Sciency Thoughts: Early Eocene Climatic Maximum

Showing posts with label Early Eocene Climatic Maximum. Show all posts

Sunday, 13 October 2019

Lessiniabatis aenigmatica: A new species of Stingray from the Eocene of northern Italy.

Stingrays, Myliobatiformes, first appeared during the Early Cretaceous, and underwent a major evolutionary radiation following the End Cretaceous Extinction. The group are still highly successful, with eleven extant families and more than 360 species. However, despite this long evolutionary history, the fossil record of Stingrays is rather poor, with only their teeth being common. This is because Stingrays are Cartilaginous Fish, Chonrichthys, and lack a mineralised skeleton, so that body fossils are only preserved under exceptional circumstances, so that little is known about the total morphology of many fossil Stingray groups.

In a paper published in the journal Scientific Reports on 1 October 2019, Giuseppe Marramà of the Department of Palaeontology at the University of Vienna, Giorgio Carnevale of the Dipartimento di Scienze della Terra at the Università degli Studi di Torino, Luca Giusberti of the Dipartimento di Geoscienze, at the Università degli Studi di Padova, Gavin Naylor, of the Florida Museum of Natural History at the University of Florida, and Jürgen Kriwet, also of the Department of Palaeontology at the University of Vienna, describe a new species of Stingray from the early Eocene Monte Bolca Lagerstätte of northern Italy.

The Monte Bolca Lagerstätte comprises a suite of limestones laid down in the Tethys Ocean between about 50 and 48 million years ago, at the time of the Eocene Thermal Maximum, and subsequently uplifted during the closure of the Tethys Ocean and subsequent formation of the Alps. The limestones extend laterally for about 19 km, with several layers producing marine fossils with exceptional preservation. The Monte Bolca is one of the oldest recognised fossil producing sites in Europe, having been worked since at least the sixteenth century.

The new species is named Lessiniabatis aenigmatica, where 'Lessiniabatis' means 'Ray from Lessinia' after the region where the Monte Bolca Lagerstätte outcrops, and 'aenigmatica' means 'enigmatic', due to the puzzling nature of the fossil. The species is described from three specimens between 375.1 and 568.2 mm in width. Lessiniabatis aenigmatica is unique in having a thoracolumbar synarcual (the extended flattened cartilage that surrounds the spine and gives rays their distinct shape) that extends backwards past the pelvic girdle, forming an extended pectoral disc, combined with a very short tail that does not protrude beyond this disk.

Lessiniabatis aenigmatica from the Eocene of Bolca Lagerstätte. (a), (b) the paratype MSNFI IGF 103555 in part and counterpart; (c) the paratype MFSN GP.864. Scale bars equal 100 mm. Marramà et al. (2019).

Most new species are described from a holotype, a specimen kept in a museum or university collection (in some living species from groups considered to be conservation priorities this is replaced with genetic material or even photographs). The specimen designated as the holotype of Lessiniabatis aenigmatica by Marramà et al., MNHN F.Bol.566 (previously labelled as 10997–11001) is in the collections of the Museum National d’Histoire Naturelle of Paris, where it is identified as the specimen designated as the holotype of Urolophus crassicaudatus by Henri Marie Ducrotay de Blainville in 1818. However the specimen is nothing like Blainville's description, and it is assumed that the specimens have been mislabled at some point, and the holotype of Urolophus crassicaudatus is lost.

Lessiniabatis aenigmatica from the Eocene of Bolca Lagerstätte. Details of the pelvic girdle and tail region in MNHN F.Bol.566 (a) and MFSN GP.864 (b). Abbreviations: mpt, metapterygium; pg, pelvic girdle; syn2, thoracolumbar synarcual; tv, tail vertebrae. Scale bars equal 50 mm. Marramà et al. (2019).

