ALBERT

Description: Students of Earth history have long recognized the correlation between the quantity of preserved sedimentary rock and the diversity of life recorded as fossils. But paleontologists have yet to determine whether this pattern reflects a causal relationship or a unidirectional sampling bias in fossil data imposed by preserved rock quantity. Distinguishing between these two alternatives has been complicated by the fact that many of the basic patterns of paleontologic and lithologic covariation have yet to be quantified rigorously. Here we present the first analyses of the covariation between the macrostratigraphic and macroevolutionary histories of North America based on geographically and temporally explicit co-occurrences of rocks and fossils. The analyses use independent quantitative summaries of the stratigraphic and fossil records by integrating the Paleobiology Database (PaleoDB) and Macrostrat, a macrostratigraphy database for North America, which allows a more direct comparison of the stratigraphic and biological histories of the continent than has heretofore been possible. Within the Macrostrat database, the rock record is divided into discrete packages of sediment that are bound by hiatuses resolvable at the stage-level. Using per interval, per package rates of sediment package initiation and truncation, and genus first and last appearances (herein regional origination and extinction), we find a substantially stronger positive correlation between sediments and biology for extinction-like parameters than we do for origination-like parameters. Four of the largest coincident pulses of regional extinction and sediment truncation occur during the widely recognized end-Ordovician, late Permian, end-Triassic, and end-Cretaceous mass extinction intervals. A further comparison of the global ranges of North American genera to North American macrostratigraphy indicates that the regional and global extinction of genera are more likely to occur in the same stage than are global and regional originations. Together, these results suggest that our general understanding of biodiversity dynamics from the fossil record may not be strongly biased by the preservation of sediments and leaves open the possibility that certain large perturbations to the Earth system are responsible for major changes of state in both the sedimentary and biological systems.

Description: New collections of trilobites from the type section of the Parahio Formation in the Parahio Valley, Spiti, and from the Parahio, Karsha, and Kurgiakh formations in the Zanskar Valley, permit biozonation based on material precisely located within measured stratigraphic sections. Specimens preserved in limestone with mild tectonic deformation clarify the features of several Himalayan taxa known previously only from severely deformed specimens preserved in shale. A total of 75 trilobite taxa from the Cambrian of Spiti and Zanskar can be referred, questionably at least, at the generic level or below, and 61 of these are present in our new collections. This new material is assigned with confidence to 29 existing species, and to 12 new species. Three new genera, Haydenaspis, Bhargavia, and Himalisania, are established; new species include Haydenaspis parvatya, Prozacanthoides lahiri, Probowmania bhatti, Xingrenaspis parthiva, X. shyamalae, Bhargavia prakritika, Kaotaia prachina, Gunnia smithi, Sudanamonocarina sinindica, Proasaphiscus simoni, Koldinia odelli, and Torifera jelli. Ten additional Himalayan forms are assigned at the generic level only, and another 11 are questionably assigned to genera or species. The zonation proposed includes 6 zones and 3 levels, including the Haydenaspis parvatya level, the Oryctocephalus indicus level, the Kaotaia prachina Zone, the Paramecephalus defossus Zone, the Oryctocephalus salteri Zone, the Iranoleesia butes level, the Sudanomocarina sinindica Zone, the Lejopyge acantha Zone, and the Proagnostus bulbus Zone. The sections span from the upper part of the informal Stage 4, Series 2 of the Cambrian System, about 511 Ma old, to the Proagnostus bulbus zone of the Guzhangian Stage near the top of Series 3, dated at about 501 Ma. This time interval is represented by about 2000 m of section, which is thick compared to similar intervals elsewhere and is consistent with high rates of sedimentation along the Himalayan margin at the time. The fauna resembles others from equatorial peri-Gondwanaland, with closest similarity to that of South China. It also bears strong affinity to the North China fauna. Juvenile trilobites are described for the first time from India. A new Chinese species, Monanocephalus liquani, is also described.