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Paleobotany |
Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Del. Coyoacan, 04510 México D.F., Mexico
Received for publication December 21, 2006. Accepted for publication August 7, 2007.
ABSTRACT
Recently discovered fossil flowers from the Cretaceous Cerro del Pueblo and flowers and fruits from the Oligocene Coatzingo Formations are assigned to the Rhamnaceae. The Cretaceous flower, Coahuilanthus belindae Calvillo-Canadell and Cevallos-Ferriz, gen. et sp. nov., is actinomorphic with fused perianth parts forming a slightly campanulate to cupulate floral cup, with sepals slightly keeled and spatulate clawed petals. The Oligocene fossils include Nahinda axamilpensis Calvillo-Canadell and Cevallos-Ferriz, gen. et sp. nov. (characterized by its campanulate bisexual flower with stamens opposite, adnate to and enfolded by petals; and with the ovary ripening into a drupe), and a winged fruit assigned to Ventilago engoto Calvillo-Canadell and Cevallos-Ferriz, sp. nov. The flowers and drupe features indicate closer affinity to Zizipheae and/or Rhamneae, while the single samaroid fruit suggests the presence of Ventilagineae. However, the unique character combination in the fossil flowers precludes placing them in extant genera. Nevertheless, the history of the family is long and can be traced back to the Campanian. A detailed phylogenetic revision of the group that uses morphological characters from both extant and fossil plants is needed to better understand the significance of these records as well as other important fossils of the family.
Key Words: Cretaceous • fossil flowers • Mexico • Oligocene • Rhamnaceae
Recent findings of fossil angiosperms document a larger diversity than previously known from low latitude North America and support new hypotheses on the origin and diversification of ancient flowering plant lineages in the area (e.g., Magallón-Puebla and Cevallos-Ferriz, 1994a
–c
; Velasco-de León et al., 1998
; Ramírez et al., 2000
; Velasco-de León and Cevallos-Ferriz, 2000
; Calvillo-Canadell, 2000
; Calvillo-Canadell and Cevallos-Ferriz, 2002
, 2005
). This fossil record indicates the presence during Cretaceous and Paleogene of lineages otherwise thought to have arrived in low latitude North America during the Plio-Pleistocene (Cevallos-Ferriz and Ramírez, 1998
; Ramírez and Cevallos-Ferriz, 2000
). Furthermore, these discoveries aid in proposing new biogeographic routes and establishing the minimum time for the appearance of endemic and the so-called relict and refugee taxa in the area (e.g., Magallón-Puebla and Cevallos-Ferriz, 1994b
; Martínez-Cabrera, 2001
; Martínez-Millán, 2000
, 2003
; Ramírez and Cevallos-Ferriz, 2000
; Ramírez et al., 2000
; Calvillo-Canadell and Cevallos-Ferriz, 2005
). They also offer evidence that links low latitude and high latitude paleofloras of North America, Asia, Europe, and South America (e.g., Magallón-Puebla and Cevallos-Ferriz, 1994a
–c
; Velasco-de León et al., 1998
; Ramírez et al., 2000
; Velasco-de León and Cevallos-Ferriz, 2000
; Calvillo-Canadell, 2000
).
Rhamnaceae is a family whose phylogenetic relationships have been difficult to establish. Recent molecular analyses confirm its monophyly, and infrafamiliar rearrangements have been proposed (Richardson et al., 2000a
, b
; Medan and Schirarend, 2004
). In these studies, traditional classifications based on fruit types (Suessenguth, 1953
) have also been questioned. Unfortunately, these analyses have used few morphological data, and more detailed studies based on larger sets of morphological characters with a more accurate coding may better reflect phylogeny (Richardson et al., 2000a
, b
). Because information from fossil plants (Table 1) was not used in these studies, and estimates of the time of origin and diversification of taxa within Rhamnaceae are based on few fossils not closely related to the family (e.g., Richardson et al., 2000a
, b
), the new records introduced here should aid our historical understanding of the group.
