SYSTEMATIC PALEONTOLOGY

Material examined. FCMP 00/497, a complete and articulated fish from El Espinal quarry preserved as the impression of its left lateral side (Figure 3.1, 3.2).

Description. This is a drop-shaped and prognath fish with total length (TL) and standard length (SL) equal to 255 and 195 mm, respectively. The maximum body depth is about 58 % of SL. The head length is about 38 % of SL. The dorsal and anal fins rise at 64 and 70 % of SL, respectively. The pelvic fin is opposed to the origin of the dorsal fin (Figure 3.1).

The skull of this fish shows a well-defined parietal process and a dermocranial fenestra bordered by the frontal, parietal, and dermal supraoccipital bones (Figure 3.2). The details of both jaws are not well preserved; nevertheless, it is possible to notice two incisiform teeth in the premaxilla and another two in the anterior dentary end. Only some stout crushing teeth are preserved in the vomer and prearticular.

Regarding the criteria suggested by Poyato-Ariza and Wenz (2002, p. 118, figures 34, 36), the shape of the anal and dorsal fins of FCMP 00/497 is falcate [the rays (lepidotrichia sensu Poyato-Ariza and Wenz 2002), i.e., the prominent and triangular anterior sections of these fins are at least twice as long as the posterior ones], and the caudal fin shape is double emarginated (Figure 3.1).

The body of this fish is not covered by scales except in the area in front of the anal and dorsal fins (Figure 3.1). Three rows of flat, wide, and triangular-rhomboidal scales cover the ventral and middle part of the abdominal area, and probably four rows of stout bar-like scales cover the remaining abdominal area and all the area between the occiput and the dorsal fin. Some ridges ornament the external surfaces of the scales on the abdominal area.

Thirteen smooth and triangular dorsal ridge scales cover the anterior dorsal border of the body, between the occiput and the dorsal fin. These dorsal ridge scales, except the anterior one, are regular in size. The anterior one is about twice as large as the following posterior ones. Each of these scales shows a middle posterior sharp protuberance connected to a middle anterior notch of the next posterior scale. The maximum depth of the body is located just in the back of the occiput. The details of the ventral keel scales are obscured due their bad preservation.

Remarks. Poyato-Ariza and Wenz (2002) performed the last comprehensive review on the order Pycnodontiformes. Later Poyato-Ariza and Wenz (2004, 2005), Kriwet (2004), and Machado and Brito (2006) provided additional taxonomical information. The geologic range of this group is Triassic-Eocene, and it involves about 650 nominal species belonging to about 40 genera, 10 of which are based entirely on dental remains (Kriwet 2004). Diversity of Mexican pycnodontiforms includes numerous unnamed taxa from localities within Nuevo León, Coahuila, Hidalgo, San Luis Potosí, Puebla, and Chiapas (Applegate et al. 2004), as well as Guerrero (Garibay-Romero, personal commun., 2006).

Although the complete description of FCMP 00/497 is under preparation, in advance and based on a brief comparative analysis, it can be demonstrated that it represents a new form within the family Pycnodontidae. This fish shows the parietal process (Figure 3.2) that currently represents the only unambiguous synapomorphy of this family (Machado and Brito 2006). Table 1 summarizes comparative characters that support the singularity of FCMP 00/497. Among pycnodontids, the dermocraneal fenestra is present in Ocleodus Poyato-Ariza and Wenz 2002; Oropycnodus Poyato-Ariza and Wenz 2002; Pycnodus Agassiz 1833; Tepexichthys Applegate 1992; and Potiguara Machado and Brito 2006; as well as FCMP 00/497 (Figure 3.2). In all these nominal genera the body shape is either diamond or rhomboidal, but Pycnodus (Lambers 1991, figure 20.l) shows a similar drop-like body shape as FCMP 00/497. In drop-like pycnodonts, the dorsal fin is located behind the highest point of the dorsal outline [the dorsal apex sensu Poyato-Ariza and Wenz (2002)]; in contrast, in the other genera listed above, the dorsal fin originates just in this highest point of the body or dorsal apex. In FCMP 00/497 and Pycnodus, the dorsal border between the occiput and the dorsal fin is slightly curved and convex; whereas the diamond or rhomboidal pycnodonts have a remarkable dorsal apex forming an acute angle.

