Miguel A. Torres-Martínez

Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico

Torres-Martínez, M.A., Sour-Tovar, F. & Barragán, R., November 2017. Kukulkanus, a new genus of buxtoniin brachiopod from the Artinskian–Kungurian (Early Permian) of Mexico. Alcheringa 42, 268–276. ISSN 0311–5518. Kukulkanus is the first genus of the tribe Buxtoniini recorded from rocks of the late Cisuralian (Artinskian–Kungurian). The Early Permian (Cisuralian) outcrops of the Santa Rosa Group, from southeastern Chiapas, are one of the most important marine Palaeozoic successions of Mexico. The Artinskian–Kungurian Paso Hondo Formation is the youngest unit in the succession and is dominated by massive limestone. Different marine invertebrates deposited in massive calcareous rocks characterize this formation. The buxtoniin Kukulkanus spinosus gen. et sp. nov. is reported from a single bed within the unit. The outcrops are located in southeastern Chiapas, very near the Guatemala–Mexico border. The lithological features and the preservation of fossils indicate that the fossil-bearing rocks were deposited in a low-energy open-waters paleoenvironment over the continental platform. Fusulinids, cephalopods and brachiopods previously described for the Paso Hondo Formation have been correlated with faunas of different coeval localities from Texas, New Mexico, Coahuila, Chiapas and Venezuela, regions that form part of the biotic Grandian Palaeo-Province. Miguel A. Torres-Martínez [miguelatm@geologia.unam.mx] Departamento de Paleontología, Instituto de Geología, Circuito de la Investigación Científica, Avenida Universidad No. 3000. Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico. Francisco Sour-Tovar [fcosour@ciencias.unam.mx] Museo de Paleontología, Facultad de Ciencias, Universidad Nacional Autónoma de México. Av. Universidad No. 3000, Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico. Ricardo Barragán [ricardor@geologia.unam.mx] Departamento de Paleontología, Instituto de Geología, Circuito de la Investigación Científica, Avenida Universidad No. 3000. Colonia Universidad Nacional Autónoma de México, Delegación Coyoacán, Cd. Mx. C.P. 04510, Mexico.

Influencia de las variables fisicoquímicas en la estructura de tallas y distribución de Meoma ventricosa grandis (Echinodermata: Brissidae) dentro del canal Boca Chica, Acapulco, México

espanolEn este trabajo se examinaron diferentes variables fisicoquimicas (textura del sedimento, temperatura, salinidad, oxigeno disuelto, turbidez, nitrito, nitrato, amonio, fosfato, materia organica de nieve marina, materia organica del sedimento y materia organica del tracto digestivo) y su influencia en la estructura de tallas y la distribucion de Meoma ventricosa grandis. El estudio fue realizado en 3 estaciones de trabajo (E1: La Playa, E2: El Jardin, E3: Palmitas) localizadas a traves del canal Boca Chica, Acapulco, Mexico, durante 2006 y 2007. Los resultados de las mediciones del tamano corporal mostraron un menor porcentaje de individuos adultos en las estaciones 1 y 2 (13 y 5%, respectivamente), por el contrario en la estacion 3 el porcentaje fue de 51%. El analisis de varianza senalo una diferencia significativa en el tamano de los individuos de la estacion Palmitas con respecto a las otras dos, presentando los ejemplares mas grandes a traves de todo el estudio. La textura del sedimento en la estacion 1, La Playa y en la estacion 2, El Jardin se caracterizo por clastos asimetricos de arena gruesa y grava, de diversos tamanos, con una profundidad de la capa de sedimentos de 20 a 30 cm, en contraste con la estacion 3, Palmitas, la cual presento clastos casi simetricos de arena gruesa, de tamano similar, con profundidad de 50 cm; en todas las estaciones los individuos juveniles estaban enterrados entre los 10 y 20 cm de profundidad y los adultos entre 15 y 40 cm. El indice gonadico fue de tipo asincronico durante el estudio, presentando los picos reproductivos mas altos en Palmitas. El analisis de arboles de regresion establecio que la materia organica consumida por los individuos actua como la principal variable fisicoquimica que favorece la distribucion de este equinoideo dentro del canal, localizando hasta 6,571 individuos en relacion a este recurso. La mayor proporcion de ejemplares (11,330) se alcanzo en presencia de la materia organica, los nitratos y los fosfatos. Se registra por primera vez para el genero Meoma la existencia de una seleccion especifica del tipo de sustrato dependiente principalmente de su talla corporal. EnglishIn this study we examine different physicochemical variables (sediment texture, temperature, salinity, dissolved oxygen, turbidity, nitrite, nitrate, ammonium, phosphate, organic matter of marine snow, organic matter of sediment and organic matter of digestive tract) and their influence on the size structure and distribution of Meoma ventricosa grandis. The study was conducted in 3 workstations (E1: La Playa, E2: El Jardin, E3: Palmitas) located across the Boca Chica Channel, Acapulco, Mexico, during 2006 to 2007. The results of the measurements of the body size showed a higher percentage of adults in workstation 1 and 2 (13 and 5%, respectively); however, in workstation 3 the percentage was of 51%. The variance pointed a significance in the size of the individuals from the workstation Palmitas, showing the largest specimens throughout the study. The sediment texture in workstations La Playa and El Jardin was characterized by asymmetric clasts of coarse sand and gravel of different sizes, with a sediment layer with a depth of layer of 20-30 cm. Unlike workstation of Palmitas wich was distinguished by almost symmetrical gravel clasts, similar in size and with depth of 50 cm; in all workstations juveniles were buried between 10 and 20 cm and adults between 15 and 40 cm of depth. The gonadal index was asynchronous, presenting the highest reproductive peaks in Palmitas. Regression Trees analysis established that the organic matter deposited in the sediment acts as the primary physicochemical variable in the distribution of the echinoid within the channel, locating until 6,571 individuals in direct relation to it. The largest number of specimens (11,330) was obtained in the presence of organic matter, nitrates and phosphates. This is the first time that genus Meoma is related to a specific substrate according to the body size.

New productide brachiopods (Productoidea) from the Carboniferous of Ixtaltepec Formation, Oaxaca, Mexico

Abstract. From the Santiago Ixtaltepec area, in Oaxaca State, southern Mexico, 11 species of productoid brachiopods, including a new genus and five new species, are described. Semicostella sp., Antiquatonia sp., Keokukia? sp., Inflatia inflata, Reticulatia cf. R. huecoensis, Buxtonia websteri, Weberproductus donajiae n. gen. n. sp., Dictyoclostus transversum n. sp., Inflatia coodzavuii n. sp., Buxtonia inexpletucosta n. sp., and Flexaria magna n. sp. were collected from eight stratigraphic levels of the Ixtaltepec Formation. The presence of Semicostella sp., Keokukia? sp. and Inflatia inflata in the basal strata, Units 1 to 3, of the formation indicate a Viséan-Serpukhovian (Late Mississippian) age. Reticulatia cf. R. huecoensis and Buxtonia websteri, found in Units 6 to 8, confirm the Pennsylvanian age for upper strata of the Ixtaltepec Formation. Inflatia and Flexaria are present in the uppermost beds of the formation so it is possible to extend their upper stratigraphic range to the Middle Pennsylvanian. All these taxa also occur in the United States Midcontinent, suggesting that during the Carboniferous the epicontinental sea extended at least to central Mexico.