Lessiniabatis aenigmatica exhibits a unique bodyplan, unlike any other known fossil or living Stingray, while showing enough typical features to be confidently placed in the group (the absence of a rostral cartilage, its dentition, etc.). It lacks a sting on its tail, but this is thought to be a secondary loss and is seen in other Stingray species, such as the Manta Ray and some Eagle Rays. More surprising is the effective loss of the tail as a locomotive organ, as this is the main means of forward propulsion in modern Rays. Marramà et al. suggest that Lessiniabatis aenigmatica must have been more reliant on undulating movement than modern Stingrays, and that its evolution represents a unique evolutionary experiment in the period between the End Cretaceous Extinction and Eocene Thermal Maximum.

Silhouettes of selected living and fossil taxa as representatives for the modern Stingray families and holomorphic fossil taxa. (a) Hexatrygon bickelli (Hexatrygonidae, Sixgill Stingrays); (b) Dasyatis marmorata (Dasyatidae, Whiptail Stingrays); (c) Potamotrygon tigrina (Potamotrygonidae, South American Freshwater Stingrays); (d) Urobatis halleri (Urobatidae, Round Stingrays); (e) Plesiobatis daviesi (Plesiobatidae, Deepwater Stingrays); (f) Urolophus kapalensis (Urolophidae, Stingarees); (g) Lessiniabatis aenigmatica (this study, Eocene, Monte Bolca, Italy); (h) Asterotrygon maloneyi (Eocene, Green River Formation, Wyoming); (i) Heliobatis radians (Eocene, Green River Formation, Wyoming); (j) Gymnura altavela (Gymnuridae, Butterfly Rays); (k) Promyliobatis gazolai (Eocene, Monte Bolca, Italy); (l) Myliobatis hamlyni (Myliobatidae, Eagle Rays); (m) Aetobatus laticeps (Aetobatidae, Longheaded Eagle Rays); (n) Rhinoptera bonasus (Rhinopteridae, Cownose Rays); (o) Mobula mobular (Mobulidae, Manta Rays). Figures not to scale. Marramà et al. (2019).

Sunday, 2 October 2016

Septencoracias morsensis: A Roller from the Early Eocene of Denmark.

Rollers, Coracii, are large-headed, large-beaked insectivorous Birds related to Kingfishers, Bee-eaters, Hoopoes and Hornbills. They are restricted to the Old World today, with a but two species found the tropics or subtropics, but appear to have been more widely distributed in the past. Like many living Bird-groups, they appear to have arisen shortly after the End Cretaceous extinction (before which Avian faunas were dominated by the extinct Toothed Birds), though precisely where and when is unclear due to a lack of good Bird-producing sites from the Palaeocene. Fossil Rollers have been described from the Early Eocene Messel Shale and Green River Formation of Wyoming, as well as the Late Eocene Quercy deposits of France, and fragmentary remains not described to species level from the Early Eocene of Condé-en-Brie, also in France.

In a paper published in the journal Scientific Reports on 27 September 2016, Estelle Bourdon of The Natural History Museum of Denmark and Section of Biosystematics at the University of Copenhagen, Anette Kristoffersen of the Department of Geosciences and Natural ResourceManagement at the University of Copenhagen and Niels Bonde, also of The Natural History Museum of Denmark and Section of Biosystematics at the University of Copenhagen, as well as the Fur Museum (MuserumSalling), describe a new species of Roller from the Early Eocene Fur Formation of Klovbakker Quarry on the Island of Mors, off northwestern Jutland.

The Fur Formation is a marine diatomite, i.e. a sedimentary rock formed from the tests (shells) of planktonic Diatoms; such diatomites can form in both marine and lake deposits, but only far enough from the shore that the Diatom tests are able to build up without significant input of sediments from terrestrial environments. These deposits are noted for the production of numerous Insects and Vertebrates, the later including Fish, Turtles and Birds. Importantly the Fur Formation also included numerous layers of volcanic ash, allowing very precise radiometric dating of the deposits.

The new Bird is named Septencoracias morsensis, where 'Septencoracias' means 'Northern Roller' and 'morsensis' means 'from Mors'. It is described from a single, largely-intact, three-dimensionally preserved specimen, which also has preserved stomach contents. The living Bird would have been about 25 cm in length, towards the minimum end of the size range seen in living Rollers.

