Phylogeny, ancestral ranges and reclassification of sand dollars.

Classification of the Class Echinoidea is under significant revision in light of emerging molecular phylogenetic evidence. In particular, the sister-group relationships within the superorder Luminacea (Echinoidea: Irregularia) have been considerably updated. However, the placement of many families remains largely unresolved due to a series of incongruent evidence obtained from morphological, paleontological, and genetic data for the majority of extant representatives. In this study, we investigated the phylogenetic relationships of 25 taxa, belonging to eleven luminacean families. We proposed three new superfamilies: Astriclypeoidea, Mellitoidea, and Taiwanasteroidea (including Dendrasteridae, Taiwanasteridae, Scutellidae, and Echinarachniidae), instead of the currently recognized superfamily Scutelloidea Gray, 1825. In light of the new data obtained from ten additional species, the historical biogeography reconstructed shows that the tropical western Pacific and eastern Indian Oceans are the cradle for early sand dollar diversification. Hothouse conditions during the late Cretaceous and early Paleogene were coupled with diversification events of major clades of sand dollars. We also demonstrate that Taiwan fauna can play a key role in terms of understanding the major Cenozoic migration and dispersal events in the evolutionary history of Luminacea.

Changing surface ocean circulation caused the local demise of echinoid Scaphechinus mirabilis in Taiwan during the Pleistocene-Holocene transition.

Abundant fossil specimens of Scaphechinus mirabilis, now occurring mostly in temperate waters, have been found in the Toukoshan Formation (Pleistocene) in Miaoli County, Taiwan. Environmental changes leading to its extirpation (local extinction) have thus far been elusive. Here, we reconstruct past environmental and oceanic conditions off northwest Taiwan by analyzing clumped isotopes, as well as stable oxygen isotopes, of well-preserved fossil echinoid tests collected from the Toukoshan Formation. Radiocarbon dates suggest that these samples are from Marine Isotope Stage 3 (MIS 3). Paleotemperature estimates based on clumped isotopes indicate that fossil echinoids were living in oceanic conditions that range from 9 to 14 °C on average, comparable with the estimate derived for a modern sample from Mutsu Bay, Japan. Notably, this temperature range is ~ 10 °C colder than today's conditions off northwest Taiwan. The substantially lower temperatures during ~ 30 ka (MIS 3) compared to the modern conditions might be due to the rerouting of surface currents off northwest Taiwan when the sea level was ~ 60 m lower than today, in addition to the cooling caused by a lower atmospheric CO2 level during the Last Glacial Period. Colder waters brought here by the China Coastal Current (CCC) and the existence of shallow subtidal zones termed "Miaoli Bay" (mainly located in the present-day Miaoli county) during MIS 3 plausibly sustained generations of S. mirabilis, yielding tens of thousands of fossil specimens in the well-preserved fossil beds. The likely extirpation driver is the drastic change from a temperate climate to much warmer conditions in the shallow sea during the Pleistocene-Holocene transition.

The first complete mitochondrial genome of the sand dollar Sinaechinocyamus mai (Echinoidea: Clypeasteroida).

Morphologic and molecular data often lead to different hypotheses of phylogenetic relationships. Such incongruence has been found in the echinoderm class Echinoidea. In particular, the phylogenetic status of the order Clypeasteroida is not well resolved. Complete mitochondrial genomes are currently available for 29 echinoid species, but no clypeasteroid had been sequenced to date. DNA extracted from a single live individual of Sinaechinocyamus mai was sequenced with 10× Genomics technology. This first complete mitochondrial genome (mitogenome) for the order Clypeasteroida is 15,756 base pairs in length. Phylogenomic analysis based on 34 ingroup taxa belonging to nine orders of the class Echinoidea show congruence between our new genetic inference and published trees based on morphologic characters, but also includes some intriguing differences that imply the need for additional investigation.

Chemostratigraphic correlations across the first major trilobite extinction and faunal turnovers between Laurentia and South China.

During Cambrian Stage 4 (~514 Ma) the oceans were widely populated with endemic trilobites and three major faunas can be distinguished: olenellids, redlichiids, and paradoxidids. The lower-middle Cambrian boundary in Laurentia was based on the first major trilobite extinction event that is known as the Olenellid Biomere boundary. However, international correlation across this boundary (the Cambrian Series 2-Series 3 boundary) has been a challenge since the formal proposal of a four-series subdivision of the Cambrian System in 2005. Recently, the base of the international Cambrian Series 3 and of Stage 5 has been named as the base of the Miaolingian Series and Wuliuan Stage. This study provides detailed chemostratigraphy coupled with biostratigraphy and sequence stratigraphy across this critical boundary interval based on eight sections in North America and South China. Our results show robust isotopic evidence associated with major faunal turnovers across the Cambrian Series 2-Series 3 boundary in both Laurentia and South China. While the olenellid extinction event in Laurentia and the gradual extinction of redlichiids in South China are linked by an abrupt negative carbonate carbon excursion, the first appearance datum of Oryctocephalus indicus is currently the best horizon to achieve correlation between the two regions.

Paleontological Studies of Whale Barnacles in Taiwan Reveal New Cetacean Migration Routes in the Western Pacific Since the Miocene.

This paper reports a rediscovery of the first museum specimens of fossil whale barnacles from Taiwan. They are part of the material studied and figured by Ichiro Hayasaka in 1934. After examination of the material, which includes two cut-sections and one slice, the taxonomic assignment is revised to Coronula bifida Bronn, 1831. A petrographic study of the surrounding matrix shows that the matrix lacks slate and lithic fragments, indicating that the specimen was deposited in the pre-collision settings during the Miocene to early Pliocene. Figured specimens in Hatai's work in 1939 were examined for comparison. The distribution record of Coronula fossils shows that whales passed through the Taiwan Strait to Okinawa and moved northwards via the Pacific coast of Honshu or entered into the Sea of Japan. The fossil record in this region extends back to the upper Miocene in Yamagata prefecture (facing the Sea of Japan) and Boso Peninsula (facing the Pacific Ocean) in Honshu (~11.2 Ma-5.3 Ma). This is one of the oldest cetacean migration routes documented to date.

Function and hydrostatics in the telson of the Burgess Shale arthropod Burgessia.

Burgessia bella is a characteristic Burgess Shale arthropod (508 Ma), but the unusual preservation of its telson in both straight and bent modes leads to contradictory interpretations of its function. A reinvestigation of the fossil material, including burial attitudes, combined with a comparison with the decay sequence and mechanics of the telson in living Limulus, demonstrates that the telson of Burgessia was flexible in its relaxed state but could be stiffened in life. Evidence of fluid within the telson indicates that this manoeuvrability was achieved by changes in hydrostatic pressure and muscular control. The dual mode in the Burgessia telson is, to my knowledge, the first documented among fossil arthropods. It indicates that the requirement for a rigid telson, which is resolved by a thick sclerotized cuticle in most arthropods, may first have been achieved by hydrostatic means.