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Results 1 through 20 out of 184

in category paleontology

 

1: A crocodylian-style cloaca in a non-avialan dinosaur

Phil R. Bell, Michael Pittman et al.

20,597 downloads (posted 12 Oct 2020)

Our knowledge of the reproductive biology of dinosaurs covers a range of aspects, from brooding behaviour to nesting style and the timing of sexual maturity. Yet, the basic anatomy and function of the cloaca in non-avialan dinosaurs remains unknown. Here, we describe the outer morphology of the only known non-avialan dinosaur cloaca, preserved in an exceptional specimen of the early-diverging ceratopsian dinosaur Psittacosaurus . We clarify the position of the cloaca with respect to the ischia and caudal vertebrae and document the scales immediately adjacent to the abdomen and tail. We find that the cloaca is from a near-sexually mature subadult individual and is most similar to the cloaca of crocodylians, to the exclusion of lepidosaurians and birds. However, the sex of SMF R 4970 could not be determined as the cloaca and the rest of the specimen does not yield any sexually dimorphic information. This study highlights the ongoing role of exceptional specimens in providing rare soft tissues that help to bridge longstanding gaps in our knowledge of the basic biology of dinosaurs and other extinct reptiles. ### Competing Interest Statement The authors have declared no competing interest.

https://rxivist.org/papers/96432
https://doi.org/10.1101/2020.10.11.335398

2: Diverse genetic origins of medieval steppe nomad conquerors

Alexander S. Mikheyev, Lijun Qiu et al.

3,799 downloads (posted 16 Dec 2019)

Over millennia, steppe nomadic tribes raided and sometimes overran settled Eurasian civilizations. Most polities formed by steppe nomads were ephemeral, making it difficult to ascertain their genetic roots or what present-day populations, if any, have descended from them. Exceptionally, the Khazar Khaganate controlled the trade artery between the Black and Caspian Seas in VIII-IX centuries, acting as one of the major conduits between East and West. However, the genetic identity of the ruling elite within the polyglot an...

https://rxivist.org/papers/68872
https://doi.org/10.1101/2019.12.15.876912

3: New Evidence of the Earliest Domestic Dogs in the Americas

Angela Perri, Chris Widga et al.

3,441 downloads (posted 11 Jun 2018)

The domestication of dogs probably occurred in Eurasia by 16,000 years ago, with the initial peopling of the Americas potentially happening around the same time. Dogs were long thought to have accompanied the first migrations into the Americas, but conclusive evidence for Paleoindian dogs is lacking. The direct dating of two dogs from the Koster site (Greene Co., Illinois) and a newly-described dog from the Stilwell II site (Pike Co., Illinois) to between 10,190-9,630 cal BP represents the earliest evidence of domestic ...

https://rxivist.org/papers/17332
https://doi.org/10.1101/343574

4: The tiny Cretaceous stem-bird Oculudentavis revealed as a bizarre lizard

Arnau Bolet, Edward L Stanley et al.

3,320 downloads (posted 10 Aug 2020)

Oculudentavis khaungraae was described based on a tiny skull trapped in amber. The slender tapering rostrum with retracted osseous nares, large eyes, and short vaulted braincase led to its identification as the smallest avian dinosaur on record, comparable to the smallest living hummingbirds. Despite its bird-like appearance, Oculudentavis showed several features inconsistent with its original phylogenetic placement. Here we describe a more complete, specimen that demonstrates Oculudentavis is actually a bizarre lizard ...

https://rxivist.org/papers/93954
https://doi.org/10.1101/2020.08.09.243048

5: The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa

Ronald Clarke, Kathleen Kuman

2,768 downloads (posted 04 Dec 2018)

Here we present the first full anatomical description of the 3.67 million-year-old Australopithecus skull StW 573 that was recovered with its skeleton from the Sterkfontein Member 2 breccia in the Silberberg Grotto. Analysis demonstrates that it is most similar in multiple key morphological characters to a group of fossils from Sterkfontein Member 4 and Makapansgat that are here distinguished morphologically as A. prometheus. This taxon contrasts with another group of fossils from those sites assigned to A. africanus. T...

https://rxivist.org/papers/37924
https://doi.org/10.1101/483495

6: Fossil calibrations for the arthropod Tree of Life

Joanna M Wolfe, Allison C Daley et al.

2,734 downloads (posted 21 Mar 2016)

Fossil age data and molecular sequences are increasingly combined to establish a timescale for the Tree of Life. Arthropods, as the most species-rich and morphologically disparate animal phylum, have received substantial attention, particularly with regard to questions such as the timing of habitat shifts (e.g. terrestrialisation), genome evolution (e.g. gene family duplication and functional evolution), origins of novel characters and behaviours (e.g. wings and flight, venom, silk), biogeography, rate of diversificatio...

https://rxivist.org/papers/30133
https://doi.org/10.1101/044859

7: Functional Anatomy, Biomechanical Performance Capabilities and Potential Niche of StW 573: an Australopithecus Skeleton (circa 3.67 Ma) From Sterkfontein Member 2, and its significance for The Last Common Ancestor of the African Apes and for Hominin Origins

Robin Huw Crompton, Juliet McClymont et al.

