Armigatus carrenoae, Alvarado-Ortega & Than-Marchese & Melgarejo-Damián, 2020

Alvarado-Ortega, Jesús, Than-Marchese, Bruno Andrés & Melgarejo-Damián, Pilar, 2020, On the Albian occurrence of Armigatus (Teleostei, Clupeomorpha) in America, a new species from the Tlayúa Lagerstätte, Mexico, Palaeontologia Electronica (a 52) 23 (3), pp. 1-30 : 5-16

Armigatus carrenoae sp. nov.

( Figures 3-10 ; Table 1)

zoobank.org/ 3FE49A65-4103-407E-AA74-80E201FAE866

Holotype. Specimen IGM 11536 , complete skeleton from the level Zone XX ( Figure 3 ).

Paratypes. IGM 11537 , complete skeleton from unknown level ( Figure 4A ) . IGM 11538 , complete skeleton from unknown level ( Figure 4B ) . IGM 11539 , complete skeleton from known level Zone X . IGM 11540 , complete skeleton from known level Zone XIII ( Figure 7 ) . IGM 11541 , complete skeleton from unknown level ( Figure 4C ) . IGM 11542 , complete fish from known level Zone XV . IGM 11543 , resin-transferred incomplete skeleton from known level Zone XVII .

Range. 103 to 100.5 Ma, middle to late Albian ( Benammi et al., 2006).

Occurrence. Marine laminar limestones of the Middle Member of Tlayúa Formation, exposed in Tlayúa quarry ( Figure 1 ), near Tepexi de Rodríguez town, Puebla, Mexico (Applegate, 1987; Cantú-Chapa, 1987; Pantoja-Alor,1992; among others).

Etymology. The species name honors our colleague, Ana Luisa Carreño, for her valuable contributions to geology and paleontology of the Baja California Peninsula. The combination of the genus and species names mean “Carreño’s armored fish.”

Diagnosis. This is a deep-bodied Armigatus species in which the larger specimen known displays a maximum standard length (SL) of about 64.2 mm; this species differs from other species of Armigatus by the following combination of characters: the maximum body height is around 50.4 (47.1-53.8) % of SL; the head length represents about 37.9 (35.8-40.2) % of SL; the dorsal fin is relatively small, consists of 11 (rarely 12) dorsal rays, originates at 56.7 (54.8-57.8) % of SL, and its length represents 16.1 (14.8-17.3) % of SL; the anal fin is longer than the dorsal fin, consists of 17 (rarely 15) rays, originates at 78.8 (76.7-81.4) % of SL, and is extended over 17.5 (16.5-18.9) % of SL; the pelvic fin base is opposed to the posterior half of the dorsal fin and is placed at 58.9 (56.8-60.4) % of SL; the frontal, parietal, and pterotic bones are ornamented with ridges wide and conspicuous; the basal region of the opercular surface is ornamented with shallow and straight ridges, projecting dorsally from the ventral edge; it vertebral column has about 34 (33-35) vertebrae, including 16 (15- 17) abdominals, 17 (15-17) caudals, and two urals; the dorsal and abdominal edge of the trunk show two series of smooth scutes, the predorsal series has eight scutes; the abdominal series consists of 23 (rarely 22) prepelvic scutes and six postpelvic scutes; the last predorsal scutes are subrectangular, larger than the anterior ones, and, bear a prominent posterior spine.

Description

General features and proportions. Table 1 summarizes the measurements and body proportions of the specimens described here as Armigatus carrenoae sp. nov. The overall body shape of this species resembles that of Armigatus brevissimus the type species of the genus. This high-bodied fish has a large triangular head, on average 37.9 % of SL (ranging between 35.8 and 40.2 %), that is about 1.3 times longer than high. The short mouth opens slightly upward, the lower jaw is articulated with the skull below the level of the middle of the orbit. The maximum body height is in the predorsal region of the trunk and represents 50.4 (47.1- 53.8) % of SL. The unpaired fins are in the posterior half of the body. The predorsal and preanal lengths are 56.7 (54.8-57.8) and 78.8 (76.7- 81.4) % of SL, respectively. The anal fin is posterior to and slightly longer than the dorsal fin (1.08 times). The pelvic fin is placed in opposition to the posterior half of the dorsal fin and rises at the beginning of the posterior half of the body length, at 58.9 (56.8-60.4) % of SL. The caudal peduncle is narrow and precedes a wide caudal fin that consists of two symmetrical caudal lobes that are approximately equal-sized.

