Journal of Paleontology, 85(3), 2011, p. 524–536 Copyright ’ 2011, The Paleontological Society 0022-3360/11/0085-0524$03.00

EPIZOIC STRAMENTID CIRRIPEDES ON AMMONITES FROM LATE CRETACEOUS PLATY LIMESTONES IN MEXICO

CHRISTINA IFRIM,1 FRANCISCO J. VEGA,2 AND WOLFGANG STINNESBECK1 1Institut fu¨r Geowissenschaften, Ruprecht-Karls-Universita¨t, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany, ,[email protected].; and 2Instituto de Geologı´a, Universidad Nacional Auto´noma de Me´xico, Ciudad Universitaria, Coyoaca´n, 04510 Me´xico, D.F., Mexico

ABSTRACT—The discovery of platy limestone deposits in northeastern Mexico has led to the collection of well- preserved stramentids of early Turonian age from Vallecillo, state of Nuevo Leo´n, and of early Coniacian age from El Carranza, state of Coahuila. Stramentum (Stramentum) pulchellum (Sowerby, 1843) colonized the ammonite shells during the lifetime of the animals, occasionally in two subsequent generations. Colonization of the ammonite shell by Stramentum (S.) pulchellum was hindered by strong ornamentation only. The ammonites did not interfere with their epizoans. Colonization during lifetime shows that these ammonites dwelled in well-oxygenated water levels near the surface, and most stramentids were embedded alive. The known paleobiogeographic occurrence of Stramentum (S.) pulchellum and its long stratigraphic occurrence are considerably enlarged by our findings. The pseudoplanktonic mode of life of Stramentum, and attachment to ammonite shells, may have been a response of a once benthic organism to repeated oxygen-deficient conditions on the seafloor of mid-Cretaceous oceans, i.e., to oceanic anoxic events (OAEs).

INTRODUCTION matter are preserved as black stains. The sediment was thus HE THORACIC crustacean Stramentum sp. is widespread in originally black, rich in organic matter, which is typical for T sediments of Cenomanian-Coniacian age. Most reports fine-grained sediment with good fossil preservation (Martill, for Stramentum sp. are from Europe and North America, as 1987; Allison, 1988; Seilacher, 1990; Hemleben and Swin- summarized by Hauschke (1994) and Hattin and Hirt (1991). burne, 1991). Few reports exist from South America (Royo y Go´mez, 1941; The platy limestone is laminated below millimeter scale. It Villamil and Arango, 1998). Nomura et al. (2009) provided the splits perfectly parallel to lamination when dry, and preferably most recent summary, although the specimen reported from through fossils contained in the sediment. Japan is incomplete. During recent years, the discovery of The platy limestones are best described as mud- to several new localities with platy limestone deposition, namely wackestones (Dunham, 1962) and indicate a pelagic environ- the early Turonian Platy Limestone at Vallecillo, Nuevo Leo´n, ment, consistent with the paleogeographic position of and the early Coniacian Yellow Platy Limestone Member at Vallecillo on the outer shelf. Clastic components reach Rosario and Carranza to the northwest of Muzquiz, led to the between 10 percent and 25 percent of the sediment and were collection of well-preserved stramentids from the early Late supplied to the Vallecillo region by aeolian transport. The Cretaceous of northeastern Mexico. The stramentid specimens calcite component is biogenic in origin, whereas the Fe-oxides known from these localities grew on ammonite shells and were result from precipitation of sulfides on the Vallecillo seafloor previously only superficially figured (Stinnesbeck et al., 2005; in a very hostile, low-oxygen environment (Ifrim, 2006). Ifrim and Stinnesbeck, 2007; Vega et al., 2007). The present Fossils are found throughout the section. Ammonites are paper aims for a detailed description and interpretation of preserved as flattened impressions. Some body chambers are Stramentum Logan, 1897 from these localities. They allow us filled with sediment and preserved as flat internal molds. to draw conclusions on the paleoecology of their hosts. Phragmocones are less well preserved, because the empty The early Turonian Vallecillo Platy Limestone Member.— shells broke under lithologic overburden, and septae crushed Vallecillo is located 100 km north of Monterrey, Nuevo Leo´n, irregularly. in northeastern Mexico, and has been known since the The abundant and diverse assemblage of ammonites and 1990s for well-preserved fossil fishes, ammonites and marine inoceramid bivalves, and also the planktic foraminifers reptiles. The most complete section is exposed in a quarry at preserved in the sediment, allow for a detailed biostratigraphic N26u39.329 and W 100u00.829 (Fig. 1). zonation of the Vallecillo section (Ifrim and Stinnesbeck, 2007, The sedimentology, microfacies, age, preservation of fossils, 2008). The base of the Turonian stage is present in the lowest and composition of the fossil assemblage were described in part of the section at the 0.21 m-level (Watinoceras- and detail by Ifrim et al. (2005), Ifrim (2006), Ifrim et al. (2007; Mytiloides puebloensis zones), followed by 5.5 m sediments of 2008), and Ifrim and Stinnesbeck (2007; 2008), so only a short the early Turonian (Pseudaspidoceras flexuosum to Mammites summary is provided here. nodosoides Zone, and Mytiloides kossmati Zone), and by the The composite section of platy limestone exposed at middle Turonian above the 5.70 m-level (Collignoniceras Vallecillo is approximately 8 m thick and consists of pink to woollgari and Mytiloides mytiloides zones). All stramentid yellow marly limestone beds between 8 and 40 cm thick, crustaceans known from Vallecillo are therefore of early- intercalated by white or grey mudstone beds with thicknesses middle Turonian age (Fig. 2). between 1 and 30 cm (Fig. 2). The mudstone beds occasionally The planktonic foraminifers, the most abundant bioclasts, contain crusts of goethite and/or hematite, in part with are rare in the lower section, and the specimens are goethite concretions with cubic pseudomorphs, probably after small. They represent the Whiteinella archaeocretacea Zone. pyrite. In the most carbonaceous beds, traces of organic Upsection, in the Helvetoglobotruncana helvetica Zone, the 524 IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 525