Regarding the ossification patterns of pycnodontiform scales described by Poyato-Ariza and Wenz (2004, character 64), it is possible to recognize that FCMP 00/497 and Pycnodus differ from other pycnodontids. In FCMP 00/497, as in Tepexichthys and Ocleodus, the abdominal area shows wide and flat scales (also named as complete ossified scales) and above them there are solid bar-like scales (or incomplete ossified scales) (Figure 3.1). In contrast, all the scales in Pycnodus and Oropycnodus are solid bar-like. In Potiguara the abdominal scales are unknown (Machado and Brito 2006)

Those 13 dorsal ridge scales found in FCMP 00/497 fall within the ranges of Ocleodus and probably Potiguara (12-14); in contrast, the dorsal ridge scales are 17 in Tepexichthys and 9-7 in Oropycnodus and Pycnodus. In FCMP 00/497, Pycnodus, and Oropycnodus, the most anterior dorsal ridge scale is slightly larger than the posterior ones; whereas in Tepexichthys, Ocleodus, and probably Potiguara, all dorsal ridge scales have a similar size (Applegate 1992, p. 171; Poyato-Ariza and Wenz 2004, characters 69 and 71; Machado and Brito 2006, p. 4 and figure 2).

FCMP 00/497 has two incisiform teeth in the premaxilla and dentary, like the rest of the pycnodontid genera with dermocranial fenestra except Tepexichthys, which has three incisiform teeth on each of such bones (Applegate 1992; Poyato-Ariza and Wenz 2004,). In Potiguara, these teeth are unknown (Machado and Brito 2006).

Finally, the caudal fin is double marginated in FCMP 00/497 (Figure 3.1), as well as in Oropycnodus, Ocleodus, and Pycnodus (Poyato and Wenz 2002, character 73). In contrast, the caudal fin is concave in Tepexichthys and straight in Potiguara (Applegate 1992, figure 4; Machado and Brito 2006).

Type species – Macrosemiocotzus americanus González-Rodríguez, Applegate, and Espinosa-Arrubarrena, 2004; Tlayúa Formation (Cretaceous, Albian), Puebla, Mexico.

Material examined – IHNFG 2981 (Figure 3.3), complete articulated specimen from El Espinal quarry showing its left side.

Description – The skeleton of the specimen is complete and articulated. The total and standard lengths are 93 and 75 mm, respectively. The head length is 23 mm ( » 33% of SL). The maximum body depth is about 20 mm (» 26.6 % of SL), it is located just in the back of the head and is about two times the depth of the caudal peduncle. The dorsal fin is long and occupies almost all the trunk length. The anal fin is short and includes seven branched rays. The preanal length is 53 mm (70 % of SL). Both paired fins are located in the ventral border of the body; the pectoral one is rounded and larger than the pelvic one, which is located in the middle of the trunk. The caudal fin includes 11 branched rays, and its posterior border is rounded (Figure 3.3).

IHNFG 2981 shows a well preserved infraorbital bone located close to the ventral posterior edge of the orbit (probably the seventh within the circumorbital series). The infraorbital is a tube with a small rectangular sheet extended ventrally. This specimen partially preserves the interopercle bone located behind the preopercle and far from the lower jaw. The anterior teeth on the dentary and premaxilla are large, stout, and sharp pointed (Figure 3.3).

The elongated dorsal fin occupies all the back of the body, from the occiput to the caudal fin base, including 36 rays. The first dorsal fin ray is short, unbranched, and unsegmented. The other dorsal rays are almost regular in size (about four times as large as the first one); however, those three or four dorsal fin rays located in the positions 15 and 18 are slightly shorter than those located behind them (see arrows in Figure 3.3). It means that the dorsal fin includes two continuous lobes with 18 rays in each one.