Skull. The head is laterally preserved in all specimens referred to Armigatus carrenoae sp. nov. ( Figure 4 ). The skull is triangular, about 1.3 times longer than deep; its otic-occipital, orbital, and ethmoid sections are approximate of the same length. The frontal bones are roughly triangular, anteriorly sharp, and posteriorly wide; these form most of the skull roof. The posterior part of each frontal articulates the parietals posteriorly, the pterotic lateroposteriorly, and the dermosphenotic laterally. There are no interfrontal fontanelles. The parietals are large sub-square bones that meet each other along the midline, separating the supraoccipital from the frontals. The supraoccipital is a small bone that forms a delicate crest. The parietals entirely suture the frontals, epioccipital, and pterotic bones; therefore, there is no temporal foramen or the pre-epiotic fossa. The pterotic is a roughly rectangular bone on the lateral skull wall. There is no evidence of the recessus lateralis on lateral skull bones. The anterior part of the frontals, as well as the parietals and pterotics, are strongly ornamented with a reticular pattern of ankylosed sigmoid ridges that enclose the temporal and supraorbital canals. The parietals carry the supratemporal commissural sensory canal.

The orbitosphenoid has a ventral projection that protrudes into the orbit below the frontals. The pterosphenoid and basisphenoid bones form the posterior inner wall of the orbit. The orbital part of the parasphenoid is edentulous and bears an anteroventral elongated basipterygoid process. Behind its basipterygoid process, the postorbital part of the parasphenoid has the osteoglossid-like tooth patch with at least seven short and conical teeth with sharp tips ( Figure 7 ). The anterior tip of the parasphenoid bone sutures a smooth small bone here identified as the vomer.

The mesethmoid is a complex and unpaired bone posteriorly overlapped and articulated with the frontals ( Figure 5 ). IGM 11540 shows that in dorsal view the mesethmoid is a star-shaped bone, which has a rounded anterior process, two lateral processes projected anteroventrally, and a flat rear that is somewhat laterally expanded. Between the middle-anterior and each lateral-posterior process, there is a deep rounded depression that contains the articular facet for the maxilla and premaxilla. The tip of the lateral-posterior process has a slightly concave facet for the palatine head. The lateral ethmoid is a roughly rectangular bone that separates the nasal capsule from the orbit and is strongly attached to the anterodorsal edge of the parasphenoid and the inner ventral surface of the respective frontal. The nasal is a small tubular bone.

Upper jaw. This consists of four flat and thin bones: the premaxilla, maxilla, and two supramaxillae ( Figure 5 ). The maxilla is a saber-shaped bone with two sections; its anterior toothless section is a rod-like and slightly curved structure that occupies approximately 40 % of the anterior part of the bone and dorsally bears two short dorsal articular processes, the terminal mesethmoid processes and the palatine processes located in the middle. The toothed section of the maxilla is a curved spatulalike structure that has a middle thick bar extending for the full length of the bone, forming a noticeable bulge exposed on the labial surface. A row of small conical teeth occupies the entire ventral edge of the toothed section. These teeth are regular-sized, closely spaced, and have tips that curve slightly backward.

The premaxilla is sickle-shaped bone with a thick dorsal edge, in which the alveolar region is expanded, the ventral edge is slightly curved, and the anterior ascending process is small ( Figure 5 ). The premaxilla lies below the anterior half of the toothless section of the maxilla. A large part of the premaxillary labial surface is smooth; however, this surface shows numerous pores and a series of sinuous dorsoventral grooves near the alveolar bor- der. A single row of small conical teeth occupies the premaxillary alveolar border. These teeth have acute tips curved backward that become slightly smaller in posterior positions and are uniformly spaced, leaving empty inter-dental spaces.