The early Coniacian Yellow Limestone Member, Mu´zquiz.— Platy limestone is also known from northern Coahuila (Fig. 1) from two commercial quarries northwest of Mu´zquiz. The El Rosario quarry is located approximately 100 km northwest of the town, at N 28u52.5869, W 102u24.2229 and was document- ed by Stinnesbeck et al. (2005). Our material is from Carranza, 30 km north of Rosario, at N 29u10.7759, W 102u27.1939.In this quarry, the limestones are extracted along a 10 km outcrop of a single bed corresponding to beds R40–42 of El Rosario. Other layers occasionally exposed are correlated to layers R38–46, i.e., to the middle Yellow Limestone Member at Rosario (Fig. 3) by their similar lithology, thickness and fossil content. The abundant presence of the inoceramid Cremnoceramus deformis erectus (Meek, 1877) permits assign- ment of an early Coniacian age (Walaszczyk and Wood, 1998; Gradstein et al., 2004) to all layers exposed at Carranza (Fig. 3). The colonized specimen of Peroniceras tridorsatum de Grossouvre, 1894 studied here was collected from the Carranza quarry and erroneously included into the Rosario assemblage (Stinnesbeck et al., 2005; Ifrim et al., 2007) due to the similarity of lithology. Platy limestones at Carranza and Rosario are mud- to wackestones (Dunham, 1962), with planktonic foraminifers, and less frequently calcispheres and recrystallized radiolarians. This microfossil content, particularly the keeled planktonic foraminifers Dicarinella Porthault, 1970 and Marginotruncana Hofker, 1956, indicates a pelagic environment with water depths .50 m (Leary et al., 1989; Leckie et al., 1998). The cirriped Stramentum (S.) pulchellum is represented by fifty specimens attached to a shell of the ammonite Peroniceras tridorsatum (Fig. 4), and some more attached to a Forresteria Reeside, 1932 (Vega et al., 2007), possibly also from Carranza. Only nektic forms have been recognized in the crustacean assemblage of the Yellow Limestone Member. The Yellow Limestone Member is another example of formation of platy limestone in the open sea, comparable to the Vallecillo platy limestone (Ifrim et al., 2007). During deposition, the North American coastline was located at least 200–300 km to the west of Carranza (e.g., Young, 1963; Corbett et al., 1987; Kennedy and Cobban, 1991; Gold- hammer and Johnson, 2001) or 500 km to the North FIGURE 1—Map of Mexico with inset of northeastern Mexico. Fossil (Salvador, 1991). The deep water may have been stagnant localities are marked with an asterisk. due to the location in the Rio Grande Embayment, where only the surface waters may have been connected to major currents; assemblages become gradually more diverse, more abundant, even though, the presence of occasional benthic foraminifers and individuals are larger. These changes in the planktonic and trace fossils at Rosario suggest a less hostile environment foraminiferal assemblages appear to be related to the recovery than at Vallecillo. of the marine ecosystem from Oceanic Anoxic Event 2, a black shale event of global scale during the latest Cenomanian. OAE SYSTEMATIC PALEONTOLOGY 2 persisted into the early Turonian and affected deep-dwelling, The systematics of ammonites follows the Treatise of large, keeled planktonic foraminifers by an expanded oxygen Invertebrate Paleontology (Wright et al., 1996), the System- minimum zone (Leary et al., 1989; Leckie et al., 1998; Keller atics of the stramentids follows Buckeridge and Newman and Pardo, 2004). (2006). Synonymy lists are abbreviated to the most important Crustaceans are represented in Vallecillo solely by the sessile citations and references used for determination. More cirripedian Stramentum (S.) pulchellum (Sowerby, 1843). All complete synonymies are indicated where available. specimens were attached to ammonite shells. Whereas the A systematic description of the early Turonian ammonites nacreous shells of the ammonites were dissolved during early was given by Ifrim and Stinnesbeck (2007) and is not repeated diagenesis, the calcite of their epizoans is preserved, but here. Ammonite taxa colonized by Stramentum (S.) pulchellum recrystallized in some specimens. In cases when the carapaces studied there are Pseudaspidoceras flexuosum Powell, 1963, cf. fell out during collection or preparation of the samples, they Vascoceras and an unidentifiable small ammonoid registered left detailed impressions. Among 195 ammonites identified as Cephalopod indet. Here we only refer to Peroniceras during scientific excavation, three are colonized by stramen- tridorsatum from Carranza, not described previously. tids. Two more with epibiotic Stramentum were recognized Dimensions.—All dimensions are given in mm, dimensions among 124 ammonites collected randomly, e.g., by the in brackets are % of diameter. D5diameter; WH5whorl quarrymen and from spoil heaps. height; U5umbilical diameter. 526 JOURNAL OF PALEONTOLOGY, V. 85, NO. 3, 2011

