Late Cretaceous Dwarf Decapods from Guerrero, Southern Mexico and Their Migration Patterns

Contributions to Zoology, 75 (3/4) 121-132 (2006)

Late Cretaceous dwarf decapods from Guerrero, southern Mexico and their migration patterns

René H.B. Fraaije1 , Francisco J. Vega2, Barry W.M. van Bakel1 and Luis M. Garibay-Romero2,3 1 Oertijdmuseum De Groene Poort, Bosscheweg 80, NL-5283 WB Boxtel, The Netherlands, E-mail: info@ oertijdmuseum.nl; 2 Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510, México, D. F., México, E-mail: [email protected]; 3 Unidad Académica de Ciencias de la Tierra, Universidad Autónoma de Guerrero, Ex Hacienda de San Juan Bautista, 40200, Taxco el Viejo, Guer- rero, México

Key words: Dwarﬁ sm, decapoda, Cretaceous, new species, Mexico

Abstract Introduction

Two new brachyuran species are described for the Upper Cre- The Mexcala Formation crops out in southern Mexi- taceous Mexcala Formation, Guerrero State, Mexico. Longu- co. It is reported from the states of Puebla, Morelos sorbis quadratus new species (Coniacian, Temalac region) is the oldest and southernmost record for the genus. Xanthosia and Guerrero. This lithostratigraphic unit is a com- zoquiapensis new species (Campanian, Zoquiapa region) is the plex sedimentary sequence, as it includes deep-wa- fi rst record for the genus in Mexico. In addition, the age for ter facies as well as very shallow marine sediments, Costacopluma bishopi Vega and Feldmann is discussed (Co- with lateral and vertical changes, overlying Lower niacian, Temalac region) and represents the oldest and south- Cretaceous limestones of the Morelos Formation. ernmost record for Cretaceous representatives of this genus in North America. All specimens are considerably smaller com- Defi ned by Fries (1960) as a 1,220 m fl ysh-like se- pared to other species of the same genera and are interpreted as quence of pelagic limestones and marls at its base, the fi rst example of brachyuran dwarfi sm in the geological the Mexcala Formation grades upward to shales, record. These species add new insight into possible migratory siltstones, sandstones, and conglomeratic lenses. An routes during the Late Cretaceous. Within Longusorbis, a north- early Coniacian age was proposed by Bohnenberg- western migratory route is documented from the Coniacian in Mexico to the Campanian - Maastrichtian of the west coast of Thomas (1955) for the Mexcala Formation. Cserna North America (Canada), whereas within the genus Xanthosia, (1965) named, described, and interpreted the litho- a western migratory route from the Albian of Europe to the logical units in the area. More recent stratigraphic Campanian of Mexico is indicated. Costacopluma migrated east reports have detailed facies distribution, sedimen- and north to the west coast of Africa, southeast North America tology, diagenesis, and subdivided the formation into and Greenland. members (Ontiveros-Tarango, 1973; Cserna et al., 1980; Ortega-Gutierrez, 1980; González-Pacheco, Contents 1988; Hernández-Romano et al., 1998; Hernández- Romano, 1999, among others). Most authors agree

Introduction ...... 121 that deposition of the ﬁ rst sediments of the Mexcala Systematic palaeontology ...... 124 Formation occured in Turonian times, while the last Longusorbis quadratus n. sp...... 124 marine deposits are found in late Maastrichtian silt- Xanthosia zoquiapensis n. sp...... 125 stones and sandstones of the study area (Alencáster, Costacopluma bishopi Vega and Feldmann, 1992 ...... 128 1980; Perrilliat et al., 2000). Discussion ...... 128 Acknowledgements ...... 129 Fossil content of the Mexcala Formation includes References ...... 129 foraminifera (Hernández-Romano et al., 1997; Lang 122 Fraaije et al – Dwarf decapods from Mexico

