FIGURE 1. Map of the Tzimol-Comitán region showing the outcrops of the Angostura Formation (in green color) exploited at the Tzimol Quarry (red star), outside of the Ochuxhob town, Tzimol Municipality, Chiapas, southeastern (Based on Alvarado-Ortega et al., 2020, figure 1).
FIGURE 2. IGM 14027, holotype of Amakusaichthys benammii sp. nov. from the Tzimol Quarry, Chiapas, Mexico. A, part (IGM 14027a) of the specimen transferred to resin and observed under white light. B, the counterpart of the specimen (IGM 14027b) transferred to resin and observed under white light. C, X-ray image of IGM 14027b.
FIGURE 3. Dr. Mouloud Benammi (summer, 2024), Moroccan paleomagnestostratigrapher, to whom the specimen described in this manuscript is dedicated.
FIGURE 4. Some paratypes of Amakusaichthys benammii sp. nov. from the Tzimol Quarry, Chiapas, Mexico. A, IGM 14028a, a complete specimen. B, IGM 14029, close-up of the head.
Abbreviations: af, anal fin (origin); df, dorsal fin (origin).
FIGURE 5. Close-up of the left side of the skull of IGM 14027b, counterpart of the holotype of Amakusaichthys benammii sp. nov. transferred to resin and coated with magnesium.
Abbreviations: boc, basioccipital; bptp, basipterygoid process; bsc, basal sclerotic bone; bsp, basisphenoid; ect, ectopterygoid; epi, epioccipital; etpa, ethmopalatine; exo, exoccipital;exsc, extrascapular; fpf, frontoparietal fontanel; fr, frontal; int, intercalar; let, lateroethmoid; mlp, masticatory-like processes in the parasphenoid bone; mp, mesoparietal (=parietals fused); ors, orbitosphenoid; pas, parasphenoid; pto, pterotic; pts, pteroshpenoid; rode, rostrodermethmoid; soc, supraoccipital; sop, subopercle; sph, sphenotic; stt, supratemporal; suo, supraorbital.
FIGURE 6. Close-up of the skull of IGM 14030, paratype of Amakusaichthys benammii sp. nov. preserved in part and counterpart transferred to resin and coated with magnesium. A, dorsal view of the skull in IGM 14030a. B, Ventral view of the skull in IGM 14030b.
Abbreviations: boc, basioccipital; bptp, basipterygoid process; bsh, basisphenoid; ect, ectopterygoid; epi, epioccipital; etpa, ethmopalatine; exo, exoccipital; exsc, extrascapular; fpf, frontoparietal fontanel; fr, frontal; int, intercalar; let, lateroethmoid; mlp, masticatory-like processes in the parasphenoid bone; mp, mesoparietal (=parietals fused); ors, orbitosphenoid; pas, parasphenoid; pro, prootic; pto, pterotic; pts, pteroshpenoid; rode, rostrodermethmoid; soc, supraoccipital; sop, subopercle; sph, sphenotic; suet, supraethmoid; suo, supraorbital; vo, vomer; (l), paired bone of the left side; (r), paired bone of the right side.
FIGURE 7. Idealized skull reconstruction of Amakusaichthys benammii sp. nov., from Tzimol, Chiapas, Mexico. A, skull in lateral view. B, skull in in dorsal view. C, skull in ventral view. D, profile of the skull in lateral view showing the angles of parasphenoid inflection and inclination of the hyomandibular fossa. E, insolated parasphenoid bone in ventral view.
Abbreviations: amlp, masticatory-like processes in the parasphenoid bone; boc, basioccipital; bptp, basipterygoid process; bsh, basisphenoid; epi, epioccipital; etpa, ethmopalatine; exo, exoccipital; fetpa, articular facet of the ethmopalatine; fpf, frontoparietal fontanel; fr, frontal; hf, hyomandibular fossa; int, intercalar; let, lateroethmoid; mp, mesoparietal (=parietals fused); ors, orbitosphenoid; pahf, principal axis of the hyomandibular fossa; pas, parasphenoid; pro, proptic; pto, pterotic; pts, pteroshpenoid; rode, rostrodermethmoid; soc, supraoccipital; sph, sphenotic; suet, supraethmoid; vo, vomer.
FIGURE 8. Specimen IGM 14031, Amakusaichthys benammii sp. nov. paratype, from Tzimol, Chiapas, Mexico. A, close-up of the head. B, idealized line drawing based on A of bones of the opercular series, pectoral fin, and jaws (the lower jaw exposes its lingual surface). C, idealized line drawing based on B of the palatine and maxillae.
Abbreviations: ang, angular; art, articular; cha, ceratohyal anterior; den, dentary; exsc, extrascapular; io, infraorbital; iop, interopercle; middle triangular process (of the palatine); mx, maxilla; op, opercle; pal, palatine; paln, palatine notch; pop, preopercle; q, quadrate; rar, retroarticular; sc, sclerotic bone; sop, subopercle; (l), bones of the left side; (r), bones of the right side.