FIGURE 2—The composite section at Vallecillo with biostratigraphy, microfacies and distribution of Stramentum (S.) pulchellum (Sowerby, 1843). Left, the Vallecillo Platy Limestone in the quarry; Middle, biostratigraphic subdivision of the Vallecillo section, A5ammonites, I5inoceramids, PF5planktonic foraminifers (Ifrim and Stinnesbeck, 2008), the arrows marked with S indicate the layers of occurrence of Stramentum (S.) pulchellum in the section; Right, microfacies at Vallecillo: 1, a sample from the upper water column shows a healthy, large-sized Turonian microfauna; 2, sample near the layer of origin of UANL-FCT-VCIX10 and 16 also shows improved oxygenation; 3, this sample shows dwarfed, rare planktonic foraminifers, indicating the crisis in planktonic foraminifers during the persistence of OAE 2; 4, the sample near the layer of origin of CPC-161 shows dwarfed, but abundant planktonic foraminifers, indicating a short period of improvement of conditions. Sample 1 and 3 represent extreme end-members in the development of planktonic foraminifers affected by OAE 2 and are included for comparison.

Collections.—CPC, Coleccio´n de Paleontologı´a de Coa- figs. 5–11; pl. 14, figs. 1, 4; text-figs 13g, l, 18c–e, 19; huila, Museo del Desierto, Saltillo, Coahuila, Mexico; UANL- KLINGER AND KENNEDY, 1984, p. 139, figs. 3–15, 16d–e FCT-VC, Collection of the Universidad Auto´noma de Nuevo (with full synonymy). Leo´n (UANL) at the Facultad de Ciencias de la Tierra (FCT) Type.—The holotype, by original designation of Schlu¨ter, in Linares, Nuevo Leo´n, Mexico, VC for Vallecillo. 1967, p. 26, pl. 5, fig. 1, is lost, according to Klinger and Phylum MOLLUSCA Kennedy, 1984, p. 140. Class CEPHALOPODA Cuvier, 1797 Material.—CPC-159 from the lower Coniacian Yellow Order AMMONOIDEA Zittel, 1884 Limestone Member of Carranza, layer of origin unknown. Description.—Evolute coiling, with U being approximately Suborder AMMONITINA Hyatt, 1889 60 percent of the diameter. Greatest whorl width at the Superfamily ACANTHOCERATOIDEA de Grossouvre, 1894 umbilicolateral bullae. Low umbilical wall, umbilical shoulder Family COLLIGNONICERATIDAE Wright and Wright, 1951 narrowly rounded. The rest of the whorl section cannot be Subfamily PERONICERATINAE Hyatt, 1900 reconstructed due to crushing of the specimens from The subfamily was discussed by Klinger and Kennedy flattening. Twenty-four broad umbilical bullae per half whorl, (1984). connected to ventrolateral tubercles by broad, single ribs. These arise at the umbilical wall prorsiradiately, are straight Genus and Subgenus PERONICERAS de Grossouvre, 1894 between the tubercles, and concave at the ventrolateral Type species. Peroniceras moureti de Grossouvre, 1894, shoulder. Ventrolateral carina visible, ventral carina marks p. 100, pl. 11, fig. 4 (5 A. tridorsatus Schlu¨ter, 1867, p. 26, the outline of this fossil. Traces of lobes and saddles in CPC- pl. 5, fig. 1) by original designation. For diagnosis and dis- 159 from a weakly incised suture line. cussion of genus and subgenus see Klinger and Kennedy, 1984. Dimensions.—CPC-159: D5365, WH577 (21%); U5221 (61%). PERONICERAS (PERONICERAS) TRIDORSATUM (Schlu¨ter, 1867) Discussion.—Despite the flattened preservation, the pres- Figure 4.1–4.3 ence of a ventral tricarinate keel is visible on CPC-159, Ammonites tridorsatus SCHLU¨ TER, 1867, p. 26, pl. 5, fig. 1. suggesting it was embedded slightly obliquely. Peroniceras moureti DE GROSSOUVRE, 1894, p. 100, pl. 11, figs. The very rare occurrence of intercalated ventrolateral ribs 3, 4; text-figs 37, 39. (one per whorl) as noted in CPC-159 is also present on Peroniceras (Peroniceras) tridorsatum (Schlu¨ter, 1867). KEN- specimens described from South Africa (e.g., Klinger and NEDY, 1984, p. 62, pl. 11, figs. 3–6; pl. 12, figs. 1–5; pl. 13, Kennedy, 1984, fig. 14c). Despite the flattened preservation IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 527