Fig. 1. Location map of the two studied localities in northeast Guerrero state, Southern Mexico. and Frerichs, 1998; Aguilera-Franco, 2000; 2003; tion in Guerrero. Locality IGM-2448 is found 5 Aguilera-Franco et al., 2001; Aguilera-Franco and km north of Temalac, a small village located 35 km Hernández-Romano, 2004; Aguilera-Franco and Al- southeast of Iguala, Guerrero. Locality IGM-3557 lison, 2005), gastropods and bivalves (Böse, 1923; is found near the town of Zoquiapa, northeast Alencáster, 1980; Alencáster et al., 1987; Perrilliat Guerrero (Fig. 1). and Vega, 1996; 2001; Garibay-Romero et al., 1998; Vega and Feldmann (1992) described Costaco- 2002; Kiel et al., 2000; 2002; Perrilliat et al., 2000; pluma bishopi based on very small specimens found Kiel and Perrilliat, 2001; 2004; Reyes-Prieto, 2004; on light-brown siltstones of locality IGM-2448. Vermeij et al., 2004); ammonoids (Burckhard, 1919; They proposed a Maastrichtian age for these sedi- González-Arreola, 1977); crustaceans (Vega and ments, but from recent studies on foraminifera and Feld mann, 1992); sea urchins and planktic crinoids rudists it is now clear that the age is Coniacian. Al- (Barrios-Matías, 1992; Sánchez-Rodríguez, 1997; though no complete section was measured due to Rosendo-Brito et al., 2002); ﬁ shes (Garibay-Romero intense folding and covered outcrops, a composite and Alvarado-Ortega, 2004; Alvarado-Ortega et al., column of 25 m of limestones, siltstones and sand- 2004, and dinosaur ichnites (Ferrusquía-Villafranca stones has been constructed (Fig. 2). The base of et al., 1993). this sequence is represented by an alternation of The brachyuran decapods described herein were dark-brown limestones and light-brown siltstones collected at two localities of the Mexcala Forma- and mudstones, with a rich content of fossils (fo- Contributions to Zoology, 75 (3/4) – 2006 123

raminifera, rudists, ostreids, echinoids and plant remains). This locality is interpreted to be the tran- sitional contact between the Morelos and Mexcala formations, marking the fi rst pulses of terrigenous sediments. Some well-preserved rudists are found on limestone layers of the Morelos Formation at the base of the section, and belong to the genus Touca- sia, of possible Turonian age. Based on foraminifera studies, Lang and Frerichs (1998) proposed a Coni- Fig. 2. Composite stratigraphic section at localities IGM-2448 acian age for the fi rst Laramide pulses in the study and IGM-3557, showing lithology and thickness of Morelos and area, marking as a change in the sedimentary regi- Mexcala formations. men from carbonates to fi ne siliciclastic sediments. Based on identifi cation of the Di ca rinella concavata cies, was found both in the uppermost limestone biozone, Lang and Frerichs (1998) placed the fi rst layers of the Morelos Formation, and in siltstones of strata of the Mexcala Formation in the Coniacian the lower part of the Mexcala Formation. It is im- just above what they called the Cuautla Formation portant to note that Lang and Frerichs (1998) pro- limestones. An interesting fact is that one of the spe- posed that the southern margin of the North cies here reported, Longusorbis quadratus new spe- American Plate in northern Guerrero was isolated 124 Fraaije et al – Dwarf decapods from Mexico from the Coniacian-early Santonian Pacifi c Ocean. and outwardly directed, massive outer orbital spine. However, occurrence of the other representative Including the outer orbital spine, the lateral margin species of Longusorbis, L. cuniculosus Richards, is armed with 4 equally outwardly directed spines 1975 in upper Campanian – lower Maastrichtian decreasing in size posteriorly. Regions are distinct sediments of the Shelter Point locality at Vancouver and demarcated by furrows. The anterior process of Island, Canada (Richards, 1975; Schweitzer et al. the relatively small mesogastric region extends al- 2003), clearly indicates a northwest migration of most to the frontal, the distinct top fading into the this genus during the Late Cretaceous. The upper- downturned sulcus of the rostrum. The most promi- most part of the Mexcala Formation is represented nent furrow is the cervical furrow extending sinu- by siltstones and sandstones of early to late Maas- ously from the base of the mesogastric lobe ending trichtian age in the Temalac – Mitepec area (Perril- below the outer orbital spine defi ning the posterior liat et al., 2000). margin of the swollen protogastric and hepatic re- The Mexcala Formation is represented by shal- gions. The forwardly-directed hepatic furrow sepa- low marine light brown siltstones nearby Zoquiapa rates the protogastric and hepatic regions. The width town, northeastern Guerrero, where a composite of the urogastric region is smaller than the maxi- section of 25 m (Fig. 2) contains several species of mum width of the mesogastric region. The broad gastropods and bivalves of Campanian age. shield shaped cardiac region is separated from the The material studied is deposited in the Colec- branchial regions by broad shallow furrows. The ción Nacional de Paleontología, Instituto de Ge- mesobranchial lobes bear three tubercles forming a ología, Universidad Nacional Autónoma de México. triangle. The posterolateral margins are long and Types are included in the Type Collection and clas- converging posteriorly, slightly concave at the prob- sifi ed under the acronym IGM. able point of attachment of the fi fth pereiopods.