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; Manchester and Tiffney, 2001
; Crepet et al., 2004
; Graur and Martin, 2004
). In the present study, we describe fossil flowers and fruits that are morphologically similar to those of extant Rhamnaceae. These findings expand our understanding of the combination of characters and taxa within this family, providing new information to refine future systematic and phylogenetic studies of the group. MATERIALS AND METHODS
The fossil material was collected at two different localities. The Late Cretaceous (late Campanian) El Almácigo locality (Cerro del Pueblo Formation) is located in General Cepeda County, Coahuila (25°31' N and 101°19' W, Fig. 1) (Boyd, 1959
; Murray et al., 1962
; McBride et al., 1974
; Vega-Vera and Perrilliat, 1990
; Kirkland et al., 2000
). The Oligocene Los Ahuehuetes locality (Coatzingo Formation) is located ca. 4.5 km NNE of Tepexi de Rodríguez, Puebla (18°35'15'' N and 97°55'30'' W, Fig. 2) (Calvillo-Canadell and Cevallos-Ferriz, 2005
; Beraldi et al., 2006
).
|
|
; Murray et al., 1962
; McBride et al., 1974
; Vega-Vera and Perrilliat, 1990
; Kirkland et al., 2000
). The Cerro Huerta Formation has been dated as Maastrichtian based on the presence of a bivalve (Exogyra costata Say) and a cephalopod (Sphenodiscus pleurisepta Conrad), while a late Campanian age has been suggested for the Cerro del Pueblo Formation based on physical geology and the presence of E. ponderosa Römer (Boyd, 1959
; Murray et al., 1962
; McBride et al., 1974
; Vega-Vera and Perrilliat, 1990
; Kirkland et al., 2000
).
The Los Ahuehuetes locality was formerly assigned to the Pie de Vaca Formation based on geological observations of Pantoja-Alor (1992)
; however, a review of the geology on a regional scale places Los Ahuehuetes as part of the Ahuehuetes Unit, Coatzingo Formation (Silva-Romo, 1998
). Toward the base, this unit is composed of chert and limestone followed by fossiliferous volcanic ashes and sandstones. The sedimentary sequence has been interpreted as deposited in a low energy lacustrine basin (Beraldi et al., 2006
). A minimum Oligocene age of these sediments has been suggested based on physical stratigraphic correlations, a preliminary palynological study, and plant macrofossil time ranges (Martínez-Hernández and Ramírez-Arriaga, 1996
; Silva-Romo, 1998
). However, this age still needs to be confirmed by radiometric dating.
Eighteen fossil flower impressions were collected from the Cerro del Pueblo Formation and 24 from the Coatzingo Formation. Additionally, from the latter, two different fruit types also related to Rhamnaceae have been distinguished, one represented by several drupes, while the second one is known from a single-winged fruit. The fossils were studied using an SHZ Olympus (Tokyo, Japan) stereoscopic microscope equipped with a camera lucida. Terminology follows Radford et al. (1974)
, Roth (1977)
, Moreno (1984)
, and Harris and Harris (2003)
. Comparisons with extant plants were based on material deposited in the National Herbarium of Mexico (MEXU) and data in the literature. When similarities between fossil and extant material were observed, all available extant flowers and fruits of these particular taxa were studied, as were those of closely related plants.
SYSTEMATIC DESCRIPTION
Family: Rhamnaceae
Tribe: Rhamneae/Zizipheae
Genus: Coahuilanthus gen. nov. Calvillo-Canadell and Cevallos-Ferriz
Species: Coahuilanthus belindae gen. et sp. nov. Calvillo-Canadell and Cevallos-Ferriz
Etymology: The generic name refers to the Mexican state of Coahuila where the fossils were collected; the specific epithet honors Belinda Martínez for her discovery of the El Almácigo locality and fossil conservation work in Coahuila.
Holotype: Paleontological Collection of the Instituto de Geología, UNAM, catalog no. IGM-PB 2573.
Other examined specimens: 17 (IGM-PB 2574–2590).
Locality: El Almácigo, Cerro del Pueblo Formation, General Cepeda County, Coahuila, Mexico, 25°31' N, 101°19' W.
Age: Late Cretaceous (late Campanian).
Number of examined specimens: 18
Diagnosis: Small actinomorphic, pediceled, pentamerous, bisexual flowers; floral cup campanulate to cupulate; calyx lobes 5, lobes deltoid to ovate, slightly keeled, inserted in the margin of the floral cup; five spatulate, clawed petals, shorter than the calyx-lobes; epipetalous stamens with sub-basifixed anthers; nectariferous lobed ring.