Two laminar, elongated, and drop-shaped supramaxillae overlap the posterior section of the maxilla ( Figure 5 ). The anterior supramaxilla is smaller than the posterior one. The posterior supramaxilla is noticeably expanded, long, and almost reaches the anterior tip of the anterior supramaxilla. Sinuous wrinkles ornament the expanded sections of the supramaxillae.

Lower jaw. This consists of the dentary, anguloarticular, and retroarticular bones. The lower jaw is a triangular structure with a short ventral postarticular process, shallow symphyseal edge, and a smoothly convex ventral edge ( Figures 5 , 6 ). Here the alveolar edge is short, sinuous, and strongly tilted upward while the coronoid process is rounded but hardly distinguishable.

In labial view, the dentary is a triangular bone deeply forked posteriorly, in which the dorsal limb forms the coronoid process and extends backward along the dorsal edge of the retroarticular bone ( Figures 5 , 6 ). The ventral dentary limb is extended backward almost up to the base of the postarticular process. Below the posterior part of the alveolar border, the labial surface of the dentary shows a conspicuous, shallow, and oval depression for the attachment of the infralabial ligament or dento-maxillar ligament (i.e., Osse, 1969; Datovo and Vari, 2013). In this bone, a tooth row is present along the alveolar border. Dentary teeth resemble those of the premaxilla.

The anguloarticular bone occupies about the last third of the lower jaw, forms the bulk of the postarticular process, and forms the entire articular facet for the quadrate ( Figures 5 , 6 ). A small retroarticular occupies the ventral end of the postarticular process and does not participate in the articular facet for the quadrate. The articulation between the quadrate and lower jaw is exposed laterally. The mandibular sensory canal runs near the ventral border of the dentary and retroarticular bones and opens through small pores near the symphysis, four or five large pores in the dentary, and at least two pores in the anguloarticular.

Circumorbital bones. These flimsy and flat bones almost enclose the orbit ( Figure 5 ). Unfortunately, the circumorbitals are poorly preserved in referred specimens because these were strongly deformed or broken by the compression against the skull. These bones include a comparatively small oval antorbital bone that is higher than long and covers the lateral surface of the nasal capsule. An elongated supraorbital bone borders the anterodorsal orbital section. The dermosphenotic is an elongated subtriangular curved bone, expanded posteriorly, which borders the posterodorsal orbital region. At least five infraorbitals are present; the first two are elongated and border the ventral orbital section while infraorbitals 3-5 are somewhat rectangular and form the posterior border of this cavity. The infraorbital sensory canal runs alongside the orbital edges of the infraorbital bones and opens through some inconspicuous and scattered pores. The orbit is occupied by a couple of large flat wedge-shaped sclerotic bones.

Suspensorium. Bones of the suspensorium are only partially exposed ( Figures 5 , 6 ). The hyomandibular is a hatchet-like bone with a single stout head and a narrow long ventral shaft bearing a posterior opercular process that is poorly developed. The quadrate is a flat triangular bone placed beneath the anterior half of the orbit and has a stout articular head inclined forward and downward. The posterior process of the quadrate is thin and slightly dorsally expanded. The symplectic is a stake-shaped bone that is tilted backward and higher than the quadrate.

The metapterygoid is roughly triangular, and its lingual surface seems to be toothless. The ectopterygoid is gracile and boomerang-shaped, in which the vertical and horizontal limbs form an obtuse angle of about 100°. The ectopterygoid meets the ventral border of endopterygoid and the anterior edge of the quadrate. In the holotype, the ectopterygoid bears a patch of small teeth ( Figure 5 ). The endopterygoid is an oblong and flat bone that bears numerous short conical teeth of regular size. The palatine is a robust bone medially expanded and posteriorly pointed. The palatine head is small, stout, and joins with the lateral-posterior process of the mesethmoid and the posterior maxillary palatine facet ( Figures 5 , 6 ).