Material. Two specimens. Holotype IGM-8969, and Systematic palaeontology paratype IGM-8970. Coniacian, Mexcala Forma- tion, Temalac, Guerrero. Order Decapoda Latreille, 1802 Section Heterotremata Guinot, 1977 Measurements. Holotype IGM-8969 length ca. 5.0 Superfamily Portunoidea Rafi nesque, 1815 mm, width ca. 5.0 mm. Paratype IGM-8970 length Family Carcineretidae Beurlen, 1930 ca. 13.0 mm, width ca. 13.8 mm. Genus Longusorbis Richards, 1975 Etymology. Refers to carapace outline. Type species. Longusorbis cuniculosus Richards, 1975 by monotypy. Remarks. This new species differs from L. cuniculosus in having a quadrate outline, a spinose poste- Longusorbis quadratus new species ro-lateral margin, a signifi cantly narrower urogastric Figures 3.1, 3.2, 4.1 region and a more robust front. This genus migrated at the end of the Cretaceous Diagnosis. Relatively small Longusorbis, with quad- to the north where, in the late Campanian-early rate carapace, ornamented margins and narrow uro- Maas trichtian, the closely related L. cuniculosus gastric region. reaches up to 5 cm in carapace width (4 times larger than L. quadratus n. sp.) in the Shelter Point locality Description. Relatively small carapace, quadrate in at Vancouver Island, Canada (Richards, 1975; Sch- outline, widest across the anterior third located at weitzer et al. 2003). the outer orbital spines, weakly convex transversely An eastward migration has also to be taken in ac- and longitudinally. Rostrum medially sulcate and count considering the close evolutionary relationship downturned, broadly rimmed and bicornate base. with the genus Carcineretes known from the Maas- Wide orbits cut by two fi ssures, inner third concave, trichtian of SE Mexico, Belize and Jamaica (Vega et outer two-third fi rst sinuous ending in a forwardly al. 1997; 2001). Longusorbis and Carcineretes have Contributions to Zoology, 75 (3/4) – 2006 125 a very similar quadratic outline, bicornate and down- the margins transversely, length about two-thirds the turned rostrum, orbital incisions, carapace groove- width. The frontal area is bilobed and slightly ex- arrangement and posterior margin morphology. tended beyond the orbits; a deep median sulcus di- The genera Withersella, Torynomma and Bink- vides around the anterior part of the mesogastric horstia, all belonging to the Torynommidae (van process. The orbits are extremely large, elliptical and Bakel et al., 2003), also have very similar to almost outward facing. The rimmed orbital margin bears identical dorsal carapace morphologies as seen in two short notches. Orbitofrontal margin covers about the carcineretids. Distinction often can only be made 70% the total carapace width. The anterolateral mar- on the ventral characters. Torynommidae differ only gin is straight starting at the large, blunt outer orbital from the Carcineretidae in having a dorsally orien- spine, and regularly divided by four notches. The tated, strongly reduced fourth and/or fi fth pair of widest part of the carapace is at the epibranchial an- pereiopods, and being much smaller in overall size. gle. The posterolateral