Description: The fossil material consists of 18 specimens, some of them fragmented, some with possible negative or positive counterparts. These small, bisexual, and pentamerous flowers have actinomorphic symmetry, with fused perianth parts forming a slightly campanulate to cupulate floral cup, 2.5–3.5 mm long and 1.1–2.0 mm wide (Figs. 3, 6, 9, 14, 15, 17). The pedicel is 1.0–3.0 mm long (Figs. 3, 4, 6, 14). Five sepals are well preserved and fused in their lower part, forming part of the floral cup; their distal portion is free, and the lobes are deltoid to ovate with a slightly keeled surface (Figs. 3, 5, 7–9), reaching 0.8–1.2 mm wide and 1.2–1.8 mm long. The spatulate, clawed petals, when present, are very small, 0.3 mm wide and 0.7 mm long (Figs. 4, 13); frequently they are not well preserved, but some scars that alternate with the sepals strongly suggest their presence. Opposite and adnate to them are the stamens (obhaplostemonous) that are slightly shorter than the petals. They are composed of a subulate filament, 0.6 mm long, and sub-basifixed dithecal anthers, 0.08 mm in diameter (Fig. 16).
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Comparative morphology: The floral morphology of Coahuilanthus belindae is consistent with Rhamneae (e.g., Rhamnus and Sageretia) (Figs. 40, 41) and Zizypheae (e.g., Berchemia) (Fig. 44). Floral cup structure and parts of the perianth are very much like those of Rhamnus and Berchemia. For example, they share five acute, triangular, slightly keeled sepals lacking a thickening on the adaxial surface, and an acute campanulate floral cup. Coahuilanthus belindae shares with Sageretia a nectariferous ring with an irregular crenate margin (Brizicky, 1964
). Nevertheless, they differ in other floral characters like the conspicuously keeled petals in Zyzypheae, obovate petals in Sageretia and Berchemia, or flat and bilobed petals in Rhamnus; these differences support the recognition of a new taxon.
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Species: Nahinda axamilpensis gen. et sp. nov. Calvillo-Canadell and Cevallos-Ferriz
Holotype: Paleontological Collection of the Instituto de Geología, UNAM, catalog no. IGM-PB 2591.
Number of examined specimens: 24 (IGM-PB 2592–2614).
Locality: Los Ahuehuetes, Coatzingo Formation, in the southern part of the Axamilpa River, 4.5 km NNE of Tepexi de Rodríguez, Puebla, 18°35'15'' N, 97°55'30'' W.
Age: Oligocene.
Etymology: The generic name derives from the word flower in the "mixteco" dialect; the specific epithet refers to the Axamilpa River along which the fossil flowers were collected.
Diagnosis: Small actinomorphic, pedicellate, pentamerous, bisexual flowers; campanulate floral cup, calyx lobes five, deltoid and clearly keeled with thickened apex, inserted in floral cup margin; five spatulate to cucullate, short-clawed petals with apical notch, generally shorter than calyx lobes; stamens opposite, adnate to and enfolded by petals, with subulate filament and sub-basifixed anthers; three-carpellate gynoecium with a single style ending in three stigmatic lobes and three locules; pentagonal, lobed, nectariferous ring; pedunculate, cyma-like umbella.
Description: The fossil material consists of 24 specimens with their counterparts, but some of them are fragmentary. Most flowers are at anthesis; a few represent fruits, and there is a single inflorescence. These small, bisexual, pentamerous, and actinomorphic flowers are 2.0–6.8 mm long and have a campanulate floral cup 2.5–5.0 mm long by 1.5–3.5 mm wide (Figs. 22–24, 29, 34); some have a pedicel up to 6.0 mm long. The calyx consists of five triangular or deltatoid sepals up to 2.0 mm wide and 3.0 mm long (Figs. 18–26), with a conspicuous keel and notch near the sepal tip. The corolla generally consists of five petals; some petals did not persist in fossil material, but their attachment scars are evident. The petals are spatulate to cucullate, short, clawed, with an apical notch, 1.1 mm long and 0.9 mm wide (Figs. 21–24, 31, 34, 35). Adnate to and opposing them are the stamens; each one consists of a triangular or subulate filament, 2.0 mm long, and a bilocular oval anther, 1.0 mm long and 0.5 mm wide, slightly longer than the petals (Figs. 19, 21, 26, 30, 31, 34).