There are 39 or 40 scale rows covering the whole body except in the area along the dorsal fin base. This nude area represents about a quarter of the body deep. All the scales are rhomboidal, and their size decreases progressively in an anterior to posterior order.

Remarks – González-Rodríguez et al. (2002) and González-Rodríguez (2004) identified IHNFG 2981 as Macrosemius cf. M. fourneti (Thiollère 1850) without any further discussion supporting such identification. Based upon the present description we disagree with that previous study as it is discussed below.

The macrosemiids are a Triassic-Early Cretaceous halecostom group with a constrained geographical distribution that includes localities in Europe and Mexico (Bartram 1977; González-Rodríguez et al. 2004). Recently, Murray et al. (2007) discovered Macrosemiids in Late Cretaceous deposits of Morocco. Apart from the present specimen from Sierra Madre Formation, these fishes are present in America only in the Albian limestones of the Tlayúa Formation (Applegate 1996; González-Rodríguez 2004).

IHNFG 2981 shows two synapomorphies of Macrosemiidae (González-Rodríguez et al. 2004, p. 285-286) supporting its inclusion within this family: 1) Scroll-like shaped infraorbital series (see label io 7? in Figure 3.3); and 2) the location of the interopercle, which is preserved behind the preopercle and far from the lower jaw (see label iop in Figure 3.3).

According to Bartram (1977) and González-Rodríguez et al. (2004, character 8), there are only three genera among macrosemiids with a nude back or an incomplete squamation area along the base of the dorsal fin (in these fossils, the dorsal pterygiophores are exposed because the scales do not cover them): Legnonotus Egerton 1854; Macrosemius Agassiz 1844; and Macrosemiocotzus. Table 2 summarizes a comparison between these three genera. Legnonotus has a short dorsal fin that comprises 25 dorsal rays forming a continuous lobe located in the middle of the trunk, far from the occiput and the caudal peduncle (Bartram 1977). In contrast, 30 or more dorsal rays are present in Macrosemiocotzus and Macrosemius (30-32 and 32-39, respectively). In addition, in these last two genera the dorsal fin occupies almost all the back area.

Besides, Macosemiocotzus has a dorsal fin divided in two continuous lobes (González-Rodríguez et al. 2004), whereas in Macrosemius this fin has a single lobe. These two genera also differ from each other because in Macrosemius the area below the posterior part of the dorsal fin shows very small scales (Bartram 1977, figure 1), whereas in Macosemiocotzus this area is covered with scales undistinguishable from those on other parts of the body (González-Rodríguez et al. 2004, figure 8). Bartram (1977) described the area with small scales in Macrosemius (which represent a diagnostic character of this genus) as the intercalation of primary and secondary scale rows. IHNFG 2981 is recognized as a Macrosemiocotzus specimen because it has a long dorsal fin with two continuous lobes and scales with regular size along the whole body (Figure 3.3, Table 2).

Macrosemius is a Jurassic (Kimmeridgian) European fish that includes two species: M. rostratus, from Eichstätt and Kelheim, Germany, and M. fourneti from Cerin, France (Bartram 1977). In contrast, Macrosemiocotzus includes a single species from the Cretaceous (Albian) limestones of the Tlayúa quarry, Mexico (González-Rodríguez 2004). Comparing these temporal and geographical ranges, the taxonomical recognition of IHNFG 2981 as a Macrosemiocotzus specimen increases the geographic range of this genus, which remains as an exclusive Albian-Cenomanian American taxon. At the same time, Macrosemius is retained as an exclusive Jurassic European fish.

The small anatomical difference (the amount of dorsal fin rays) noted between Macrosemiocotzus americanus (30-32) and the specimen IHNFG 2981 (36), suggests that the latter could represent a new Macrosemiocotzus species; however, an extensive comparative study involving these fishes is still required.

Material examined – IHNFG 2985 (Figure 4.1, 4.2), IHNFG 2994 a and b (part and counterpart), and IHNFG 3000; all from El Chango quarry.