UANL FCT VC109, 34 specimens attached to UANL-FCT- VC500, 109 specimens attached to CPC-161; early Coniacian of Carranza: 50 specimens attached to CPC-159. All stages from juvenile (L54.5 mm) to adult (L525.5 mm), and from articulated to disarticulated. Description.—Capitulum and peduncle typical for family, comprising 10 plates and eight columns, respectively. Scutum subtrapezoidal, upper margin narrow; upper latus semitrian- gular, as high as scutum; tergum subtrapezoidal, about equal to height of upper latus; carina latus triangular, slightly higher but narrower than tergum. Peduncle joins capitulum oblique- ly. Peduncle widest at summit. Scutal column plates sub- trapezoidal, elongated. Upper lateral column plates of similar shape and size as those of scutal column. Carinal lateral column plates slightly narrower than the scutal and upper lateral column plates. Discussion.—Hauschke (1994) subdivided the nine known species of Stramentum into two subgenera, based on the shape of the tergal growth lines. The stramentid specimens from Vallecillo show straight tergal growth lines, which permits classifying them as the subgenus Stramentum. Stramentum (S.) haworthi (Williston, 1896) from the Santonian of Kansas is larger, has a longer peduncle, and is wider at midlength. S. (S.) canadensis (Whiteaves, 1889) from the lower Turonian of Kansas and Manitoba has a longer capitulum with a much more prominent tergum. S. (S.) elegans Hattin, 1977 from the Turonian of Kansas is more elongated, with a longer capitulum, including carina, carinalelatus and tergum being FIGURE 3—The Carranza section and its correlation to the Yellow much more projected. Stramentum (?S.) biplicatum Jagt and Limestone Member at Rosario (Stinnesbeck et al., 2005), and to the early Coniacian Cremnoceramus deformis erectus Zone. The layer of origin of Collins, 1989 from the upper Campanian of Belgium is more CPC-159 within the Carranza quarry is unknown. elongated, with a more prominent capitulum. Stramentum (S.) inconstans Collins, 1986 from the Turonian of Nigeria is and partial crushing of the shell in the Mexican platy widest at midlength of peduncle and capitulum is more limestone, dimensions and ornament agree with the material projected. The Vallecillo specimens fit morphological features described by Kennedy (1984) and Klinger and Kennedy of specimens of S. (S.) pulchellum Sowerby from the upper (1984). Cenomanian–upper Turonian of Europe. Occurrence.—This species occurs in the lower Coniacian Occurrence.—The specimens from Vallecillo and Carranza Cremnoceramus deformis erectus zone at Carranza. Elsewhere represent the first reports for S. (S.) pulchellum (Sowerby, it is known from the lower Coniacian of Texas, France, 1843) from America. Elsewhere, it was recorded from the northern Germany, northern Spain, Italy, Romania, north Cenomanian-Turonian of England, the Turonian of Ireland, Africa, South Africa, and Madagascar (Kennedy, 1984; France, Germany, the Czech Republic, and possibly Spain and Klinger and Kennedy, 1984). Japan (see summaries in Hauschke, 1994; and Nomura et al., 2009). Specimens from Carranza, Mexico, extend the range of Phylum CRUSTACEA S. (S.) pulchellum to the lower Coniacian. Superorder THORACICA Darwin, 1854 STRAMENTUM (S.) PULCHELLUM ON AMMONITES FROM MEXICO Order SCALPELLIFORMES Buckeridge and Newman, 2006 Suborder SCALPELLOMORPHA Newman, 1987 Taphonomic interpretation.