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A nectary-bearing ring is prominent (4.5 mm in diameter) and highly lobed (Fig. 20).
One of the specimens is a well-preserved cyme or umbel-like inflorescence (Fig. 33), consisting of about four pedicelate flowers developing from the same point; two of them are missing, being represented by the persistent pedicel (4.0 mm long); the other two have flowers in different developmental stages. One is a mature flower with withered sepals (4.0 mm in diameter), while juvenile flowers are still closed (2.0 mm in diameter). The largest flower is located in the middle of the inflorescence and could suggest the maturation sequence of the inflorescence (Fig. 33).
Comparative morphology: Nahinda axamilpensis fossils can be organized into an ontogenetic series to document how these reproductive organs grew and matured from a floral bud to mature perfect flowers in a small cyme-like inflorescence (Figs. 29, 33), and then how they ripened to an oval drupe-like structure (Figs. 25, 27–28, 30, 32). However, their taxonomic affinities remain uncertain. The type of inflorescence (pedunculate "umbel-like cyme") documented in the fossil plant is similar to that of Adolphia, which consists of very few small flowers. As the flower buds of Adolphia mature and reach anthesis, morphological similarities among the extant and fossil reproductive structures continue to be seen. At this stage, perhaps size is the most significant difference, but the fact that the fossil fruits seem to remain as a single unit, while in Adolphia they split into mericarps limits their similarity.
Morphological flower characteristics of Nahinda axamilpensis suggest further similarities to Adolphia (Colletiaea) and to some members of Zizypheae (Paliureae in Richardson et al., 2000a
, b
; Ziziphus, Berchemia, Karwinskia) (Figs. 36–39, 42–48), and Rhamneae (Hovenia, Rhamnus) (Figs. 40–41). Though similarities of Nahinda to members of Zizypheae are important, no single extant taxon has all characters found in the fossil material. For example, in Ziziphus amole (Sesse & Mociño) M. C. Johnston, Z. obtusifolia (Hook. ex. Torrey. & A. Gray) A. Gray, Z. mexicana Rose (Figs. 36–38, 43), Berchemia racemosa Sieb. et Zucc., and B. scandens (Hill) K. Koch (Fig. 44), the perianth structure, campanulate floral cup, and triangular-ovate sepals with prominent keel and apical thickness are comparable morphologically to those of Nahinda, but otherwise the floral characters are different. Another morphological character found in the fossil material that can be compared with Ziziphus amole is the presence of a three-lobed stigma (Fig. 43). The flower of Ziziphus mauritiana Lam. is most similar to the fossil flowers in having subulate filaments with sub-basifixed anthers enfolded by petals, but further comparison limits their similarity. Karwinskia (Fig. 39) has petals comparable with those of the Oligocene material, but again, they are different otherwise. Berchemia reproductive organs (Fig. 44) are also similar to the fossils in having a drupaceous elliptical fruit, but its flowers are unisexual by abortion and borne in a thyrse (Brizicky, 1964
). These characters contrast with a cyme-like inflorescence bearing hermaphroditic flowers in the fossil material. The fossil drupe-like fruit can be compared with Ziziphus mexicana, Z. amole and Condalia microphylla Cav. (Figs. 45, 48, 49). The characters preserved in the fossil material and the inferred developmental sequence support affinities to Rhamnaceae, but the differences discussed justify the recognition of a new taxon within this family.
Tribe: Ventilagineae
Genus: Ventilago Bent.
Species: Ventilago engoto sp. nov. Calvillo-Canadell and Cevallos-Ferriz
Etymology: The specific epithet is in recognition of Enrique González Torres, for his interest in explaining Cenozoic geologic history of Mexico to biologists pursuing a more geologically grounded history of plant lineages growing at present in Mexico and introducing young paleontologists to geology.
Holotype: Paleontological Collection of the Instituto de Geología, UNAM, catalog no. IGM-PB 2875.
Locality: Los Ahuehuetes, Coatzingo Formation, in the southern part of the Axamilpa River, 4.5 km NNE of Tepexi de Rodríguez, Puebla, 18°35'15'' N, 97°55'30'' W.
Age: Oligocene.