margin is clearly convex and Either the Carcineretidae and the Torynommidae indented by a relatively long, frontally directed mes- are evolutionary very closely related or the dorsal obranchial notch. Carapace separated into distinct similarities are a matter of convergence. In the fi rst regions by shallow groove system. Cervical furrow case the Torynommidae should also be placed in the strongly sinuous. Posterior margin concave, bor- Superfamily Portunoidea. To solve this matter more dered with distinct ridge and about half the total study and material is needed. carapace width. The carcineretids and torynommids, although relatively successful during the Cretaceous, fi nally Material. Two internal moulds of carapace. Holo- didn’t cross the K/T boundary. It seems that they type IGM-8971, and paratype IGM-8972. Campa- couldn’t cope with the thinner, more spinose and nian, Mexcala Formation, Zoquiapa, Guerrero. hexagonal carapaces (better swimming morphology) and much larger orbits (better predatory mor- Measurements. Holotype IGM-8971 length ca. 9.0 phology) of the Late Cretaceous radiating genera mm, width ca. 6.0 mm. Paratype IGM-8972 length like Xanthosia and Cretachlorodius (Fraaye, 1996). ca. 9.0 mm, width ca. 7.0 mm. Distribution of the two known species of Longu- sorbis is given in Figure 5. Etymology. Named after Zoquiapa town, nearby locality IGM-3557. Section Podotremata Guinot, 1977 Family Etyidae Guinot and Tavares, 2001 Remarks. Xanthosia zoquiapensis n. sp. differs clear- Genus Xanthosia Bell, 1863 ly from the American Gulf Coast Plain species (Sch- weitzer Hopkins et al., 1999) in having a much wider Type species. Xanthosia gibbosa Bell, 1863 (= Po- orbitofrontal area, a strongly convex posterolateral dophthalmus buchii Reuss, 1845) by subsequent margin and the absence of granular ornamentation. designation of Glaessner (1929). Concerning groove arrangement, orbit and margin morphologies, X. zoquiapensis n. sp. is most closely Xanthosia zoquiapensis new species related to X. buchi (Reus, 1845) (Albian-Cenomani- Figures 3.3, 3.4, 4.2 an), X. socialis Bakel, Fraaije & Jagt, 2005 (Campa- nian) and X. semiornata Jagt, Collins & Fraaye, 1991 Diagnosis. Very small etyid; carapace sub-hexago- (Maastrichtian) all known from NW Europe. nal in outline, wider than long; anterolateral margin It differs from X. buchi and X. socialis in having scalloped and posterior margin convex; front sul- a much more convex posterolateral margin and a cate; orbits very large; orbitofrontal margin more shorter and interrupted mesobranchial furrow and than half total width; prominent sinuous cervical from X. semiornata in lacking a strong anterior or- furrow, several branchial furrows. namentation. In addition, the new species is stockier than most species of Xanthosia. Description. The carapace is subhexagonal in out- Van Bakel et al. (2005) drew attention to a pos- line, almost fl at longitudinally and gently inclined at sible westward migration from the possible ancestor 126 Fraaije et al – Dwarf decapods from Mexico Contributions to Zoology, 75 (3/4) – 2006 127