2,722 downloads (posted 29 Nov 2018)

StW 573, from Sterkfontein Member 2, dated ca 3.67 Ma, is by far the most complete skeleton of an australopith to date. Joint morphology is in many cases closely matched in available elements of Australopithecus anamensis (eg. proximal and distal tibial and humeral joint-surfaces) and there are also close similarities to features of the scapula, in particular, of KSD-VP-1/1 A. afarensis from Woranso-Mille. The closest similarities are, however, to the partial skeleton of StW 431 from Sterkfontein Member 4. When consider...

https://rxivist.org/papers/37629
https://doi.org/10.1101/481556

8: A Cretaceous bug with exaggerated antennae might be a double-edged sword in evolution

Bao-Jie Du, Rui Chen et al.

2,236 downloads (posted 12 Feb 2020)

In the competition for the opposite sex, sexual selection can favor production of exaggerated features, but the high cost of such features in terms of energy consumption and enemy avoidance makes them go to extinction under the influence of natural selection. However, to our knowledge, fossil on exaggerated traits that are conducive to attracting opposite sex are very rare. Here, we report the exaggerated leaf-like expansion antennae of Magnusantenna wuae Du & Chen gen. et sp. nov. (Hemiptera: Coreidae) with more abunda...

https://rxivist.org/papers/73690
https://doi.org/10.1101/2020.02.11.942920

9: Uneven Data Quality and the Earliest Occupation of Europe: The Case of Untermassfeld (Germany)

Wil Roebroeks, Sabine Gaudzinski-Windheuser et al.

2,080 downloads (posted 31 Oct 2017)

The database regarding the earliest occupation of Europe has increased significantly in quantity and quality of data points over the last two decades, mainly through the addition of new sites as a result of long-term systematic excavations and large-scale prospections of Early and early Middle Pleistocene exposures. The site distribution pattern suggests an ephemeral presence of hominins in the south of Europe from around one million years ago, with occasional short northward expansions along the western coastal areas w...

https://rxivist.org/papers/30123
https://doi.org/10.1101/211268

10: How many dinosaur species were there? Fossil bias and true richness estimated using a Poisson sampling model (TRiPS)

Lee Hsiang Liow

2,060 downloads (posted 02 Sep 2015)

The fossil record is a rich source of information about biological diversity in the past. However, the fossil record is not only incomplete but has inherent biases due to geological, physical, chemical and biological factors. Our knowledge of past life is also biased because of differences in academic and amateur interests and sampling efforts. As a result, not all individuals or species that lived in the past are equally likely to be discovered at any point in time or space. To reconstruct temporal dynamics of diversit...

https://rxivist.org/papers/30135
https://doi.org/10.1101/025940

11: A primitive starfish ancestor from the Early Ordovician of Morocco reveals the origin of crown group Echinodermata

Aaron W. Hunter, Javier Ortega-Hernandez

1,940 downloads (posted 09 Nov 2017)

The somasteroids are Ordovician star-shaped animals widely regarded as ancestors of Asterozoa, the group of extant echinoderms that includes brittle stars and starfish. The phylogenetic position of somasteroids makes them critical for understanding the origin and early evolution of crown group Echinodermata. However, the early evolution of asterozoans, the origin of their distinctive body organization and their relationships with other Cambrian and Ordovician echinoderms, such as edrioasteroids, blastozoans, crinoids, a...

https://rxivist.org/papers/30122
https://doi.org/10.1101/216101

12: Multi-proxy evidence for the impact of the Storegga Slide Tsunami on the early Holocene landscapes of the southern North Sea

Vincent Gaffney, Simon Fitch et al.

1,916 downloads (posted 26 Feb 2020)

Doggerland was a land mass occupying an area currently covered by the North Sea until marine inundation took place during the mid-Holocene, ultimately separating the British land mass from the rest of Europe. The Storegga Slide, which triggered a tsunami reflected in sediment deposits in the Northern North Sea, North East coastlines of the British Isles and across the North Atlantic, was a major event during this transgressive phase. The spatial extent of the Storegga tsunami however remains unconfirmed because to date ...

https://rxivist.org/papers/75053
https://doi.org/10.1101/2020.02.24.962605

13: Life Inside A Dinosaur Bone: A Thriving Microbiome

Evan T. Saitta, Renxing Liang et al.

1,875 downloads (posted 07 Sep 2018)

Fossils were long thought to lack original organic material, but the discovery of organic molecules in fossils and sub-fossils, thousands to millions of years old, has demonstrated the potential of fossil organics to provide radical new insights into the fossil record. How long different organics can persist remains unclear, however. Non-avian dinosaur bone has been hypothesised to preserve endogenous organics including collagen, osteocytes, and blood vessels, but proteins and labile lipids are unstable during diagenesi...

https://rxivist.org/papers/32193
https://doi.org/10.1101/400176

14: Earliest-known intentionally deformed human cranial fossil from Asia and the initiation of hereditary hierarchy in the early Holocene

Xijun Ni, Qiang Li et al.

