Javier Luque

Miocene flooding events of western Amazonia

Two distinct and short-lived flooding events of shallow marine waters covered western Amazonia during the Miocene. There is a considerable controversy about whether western Amazonia was ever covered by marine waters during the Miocene [23 to 5 Ma (million years ago)]. We investigated the possible occurrence of Miocene marine incursions in the Llanos and Amazonas/Solimões basins, using sedimentological and palynological data from two sediment cores taken in eastern Colombia and northwestern Brazil together with seismic information. We observed two distinct marine intervals in the Llanos Basin, an early Miocene that lasted ~0.9 My (million years) (18.1 to 17.2 Ma) and a middle Miocene that lasted ~3.7 My (16.1 to 12.4 Ma). These two marine intervals are also seen in Amazonas/Solimões Basin (northwestern Amazonia) but were much shorter in duration, ~0.2 My (18.0 to 17.8 Ma) and ~0.4 My (14.1 to 13.7 Ma), respectively. Our results indicate that shallow marine waters covered the region at least twice during the Miocene, but the events were short-lived, rather than a continuous full-marine occupancy of Amazonian landscape over millions of years.

PHYLOGENY AND CLASSIFICATION OF RANINOIDA (DECAPODA: BRACHYURA)

Phylogenetic analysis of most genera within fossil and extant Raninoida (Brachyura) based on 72 adult morphological characters yielded a new superfamily and family level classification for the section. The section was most diverse at the family level during the Late Cretaceous but remains diverse at the genus and species level in the Holocene. New subfamilies include Bicornisranininae, Macroacaeninae, and Rogueinae within Lyreididae. New genera include Colombicarcinus, Alessandranina, Claudioranina, Giulianolyreidus and Italianira, and one new species, Colombicarcinus laevis, is described. New combinations include Alessandranina ornata (Wright and Collins, 1972), Claudioranina oblonga (Beschin, Busulini, de Angeli, and Tessier, 1988), Heus manningi (Bishop and Williams, 2000), Italianira punctulata (Beschin, Busulini, de Angeli, and Tessier, 1988), Giulianolyreidus bidentatus (Rathbun, 1935a), G. johnsoni (Rathbun, 1935a), Lyreidus teodorii (van Bakel et al., 2012), Macroacaena tridens (Roberts, 1962), M. teshimai (Fujiyama and Takeda, 1980), M. yanini (Ilyin and Alekseev, 1998) and Quasilaeviranina eocenica (Rathbun, 1935a).

A puzzling frog crab (Crustacea: Decapoda: Brachyura) from the Early Cretaceous Santana Group of Brazil: frog first or crab first?

The evolutionary origin of frog crabs (Raninoida) remains puzzling partly due to their astonishing morphological disparity, ranging from broad and heavily ornamented ‘crab-like’ extinct families (necrocarcinids and allies), to elongate and smoother ‘frog-like’ extant ones (raninids and allies). However, an ancient Cretaceous clade (Palaeocorystidae) displays a combination of plesiomorphic and apomorphic traits that might advocate for either evolutionary scenario: from ‘crab-like’ to ‘frog-like’, or vice versa. This lack of agreement is partly fuelled by the scarcity of Early Cretaceous fossils, a time from which the first raninoidans are known. A close re-examination of an Early Cretaceous fossil from the Santana Group of Brazil, Araripecarcinus ferreirai Martins-Neto, 1987, combined with phylogenetic analysis including all main clades of podotreme crabs, reinforces its raninoidan condition, and rejects the initial hypothesis of a Portunoidea affinity. Furthermore, comparisons with other raninoidans support the hypothesis that a more ‘crab-like’ body plan is the plesiomorphic condition for raninoidans, and that the ‘frog-like’ architecture of Palaeocorystidae, and perhaps the Raninoidea as a whole, reflects a derived condition related to a specialized burrowing lifestyle. Phylogenetic analyses are fundamental to evaluate the position of Palaeocorystidae with respect to raninoidean and necrocarcinid-like families, helping to better resolve the Raninoida evolutionary tree of life, and to gain a broader understanding on their relatedness by common ancestry throughout geological time.

Reproducing on Time When Temperature Varies: Shifts in the Timing of Courtship by Fiddler Crabs

Many species reproduce when conditions are most favorable for the survival of young. Numerous intertidal fish and invertebrates release eggs or larvae during semilunar, large amplitude, nocturnal tides when these early life stages are best able to escape predation by fish that feed near the shore during the day. Remarkably, some species, including the fiddler crabs Uca terpsichores and Uca deichmanni, maintain this timing throughout the year as temperature, and thus the rate of embryonic development, vary. The mechanisms that allow such precision in the timing of the production of young are poorly known. A preliminary study suggested that when temperature decreases, U. terpsichores mate earlier in the tidal amplitude cycle such that larvae are released at the appropriate time. We tested this idea by studying the timing of courtship in U. terpsichores and U. deichmanni as temperature varied annually during two years, at 5 locations that differed in the temperature of the sediment where females incubate their eggs. Uca terpsichores courted earlier at locations where sediment temperature declined seasonally but not where sediment temperature remained elevated throughout the year. In contrast, clear shifts in courtship timing were not observed for U. deichmanni despite variation in sediment temperature. We discuss other mechanisms by which this species may maintain reproductive timing. These two species are likely to be affected differently by changes in the frequency and intensity of cold periods that are expected to accompany climate change.