Opercular bones. The opercle is a flat kidneyshaped bone, higher than long, in which the anterior edge is straight and thickened. The hyomandibular facet is located near the anterior edge and at the beginning of the upper quarter of the opercular height. This bone is superficially smooth except for its basal quarter that is covered with shallow, straight, and parallel grooves of uneven height and uniformly spaced, which extend from the ventral edge. The subopercle is a flat, semicircular, smooth, and dorsally straight bone with a sharp anterior ascending process that is extended along the ventral edge of the opercle.

The preopercle is a flat and inverted L-shaped bone with smooth edges, in which the vertical limb height is twice the horizontal limb length ( Figure 5 ). The dorsal tip of this bone reaches the opercular dorsal edge. The preopercular sensory canal runs close to the anterior edge of its vertical limb and dorsal edge of its horizontal limbs; around the commissure of these limbs, this sensory canal shows four to seven wide and sinuous branches. The interopercle is a flat, smooth, and spatula-shaped bone.

Branchiostegal rays and branchial arch. In the available specimens, the branchial arch elements known are partially covered ( Figures 5 , 6 ). The hypohyals are thick, flat, and smooth rectangular bones; the dorsal hypohyal is slightly higher than long while the ventral hypohyal is about twice higher than long.

The anterior ceratohyal is rectangular, about twice longer than high, centrally pierced by a large beryciform foramen, and has a horizontal groove for the afferent hyoidean artery. The posterior ceratohyal is flat, semicircular with the anterior edge straight and centrally pierced by an elongated small foramen. The urohyal is a complex elongated bone with an anterior small and massive head, a basal flat wing that is laterally expanded, and a central flange upward expanded. There are 10 or 11 flat blade-like branchiostegal rays.

Bones of the branchial series are largely covered by more superficial bones. Despite this situation, in IGM 11537, the anterior part of the basihyal bone is exposed showing a noticeable dorsal patch of numerous, small, and conical teeth ( Figure 6 ).

Axial skeleton. The vertebral column consists of 33 to 35 total centra, including 15-17 abdominals, 15-17 preurals, and two urals ( Figure 8 , Table 1). All centra are constricted in the middle and superficially sculpted with longitudinal cavities. The abdominal and anterior caudal centra are slightly higher than long; beyond, the middle caudal centra become longer than high, being in the most extreme cases about 1.25 times longer than high. The posterior preural centra and both urals tend to be smaller. The intervertebral surfaces of centra are concave and pierced by a small notochordal foramen.

The anterior abdominal centra have hypertrophied neural arches consisting of unfused hemiarches that are rounded and slightly expanded that fit into the dorsolateral cavity of the respective centrum; therefore, there are bifid neural spines on each of these abdominal centra. Posteriorly, the neural arches are tightly attached or perhaps fused with the centra, are progressively less high, and have a single neural spine. All caudal centra are fused with the respective neural and hemal arches that carry a single neural and hemal spine. In IGM 11536, the arch of preural centrum 4 has two spines, one in front of another ( Figure 8 ).

The abdominal cavity is almost entirely enclosed by 14 or 15 pairs of long curved ribs ( Figure 8 ). Two-thirds of these ribs have expanded heads to articulate with the ventrolateral cavities of the respective abdominal centra. The other ribs have expanded heads to articulate with the parapophyses developed in the anterior part of the most posterior eight abdominal centra. The sizes of the parapophyses increase in anterior to posterior order. There are six stick-like and slightly curved predorsals located between the occiput and the dorsal pterygiophores. In these bones, there is an anterior laminar extension that tends to be reduced in larger specimens.

Long and flat epineural bones are associated with all the neural arches and spines except for those of the preurals 1 to 3. In the abdominal region, the epineurals have anterior tips forked, are very thin, curved upward, and as long as five to six centra. In the anterior caudal centra, the epineurals are comparatively stouter, shorter, and exhibit a peculiar Y-shape, in which the three radiating limbs are equally long and those projected forward form an acute anterior angle. In the posterior caudal centra, the epineurals are parallel with the vertebral column and comparatively broader and shorter. Parapophyses of the abdominal centra and the neural arches and spines of the caudal centra, except for the last three preurals, are associated with long flat epipleurals. The shapes and sizes of the epipleurals are mirrored symmetrically to those of the epineurals above. There are no epicentral bones.