—Ammonite shells are frequent- Family STRAMENTIDAE Withers, 1920 ly overgrown post-mortem during a phase of floating of the Genus and subgenus STRAMENTUM Logan, 1897 empty shell or on the seafloor, but colonization during its lifetime is occasionally documented (Taylor and Wilson, Type species. Pollicipes haworthi Williston, 1896; late 2003). A taphonomic interpretation of the overgrowth has Santonian of Kansas. thus to be done for each ammonite shell separately. Table 1 STRAMENTUM (STRAMENTUM) PULCHELLUM (Sowerby, 1843) summarizes the criteria we used for further interpretation of Figure 5.1–5.7 our specimens. Long-lasting post-mortem drift of ammonite shells is Loricula pulchella SOWERBY, 1843, p. 260, figs. 1, 2. considered uncommon in epeiric seas (Page, 1996; Wester- Stramentum pulchellum Sowerby, WITHERS, 1920, p. 70, pl. 3, mann, 1996) such as the Vallecillo and Rosario sea. Most figs. 1–3; pl. 13, fig. 1. ammonites from Mexican Platy Limestones were rapidly Stramentum (Stramentum) pulchellum Sowerby, HAUSCHKE, buried. This is indicated by the good preservation of their 1994, p. 15, pls. 1–5 (with full synonymy) aperture and by the excellent in situ preservation of long, Types.—The holotype is BMNH 59150, the original of delicate spines in about a third of specimens of Pseudaspido- Sowerby (1843, figs. 1, 2) from the Upper Chalk of Rochester, ceras flexuosum Powell, 1963 (Figs. 6, 7) (Ifrim, 2006) as they U.K. would have broken off during a drift-phase long enough for Material.—Early Turonian of Vallecillo: four specimens stramentid larvae to settle, undergo metamorphosis and grow attached to UANL FCT VCXI/16, 61 specimens attached to to their preserved sizes. 528 JOURNAL OF PALEONTOLOGY, V. 85, NO. 3, 2011

FIGURE 4—1, Peroniceras tridorsatum with 50 specimens of Stramentum (S.) pulchellum, the first half whorl is a flattened internal mold of the body chamber seen from upside, the rest preserves the lower side of the ammonite shell, CPC-159, 30.5; 2, drawing showing the distribution of the stramentids on the shell and the suture line where preserved; 3, the size class distribution of stramentids shows two peaks at 5–10 mm and at .20 mm, indicating two generations of stramentids. IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 529

FIGURE 5—Stramentum (S.) pulchellum from Vallecillo and Carranza: 1, hypotype CPC-161, 315; 2, hypotype on UANL-FCT-VC109, 315; 3, hypotype on UANL-FCT-VCIX16A, 313, note juvenile specimen attached; 4, hypotype on CPC-159, juvenile specimen, 320; 5, hypotype on CPC-159, 317; 6, hypotype on CPC-159, 321; 7, hypotype on CPC-159, 335. 530 JOURNAL OF PALEONTOLOGY, V. 85, NO. 3, 2011

TABLE 1—Criteria for a taphonomic interpretation of ammonite shells colonized by Stramentum (S.) pulchellum.