The Oldest Frog Crabs (Decapoda: Brachyura: Raninoida) from the Aptian of Northern South America

ABSTRACT Raninoida, also known as “frog crabs,” is a clade of extant true crabs (Brachyura) characterized by a fusiform carapace (raninid-type), narrow thoracic sternum, pleon partially exposed dorsally, and paddle-like limbs, all of which are well suited to their cryptic burrowing lifestyle. However, the most basal raninoids from the Cretaceous were morphologically different, with ornamented carapaces that were wider than long (necrocarcinid-type), a broader thoracic sternum, and the pleon fitting between the legs assisted by pleonal locking mechanisms. During Albian times (∼112 to 99.6 Ma.) both body plans flourished worldwide. In contrast, pre-Albian (older than ∼112 Ma.) fusiform families have not yet been reported. The discovery of Notopocorystes kerri n. sp., a fusiform crab from the upper Aptian (∼115 Ma.) of Colombia, South America, and the re-examination of Planocarcinus olssoni (Rathbun, 1937) n. comb., a necrocarcinid-like crab from the same age and locality, extend the record of the two body plans back into the Aptian of the equatorial Neotropics. Notopocorystes kerri is the oldest fusiform raninoid known to date, revealing that the morphological innovation of a fusiform carapace was already evolved in Raninoida before the rapid radiation experienced during Albian times. Our findings are suggestive of a still unresolved Palaeocorystidae, containing the rootstock for the post-Aptian Raninidae/Symethidae clade, with the most basal palaeocorystids lying in proximity to, and possibly derived from, a necrocarcinid-like ancestor.

Phylogeny and Classification of Necrocarcinoidea Förster, 1968 (Brachyura: Raninoida) with the Description of Two New Genera

Phylogenetic analysis of most species within Necrocarcinoidea based upon 55 adult morphological characters supports the inclusion of 5 families within the superfamily. Two new genera are recognized within Necrocarcinidae, Arcticocarcinus n. gen. and Elektrocarcinus n. gen., and numerous new combinations have resulted. Necrocarcinoidea exhibited diversity peaks in the Albian (Early Cretaceous) and Campanian (Late Cretaceous), and displayed niche partitioning at the family level. Most Paleogene occurrences of Necrocarcinoidea are in carbonate rocks of Northern Europe.

A new fossil bristle worm (Annelida: Polychaeta: Aphroditiformia) from the late Cretaceous of tropical America

Abstract. A new species of aphroditiform polychaete, Protopholoe colombiana, is described from the Coniacian of Colombia, South America, increasing the number of species of this genus known from the fossil record to two. This is the first occurrence of fossil soft-bodied polychaetes in the Tropical Americas, and indicates that aphroditiforms were spread worldwide during the Mesozoic.

Quaternary intertidal and supratidal crabs (Decapoda, Brachyura) from tropical America and the systematic affinities of fossil fiddler crabs

Concentrations of fully articulated crabs are rare in the fossil record, especially for terrestrial and semi-terrestrial taxa, which tend to be represented by scarce, fragmentary and poorly preserved fossils due to preservational biases. A newly discovered fossiliferous locality at Bahia Bique, west of Panama City, Panama, yielded a collection of supratidal, intertidal and shallow subtidal invertebrates and vertebrates of mid-Holocene age. Notable discoveries include the first fossils of the sally lightfoot crab Grapsus, the first for the land crab Cardisoma in the Eastern Pacific and, remarkably, the most complete and abundant collection of fossil fiddler crabs, Uca, yet discovered. The abundance and exceptional preservation of fossil male, female, juvenile and adult individuals of Uca aff. ornata in eroded burrow infills suggest that rapid entombment and early diagenesis were crucial for their preservation. The habitat preference of extant U. ornata for soft muds of open intertidal mudflats indicates that part of Bahía Bique must have been a large estuarine mudflat with close proximity to freshwater influx, in contrast to the present-day gravel field where the fossils are found as ex situ boulders, cobbles and gravel-sized clasts eroded from rocks of the poorly known Pacific Muck. We examine the systematic relationships of fossil fiddler crabs from Bahía Bique via synthetic and cladistic approaches, and conclude that they were from an extinct population of the extant Uca ornata. The fidelity of living–death assemblages between the Bique faunule and extant faunas of the tropical Eastern Pacific confirm the Quaternary age of the assemblage, and stimulate a detailed discussion of the preservation and palaeoecology of terrestrial and semi-terrestrial crabs in tropical assemblages.