1 2 3

Fig. 4. 1. Reconstruction of Longusorbis quadratus new species. 2. Reconstruction of Xanthosia zoquiapensis new species. 3. Recon- struction of Costacopluma bishopi Vega and Feldmann.

ᮡ Fig. 5. Coniacian – Paleocene paleobiogeographic distribution of brachyuran species of genera present in Temalac and Zoquia- pa study areas, Guerrero. Base map modiﬁ ed from Barron, 1981; Dhondt, 1992 and Smith, 1994. Data based on: Collins and Mor- ris, 1975; Richards, 1975; Vega and Perrilliat, 1989; Collins and ᮤ Fig. 3. 1, 2, Longusorbis quadratus new species. 1. Holotype Rasmussen, 1992; Collins et al., 1994; Feldmann and Matins- IGM-8969. 2. Paratype IGM-8970. 3, 4, Xanthosia zoquiapensis Neto, 1995; Vega et al., 1995; Feldmann et al., 1997; Schweitzer new species. 3. Holotype IGM-8971. 4. Paratype IGM-8972. 5, et al., 1999; Guinot and Tavares, 2001; Schweitzer et al., 2003; 6, Costacopluma bishopi Vega and Feldmann. 5. Paratype IGM- Nyborg et al., 2003; Araujo-Távora and Da Cruz-Miranda, 2004; 8973. 6. Paratype IGM-8974. Scale bars equals 5.0 mm. van Bakel et al., 2005. 128 Fraaije et al – Dwarf decapods from Mexico

X. buchi towards the Campanian species from the from the Upper Cretaceous of Nigeria, Collins and American Western Interior and Atlantic Coastal Morris (1975) mentioned presence of two paratypes Plain. The occurrence of X. zoquiapensis n. sp. in from the Coniacian of the Awgu Limestone, Abaka- the Campanian of Mexico perfectly fi ts into this liki Province. However, none of these paratypes is paleomigratory model. Figure 5 illustrates distribu- illustrated and although their morphology may re- tion of species of Xanthosia during the Late Creta- semble Costacopluma, it is not clear if these speci- ceous. mens do belong to this genus. Thus, C. bishopi is the fi rst well-documented report for Costacopluma in Superfamily Retroplumoidea Gill, 1894 Coniacian beds and may represent the oldest occur- Family Retroplumidae Gill, 1894 rence of a widely distributed genus during Late Cre- Genus Costacopluma Collins and Morris, 1975 taceous – Northeastern Mexico, Greenland, Nigeria, Northern India – (Collins and Morris, 1975; Gaetani Type species. Costacopluma concava Collins and et al., 1983; Vega and Perrilliat, 1989; Collins and Morris, 1975 by original designation. Rasmussen, 1992; Vega and Feldmann, 1992;), and the Paleocene – California, Venezuela, Senegal, Bra- Costacopluma bishopi Vega and Feldmann, 1992 zil, Argentina – (Collins et al., 1994; Feldmann and Figures 3.5, 3.6, 4.3 Martins-Neto, 1995; Feldmann et al., 1995; 1997; De Araújo-Távora and Da Cruz-Miranda, 2004; Ny- Description. Carapace small, ovate in transverse borg et al. 2003) (Fig. 5). section, widest at level of mesobranchial areas, with C. binodosa from the upper Campanian of Green- three prominent, rounded transverse ridges. Antero- land was described by Collins and Rasmussen, 1992 lateral margins straight, with a small spine at level on the basis of one incomplete specimen. It is larger of cervical groove; posterolateral margins rounded; than C. bishopi and bears straight lateral margins. posterior margin straight; anterior margin nearly If the genus raised in America, it must have mi- straight, slightly concave above orbits, bordered by grated eastwards to Africa, and northwards to Green- two prominent, forward directed spines. Orbits large, land. African retroplumids also migrated to the east, rounded. Rostrum prominent, bilobulate. Fused pro- to reach the north part of India, and by Paleocene togastric and mesogastric lobes form anterior trans- times, Costacopluma prevailed in the Paleocene verse ridge, slightly inclined backwards in central seas of Senegal (Fig. 5). Although abundant in part to ovate mesogastric lobe. Cervical groove northeastern Mexico during Maastrichtian times, deep, parallel to protogastric lobes, curved at level the genus vanished in this area by Paleocene times, of mesobranchial lobes. Second ridge formed by fu- and dispersed west to California and south to the sion of epibranchial and mesobranchial lobes, of north and central parts of South America (Fig. 5). nearly uniform width, inclined posteriorly to base During Eocene times in Europe, Costacopluma of mesogastric lobe where they become narrower. may have given rise to the extant genus Retropluma Posterior ridge formed by metabranchial lobes and Gill, 1894 (see Via, 1982), known from deep-water cardiac/intestinal regions. Metabranchial lobes per- settings of the modern Indopacifi c sea (Saint Lau- pendicular to carapace length, half as long as epi- rent, 1989). branchial/mesobranchial lobes. Cardiac region subtrapezoidal, intestinal region narrow at base of cardiac region. Discussion