Description – IHNFG 2985 preserves the head and the first 33 vertebrae, the length of the head is 75 mm; the length of the remaining section of the spinal column is 200 mm (Figure 4.1, 4.2). IHNFG 2994 is preserved as part and counterpart of the head and 26 disarticulated vertebrae; the head length reaches 70 mm. IHNFG 3000 is a section of the trunk, 120 mm in length, which goes from the pelvic girdle to the anterior part of the dorsal fin, along with 16 vertebrae.

This fish shows the characteristic head of the Cretaceous ichthyodectiforms. In IHNFG 2985, the floor of the nasal capsule shows a well-ossified ethmopalatine, the premaxilla-maxilla attachment involves their complete depth, there is a high and triangular supraoccipital crest, the otic and ocular sections of the parasphenoid form an angle of about 131º, and there is a basal sclerotic bone with serrated margins occupying the orbit (Figure 4.2). In IHNFG 2994, the lower jaw is rectangular with a deep dentary symphysis and a straight alveolar border parallel to its slightly convex ventral border.

In IHNFG 2985, the teeth in the premaxilla and anterior maxilla are regular in size; they are conical, straight, and sharp (Figure 4.2). There are about 20 teeth along the anterior and ventral border of the premaxilla that increase in length from 0.5 mm to about 1 mm. In this specimen, the larger premaxilla teeth are similar to those present in the maxilla.

Pelvic, anal, and dorsal fins are preserved in IHNFG 3000. The anal fin includes at least 28 rays, six of which (the first) form a triangular lobe. The triangular dorsal fin is opposed to the anal fin and located behind its lobe. The distance between the pelvic and anal fins is equal to that of eight or nine centra. The first rays in the pectoral and pelvic fins are wide and flat.

Remarks – The order Ichthyodectiformes includes Jurassic and Cretaceous fishes characterized by the presence of the ethmopalatine bones occupying the nasal capsule floor, large coracoids meeting each other forming a middle longitudinal symphysis, and uroneurals covering the lateral surfaces of the first preural centra (Patterson and Rosen 1977; Taverne 1986; Maisey 1991). The occurrence of the ethmopalatine bones in the specimens here referred supports their inclusion into the order Ichthyodectiformes (see Figure 4.2).

The suborder Ichthyodectoidei includes all Cretaceous forms so far known plus Thrissops Agassiz 1833, a Jurassic European form (see Patterson and Rosen 1977; Stewart 1999; Alvarado-Ortega 2005; among others). Cretaceous taxa within this suborder form a monophyletic group that is characterized by the presence of a rectangular lower jaw and a wide premaxilla-maxilla attachment. These characters are present in the specimens here referred from El Chango quarry supporting their inclusion into this nominal suborder (Figure 4.2).

The interrelationships of ichthyodectiforms remain controversial because there are several forms that still need to be described or redescribed before performing a comprehensive study. However, two crown monophyletic ichthyodectoid families are clearly to be recognized: a) Saurodontidae includes genera with a prognathic lower jaw and an edentulous predentary bone (see Stewart 1999); and b) Ichthyodectidae involves genera with a broad parasphenoid angle (149°-160°, formed between the orbital and the otic sections of the parasphenoid) and a hyomandibular fossa laying in parallel to the orbital section of parasphenoid (see Taverne 1986; Blanco-Piñón and Alvarado-Ortega 2007). Because the specimens here referred do not show these diagnostic characters, we are unable to place them within any of these families.

Although we concluded in the previous paragraph that the relatives of the ichthyodectiforms from El Chango must be placed among basal ichthyodectoid taxa, which include well-known fishes as Unamichthys Alvarado-Ortega 2004 and Cladocyclus Agassiz 1844, as well as a large number of scarcely documented genera, such work is beyond the scope of the present work, and additional research is required to recognize the accurate taxonomical identity of these Mexican fishes.

Prymnetes longiventer Cope 1871 is the other ichthyodectiform known from Chiapas. Unfortunately, this species is represented by a single specimen from an unknown locality near Tuxtla Gutiérrez. The head of this specimen is distorted; therefore all its diagnostic characters are based on the postcranial skeleton (its specific epithet is based on the large number of abdominal vertebrae). Unfortunately, none of the specimens recently collected in El Chango quarry preserves the whole body precluding a better anatomical comparison with Prymnetes and other basal Ichthyodectoids.