Pectoral girdle and fins. The posttemporal is a flat, oval, and long bone that has an elongated and thin rectangular dorsal process and an expanded ventral process ( Figure 5 ). The posterior ventral edge of this bone is crenulated. In comparison with the posttemporal, the ovoidal extrascapular bone is small.

The supracleithrum is flat, subrectangular, slightly curved, and rests on the dorsal limb of the cleithrum ( Figures 5 , 6 ). In lateral view, the cleithrum is an S-shaped structure, in which the extremely short horizontal middle region separates the high posterior vertical limb from the relatively low anterior vertical limb. Posterior to the anterior vertical limb of the cleithrum, parts of the coracoid and the scapula are exposed. Two long, ovoidal, and flat postcleithra are present; the ventral one has a narrow ventral end.

At least five radials are inserted between the scapular and the pectoral fin rays; these are short and rod-like bones with both extremes rounded and expanded. The pectoral fin consists of a series of 15 distally branched and segmented rays ( Figure 6 ), in which the first ray is as long as seven abdominal centra and almost covers the distance between the pectoral and the pelvic fins. Other pectoral rays become shorter.

Pelvic girdle and fins. This small fin is opposed to the anterior half of the dorsal fin and consists of five to seven distally branched and segmented rays that are extended backward beneath the sixth and seventh abdominal centra. The pelvic girdle consists of two unfused elongated triangular pelvic bones that lie beneath three abdominal centra, have sharp anterior tips, and are about twice longer than wide ( Figure 8 ).

Dorsal fin. This short triangular fin originates just behind the middle of the body and extends above eight abdominal centra. This fin consists of two procurrent rays plus 11 to 13 rays. The fourth dorsal ray is the longest ( Figure 8 ).

A series of 11 to 12 rod-like proximal pterygiophores support the dorsal fin. These have expanded articular heads. Among these bones, the anterior six have anterior and posterior laminar wings. Some elongated dorsal middle pterygiophores and rounded dorsal distal pterygiophores are exposed in the dorsal fin of the referred specimens. A short hook-like dorsal fin stay is present at the end of the dorsal fin support.

Anal fin. This long triangular fin lies beyond the dorsal fin and its base equals the length of 9-10 caudal centra ( Figure 8 ). This fin consists of two small procurrent rays plus 15-17 elongated rays. The fourth anal fin ray is the longest. A series of 16 to 18 proximal pterygiophores supports this fin. These rod-like pterygiophores occupy the interhemal spaces and show articular heads anterior and posteriorly expanded. Inconspicuous anterior and posterior laminar wings are present in the anterior two or three proximal pterygiophores. Some rounded middle or distal pterygiophores are preserved. A short and stout anal fin stay is present at the end of the fin support.

Caudal fin. The hemal and neural spines of preurals 1-3 are thick and tilted backward supporting the caudal fin ( Figure 9 ). This fin is deeply forked and has two elongated triangular lobes preceded by a single large drop-shaped caudal scute. The ventral caudal lobe is slightly longer than the dorsal one. The caudal formula is x+I+9—8+I+ix. The proximal ends of the principal rays are acute except for the inner rays of both lobes that rest on the hypurals 2-4, whose proximal ends are slightly branched and expanded.

The parhypural is thick, wide, and fused with the preural 1. The neural arch of preural 1 is triangular and shorter than the anterior neural spines. The ural centrum 1 has a small neural arch. There are three stout, rod-like, and equally long epurals. Ural centrum 1 is slightly larger than ural centrum 2; the first is in contact with the anterior tip of hypural 1 and fused with hypural 2 whereas the ural centrum 2 bears the hypurals 3 to 6. There are six hypurals, the first is triangular and the wider in the series; others are rectangular and progressively smaller except for the hypurals 3 and 4 that are fused forming a triangular hypural plate. There is no caudal diastema or space between the hypural 2 and hypural 3. There are no urodermals. Three uroneurals cover the dorsal surface of preural 1 and both ural centra. Uroneural 1 is the longest in the series, somewhat curved, and anteriorly expanded. The distal tip of uroneural 2 reaches the distal tip of uroneural 1. Uroneural 3 is the smallest in the series and rests near the distal ends of uroneurals 1 and 2.

