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1. Introduction
Marine strata of the Upper Jurassic (Kimmeridgian-Tithonian) to lowermost Cretaceous (Berriasian) La Caja Formation is widespread in northeastern and central Mexico and known for their abundant and diverse well-preserved ammonites (e.g. , Burckhardt, 1906, 1930; Imlay, 1938; Peña-Muñoz, 1964; Verma and Westermann, 1973; López-Caballero, 2009; Villaseñor et al. , 2012, 2015). Here we document ammonites of the genus Salinites (Cantú-Chapa, 1968) from these lithostratigraphic units and discuss their stratigraphic and paleoecological importance. Salinites grossicostatum (Imlay, 1939) is restricted to the uppermost Tithonian Crassicollaria Zone (Adatte et al. , 1994) and only occurs in outer shelf environments in the transitional zone between the continental platform and slope, as discussed below.
1.1. Location
The Salinites -bearing interval investigated here is located at Puerto Piñones (N25°02.719'/W101°03.396') in southern Coahuila state (Adatte et al. , 1994; Zell et al. , 2013, 2015; Zell and Stinnesbeck, 2015). A precise description of the locality and the section is provided by Zell and Stinnesbeck (2016, fig. 1). The Salinites -bearing layer consists of an approximately 0.3 m thick hemipelagic shaly limestone rich in ammonites. The assemblage is relatively diverse and is numerically dominated by Salinites grossicostatum (Imlay, 1939), but Himalayites , Kossmatia and Durangites are also present. The assemblage characterizes the "Kossmatia- Durangites-Salinites beds" (cf.Cantú-Chapa, 2006); calpionellids from the layer are indicative of the uppermost Crassicollaria Zone (Adatte et al. , 1994).
1.2. Material and methods
Our collection of Salinites grossicostatum consists of 169 specimens preserved three-dimensionally. They are well preserved, but suture lines are only visible in rare occasions. Specimens analyzed here were collected by WS during the late 1980s and early 1990s over a period of about eight years and are now deposited in the Colección de Paleontología de Coahuila of the Museo del Desierto in Saltillo, Coahuila, Mexico, under the collection numbers CPC-1214-1242, sample box CPC-1243 and CPC-1405-1413. The systematic description follows Arkell et al. (1957), Verma and Westermann (1973) and Wright et al. (1996). Abbreviations: D, diameter; Wh, whorl height; Ww, whorl width; U, umbilical diameter; U/D, umbilical ratio; Ww/Wh, whorl height to width ratio.
2. Systematic Paleontology
Phylum Mollusca Linnaeus, 1758
Class Cephalopoda Cuvier, 1797
Order Ammonoidea Zittel, 1884
Superfamily Haploceratacea Zittel, 1884
Family Haploceratida Zittel, 1884, sensu Ziegler, 1974
Genus Salinites Cantú-Chapa, 1968
Type species. Hildoglochiceras grossicostatum Imlay, 1939
Salinites grossicostatum (Imlay, 1939)
Figure 1 Representative specimens of Salinites grossicostatum (Imlay, 1939) from the uppermost Tithonian at Puerto Piñones, Coahuila, Mexico, representing an ontogenetic series from juvenile (a) to mature (c); (a) CPC-1405; (b) CPC-1408, microconch; (c) CPC-1413, macroconch. The specimens were previously illustrated in Zell and Stinnesbeck (2016, fig. 3).
Hildoglochiceras grossicostatum sp. nov. Imlay, 1939, p. 27, pl. 2, figs. 5-11, pl. 3, figs. 1-7, 9-11; Imlay, 1942, p. 1444, pl. 2, figs. 3-5; Carreño et al. , 1989, p. 219, fig. 77e.
Haploceras cubensis sp. nov. Judoley and Furrazola-Bermúdez, 1968, p. 55, pl. 3, figs. 2-3.