Material. Hypotypes IGM-8973 to IGM-8974. Vega and Feldmann (1992) described Costacopluma bishopi on the basis of eight carapaces. Because of Measurements. Hypotype IGM-8973 length ca. 6.5 the extremely small size (average width: 4.9 mm) of mm, width ca. 7.5 mm. Hypotype IGM-8974 length their material, these authors interpreted them as ju- ca. 6.3 mm, width ca. 9.0 mm. veniles, yet, at the same time, they also noted overall carapace morphology to be closely similar to Remarks. In documenting Costacopluma concava adults of the related taxa, Costacopluma mexicana Contributions to Zoology, 75 (3/4) – 2006 129

Figure 6. Costacopluma mexicana Vega and Perrilliat, 1989. 1. Juvenile specimen, Maastrichtian, Potrerillos Formation, Nuevo León, northeastern México. 2. Adult specimen, Maastrichtian, Potrerillos Formation, Nuevo León, northeastern México. Scale bars equals 5.0 mm.

and C. concava. Comparing the mean carapace width predators and/or strong fl uviatile input/admixture of C. bishopi (ten specimens and four fragmentary inducing brackish waters might be worthwhile pur- carapaces known to date), with that of C. mexicana suing in detail to understand the observed size ab- (numerous specimens known) and C. concava (four normality. known specimens) yields ratios of 1:3.5 and ca. 1:4, respectively. A comparison of average carapace width in Lon- Acknowledgements gusorbis quadratus n. sp. and Xanthosia zoquiapensis n. sp. with their closest relatives reveals a striking We thank R.M. Feldmann, D. Guinot, J.W.M Jagt similarity; that of the former species (two specimens and F. Schram for comments that improved the known) is approximately 3.5 times less than of L. manuscript and R.M. Feldmann for supplying us an cuniculosus (numerous specimens available) and item of literature. that of the latter (two specimens at hand) equals around 30% of that of X. buchi, around 30% of that References of X. socialis (a single specimen known) and around 25% of that of X. semiornata (six specimens). Aguilera-Franco N. 2000. High Resolution Stratigraphy and The above-mentioned consistency in width ratios Palaeoecology of the Cenomanian-Turonian Succession, South- in all three species described, i.e. all being about 3.5 ern México: Ph.D. Dissertation, T.H. Huxley School of Envi- times smaller than their closest relatives, and over- ronment, Earth Sciences and Engineering, Imperial College all adult carapace morphology (Fig. 6) suggests in- of Science Technology and Medicine, University of London, U.K., 244 p. terpretation of this decapod assemblage as the fi rst Aguilera-Franco N. 2003. Cenomanian-Coniacian zonation example of brachyuran dwarfi sm in the geological (foraminifers and calcareous algae) in the Guerrero-Morelos record. The environmental selection to favour this basin, southern Mexico: Revista Mexicana de Ciencias Ge- type of dwarfi sm in this tectonically active basin ológicas 20: 202-222. Aguilera-Franco N, Allison P. 2005. Events of the Cenomanian- are still unknown, and further study is needed. Fac- Turonian Succession, Southern México. Journal of Iberian tors such as limited food supply, size-correlated Geology 31(1): 25-50. 130 Fraaije et al – Dwarf decapods from Mexico

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