Scales and scutes. The entire trunk is covered with oval cycloid scales, higher than long, ornamented with numerous concentric circulli. Unfortunately, it is not possible to know the number of scale rows and the existence of the lateral line. The predorsal and abdominal borders of the trunk are armored with scutes ( Figure 10 ).

The predorsal scute series consists of eight scutes that lay over the posteriormost three predorsal bones and covers the posterior half of the predorsal edge of the body, near the dorsal fin base. Each predorsal scute rests on the anterior part of the successive one. The size and shape of these scutes change along the series; the anterior ones are small and oval while the posteriors become larger and subtriangular because they are laterally expanded. All predorsal scutes have a thick longitudinal middle keel; however, in the posteriormost ones, the keel is hypertrophied and forms a stout posterior spine. These scutes are superficially ornamented with a few inconspicuous sinuous ridges.

The abdominal scute series borders the ventral edge of the trunk, between the isthmus and the anus ( Figures 3 , 8 ). The series consists of 22 to 23 scutes, including 16 to 17 prepelvics and six postpelvics. Overall, these smooth scutes have a triangular wing extended over each abdominal side, an anterior rounded tip, and an acute posterior projection; the posterior tip of one scute covers the anterior tip of the subsequent posterior one. These scutes also have a thick anteroposterior middle keel, which becomes a spine in the postpelvic scutes. The lateral wings of these scutes change along the series; in the middle, the ventral quarter of the abdominal cavity is covered by the largest lateral wings, anterior and posteriorly the wings of remaining scutes are progressively smaller.

Soft tissues and gut contents. As it occurs in other fossil fishes of Tlayúa reported by Alvaradostandard length (SL).

Ortega et al. (2007); the specimens studied here have phosphatized masses forming whitish and soapy patches preserved in different parts of the body. These patches have a null reaction in acid solutions and under UV light are faint pink in color. In the trunk, these patches, mainly at the back and base of the unpaired fins, are muscle tissues. Beneath the opercular bones, there are phosphatized gill rakers and filaments. And into the abdominal cavity, these phosphatized materials form bumps along the digestive tract, from the back of the pelvic girdle to the anus. The abdominal cavity of IGM 11541 preserves isolated bones and the pelvic fins of a small fish. Although it is impossible to identify the species of such a swallowed fish; this observation demonstrates that Armigatus carrenoae sp. nov. fed on smaller fishes.

Figures

FIGURE 1. Specimen IGM 11532, Armigatus brevissimus from the Cenomanian shallow marine deposits of Hekel, Lebanon, coated with magnesium smoke.

FIGURE 3. IGM 11536, holotype of Armigatus carrenoae sp. nov. from the Albian deposits of Tlayúa lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico. A, photograph of the complete specimen under UV light. B, idealized drawing of the same specimen.

FIGURE 4. Paratypes of Armigatus carrenoae sp. nov. from Albian deposits of Tlayúa lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico, photographed under UV light. A, IGM 11537. B, IGM 11538. C, IGM 11540.

FIGURE 5. Head of Armigatus carrenoae sp. nov. from the Albian deposits of Tlayúa lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico. A, Closeup of IGM 11538, coated with magnesium smoke and photographed under white light. B, idealized and simplified drawing of A. Abbreviations: aa, anguloarticular; ao, antorbital; br, branchiostegal ray; cl, cleithrum; ddml depression for the dento-maxillar ligament; den, dentary; dsph, dermosphenotic; ect, ectopterygoid; ent, endopterygoid; epo, epioccipital; epn, epineurals; ext, extrascapular; fr, frontal; hm, hyomandibular; io, infraorbital; iop, interopercle; le, lateral ethmoid; mes, mesethmoid; mp, metapterygoid; mx, maxilla; na, nasal; naac, neural arches + spines of abdominal centrum; op, opercle; os, orbitosphenoid; os, orbitosphenoid; pa, parietal; pal, palatine; pcl, postcleithrum; pd, predorsal; pfr, pectoral fin ray; pop, preopercle; prvas, prepelvic abdominal scutes; psp, parasphenoid; pto, pterotic; pts, pterosphenoid; ptt, posttemporal; q, quadrate; r, rib; rar, retroarticular; sc, sclerotic; scl, supracleithrum; smx, supramaxilla; soc, supraoccipital; sop, subopercle; suo, supraorbital; dark arrow shows the basipterygoid process of the parasphenoid bone; (l) and (r) indicates the left and right side.

