Figure 1.
A, Reconstruction of the hyolithid conch Joachimilites novaki [23] with proturding helens and in situ operculum. External (left) and internal (right) surfaces of operculum are detailed. l: ligula; h: helens; CaS: cardinal shield; r: rooflet; CoS: conical shield; cp: cardinal process; cl: clavicle; modified after [8], [56]. B, Reconstruction of the orthothecid conch Nephrotheca housina [23] with in situ operculum and detail of external (left) and internal (right) surfaces of operculum. p: process; lc: clavicle-like structure; modified after [23].
Figure 2.
A, Hyolithid specimen with three-dimensionally preserved digestive tract from Cambrian Stage 4 of northern Canada, reprinted from [30] under a CC BY license, with permission from Oxford University Press, original copyright 2003, and reconstruction of the simple U-shaped hyolithid digestive system. B, Specimen of the orthothecid Girvanolithes thraivensis [75] with three-dimensionally preserved digestive tract from the upper Ashgill of the Girvan district, Scotland, reprinted from [33] under a CC BY license, with permission from Paleontological Society original copyright 2003, and reconstruction of the partially folded U-shaped orthothecid digestive system.
Figure 3.
Geological features of the Montagne Noire.
A, Location of the Massif Central and the Montagne Noire in France. B, Structural sketch of the Montagne Noire, after [41], [46], [49]. C, Geological sketch of the Avène-Mendic parautochthon with location of the sections yielding hyolith with three-dimensionally preserved digestive tracts, after [41], [48], [49]. D- Litho- and chronostratigraphic setting of the Avène-Mendic parautochthon, after [41].
Figure 4.
Conotheca subcurvata[38].
A-C, USTL1264/3; phosphatic internal mould; A- Lateral view; B, Oblique view of the circular aperture; C, Oblique view of the blunt apex. D, USTL1210/9, Lateral view of internal mould. E, USTL2786/5, lateral view of internal coating of conch with phosphatised guts visible. F-H, USTL2785/5; F, Lateral view of internal coating of conch with phosphatised guts visible, squared area magnified in G; G, Detail of blunt apex; H, Oblique apical view of blunt apex. I-M, USTL2786/1; I, Lateral view of internal coating of conch with coating of operculum and preserved guts, squared area magnified in L; J, Oblique lateral view, showing the lateral continuity of conch coating (right-hand side), squared area magnified in M; K, Detail of junction of operculum and conch coatings; L, Detail of operculum coating and folded digestive tract; M, Detail of coating-imprint of operculum external surface. Scale bars are: G, K, 100 µm; B, C, H, L, M, 200 µm; A, D, E, F, I, J, 500 µm.
Figure 5.
Conotheca subcurvata[38].
A-C, USTL1251/13; A, Lateral view of broken internal coating of conch with preserved digestive tract; B, Oblique apertural view with internal surface of phosphatic coating of operculum visible, squared area magnified in C and orientation of D arrowed; C, Detail of proximal round extremity of the phosphatised gut; D, Inner coating of the conical conch by lining biofilms made of amalgamated coccoids. E-F, USTL2785/3, apertural phosphatic exterior compartment with coating of operculum inner surface; E, Oblique lateral view; F, Internal view. G, USTL2783/4, lateral view with detail of junction of operculum and conch coatings. H-K, USTL2782/13; H, Coating of operculum external surface, squared area magnified in I; I, Detail of radially ornamented embryonic part of the operculum coating; J, Oblique lateral view of operculum external surface coating and proximal compartment with coccoidal phosphate filling; K, Lateral view of transition between withdrawn operculum and proximal compartment with coccoidal phosphate filling, filaments on operculum external surface. Scale bars are: D, 10 µm; C, I-K, 100 µm; E, F, H, 200 µm; A, B, G, 500 µm.
Figure 6.
Conotheca subcurvata[38].