Septencoracias morsensis. (a) Photograph of whole specimen. (b) 3D white light scanning of the whole specimen. (c) Interpretative drawing with damaged areas of the skull, fish remains and soft tissues represented in dark grey. Abbreviations: al1–2, phalanges of alular digit; ap, narial opening; at, atlas; ax, axis; c, cervical vertebrae; ca, carpometacarpus; cd1–7, caudal vertebrae; co, vertebral costae; cp, costal process; cr, cranium; d, damage in the skull area; dm, phalanx of minor digit; dM1, proximal phalanx of major digit; dM2, distal phalanx of major digit; ec, ectethmoid; f, femur; fi, fish remains; ft, foramina intertransversaria; fv, fish vertebra; h, humerus; if, ilioischiadic foramen; is, ischium; md, mandibula; me, mesethmoid; mx, maxilla; mI, metatarsal I; pa, palatine; pb, pubis; po, postacetabular wing of ilium; pr, preacetabular wing of ilium; pt, pterygoid; pu, uncinate process; py, pygostyle; ra, radius; rd, radial carpal bone; sc, scapula; st, soft tissues; sy, synsacrum; ta, tarsometatarsus; tb, tibiotarsus; u, ulna; ul, ulnar carpal bone; I1–2, phalanges of pedal digit I; II1–3, phalanges of pedal digit II; III1–4, phalanges of pedal digit III; IV1–5, phalanges of pedal digit IV. The ‘r’ and ‘l’ prefixes indicate right and left, respectively. Estelle Bourdon in Bourdon et al. (2016).

The specimen was found directly above an ash layer dated to 54.04 million years ago, making it about 54 million years old. This makes it the oldest known Roller, and places it directly after the Early Eocene Thermal Maximum, a time when tropical climates could be found as far north as Denmark. Since other fossil Rollers found in northerly locations in Europe and America also come from warm Eocene deposits, it is likely that the preference for hot climates seen in modern Rollers arose early in the history of the group.

Septencoracias morsensis. (a) Skull in left lateral view. (b) Right foot in medial view. (c) Left foot in dorsal view. (d) Right humerus in cranial view. (e) Right carpometacarpus in ventral view. Bourdon et al. (2016).

The stomach contents of Septencoracias morsensis comprise the skeletons of at least two Argentinoid Fish. These Fish reached about 10 cm in size, and are very abundant in the Mors Formation, apparently having been a food source for many of the other animals found there. The consumption of Fish is outside the behaviour of modern Rollers, and may suggest some unrollerlike habits for Septencoracias morsensis. However this does not necessarily mean the Bird was capable of hunting Fish like a Kingfisher; most Birds will scavenge opportunistically when the opertunity arises, and the consumption of Fish may have been an example of such behaviour in a Roller with more conventional habits.

Life reconstruction of Septencoracias morsensis. Salient diagnostic features of the new fossil relative to other rollers include the larger skull and the small, ovoid and dorsally positioned narial openings. Septencoracias is represented with a brownish and bluish plumage, because brownish and/or bluish feathers occur in all species of Rollers and most species of Ground-rollers, and are probably primitive within the Coracii. Estelle Bourdon in Bourdon et al. (2016).

Thursday, 8 January 2015

The Antarctic Summer Monsoon.

The Eocene palaeoflora of the Antarctic Peninsula and neighbouring islands has been studied since the early twentieth century, with fossil sites on the Peninsula itself as well as on Seymour, Alexander and King George islands yielding a large number of wood fossils, plus lesser amounts of leaves, pollen, seeds and fruit. This flora is dominated by Myrtles, Arals, Podocarps, Cypresses and Southern Beeches, showing strong taxonomic affinity for the flora of the modern Valdevia Region of Chile, and suggesting a warm temperate climate with high rainfall. However global climate models for the Early-to-Middle Eocene, a period of extreme global warming when these fossils were deposited, do not suggest such a climate for the area, implying there is a problem with either the plant based regional palaeoclimate reconstruction, or with the global climate models.