FIGURE 6. Part of the pectoral girdle, lower jaw, branchial arch, and branchiostegal rays of Armigatus carrenoae sp. nov. from the Albian deposits of the Tlayúa lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico. A, closeup of the head of the paratype IGM 11537 under UV light. B, idealized and simplified drawing based on A. Abbreviations: aa, anguloarticular; ac, anterior ceratohyal; bh, basihyal; br, branchiostegal ray; cl, cleithrum; cor, coracoid; ddml depression for the dento-maxillar ligament; den, dentary; dh, dorsal hypohyal; iop, interopercle; pc, posterior ceratohyal; pcl, postcleithrum; pfr, pectoral fin ray; prvas, prepelvic abdominal scutes; q, quadrate; rar, retroarticular; rad, radial; sca, scapula; sop, subopercle; sy, symplectic; uh, urohyal; vh, ventral hypohyal.

FIGURE 7. Closeup of the postorbital region of IGM 11539 showing the osteoglossid-like tooth patch on the parasphenoid bone (black arrows). Abbreviations: hm, hyomandibular; mtp, metapterygoid; pop, preopercle; psp, parasphenoid.

FIGURE 8. Idealized and simplified drawing of the trunk and pelvic, anal, and dorsal fins of IGM 11536, holotype Armigatus carrenoae sp, nov. from the Albian deposits of Tlayúa lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico (based on Figure 3). Abbreviations: afr, anal fin ray; afs, anal fin stay; appt, anal proximal pterygiophore; dfr, dorsal fin ray; dfs, dorsal fin stay; dppt, proximal pterygiophores of dorsal fin; epl, epipleural; epn, epineural; hapu, hemal arch and spine of preural centrum; naac, neural arch of abdominal centrum; napu, neural arch and spine of preural centrum; napu4, preural centrum 4 with double neural spine; pd, predorsal bone; php, parhypural; prvas, prepelvic abdominal scute; ptvas, postpelvic abdominal scute; pvfr, pelvic fin ray; r, rib; u, ural centrum; numbers under centra indicate their position along the vertebral column.

FIGURE 9. The caudal skeleton of Armigatus carrenoae sp. nov. from the Tlayúa Lagerstätte, near Tepexi de Rodríguez, Puebla, Mexico. A, closeup of the caudal skeleton of IGM 11538 coated with magnesium smoke. B, idealized and simplified drawing of A. Abbreviations: afr, anal fin ray; cs, caudal scute; ep, epural; epl, epipleural; epn, epineural; hapu, hemal arch of preural centrum; hy, hypural; napu, neural arch of preural centrum; nau, neural arch of ural centrum; php, parhypural; prl, branched and segmented caudal fin ray of the lower lobe; prlI, unbranched caudal principal fin ray of the lower lobe; pru, branched and segmented caudal fin ray of the upper lobe; pruI, unbranched caudal principal fin ray of the upper lobe; pu, preural centrum; u, ural centrum; un, uroneural.

FIGURE 10. Predorsal scutes series of A. carrenoae sp. nov. from Tlayúa. A, closeup of the predorsal region of IGM 11536 (inverted for comparative purposes). B, closeup of predorsal region of IGM 11537. C, idealized drawing of B. Abbreviations: afr, anal fin ray; pd, predorsal bone; pds, predorsal scutes; dppt, dorsal proximal pterygiophore; upds, unmodified predorsal scales.