1,835 downloads (posted 26 Jan 2019)

Hereditary hierarchy is one of the major features of complex societies. Without a written record, prehistoric evidence for hereditary hierarchy is rare. Intentional cranial deformation (ICD) is a cross-generational cultural practice that embodies social identity and culture beliefs in adults through the behavior of altering infant head shape. Therefore, ICD is usually regarded as an archeological clue for the occurrence of hereditary hierarchy. With a calibrated radiocarbon age of 11245-11200 years BP, a fossil skull of...

https://rxivist.org/papers/42490
https://doi.org/10.1101/530907

15: What do ossification sequences tell us about the origin of extant amphibians?

Michel Laurin, Océane Lapauze et al.

1,765 downloads (posted 20 Jun 2018)

The origin of extant amphibians has been studied using several sources of data and methods, including phylogenetic analyses of morphological data, molecular dating, stratigraphic data, and integration of ossification sequence data, but a consensus about their affinities with other Paleozoic tetrapods has failed to emerge. We have compiled five datasets to assess the relative support for six competing hypotheses about the origin of extant amphibians: a monophyletic origin among temnospondyls, a monophyletic origin among ...

https://rxivist.org/papers/17333
https://doi.org/10.1101/352609

16: Reply to Li et al. "Is Oculudentavis a bird or even archosaur?"

Jingmai O’Connor, Lida Xing et al.

1,714 downloads (posted 14 Jun 2020)

We welcome any new interpretation or alternative hypothesis regarding the taxonomic affinity of the enigmatic Oculudentavis khaungraae. However, here we demonstrate that Li et al. have failed to provide conclusive evidence for the reidentification of HPG-15-3 as a squamate. We analyse this specimen in a matrix that includes a broad sample of diapsid reptiles and resolve support for this identification only when no avian taxa are included. Regardless of whether this peculiar skull belongs to a tiny bird or to a bizarre n...

https://rxivist.org/papers/87329
https://doi.org/10.1101/2020.06.12.147041

17: Osmunda pulchella sp. nov. from the Jurassic of Sweden—reconciling molecular and fossil evidence in the phylogeny of Osmundaceae

Benjamin Bomfleur, Guido W. Grimm et al.

1,687 downloads (posted 04 Jun 2014)

The systematic classification of Osmundaceae has long remained controversial. Recent molecular data indicate that Osmunda is paraphyletic, and needs to be separated into Osmundastrum and Osmunda s. str. Here we describe an exquisitely preserved Jurassic Osmunda rhizome (O. pulchella sp. nov.) that combines diagnostic features of Osmundastrum and Osmunda, calling molecular evidence for paraphyly into question. We assembled a new morphological matrix based on rhizome anatomy, and used network analyses to establish phyloge...

https://rxivist.org/papers/30138
https://doi.org/10.1101/005777

18: The Biogeography of coelurosaurian theropods and its impact on their evolutionary history

Anyang Ding, Michael Pittman et al.

1,647 downloads (posted 10 May 2019)

The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurs that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurs were party to dramatic geographic changes on the Earth's surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coe...

https://rxivist.org/papers/50520
https://doi.org/10.1101/634170

19: Nanjinganthus: An Unexpected Flower from the Jurassic of China

Qiang Fu, José Bienvenido Diez et al.

1,577 downloads (posted 27 Dec 2017)

The origin of angiosperms has been the focus of intensive botanical debate for well over a century. The great diversity of angiosperms in the Early Cretaceous makes the Jurassic rather expected to elucidate the origin of angiosperm. Former reports of early angiosperms are frequently based on a single specimen, making many conclusions tentative. Here, based on observations of 284 individual flowers preserved on 28 slabs in various states and orientations, we describe a fossil flower, Nanjinganthus dendrostyla gen. et sp....

https://rxivist.org/papers/30117
https://doi.org/10.1101/240226

20: A multiscale stratigraphic investigation of the context of StW 573 Little Foot and Member 2, Sterkfontein Caves, South Africa

Laurent Bruxelles, Dominic J Stratford et al.

1,546 downloads (posted 29 Nov 2018)

The Sterkfontein Caves has an 80 year history of yielding remarkable evidence of hominin evolution and is currently the world's richest Australopithecus-bearing site. Included in Sterkfontein's hominin assemblage is StW 573 (Little Foot). Discovered in the Member 2 deposit in the Silberberg Grotto, StW 573 represents the most complete Australopithecus skeleton yet found. Because of its importance to the fossil hominin record, the geological age of Little Foot has been the subject of significant debate. Two main hypothes...

https://rxivist.org/papers/37691
https://doi.org/10.1101/482711