Number of examined specimens: 1
Diagnosis: Chartaceous, elliptical, winged fruit with proximal, rounded, nut-like fruiting body; the nut-like equatorial zone marked by a prominent rim; distal wing with prominent mid vein and reticulate secondary veins.
Description: This fossil fruit is 1.5 cm long. It can be divided into a proximal nut-like zone and a distal papery-winged zone (Fig. 50). The nut-like structure is 0.3 mm long and has a diameter of ca. 0.3 mm. The fruit wall of the nut-like structure is fibrous and in its equatorial zone has a rim through which the distal zone of the nut-like body may dehisce (Fig. 52). The elliptical wing is 12.0 mm long by 4.0 mm wide; it has a middle vein, 1.0 mm in diameter, flanked by secondary veins forming a reticulum.
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DISCUSSION
Morphological characters in both fossil flowers suggest affinities to Rhamanceae; these characters include a very small, actinomorphic, perfect, and pentamerous structure with a floral cup that ranges from cupulate to campanulate (Figs. 36–44, 46, 47). This taxonomic affinity is further supported by other characters, such as the deltoid to ovate, slightly to prominently keeled sepals, that have a pad of tissue covering the distal zones (especially in the Oligocene material; Cronquist, 1981
), and the petals, that may be spatulate to cucullate, short clawed and with an apical notch. Of special interest are the adnate stamens opposite and always enfolded by petals; these features are a rare condition in angiosperms and are diagnostic of Rhamnaceae (Woodson et al., 1971
; Richardson et al., 2000a
, b
).
Even with all of these characteristics, it is difficult to identify the fossil flowers to generic or specific levels within known taxa. However, it is clear that the known characters and their similarities to those of extant Rhamnaceae are sufficient arguments to accept the inclusion of the new fossil material within the family. Furthermore, it is possible to recognize morphological characters suggestive of a relationship with a few genera of some tribes within the family. As in the Suessenguth system (1953), our tribal divisions are based on fruit characters and consist of Maesopsideae, Ventilagineae, Zizypheae, Rhamneae, Colletieae, and Gouanieae. Some large tribes that are morphologically heterogeneous, like Zizypheae, exemplify the limitation of this classification. Richardson et al. (2000a
, b
) further documented this situation, recognizing only three groups within the family. Nevertheless, we follow Suessenguth's classification while waiting for a complete review of this problem to avoid further taxonomic confusion.
It is important to note that a phylogenetic approach to resolve relationships within the family has been proposed based on rbcL and trnL-F sequences of the plastid genome but with reference to few morphological data (Richardson et al., 2000a
, b
). For this reason, it is difficult to integrate the morphology-based fossil material, and thus it would be premature to introduce the new plants using this phylogenetic scheme. All the new reports may represent plants with characters found in either the rhamnoid or ziziphoid groups of Richardson et al. (2000a
, b
).
The new taxa are referred here as morphotaxa with affinities to members of Rhamnaceae (McNeill et al., 2006
). In doing this, we recognize flower variation between the fossil and extant plants, which is evident from comparison of their detailed descriptions to those of living taxa (e.g., Weberbauer, 1896
; Brizicky, 1964
; Woodson et al., 1971
; Fernández-Nava, 1986
; Medan and Hilger, 1992
). Furthermore, this decision highlights variability through time in these reproductive structures. Further explanation of these differences needs a phylogenetic analysis that includes more morphological characters (e.g., Jeong et al., 1997
; Richardson et al., 2000a
, b
; Richardson et al., 2004
). These and other fossil materials will at this time be of great value in generating a hypothesis based on both extant and fossil evidence.
Flowers of these new fossil plants strongly suggest that the morphological pattern found in Zizypheae and Rhamneae was underway during the Late Cretaceous and certainly was present during the Paleogene. The broad geographic distribution of Eocene fruits assigned to Paliurus (Manchester, 1999
) supports an early differentiation of these tribes, especially of Paliureae (Zyzypheae). Among Rhamnaceae, the new winged fruit is characteristic of Ventilago (Ventilagineae) (Figs. 50–53), and its presence further documents the diversification that Rhamnaceae attained by the Oligocene. Furthermore, the reproductive structures of the new plants suggest varied strategies to interact with the biological and physical world. Most probably the drupe-like structure was dispersed by animals, while the winged fruit was carried by wind. The presence of a nectariferous disc in the flowers further suggests interaction with insect pollinators.