Interpretation criteria Colonization of the living ammonoid Colonization of the dead, floating ammonoid shell Distribution pattern Never within 20u from the aperture Indifferent Overgrown by succeeding whorls Present externally and in the living chamber Size class distribution Reveals definite generations One generation Grade of damaging of ammonoid shell Shell and aperture well preserved Ammonoid shell damaged from floating Relation shell damage–epizoans Well-preserved shell 5 well-preserved Density and size of S. (S.) pulchellum are opposite Stramentum (S.) pulchellum to the grade of damaging of the shell Does not exclude the possibility that S. (S.) pulchellum continued to grow after the ammonoid animal died

The interpretation of rapid burial of ammonite shells is measured in mm. The schematic drawings of the ammonite supported by Wani et al. (2005), who carried out taphonomic shells were plotted with these data (Figs. 4.2, 6.2, 7.2, 8.2, 9.2). experiments with Nautilus. These authors observed that the Stramentum (S.) pulchellum appears to have preferred phragmocone is only waterlogged after detachment of the smooth shells, or morphotypes with broad, shallow ribs. posterior mantle. This happened much faster in the shallow Ammonites with close ribbing or strong ornamentation such water due to a more rapid decay at high water temperatures. as Fagesia sp., Quitmaniceras reaseri Powell, 1963, or Large specimens became waterlogged faster than small ones Watinoceras sp. at Vallecillo (Ifrim and Stinnesbeck, 2007) because a much greater volume of decay gases developed in were apparently excluded as hosts. In addition, no specimen is the critical part of the mantle. The good preservation of large known to us attached to a heteromorph ammonoid from the ammonite shells in both Platy Limestones may point to a Platy Limestones, although Baculites sp. and ?Neocrioceras sp. similar biostratinomy. are abundant in the early Coniacian Yellow Limestone At Vallecillo, the lower lateral ammonite shell is well Member, and Scaphites sp. occur occasionally (Stinnesbeck preserved, because this side sunk into the sediment (Ifrim, et al., 2005). Hauschke and Scho¨llmann (2010) presented a 2006). The Peroniceras from Carranza was collected without stramentid attached to a Sciponoceras shell. This Cenomanian stratigraphic details, but the stramentids are also preserved on orthocone ammonoid has been repeatedly interpreted as its lower side. The body chamber of this specimen is preserved pelagic (Batt, 1989; Westermann, 1996; Monnet, 2009). as a flattened internal mold, partially exposed with its upper Two peaks are present in the size class distribution of the side (Fig. 4.1). This side is free of stramentids; they may have stramentids on ammonite specimens CPC-159 (Fig. 4.2) and decayed after the shell was deposited on the sea floor, UANL-FCT-VC109 (Fig. 8.2) and are here interpreted to comparable to the disarticulated stramentids on the venter represent two phases of colonization of the shells by of UANL-FCT-VC109 (Fig. 8.3). The possibility of ammonite stramentid larvae. In both ammonites, the largest stramentid shells representing benthic islands (Seilacher, 1982) can thus be specimens reach lengths .20 mm. They represent a first excluded for all Mexican specimens. In fact, Stramentum sp. generation, followed by a subsequent generation with ,10 mm are absent on benthic islands in the Platy Limestones, such as length. A similar pattern is noted on UANL-FCT-VCIX/16A bones, bivalve shells or upper ammonite shells. (Fig. 9.3), although only four specimens of S. (S.) pulchellum Strongest evidence of colonization during the lifetime of the are preserved on this ammonite. On this shell, a small Mexican ammonites analyzed here is provided by the Stramentum of 4.5 mm length is attached to a large specimen combination of preserved complete to subcomplete shell of 14.5 mm length (Figs. 5.3, 9.1). The peaks in size classes of apertures and even fragile spines in ammonites, along with UANL-FCT-VC500 (Fig. 6.3) and CPC-161 (Fig. 7.3) are at well-preserved large S. (S.) pulchellum (Table 1). The larger 5–10 mm and 10–15 mm length, and no large S. (S.) the stramentids grew, the longer the assumed drift phase. The pulchellum were recorded from these specimens. This colony material studied here includes ammonites with two subsequent may have been too young for a visible second phase of generations of stramentids (see below), indicating a long-term reproduction. A similar distribution was already described by colonization, but even these ammonite shells show excellently Breton and Boine´ (1993) on a three-dimensional fragment of preserved apertures and spines. the Cenomanian Acompsoceras Hyatt, 1903 with specimens of In conclusion, all ammonite shells here were colonized S. (S.) pulchellum attached to both sides of the shell. during their lifetime. The stramentids may have survived the No S. (S.) pulchellum is preserved near the aperture of any death of the ammonite, but the shell did not float for a long of the ammonites considered here. The specimen closest to a time. The well-preserved stramentids seem to have been shell aperture is a disarticulated plate at 17u on CPC-161, and embedded alive. an 11 mm long, articulated S. (S.) pulchellum at 30u on Complete and articulated (peduncle and capitulum) speci- UANL-FCT-VC109. In addition, the largest size class mens of S. (S.) pulchellum are generally found attached to (.20 mm) is never found within 90u from the aperture. It ammonite shells and/or isolated on layered sediments inter- seems that the ammonites continued to grow after settling of preted as being deposited under anoxic conditions, preventing the last stramentid larvae near the aperture. further disarticulation of the fragile organisms (Vega et al., It appears that ammonites did not remove stramentids 2007; Nomura et al., 2009, among others), consistent with the actively, indicated by small stramentids within ,90u from the paleoenvironment in which our stramentids are preserved. aperture, and by stramentids preserved on inner whorls near Attachment patterns.—Specimens of Stramentum (S.) pul- the aperture. In Turonian Lewesiceras sp. from Germany, chellum were mapped on the ammonite shells. Their position is several specimens of S. (S.) pulchellum were overgrown by recorded as distance from the ammonite umbilicus (U 5 0 mm) subsequent whorls (Wittler, 1996). This also suggests that and distance of the aperture in degrees (aperture 5 0u). The these epizoans did not interfere with their host ammonites. orientation of stramentid specimens is measured in degrees A preferred orientation of attached stramentids relative to relative to 0u, their length from the base to the apex is the host ammonites is not recognized. This strongly contrasts IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 531