Salinites grossicostatum (Imlay, 1939); Cantú-Chapa, 1976, pl. 1, figs. 1 a-d, f, g, 2 g, 7 a, 8 e, f, pl. 2, fig. 4a; non Cantú-Chapa, 1968, p. 21, pl. 4, figs. 1, 4, 7, 9, pl. 5, figs. 3, 8, 10; ? Imlay and Herman, 1984, p. 160, pl. 1, figs. 9-11; Zell and Stinnesbeck, 2016, p. 4, fig. 3.
Hildoglochiceras (Salinites ) grossicostatum (Imlay, 1939); Myczyński, 1989, p. 86, pl. 2, figs. 10-13, pl. 3, figs. 1-3, 5, 9, 12, pl. 4, figs. 10b, 11a; Myczyński and Pszczółkowski, 1990, pl. 1, fig. 3; non Myczyński, 1989, p. 86, pl. 1, fig. 4, pl. 3, fig. 8, pl. 4, figs. 1, 2, 11b.
2.1. Description
A detailed description of the ontogenetic development and interior shell parameters of Salinites grossicostatum is provided by Zell and Stinnesbeck (2016). The authors also document sexual dimorphism in S. grossicostatum based on the presence of micro- and macroconchs with diverging trends in septal spacing, especially during the post-embryonic stage. Dimensions of selected specimens are presented in Table 1.
2.2. Remarks
The genus Hildoglochiceras is characterized by an evolute compressed shell with a deep median furrow, an apophysis, and strong rursiradiate ventrolateral ribs (see Wright, in Arkell et al. , 1957). This diagnosis is only consistent with a single species (Hildoglochiceras diaboliImlay, 1939, p. 25, pl. 6, figs. 8-10) of a total of eight taxa from Mexico originally assigned to Hildoglochiceras by Imlay (1939). These Mexican specimens were revised and separated from Hildoglochiceras by Cantú-Chapa (1968, p. 19), based on their high degree of involution and the presence of a whorl depression at the dorso- to middle-lateral region of the flank. The author established a new genus, Salinites , for these Mexican representatives and included Hildoglochiceras grossicostatumImlay (1939, p. 27, pl. 2, figs. 5-11, pl. 3, figs. 1-7, 9-11) from the "Durangites beds" of the La Casita Formation at Sierra de Parras, Coahuila. Hildoglochiceras propinquumWaagen (1873-1875, p. 45, pl. 11, figs. 4a, b) and H. dieneriUhlig (1903-1910, p. 18, pl. 7, figs. 8a, b) from the Jurassic of India were considered to be similar to Salinites grossicostatum (e.g. , Imlay, 1939), but are less involute and their ribs are less pronounced. ParaglochicerasCollignon, 1959 has a larger whorl width and no lateral furrow is present, while GlochicerasHyatt, 1900 is more involute and almost smooth.
2.3. Occurrence
Salinites grossicostatum was first described by Imlay (1939) from the upper Tithonian Durangites beds in the Sierra de Parras and Sierra de Jimulco, Coahuila, Mexico. The investigated limestone containing S. grossicostatum at Puerto Piñones was assigned by Adatte et al. (1994) to the uppermost Tithonian "Durangites beds" and to the upper Crassicollaria Zone, and is stratigraphically located only a few tens of millimeters below the Jurassic-Cretaceous boundary identified on the basis of calpionellid occurrences (Adatte et al. , 1994) and the recent identification of the belemnite Rhaphibelus aciculiformisZell et al. (2013). At Puerto Piñones, Salinites grossicostatum is associated with Proniceras , Himalayites and Durangites (and related forms).
Outside the state of Coahuila, S. aff. grossicostatum was documented from a bore hole (Paras No. 1) in northern Nuevo León (Cantú-Chapa, 1968), associated with Substeueroceras ?imlayi (Cantú-Chapa, 1963) and Paradontoceras . Cantú-Chapa (1976) also identified several specimens of S. grossicostatum from the upper Tithonian portion of the La Pimienta Formation in bore hole Bejuco No. 6, 70 km south of Tampico, in Tamaulipas.