FIGURE 9. Head and anterior part of the trunk of IGM 14027b, the counterpart of the holotype of Amakusaichthys benammii sp. nov. from the Tzimol Quarry Chiapas, Mexico, transferred to resin and coated with magnesium.
Abbreviations: cl, cleithrum; cor, coracoid; ect, ectopterygoid; ent, entopterygoid; exsc, extrascapular; hy, hyomandibula; mcor, metacoracoid; mpt, metapterygoid; mx, maxilla; op, opercle; pal, palatine; pas, parasphenoid; pcfr, pectoral fin ray; pcsp, postcranial spines; pmx, premaxilla; pop, preopercle; q, quadrate; sca, scapula; sym, symplectic.
FIGURE 10. IGM 14034, paratype of Amakusaichthys benammii sp. nov., transferred to resin and coated with magnesium, showing a nearly articulated vertebral column and some associated bones. A, complete specimen. B, anterior abdominal centra with bifid neural spines. C, abdominal region in which the neural spines bifid change to normal or non-bifid neural spines. D, posterior caudal centra.
Abbreviations: numbers show the position of the centra in anterior to posterior order; a-cap-ssp, articulation between the callosal process of the neural spine and the dorsoanterior cavity of the saddle-shaped process; aha, autogenous hemal arch; ana, autogenous neural arch; bnsp, bifid neural spines; cap, callosal process; dna, disarticulated neural arch; epn, epineural; hspu, hemal spine of preural centrum; nsp, neural spine (non-bifid); nspu, neural spine of preural centrum; paro, parapophysis; pu, preural centrum; r, rib; ssp, saddle-shaped process; ssp, saddle-shaped processes of preural centrum.
FIGURE 11. Pelvic girdle (in ventral view) of Amakusaichthys benammii sp. nov. from the Campanian marine deposits of the Angostura Formation exploited in the Tzimol Quarry, Comitán Municipality, Chiapas, southeastern Mexico. A, IGM 14027a under white light. B, idealized line drawing of A.
Abbreviations: cp, central part of the pelvic bone; evw, external ventral wing; lp, lateral process; lw, lateral wing; mp, medial process; pvr, pelvic fin ray; rad, radian; (l), elements of the left side; (r), elements of the right side.
FIGURE 12. X-ray image of the unpaired fins preserved in IGM 14027b, holotype of Amakusaichthys benammii sp. nov. from the Campanian marine deposits of the Tzimol Quarry, Comitán, Chiapas, southeastern Mexico.
Abbreviations: ac, abdominal centrum; afr, anal fin ray; app, anal proximal pterygiophore; dfr, dorsal fin ray; dpp, dorsal proximal pterygiophore; pu, preural centrum; pvb, pelvic bone; pvfr, pelvic fin ray.
FIGURE 13. Caudal fin IGM 14027, holotype of Amakusaichthys benammii sp. nov. from the Campanian marine deposits of the Angostura Formation exploited in the Tzimol Quarry, Comitán Municipality, Chiapas, southeastern Mexico. A, part of the specimen (IGM 14027b) transferred to resin and observed under white light. B, idealized line drawing of A.
Abbreviations: bcfr, blanket-corner folded ridge of hypural 2; ep, epural; h, hypural; hspu, neural spine of preural centhrum; nspu, neural spine of preural centhrum; ph, parhypural; pu, preural centhrum; u, ural centhrum; un, uroneural; black arrows show principal fin ray in both dorsal and ventral caudal fin lobes.
FIGURE 14. Caudal fin of Amakusaichthys benammii sp. nov. from the Campanian marine deposits of the Angostura Formation exploited in the Tzimol Quarry, Comitán Municipality, Chiapas, southeastern Mexico. A, general view of IGM 14035, paratype of the specimen under white light with the anterior tips of the ventral caudal rays removed. B, close-up of A with some bones of the caudal skeleton are colored. C, close-up of the principal ray (in green) in the dorsal lobe of the caudal fin of IGM 14027b, under white light, showing the suture between its segments.
Abbreviations: h, hypural; nspu, neural spine of preural centhrum; ph, parhypural; ss, suture between the ray segments.
FIGURE 15. Scales of Amakusaichthys benammii sp. nov. from the Campanian marine deposits of the Angostura Formation exploited in the Tzimol Quarry, Comitán Municipality, Chiapas, southeastern Mexico. A, internal surface of an isolated scale from the dorsal trunk edge of IGM 14033a. B, external surface of imbricated scales in the lateral part of the trunk of IGM 14036.
FIGURE 16. Phylogenetic hypotheses of the Ichthyodectiformes including Amakusaichthys benammii sp. nov., showing the trees generated through 50% consensus and strict consensus criteria (see Appendix 1 for a complete description). The values expressed as X/Y in nodes B, R, S, and V show the bootstrap (above) and Bremmer (below) values obtained in the present study; in other nodes, these values are lower than 50% and 1, respectively.
