the geometry of two specimens of Maorites seymourianus. A. The geometry of CPBA 16847 (reference) is defined by a function r = h(Θ) and its domain is [0 rad; 19.90 rad] in black (solid line), the geometry of CPBA 16838 is defined by a function r = i(Θ) and its domain is [0 rad; 20.42 rad] in grey. The normalization process consists of finding the results for an appropriate radius, in this case r = 20 mm (dotted line). Following, the difference in angle must be calculated (ΔΘ = 1.38 rad) and then the domain of the functions is adjusted accordingly. B. Curves after normalization, the difference in angle was applied to the domain of CPBA 16838, the new domain of the function is [1.38 rad; 21.80 rad]. Abbreviations: Θ, angle; r, radius.

Fig. 4 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 4. Overview of the segment employed in this modeling method. A. Adoral view of the segment, the contour and measurements for this side were obtained from the CT-scan data. B. Lateral view of the segment showing the segment thickness (sgt = 10 mm). C. Adapical view of the segment. To model this side, the adoral contour was duplicated and then escalated according to the results from the equations in Table 1. Abbreviations: a, result for the angle in the adoral side for Equation (2); ah, aperture height; ad, adpical; ao, adoral; b, result for the angle in the adapical side for Equation (2); r, radius; sgt, segment thickness; wh, whorl height; ww, whorl width.

Fig. 6 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 6. Illustrations showing the function of the relative offset and object offset. In this case, the object offset is a cube rotated in the y-axis. Segments are labeled in order of appearance. Note how each segment follows the transformation of the object offset. A. The relative offset has been modified to show each segment as a separate object. B. The relative offset with the correct value forming a unified structure.

Fig. 2 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 2. Semi-landmarks in π/6 rad steps (30°) and the model curve of the geometry for Maorites seymourianus (CPBA 16847). The first landmark is expressed in polar coordinates (r; Θ). Abbreviations: Θ, angle; r, radius.

Fig. 5 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 5. Final segment in two views showing the rectiradiate ribs and the two surfaces emulating the limits of the shell wall. The external layer in black and the internal layer in grey.

Fig. 1 in Virtual 3D modeling of the ammonoid conch to study its hydrostatic properties

Fig. 1. Kossmaticeratid ammonoid Maorites seymourianus (Kilian and Reboul, 1909) from the López de Bertodano Formation, Upper Cretaceous of Antarctica. A. CPBA 16819 (microconch), lateral (A1), ventral (A2) views, scheme of apertural view (A3). B. CPBA 16841 (macroconch) showing different preservation states between the flanks, left (B1), right (B2) views. The arrowheads indicate the beginning of the body chamber.