Material examined – INAH 1941 from El Espinal quarry, almost a complete specimen exposing the left side (Figure 4.3-4.6).

Remarks A complete description of Triplomystus applegatei was performed by Alvarado-Ortega and Ovalles-Damián (2008); relatives of T. applegatei were described by Forey et al. (2003) as T. noorea and T. oligoscutatus. The genus Tryplomystus includes the so called "triple armored herrings," that differ from the rest of the Ellimmichthyiforms in their three scute series along the body borders (predorsal, postdorsal, and ventral series) instead of the regular two series (predorsal and ventral) found in other ellimmichthyiforms. The presence of these three scute series in INAH 1941 justified its inclusion within the genus Triplomystus (Figure 4.4-4.6). Alvarado-Ortega and Ovalles-Damián (2008) found differences among the three Triplomystus species, which reside mainly on the meristic data of the anal and dorsal fins, as well as in the number of scutes that form the predorsal, postdorsal, and ventral series.

Material examined – IHNFG 2984 a and b (part and counterpart), a complete fish from El Espinal quarry (Figure 4.7-4.8). IHFG 3002 a and b, part and counterpart of a fish lacking the head from El Chango quarry.

Note – Ovalles-Damián (2004) named the specimen IHNFG 2984 Paraclupea-like. Today, E.D.O. is working on the formal description of both referred specimens.

Description – Although IHNFG 2984 is a complete articulated fish, the skeleton is partially dissolved (Figure 4). The total and standard lengths of the diamond-shaped specimen are 222 and 165 mm, respectively. The maximum body depth is 115 mm (64.4 % of SL). There are 39 vertebrae along the spinal column, including 14 caudal and 25 abdominal centra. There are two scute series, the ventral and the predorsal. The ventral series includes 42 or 43 wide scutes covering the abdomen, and the predorsal series involves about 18 scutes located in front of the dorsal fin. The size of the predorsal scutes increases in an anterior to posterior order, and they are ornamented with radiating ridges. The dorsal fin includes approximately three unbranched and 21 branched rays that are connected with 19 dorsal pterygiophores. The anal fin rays are not preserved but 16 pterigiophores are present (Ovalles-Damián 2004).

Remarks The order Ellimmichthyiformes is a basal group of clupeomorph fishes named by Grande (1985). In this group, the parietals meet each other along the middle line of the skull, the anterior ceratohial has the beryciform foramen, and subrectangular scutes in the predorsal series. Clupeomorph fishes are characterized by the occurrence of the ventral scute series that form the ventral keel (Grande 1985). Recently, Alvarado-Ortega et al. (2008) suggested that this order includes two families: Paraclupeidae and Sorbinichthyidae. In the paraclupeids the size of the predorsal series increases in an anterior to posterior order, the posteriormost of these scutes show a strong spine. In contrast, the sorbinichthyids are fishes with a large supraoccipital crest, and 20-30 subrectangular scutes with serrated posterior borders forming the predorsal series. According to Ovalles-Damián (2004), IHNFG 2984 shows about 18 predorsal scutes, whose size increases in an anterior to posterior order; these characters support the inclusion of these fishes into the family Paraclupeidae.