In these sections of the Gulf coast of northeastern Mexico (Figure 2), S. grossicostatum occurs in outer shelf environments at the transition between the continental shelf and slope (e.g. , Adatte et al. , 1994). Interestingly, in other correlative sections from the region the taxon is characteristically absent in the Tithonian-Berriasian transition interval; e.g. , at Sierra de Chorreras, Chihuahua (Cantú-Chapa, 1976), San Pedro del Gallo, Durango (Burckhardt, 1912; Contreras et al. , 1988), Sierra de Catorce, San Luis Potosí (Verma and Westermann, 1973), Tamán, San Luis Potosí (Cantú-Chapa, 1984) and Mazatepec, Puebla (Cantú-Chapa, 1967; Stinnesbeck et al. , 1993). These latter sections are either considered to represent environments more shallow than the deposits at the localities with Salinites grossicostatum (e.g. , Sierra de Chorreras, Chihuahua state, Sierra de Catorce, San Luis Potosí state), or they represent a deeper marine environment on the slope or within the basin (e.g. , San Pedro del Gallo, Durango state, Tamán, San Luis Potosí state, and Mazatepec, Puebla state).
Figure 2 Tithonian paleogeographic map of the Gulf of Mexico and adjacent realms including latest Tithonian occurrences of Salinites grossicostatum (see numbers). The distribution of S. grossicostatum is restricted to shallow marine, outer shelf environments. (1) Sierra de Jimulco; (2) Sierra de Parras; (3) Puerto Piñones; (4) bore hole Paras No. 1; (5) bore hole Bejuco No. 6; (6) Sabine Parish; (7) Sierra de Los órganos. Map simplified and redrawn after Wilhem (2014), with additional information from Goldhammer and Johnson (2001); see text for locality information.
Outside Mexico, Salinites grossicostatum was reported from the Tithonian Bossier Formation at Sabine Parish, Louisiana, USA (Imlay and Herman, 1984, p. 160, pl. 1, figs. 9-11) and from the upper Tithonian of Sierra de Los órganos in western Cuba (Imlay, 1942, p. 1444, pl. 2, figs. 3-5; Judoley and Furrazola-Bermúdez, 1968, p. 19; Myczyński, 1989; Myczyński and Pszczółkowski, 1990). The records of the species in Cuba and the southern USA represent depositional environments considered to be similar to the environments containing Mexican occurrences of S. grossicostatum (see Fig. 2, localities 6 and 7).
At Puerto Piñones, S. grossicostatum is restricted to the latest Tithonian (Adatte et al. , 1994; Zell and Stinnesbeck, 2016). This is consistent with the age assigned to the specimens at other sites in Mexico (Imlay, 1939; Cantú-Chapa, 1976). According to Myczyński and Pszczółkowski (1994) and Myczyński (1999), Cuban Salinites are also restricted to the latest Tithonian based on the presence of calpionellids preserved in the upper part of the La Zarza Member of the Artemisa Formation, above the "Vinalesites- Protancyloceras " assemblage. Myczyński (1989) also identified Salinites in the El Americano Member of the Guasasa Formation. Cobiella-Reguera and Olóriz (2009) assigned Cuban Salinites -bearing beds from the El Americano Member to the latest Tithonian-early middle Berriasian (upper Crassicollaria and/or Calpionella zones). Nevertheless, the precise age of the sediments is debated (see Pszczółkowski, 2013).
Salinites finicostatum sp. nov.
Figure 3 Salinites finicostatum sp. nov. (CPC-1404) from the uppermost La Caja Formation at Cañón de Huizachal, Tamaulipas. (a) left side view; (b) right side view; (c) ventral view.
Salinites grossicostatum (Imlay, 1939); Cantú-Chapa, 1968, p. 21, pl. 4, figs. 1, 4, 7, 9, pl. 5, figs. 3, 8, 10.
