Lai Xulong

Evolution, Systematics, and Phylogeography of Pleistocene Horses in the New World: A Molecular Perspective

The rich fossil record of horses has made them a classic example of evolutionary processes. However, while the overall picture of equid evolution is well known, the details are surprisingly poorly understood, especially for the later Pliocene and Pleistocene, c. 3 million to 0.01 million years (Ma) ago, and nowhere more so than in the Americas. There is no consensus on the number of equid species or even the number of lineages that existed in these continents. Likewise, the origin of the endemic South American genus Hippidion is unresolved, as is the phylogenetic position of the “stilt-legged” horses of North America. Using ancient DNA sequences, we show that, in contrast to current models based on morphology and a recent genetic study, Hippidion was phylogenetically close to the caballine (true) horses, with origins considerably more recent than the currently accepted date of c. 10 Ma. Furthermore, we show that stilt-legged horses, commonly regarded as Old World migrants related to the hemionid asses of Asia, were in fact an endemic North American lineage. Finally, our data suggest that there were fewer horse species in late Pleistocene North America than have been named on morphological grounds. Both caballine and stilt-legged lineages may each have comprised a single, wide-ranging species.

Palaeoenvironmental changes across the Permian/Triassic boundary at Shangsi (N. Sichuan, China)

The section at Shangsi in Sichuan contains one of the most detailed and best records of events during the Permian/Triassic (P/T) mass extinction. Continuous deep water deposition is only punctuated by a minor shallowing in the late Changxingian. The micritic mudstones and wackestones of the Changxingian Dalong Formation contain abundant ammonoids and radiolaria and diverse and common benthic taxa (mostly bivalves and brachiopods) in a thoroughly bioturbated sediment. The presence of a well developed tiered burrow profile is just one line of evidence for a fully oxygenated water column in the late Permian. The faunal crisis occurs in the top few decimetres of the Dalong Formation and severely affected all groups (benthos, nekton and plankton). The extinction coincides precisely with the development of anaerobic and dysaerobic facies. The basal Triassic sediments of the Feixanguan Formation are thinnly‐bedded or laminated silicic marls and contain pyrite and several levels of elevated organic carbon concent...

Guadalupian (Middle Permian) Conodont Faunas at Shangsi Section,Northeast Sichuan Province

ABSTRACT This study recovered the Guadalupian conodont faunas from Shangsi Section in Northeast Sichuan. Four genera and nine species were identified, and three conodont zones were recognized and established; they include Jinogondolella nankingensis Zone, J. aserrata Zone, and J. postserrata Zone. The Roadian and Wordian boundary is set in the interval 5 m from the top of Bed 86 by the first appearance of the conodont J. aserrata . The Wordian and Capitanian boundary is set in the interval 2.3 m from the top of the Bed 95 by the first appearance of J. postserrata . Most of the specimens demonstrated low color alteration index (CAI) as 1.5–3, indicating that most part of the Maokou Formation may have the suitable thermal conditions for the formation of oil source rocks.

The fluctuating environment associated with the episodic biotic crisis during the Permo/Triassic transition: Evidence from microbial biomarkers in Changxing, Zhejiang Province

The environmental conditions and the biotic crisis during the Permo-Triassic (Tr/P) transition received increasing attention in the past decades. Presented herein are the molecular fossil records of cyanobacteria and green sulfur bacteria, the base of the marine ecosystem, to highlight the episodic nature of both the environment and the biotic crisis during this critical period. At least two episodes of cyanobacterial expansion are documented by 2-methylhopanes ranging from C28 to C32 in carbon number, indicative of the instable marine ecosystem and the fluctuant aquatic nutrients. Meanwhile, the index of 2-alkyl-1,3,4-trimethylbenzenes (biomarkers of green sulfur bacteria) and the ratio of pristane to phytane (Pr/Ph) witness the fluctuation of sedimentary environmental redox conditions. The above molecular evidence suggests the occurrence of highly fluctuating environmental conditions during the Tr/P transition, which is consistent with, and probably the cause of, the multi-phased biotic crisis and the prolonged faunal recovery.