According to Alvarado-Ortega et al. (2008), the family Paraclupeidae comprises the genera: Scutatuspinosus Silva-Santos and Correa 1985, from the Early Cretaceous (Neocomian) lacustrine sediments within Recôncavo Basin, Brazil; Ezkutuberezi Poyato-Ariza, López-Horgue, and García-Garmilla 2000, from the Early Cretaceous (Valangian-Barremian), deltaic and lacustrine deposits from the Villaro Formation, Spain; Ellimma Jordan 1913, from the Early Cretaceous (Aptian-Albian), brackish lagoon and open sea deposits of Riacho Doce, Muribeca Formation, Brazil; Ellimmichthys Cope 1886, from the Early Cretaceous (Hauterivian-Barremian) estuarine deposits of the Marfim Formation, Brazil, and the Early Cretaceous (Aptian-Albian) freshwater deposits of the Cocobeach Series, Equatorial (Spanish) Guinea, Central Africa; Paraclupea Sun 1956, from the Lower Cretaceous probable freshwater deposits of the Chawan Formation, China; as well as Triplomystus (see above) and the species "Diplomystus" solignaci Gaudant and Gaudant 1971, from the Late Cretaceous (Senonian) marine sediments at Calcaires rosés de Gabès, Gouvernorat de Gabès, Tunisia. Tycheroichthys dunveganensis Hay, Cumbaa, Murray, and Plint 2007, was recently described based on a single specimen from the Late Cretaceous (Cenomanian) Marine mudstone of the Dunvengan Formation, Canada; based on its description it is recognized as a paraclupeid fish. Triplomystus has three scute series (see the anterior section above), therefore it was named a "triple armored herring"; in contrast, the rest of the Ellimmichthyiformes present only two scute series (the predorsal and ventral series) and are commonly known as "double armored herrings."

Table 3 summarizes the following comparative analysis among the "double armored herrings" genera included in the family Paraclupeidae (see Zaragüeta-Bagils 2004; Hay et al. 2007; Alvarado-Ortega et al. 2008). These fishes are relatively easily distinguishable from each other because of the scutes that form the predorsal series, the rays involved within the impaired fins, and the preural vertebrae. However, Ovalles-Damián (2004) noted that IHNFG 2984 represents a new genus and species because such accounts do not match with those found in other paraclupeids, he suggested that his Paraclupea-like fish is closer to Paraclupea than to any other paraclupeid.

Type species: Enchodus lewesiensis (Mantell 1822), from the Chalk of Sussex, Cenomanian-Campanian, England.

Material examined – IHNFG 2987 (Figure 5), IHNFG 2988, IHNFG 3004 a and b, and IHNFG 3005; all from El Chango quarry.

Description – IHNFG 2987 (Figure 5) is the only complete specimen so far known. Its total and standard lengths are 110 and 88 mm, respectively. Its head length is 32 mm (36.3 % of SL). Its predorsal length is 44 mm (50 % of SL). Its preanal length is 68 mm (77.3 % of SL). The lower jaw is strong and triangular, higher in the posterior region where its joint with the quadrate is exposed. The dentary presents three finger-like processes in its anterior ventral margin (seen in IHNFG 3004). The maxilla is thin and toothless. The premaxilla is triangular and bears a large tooth (previously observed in IHNFG 3004). There is a strong fang-like tooth in the palatine of IHNFG 2988.

The pelvic girdle is opposite to the origin of the dorsal fin. There are 10 dorsal and six anal fin rays. In IHNFG 2987 and IHNFG 2988 there are 35-37 total vertebrae, 14-15 of which are abdominal. The caudal peduncle is narrow. The caudal fin is wide, deeply forked, and its lobes are similar in size and shape. The body is naked except for the single mid-dorsal scute located just in front of the dorsal fin.

Remarks According to Silva (2007), there are about 26 - 27 Enchodus species that lived between the Barremian-Eocene range and had a wide geographical distribution all over North and South America, Africa, Europe, Middle East, and Asia. Five of these species occur in North American localities with ages between the Cenomanian and the Maastrichtian (Goody 1969; Fielitz 1996; Alvarado-Ortega et al. 2006a; Silva 2007). Unfortunately, these North American species are described mainly based on isolated and fragmentary material.

The specimens studied here are identified as Enchodus because they have the diagnostic characters of this genus described by Goody (1969) and Chalifa (1996). These characters are: a robust palatine with an anterior fang or hypertrophied tooth, three symphyseal finger-like processes on the anterior ventral margin of the dentary, and an uncovered lower jaw-quadrate joint (Figure 5).