In a paper published in the journal Gondwana Research in May 2014, Frédéric Jacques of the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology and the Key Laboratory ofTropical Forest Ecology at the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences, and Gongle Shi, Haomin Li and Weiming Wang, also of the State Key Laboratory of Palaeobiology and Stratigraphy, examine a series of fossil leaves collected from Fossil Hill on the Fildes Peninsula on King George Island by Chinese expeditions.

The Fossil Hill flora has been dated to about 52 million years ago (close to the Early Eocene Climatic Maximum), by Potassium-Argon and Rubidium-Strontium dating techniques.

Potasium-Argon dating relies on determining the ratio of radioactive Potasium⁴⁰ to Argon⁴⁰ within minerals from igneous or metamorphic rock to determine how long ago the mineral cooled sufficiently to crystalize. Potasium⁴⁰ is often incorporated into cooling volcanic rocks, whereas any inert Argon present will escape as a gas. No further Potasium⁴⁰ or Argon⁴⁰ will enter the mineral from this point, but Argon⁴⁰ is produced by the decay of radioactive Potassium⁴⁰ at a steady rate, enabling scientists to establish a precise date for the crystalization of the minerals containing the two elements.

Rubidium-Strontium dating is similar, but relies on the decay of Rubdium⁸⁷ to Strontim⁸⁷. Rubidium does not readily form minrals by crystalizing with other elements as the magma cools, remaining in the liquid phase that surrounds the forming minerals until it finally solidifies as a volcanic glass. Strontium, on the other hand, readily forms minerals with a variety of other elements, and is theresfore very rare in this glass, so that it is likely that any appreciabe amount of Strontim⁸⁷ present will be due to the decay of radioactive Rubdium⁸⁷, making it possible to determine the age of the rocks from the ratio of the two isotopes in the melt matrix.

The flora has produced 25 different Angiosperm (Flowering Plant) leaves, and is dominated by the Southern Beech family (Nothofagaceae).

Selected morphotypes of the Fossil Hill flora. (A) Dicotylophyllum elegans; (B) Dicotylophyllum sp. 1; (C) Dicotylophyllum sp. 2; (D) Dicotylophyllum latitrilobatum; (E) Dicotylophyllum sp. 9; (F) Dicotylophyllum sp. 3; (G) Lomatia mirabilis; (H) Dicotylophyllum sp. 10; (I) Pentaneurum dusenii; (J) Nothofagofolia multinervis; (K) Nothofagofolia betulifolia; (L) undescribed species; (M) Dicotylophyllum sp4; (N) Rhoophyllum nordenskjoeldi; (O) Nothofagofolia carpinoides; (P) Nothofagofolia zastawniakiae. Scale bar is 1 cm. Jacques et al (2014).

Previous attempts to reconstruct the early Eocene climate of the Antarctic Peninsula have relied upon the Nearest Living Relative method, which relies upon the assumption that most fossil plants will have had similar environmental requirements to their nearest living relatives, so that where a large number of plants from different taxonomic groups are found together, all of which have nearest living relatives with similar climatic requirements, then it is highly likely that the plants occupied a similar climate zone to their modern relatives. The Eocene Antarctic flora is very close to the modern Valdevia region of Chile, which has led to the assumption that the climate would be similar. However the modern Valdevian region is also the only floristic region close to the Antarctic Peninsula, so it is unsurprising that its flora is similar, and the Nearest Living Relative model is usually only considered accurate for Neogene and Quaternary floras, making its application to the Early Eocene flora of the Antarctic Peninsula questionable.

Instead Jacques et al. used a technique called Climate Leaf Analysis to interpret the climate that produced the Fossil Hill leaves. This technique relies on an analysis of the shape of leaves without reference to their taxonomic affinities, in order to interpret the climate that the plants were living in.

The Climate Leaf Analysis for the leaves from Fossil Hill suggests a highly seasonal warm temperate climate, with a mean annual temperature of 11.5°C, and freezing occurring in winter. The climate is predicted to have been wet, with 1259.3 mm of rainfall per year, of which 60% would have fallen within three months, when rainfall would have averaged 6.4 mm of rain per day. This is comparable to the climate in parts of modern Japan, where the climate is driven by the Southeast Asian Summer Monsoon.