FIGURE 6—Pseudaspidoceras flexuosum with 34 specimens of Stramentum (S.) pulchellum: 1, the layer of origin is unknown, but the lithology of the host rock indicates that this specimen may originate from the pink layers in the upper Vascoceras birchbyi and lower Mammites nodosoides zone, UANL- FCT-VC500, 30.5; 2, the drawing of the fossil shows the distribution of stramentids on the shell and preservation of the siphon, the arrow indicates the apical end of the body chamber; stramentids on the phragmocone are much less well-preserved than on the body chamber; 3, the size class distribution shows one peak at 5–10 mm length and one generation of stramentids. 532 JOURNAL OF PALEONTOLOGY, V. 85, NO. 3, 2011

FIGURE 7—Pseudaspidoceras flexuosum with 109 specimens of Stramentum (S.) pulchellum. 1, CPC-161, 3.72 m level of the Vallecillo section. 30.33. 2, Drawing showing the distribution of stramentids, which are even present on the spines. 3, The peak at the size class of 10–15 mm length indicates a single generation of stramentids. with the patterns recorded from Jurassic ammonites colonized Ecologic constraints.—At Vallecillo, the lowest record of by the sessile Pollicipes sp, which are always attached to the Stramentum (S.) pulchellum is from the 3.72 m level of the ventral ammonite shell and oriented towards a forward section, in the lower Turonian Vascoceras birchbyi Zone. Two swimming direction of the ammonite. They gave additional more ammonites (indet. and cf. Vascoceras sp. indet.) were weight and thus stabilization to the ammonite shell (Keupp et excavated from the 5.75 m level. The precise layers of origin of al., 1999). This effect can be excluded for the symbiosis of ammonites UANL-FCT-VC109 and 500 are unknown. Stramentum with the Mexican ammonites. However, the intensely pink host rock of UANL-FCT-

R FIGURE 8—Pseudaspidoceras flexuosum colonized by 46 Stramentum (S.) pulchellum and occasional oysters: 1, two peaks in the size class distribution point to two generations of stramentids; 2, the drawing shows that stramentids are abundant on the body chamber, whereas only few large specimens were recorded from the phragmocone. These are badly preserved, and the concentration on the body chamber may be an artifact of preservation. Empty symbols for stramentids are for specimens that disarticulated before embedding; 3, between the second and third spine, disarticulated S. (S.) pulchellum indicate decay of specimens on the venter after burial. The layer of origin of this specimen is unknown, but the large diameter of this ammonite indicates that it derives from the layers with maximum diameters of P. flexuosum in the upper Vascoceras birchbyi zone (Ifrim and Stinnesbeck, 2007), UANL- FCT-VC-109, 30.5. IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 533 534 JOURNAL OF PALEONTOLOGY, V. 85, NO. 3, 2011

FIGURE 9—Vascoceras sp. with four Stramentum (S.) pulchellum from the 5.75 m level: 1, UANL-FCT-VCIX16A, 31; 2, drawing showing the position and growth direction of Stramentum on the shell; 3, size class distribution of S. (S.) pulchellum.