Unfortunately, Nahinda axamilpensis and Ventilago engoto have not been associated with leaves or other Rhamnaceae organs that would help us understand them as whole plants. Nevertheless, leaves from the same formation and assigned to Karwinskia are well known. Although the leaves have not been linked with an extant species, their characters suggest that by the Oligocene these leaves had reached the Karwinskia level of organization (Velasco-de León et al., 1998
). The presence of three Rhamnaceae organs (leaf = Karwinskia; flower/fruit = Nahinda; fruit = Ventilago) in the Los Ahuehuetes locality suggests some diversity of the family in central Mexico by the Oligocene, and a plant with a mosaic of Rhamnaceae characters probably grew in low latitude North America during the Eocene-Oligocene. This assumes that all three organs belonged to one plant; however, that the organs could represent one, two, or three separate taxa is still open to debate. Similarly, in higher latitude North America the leaves of Berhmaniphyllum (Jones and Dilcher, 1980
) may be the photosynthetic organs of a plant producing one of the discussed reproductive organs, but until the correspondence of different organs to a single plant is proven the presence of Paleogene Rhamnaceae plants with mosaic characters needs to be further documented.
A great diversity of angiosperm flowers from the Cretaceous has been documented, adding new elements to understand angiosperm history (Friis et al., 2006
). Flower structures of C. belindae and N. axamilpense can be compared with some Late Cretaceous mesofossils (Friis, 1990
; Friis et al., 2006
). Although Cretaceous mesofossils have not been discussed formally as members of Rhamnaceae, their common pentamerous, actinomorphic, and bisexual condition with nectariferous ring suggests a probable common ancestor, reinforcing the identification of the new Cretaceous Rhamnaceae and supporting the idea that the family has a long geologic history. Furthermore, the Rose Creek flower (Basinger and Dilcher, 1984
), which was originally compared to Celastraceae, has been reinterpreted as a bona fide member of Rhamnaceae, further supporting our determination of the fossils and our inference of a long evolutionary history of the family (Richardson et al., 2000a
, b
). Nevertheless, other authors do not agree that the Rose Creek flower is necessarily Rhamnaceae (Manchester, 2006; S. Manchester, Florida Museum of Natural History, University of Florida, personal communication).
Further work will certainly be needed to clarify the phylogenetic relationships of the Rhamnaceae, and the fossil record (Table 1) will provide important taxonomic information about reproductive and vegetative characters. For example, the phylogenetic work by Richardson et al. (2000a
, b
) can be reevaluated with our new data. Based on the data presented here, we can assume that the family originated at least 72 mya instead of 60–62 mya as suggested by these authors. Their analysis further suggests that some genera (e.g., Gouanaia, Ziziphus, Berchemia, Karwinskia, Paliurus) originated about half way through this period of time, but our interpretation suggests an Eocene/Oligocene rather than a Miocene appearance for these taxa. Thus, the use of data from fossils and morphology can improve our understanding of phylogeny and biogeography.
FOOTNOTES
1 The authors recognize the guidance and comments of Drs. F. C. Cabrera, Instituto de Biología, UNAM, and J. J. Morrone Lupi, Facultad de Ciencias, UNAM; the use of unpublished geological data provided by G. Sliva-Romo, Facultad de Ingeniería, UNAM, and E. González Torres, Instituto de Geología, UNAM; as well as the photographic assistance of A. Altamira. Comments of members of the Palaeobotany Laboratory (C. Castañeda-Posadas, E. Estrada-Ruiz, I. Martínez Cabrera, and G. Hernández-Castillo) enhanced our observations. Commentaries by Dr. E. M. Friis, Dr. S. R. Manchester, and M. Martínez-Millán enriched a previous version of the manuscript. M. Alcayde, Editorial Department, B. Martiny, Geochemistry Department, Instituto de Geología, UNAM, and R. Smith improved a preliminary English version. This study is part of the M.Sc. requirements at the Facultad de Ciencias, UNAM, for L.C.C. and was supported through grants 1005PT (CONACyT) and IN 207294 and IN 205597 (DGAPA-UNAM) to S.R.S.C.-F. 
2 Author for correspondence (lauretacc{at}hotmail.com
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500 m W of the El Almácigo locality; reproduced with authorization of Hernández Rivera [1977]) in Mexico.