According to Chalifa (1996, tables 3 and 4), there is a Cenomanian-Turonian group of Enchodus species that is well characterized by the occurrence of less than 40 total vertebrae, and another group with younger species that shows more than 41. In this scenario, the Mexican Enchodus species described here match with the Cenomanian-Turonian group of Enchodus species that involves E. marchesettii (Kramberger 1895) (see Goody 1969, p. 85-95); E. brevis Chalifa 1989; and E. longipectoralis (Schaeffer 1947). Nevertheless, the Mexican Enchodus shows some singular characters that are summarized in Table 4, these are: the total number of vertebrae of this Mexican species (35-37) is similar to that found in E. marchesettii (37) and E. longipectoralis (35), it has 14-15 abdominal vertebra, unlike E. marchesettii and E. longipectoralis that have only 13 and 19, respectively (in contrast E. brevis has 33 total and 10 abdominal vertebra). In addition, the head length of this Mexican Enchodus species (36.3 % of the SL) is longer than that found in other species (it is 35 % in E. brevis, 33.3 % in E. longipectoralis, and 24.1 % in E. marchesettii). Although this brief analysis suggests that the Enchodus sp. from the Sierra Madre Formation represents a new form within the Cenomanian-Turonian group of Enchodus species described by Chalifa (1996), a complete descriptive and comparative analysis is required before suggesting a new nominal specific name.

Type species: Saurorhamphus freyeri Heckel 1850, from lower Cenomanian of Comen, near Trieste, Slovenia.

Material examined – IHNFG 1916 a and b, IHNFG 2983, IHNFG 2667 a and b, and IHNFG 2982 a and b, from El Espinal quarry; IHNFG 2660 a and b, IHNFG 9084, and IHNFG 9130 from El Chango quarry (Figure 6.1-6.5).

Description – In IHNFG 2667, the most complete specimen so far known (Figure 6.4), the total and standard lengths are 305 and 265 mm, respectively. The head length is 127 mm (45 % of SL) and comprises three times its maximum depth. In IHNFG 2983 (Figure 6.1), the dorsal fin is 50 mm long; it is included three times in the trunk and is located in the anterior half. The anal fin is only 20 mm long; it is included eight times in the length of the trunk and is placed in the posterior quarter. The caudal fin is wide and deeply forked.

In IHNFG 2660, there are at least five mid-dorsal scutes located along the predorsal border, where they overlap (Figure 6.2-6.3). In these fishes there are about 38 total vertebrae, 17 abdominal plus 21 caudal (including both urals). The most anterior vertebrae are almost as twice as long as the posterior ones. In IHNFG 2982, there is a row of at least 37 scales along the flank of the trunk; the most anterior ones are located just above the spinal column but in the posterior part of the body, where these scales are covering the caudal vertebrae. Some of these anterior flank scales are disarticulated in IHNFG 2983 (Figure 6.1, 6.5) showing their rhomboidal shape and median ridge ornamented with tubercles and ridges [the shape of these scales was described as triangular by Goody (1969, p. 126) and illustrated by Chalifa (1985, p. 190, figure 3)].

Remarks – Goody (1969, p. 71, 191) named the suborder Enchodontoidei and included Saurorhamphus and the relatives of Enchodus. Among other characters, enchodontoids share the presence of an enlarged palatine tooth, scales are exclusively present along the lateral line of the body, there are scutes on the mid-dorsal line in front of the dorsal fin, and the spinal column has more caudal than abdominal centra. Although the palatine is obscured in all the specimens referred, they are included among enchodontoids because they have 21 caudal and 17 abdominal vertebrae, show scales on the lateral line of the body, and scutes in the mid-dorsal line (Figure 6).

According to Goody (1969), there are two enchodontoid families: his Eurypholidae, and Enchodontidae, firstly proposed by Woodward (1901). Although Chalifa (1985, p. 182) emended the diagnosis of the later family, she did not discuss the differences between both families; in consequence, we only consider the original diagnoses provided by Goody (1969). The diagnostic characters of eurypholids are: the articular facet of the lower jaw is not visible in the lateral external view; the scales on the lateral line and the scutes on mid-dorsal line overlap; the preopercle bears a prominent posterior ventral spine; the opercle shows a posterior spine; and the ventral section of the cleithrum is expanded posteriorly, beyond the level in which the pelvic fin attaches to the body. The first three of these eurypholid characters are present in the Mexican Saurorhamphus specimens referred here (Figure 6). In contrast, the diagnostic characters of the enchodontids are: the articular facet of lower jaw is visible in lateral external view, neither the scales on lateral line nor the scutes on the mid-dorsal line show overlapping, the preopercle and opercle do not bear posterior spines, and the ventral section of the cleithrum is not projected backward overhanging the pectoral fin.