VC500 indicates that this specimen derives from the pink islands such as bones, bivalve shells or upper ammonite shells layers in the upper Vascoceras birchbyi and lower Mammites lying on the sea floor strongly points to a low tolerance of these nodosoides zones (upper lower Turonian). UANL-FCT- cirripeds to low-oxygenated waters, consistent with the ecology VC109 is a large Pseudaspidoceras flexuosum and may derive of recent cirripedians. All well-preserved specimens on the from the upper Vascoceras birchbyi Zone, where P. flexuosum ammonite shells from Mexico appear to have been embedded is largest in the Vallecillo section (Ifrim and Stinnesbeck, alive, after the death of their host. 2007). Stramentids are thus only known from the upper part Our new records of S. (S.) pulchellum from the New World of the Vallecillo section (Fig. 2). In this interval of late early considerably enlarge the paleogeographic occurrence of this Turonian age, the pelagic ecosystem recovered from OAE 2. species. The long-lasting persistence of this species in Europe The microfauna in these layers indicates gradual improvement and southern North America suggests that it was much more of the environmental conditions in the water column, conservative regarding evolution than its hosts. The pseudo- including an increase in dissolved oxygen (Ifrim, 2006). The planktonic mode of life of Stramentum sp. by attachment to filter-feeding stramentids may thus have benefited from the ammonite shells was likely a response of a once benthic improved quality, i.e., oxygen levels of the oceanic water at the organism to repeated oxygen deficiencies in the early Late end of OAE 2. Cretaceous oceans, i.e., to the OAEs. Although the host species of S. (S.) pulchellum are different, their common epibiont indicates that they lived under similar ACKNOWLEDGMENTS ecologic conditions. As far as we are aware, there is no report WE ARE grateful to R. Gonza´lez Vazquez and family from on tolerance of recent scalpellids to oxygen-deficiency, and it is Vallecillo for providing fossils and access to the quarry, to J. unclear whether Stramentum sp. could occasionally tolerate G. Lo´pez Oliva (UANL-FCT) for logistical support and these conditions. However, the colonization and reproduction access to the collection, to A. H. Gonza´lez Gonza´lez and J. M. of S. (S.) pulchellum on ammonites shows that the host Padilla Gutie´rrez (MUDE) for logistic support and access to animals did certainly not dwell constantly in deeper oxygen- CPC collections, to S. Giersch for his introduction to deficient water layers, contrary to the interpretation of Fischer preparation techniques, E. ‘‘Dino’’ Frey (both Natural and Bottjer (1995). History Museum Karlsruhe) for vivid discussions on the fossil assemblages, T. Nyborg (Loma Linda University, California) CONCLUSIONS for reading the typescript, reviewers R. Feldman, J. W.M. Jagt Our data on early Late Cretaceous Stramentum (S.) and co-editor B. Huber for helpful suggestions and comments. pulchellum from northeast Mexico show that this cirriped Financial support of this research by the DFG (grants colonized the shells of living ammonites dwelling in well- FR1315/10, STI128/9) is gratefully acknowledged, but partic- oxygenated water levels near the surface, and that the epizoans ularly DFG grant IF61/2 enabled this study. did not interfere with the life of their hosts. Colonization of ammonite shells by Stramentum (S.) pulchellum was prevented REFERENCES by strong ornamentation only. The presence of two generations ALLISON, P. A. 1988. The role of anoxia in the decay and mineralization of of S. (S.) pulchellum on single shells suggests that Stramentum proteinaceous macrofossils. Paleobiology, 14:139–154. BATT, R. J. 1989. Ammonite shell morphotype distributions in the sp. larvae were short-lived, which prevented them from leaving Western Interior Greenhorn Sea and some paleoecological implications. the populations. The absence of Stramentum sp. on benthic Palaios, 4:32–42. IFRIM ET AL.—EPIZOIC STRAMENTID CIRRIPEDES ON LATE CRETACEOUS AMMONITES, MEXICO 535

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