Hildoglochiceras (Salinites ) grossicostatum (Imlay, 1939); Myczyński, 1989, p. 86, pl. 1, fig. 4, pl. 3, fig. 8, pl. 4, figs. 1, 2, 11b.
2.4. Material
One three-dimensionally preserved specimen (CPC-1404) from a Corg.-rich mudstone of the uppermost La Caja Formation at Cañón de Huizachal, Tamaulipas state (for locality see Montellano et al. , 2008, p. 1131, fig. 1), associated with an imprint of an ammonite assigned to Suarites . Accompanying calpionellids are rare but indicate a latest Tithonian or earliest Berriasian age. Suture-lines are not visible.
2.6. Diagnosis
A Salinites with finer and less regular ribs than those of S. grossicostatum (Imlay, 1939). The taxon is also distinguished from this latter species by a slightly wider umbilicus, higher whorl widths and a stronger serrated keel.
2.7. Description
Medium sized (D = 29.5 mm), involute (U/D = 0.2), discoidal with largest whorl width closely below the middle of the flank (Wh = 15 mm; Ww = 10.3 mm; Ww/Wh = 0.69). The umbilicus is narrow (U = 6.0 mm) and shallow; the umbilical wall is vertical. The flanks are convex, the venter rounded with a serrated keel. Fine, prorsiradiate ribs of equal strength are present between the umbilical ridge and mid-flank. Fine ventrolateral ribs of irregular strengths and spacing are present; they are simple but some bifurcate closely above mid-flank. Here they are rursiradiate but ventrolaterally become prorsiradiate.
2.8. Remarks
Imlay's type material of Hildoglochiceras grossicostatum (Imlay, 1939, pl. 3, figs. 3, 4) consists of juveniles (Dmax.= 24.5 mm); however, adult material of Cantú-Chapa (1968), as well as specimens described by Myczyński (1989) from the Tithonian of Cuba, differ from Imlay's type material of Hildoglochiceras grossicostatum and from our material from Puerto Piñones by finer ribs of irregular expression and spaced at smaller distances. These differences are here considered to be significant and permit definition of a new species of Salinites , S. finicostatum . Haploceras cubensisJudoley and Furrazola-Bermúdez (1968, p. 55, pl. 3, fig. 1) from the upper Kimmeridgian to lower Tithonian Artemisa Formation of western Cuba is similar in ribbing, but differs from S. finicostatum by slightly less involute coiling, a pronounced lateral furrow during early ontogenetic stages and by a smaller whorl width.
2.9. Occurrence
Salinites finicostatum is here reported from the upper Tithonian-lower Berriasian of Huizachal Canyon in Tamaulipas as described here, and the upper Tithonian at Rancho Las Juanas at Galeana, Nuevo León, associated with Proniceras (P.) subpronumBurckhardt (1919-1921) and Durangites spp. (Cantú-Chapa, 1968). The species is also present in the upper Tithonian of Cuba (Myczyński, 1989, p. 86, pl. 1, fig. 4, pl. 3, fig. 8, pl. 4, figs. 1, 2, 11b) and is there associated with Salinites grossicostatum (Myczyński, 1989, p. 86, pl. 2, figs. 10-13, pl. 3, figs. 1-3, 5, 9, 12, pl. 4, figs. 10b, 11a).
3. Conclusions
Salinites grossicostatum (Imlay, 1939) is restricted to the Crassicollaria Zone (Adatte et al. , 1994) of the uppermost Tithonian "Kossmatia-Durangites-Salinites Beds" (cf.Cantú-Chapa, 2006). The species, known from Coahuila and Nuevo León in Mexico, western Cuba, and the southern US, only occurs in outer shelf environments in the transitional zone between the inner continental shelf and slope. A second, closely related taxon, Salinites finicostatum sp. nov., occurs in coeval strata in the Mexican states of Tamaulipas and Nuevo León (Cantú-Chapa, 1968) and is also present in Cuba (Myczyński, 1989), but its ecological preferences are unclear. Salinites is thus endemic to the ancient Gulf of Mexico.