Goody (1969) located Eurypholis Pictet 1850 and Saurorhamphus into his family, Eurypholidae. According to Gallo et al. (2005, p. 346, character 50), the scales of these fishes along the lateral line show a typical triangular shape (the shape of these scales is described here as rhomboidal). This diagnostic character is also present in the Saurorhamphus sp. from Chiapas (Figure 6.5).

According to Goody (1969), prognathism is less conspicuous in Eurypholis than in Saurorhamphus. Eurypholis has a pelvic fin located just behind the pectoral girdle, only three mid-dorsal scutes, about 35-40 total vertebrae, and 20 caudal vertebrae. In contrast, the spinal column of Saurorhamphus is markedly prognathic [the length of the head is more than three times as deep as the head]; it includes 42 and 22 total and caudal vertebrae, respectively; its pelvic fin is located in the middle of the abdomen (the position of the pelvic fin is variable in Saurorhamphus species, see Table 5) and has 6-8 scutes along the mid-dorsal border (Chalifa 1985). The inclusion of the specimens from Chiapas here referred as Saurorhamphus is supported because they share all these diagnostic characters except the total number of vertebrae (48).

Today the genus Saurorhamphus involves three nominal species, S. freyeri Heckel 1850, from Cenomanian deposits of Slovenia; S. judeaensis Chalifa 1985, from the Cenomanian limestones of Ein-Yabrud, Near Jerusalem; and S. giorgiae Bannikov and Bacchia 2005, from Cenomanian deposits at Namoura, Lebanon. Based on a comparative study of the nominal species of Saurorhamphus performed by Chalifa (1985, table 3) and data provided by Bannikov and Bacchia (2005), four characters in the specimens from El Espinal and El Chango quarries are recognized that suggest they belong to a new species or probably to a new genus (Table 5). However, it is evident that a complete descriptive work of the Mexican Saurorhamphus is still required. These characters are:

1. The length of the body and that of the head are almost the same (the head length is 48 % of SL) in the Mexican specimens. In contrast, the head length is 33 % of SL in Saurorhamphus freyeri, it is 37 % of SL in S. giorgiae, and it ranges between 37 and 40 % of SL in S. judeaensis (see Chalifa 1985, tables 2, 3; Bannikov and Bacchia 2005, p. 518)

2. In the Mexican specimens, the dorsal fin is located in the anterior half of the SL, close to the skull (Figure 6.1). In contrast, all the nominal Saurorhamphus species show the dorsal fin located in the posterior half of the SL (see Bannikov and Bacchia 2005; Goody 1969, figure 55; Chalifa 1985, figure 3).

3. The anterior dorsal fin rays are hypertrophied in the Mexican specimens; here the length of the most anterior dorsal fin ray is equal to the length of five or six of its abdominal vertebrae (Figure 6.1). In contrast, the anterior dorsal fin ray in all the nominal Saurorhamphus species is markedly shorter; its length is contained in the length of one or two abdominal vertebrae (Goody 1969, figure 55; Chalifa 1985, figure 3E; Bannikov and Bacchia 2005, figure 3).

4. The pelvic fin is placed in the posteriormost end in the Mexican specimens; it is behind the dorsal fin and closer to the anal fin base than to the pectoral fin (Figure 6.1). In contrast, the pelvic fin in S. freyeri and S. judeaensis is located in front of the dorsal fin and closer to the pectoral fin than to the anal fin base [in S. freyi it is located closest to the pectoral girdle (Chalifa 1985, table 3, figure 3E)], whereas in S. giorgiae, it is located right in the middle point between the pectoral and the anal fins (Bannikov and Bacchia 2005, figure 3).