Laura Calvillo-Canadell

DIVERSE ASSEMBLAGE OF EOCENE AND OLIGOCENE LEGUMINOSAE FROM MEXICO

Fifteen new legume taxa based on fruits and foliage, including 10 Mimosoideae (three Inga spp., two Pithecellobium spp., Acacia, Mimosa, two Stryphnodendron spp., and Piptadenia), three Caesalpinioideae (Chamaechrista, Senna, and Apuleia), and two Papilionoideae (Cladrastis and Robinia), are described from the Eocene San José de la Popa locality, La Carroza Formation, Nuevo León, and the Oligocene Los Ahuehuetes locality, Coatzingo Formation, Puebla, Mexico. Comparing the fruit type of the Leguminosae and the leaf architecture of the family with the fossils here studied, it is possible to confirm the presence of Leguminosae in Mexican territory (= low‐latitude North America) since the Paleogene and to suggest that the family has been an important element of its flora and vegetation through the Cenozoic. The place of origin of the family is uncertain, but the diversification of some lineages through the Tertiary in North America is well supported by the fossil record. Furthermore, as the fossil record is complemented with phylogenetic studies, the importance of North America, including Mexico, as an area of diversification of plants phylogenetically related with European, Asian, and even African ones is further supported. The new fossil legumes are in part consistent with the concept of a Tertiary boreotropical flora that extended southward into Mexico, as well as with the recognition that some taxa likely evolved in low‐latitude North America rather than merely arriving as immigrants from adjacent regions.

Reproductive structures of Rhamnaceae from the Cerro del Pueblo (Late Cretaceous, Coahuila) and Coatzingo (Oligocene, Puebla) Formations, Mexico

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.

Bauhcis moranii gen. et sp. nov. (Cercideae, Caesalpinieae), an Oligocene plant from Tepexi de Rodrı́guez, Puebla, Mex., with leaf architecture similar to Bauhinia and Cercis

The Oligocene Coatzingo Formation (≈Pie de Vaca Formation), Puebla, Mexico, has yielded a diverse assemblage of plants among which Leguminosae are represented by wood, fruits and leaves or leaflets. Leaf impressions from two specimens have characteristics found in extant members of Cercideae (Caesalpinieae). Morphological observations were corroborated through a phenetic analysis suggesting that morphological differences between the fossil and extant plants correspond to natural variation within the tribe. Although the fossil material closely resembles both Bauhinia and Cercis, its set of characters support the recognition of a new taxon, Bauhcis moranii Calvillo-Canadell and Cevallos-Ferriz. The cladistic analysis further supports that the fossil represents a moment in the history of the tribe, previous to the differentiation of the two extant genera. This new plant adds to the poorly known low-latitude fossil vegetation of Central Mexico and strengthens the idea of a long and complex phytogeography history to explain the extant biodiversity of the area, in which Leguminosae is among the most important component of the flora.

Ruprechtia in the Miocene El Cien Formation, Baja California Sur, Mexico

Fossil woods from the El Cien Formation have yielded important information on the taxonomic composition and climate of a flora established in the west coast of Mexico during the Miocene. This report of a new genus and species, Ruprechtioxylon multiseptatus Cevallos-Ferriz, Martinez Cabrera et Calvillo-Canadell, is based on woods with the following combination of features: vessels solitary and in radial multiples of 2–3; vestured, alternate, oval to polygonal intervessel pits; vessel-ray and vessel-parenchyma pits similar in size to intervessel pits, but with slightly reduced to reduced borders; 2–5 septa per fibre; scanty paratracheal, unilateral and vasicentric axial parenchyma; uniseriate homocellular rays, occasionally locally biseriate; crystals in fibres. The presence of Ruprechtioxylon (Polygonaceae) in the El Cien Formation confirms that plants of lineages growing today under contrasting climates lived together in the past. This record adds a new species to the growing list of Neotropical taxa that were present in Mexico prior to the great Plio-Pleistocene exchange of biota in the Americas.

Dating of the Uppermost Part of the Cabullona Group in Esqueda (Sonora, Mexico)

The Esqueda locality is well known for its quarries, which provide shales that are used for construction and that also contain dinosaur ichnites. This study determines the age of the shale deposits. A late Campanian age is suggested for the uppermost part of the Cabullona Group for the whole Esqueda section, based on palynological assemblages and U–Pb geochronology.

Preliminary palaeobotanical notes on the Early Cretaceous Cintura Formation (Sonora, Mexico)

The Cintura Formation of Albian–Cenomanian age in the Cabullona Basin yielded an important fossil flora, including palynomorphs, leaf impressions and fossil trunks. At the base of the Marquechi Member a poorly preserved palynomorph assemblage is recognised. The palynological assemblage is dominated by gymnosperms, mainly by cheirolepidiacean genus Classopollis. A noteworthy feature is the presence of angiosperm pollen grains of the genera Clavatipollenites, Retimonocolpites and Tucanopollis. A rich, diverse and well-preserved macroflora of leaf impressions has been observed in the uppermost part of this formation belonging to the San Juan Member. There are at least eight morphospecies of leaves including an abundance of taxa with possible botanical affinities to the family Sapindaceae. The angiosperm pollen grains together with the sapindalean leaves constitute the oldest record of such remains in Mexico.