A, USTL2782/11; Lateral view showing incompletely preserved guts and external coating of withdrawn operculum. B, USTL2782/3; Lateral view of specimen with different microbial pseudomorphs in the internal and external compartments and overgrowth. C-D, USTL2782/2; C, Lateral view, squared area magnified in D; D, Detail of the preservation of the digestive tract and filamentary junction with mould (arrow), the filaments seem to cover or invade the pre-existing mould. E-F, USTL2788/7; E, Lateral view, squared area magnified in F; F. Detail of Large coccoids covering the intestine cast and preserved withdrawn operculum. G, USTL2788/8; Lateral view of conch, exogenous material (tube) in the exterior compartment arrowed. H, USTL2784/2; Detail of exogenous material (halkierid) within the conch. I-K, USTL2781/6; I, Lateral view, squared area magnified in K; J, Possible fungal hyphae (arrowed) in connection with intestine, in this case communication with exterior compartment; K, Detail of possible hyphae. L-M, USTL2789/2; L, Lateral view, squared area magnified in M; M, Intestine phosphatic meshwork denser than exterior compartment. N, USTL2789/3; Detail of relations between exterior and interior compartments and operculum. O-P, USTL2781/9; O, Lateral view, squared area magnified in P; P, Detail of diagenetic overgrowth of the intestine phosphatic cast. Scale bars are: P, 50 µm; F, H, K, N, 100 µm; D, J, M, 200 µm; A-C, E, G, I, L, O, 500 µm.
Figure 7.
Conotheca subcurvata[38].
A, USTL2784/1; Detail of distal section of digestive tract, gut content phosphatisation shows typical microbial mediation with filamentary pseudomorphs. B, USTL2784/5; Detail of section of digestive tract, gut content phosphatisation shows typical microbial mediation with filamentary pseudomorphs. Exogenous material (biogenic tube) in gut content arrowed. C, USTL2784/2; Detail of section of digestive tract with overgrown quartz inserted in the structure (arrowed). D, USTL2784/7; Detail of section of digestive tract showing quartz inserted within the structure. E-F, USTL2784/6; E, BSE image of section of digestive tract; F, Corresponding EDS analysis showing the occlusion of the porous gut by terrigenous material (mainly quartz and mica) cemented by apatite and calcite. G-H, USTL2784/7; G, BSE image of section of digestive tract; H, Corresponding EDS analysis showing terrigenous material as intraparticular infill subsequently cemented by apatite. Scale bars are: B-D, 50 µm; G, H, 60 µm; E, F, 80 µm; A, 100 µm. Al = chlorite, P = apatite, Ca = calcite, Si = quartz, Fe = pyrite.
Figure 8.
Conotheca subcurvata[38].
A-B, USTL2781/5; A, Lateral view of the conch with external surface of withdrawn operculum visible; B, Gut protruding out from a narrow gap between the withdrawn operculum and the conch internal coating. C-H, Specimens with intestine type 1 (gut and anal tube of the U-shape intestine straight or slightly undulating and parallel to each other); C, USTL2782/6; D, USTL2781/8; E, USTL2787/10; F-G, USTL2783/9; H, USTL2791. I-J, Specimens with intestine type 2 (straight anal tube and a portion of the gut loosely folded); I, USTL2785/1; J, USTL2787/11. K-S, Specimens with intestine type 3 (straight anal tube and a portion of the gut tightly folded into zigzags); K, USTL2786/2; L, USTL2783/2, squared area magnified in P; M, USTL2789/1, upper squared area magnified in Q and lower squared area magnified in R, N, USTL2790, squared area magnified in O; O-Q, Tightly folded portion of the gut; R, Detail of a cross-section of the gut; S, Detail of the upper cross-section in Q. Scale bars are: O, S, 50 µm; Q, R, 100 µm; C, P, 200 µm; A-B, D-N, 500 µm.
Figure 9.
Digestive tract type versus average apertural diameter (µm) based on 27 specimens of C. subcurvata.
Correlation coefficient: r = 0,62, coefficient of determination: r2 = 0,38 and p-value = 0,00057.
Figure 10.
Illustration of hypothetised heterochronic processes of intestine evolution in hyoliths.
a-c, based on the new data from the digestive tracts of C. subcurvata; d, from digestive tracts of Guduguwan from [9]; e, Orthotheca from [31]; f, Haplophrentis from [29], [30], [35], [36].