Elizabeth S. Carter

Timing the end-Triassic mass extinction: First on land, then in the sea?

The end-Triassic marks one of the five biggest mass extinctions, but current geologic time scales are inadequate for understanding its dynamics. A tuff layer in marine sedimentary rocks encompassing the Triassic-Jurassic transition yielded a U-Pb zircon age of 199.6 ± 0.3 Ma. The dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts. Additional recently obtained U-Pb ages integrated with ammonoid biochronology confirm that the Triassic Period ended ca. 200 Ma, several million years later than suggested by previous time scales. Published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200.6 Ma. The end-Triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years.

Catalogue of Mesozoic Radiolarian Genera. Part 2: Jurassic-Cretaceous

ABSTRACT The catalogue of Mesozoic radiolarian genera is a revision of all described genera with re-illustration of their type species. This project was organized under the auspices of the International Association of Radiolarian Paleontologists (Inter-Rad), and was carried out by the Mesozoic Working Group. This is the second of two contributions, this one devoted to the Jurassic-Cretaceous period. It contains 581 genera with re-illustration of their type species. This part shares 30 genera in common with the Triassic catalogue, most of which arose in the Carnian, Norian and Rhaetian. The sharp difference manifested between the Triassic fauna and the Jurassic-Cretaceous fauna is so evident that it justifies two independent catalogues. A comparable division between the Jurassic and Cretaceous could not be justified however, because of the similarity of the fauna, and by the greater number of genera crossing the Jurassic-Cretaceous boundary which is three times that for the Triassic-Jurassic boundary. A distinct characteristic of Jurassic-Cretaceous genera is the high number of nomina dubia (up to 131), contrary to the low number in the Triassic interval. This reflects, in part, the influence of Haeckelian taxonomy in earlier research on Jurassic-Cretaceous faunas prior to the application of SEM techniques.The Mesozoic Working Group has carefully reviewed and re-examined the taxonomy of all available genera, their family assignment and stratigraphic ranges. Following careful comparisons, 91 genera were declared as synonyms. The review has noted 26 homonyms which were duly notified to their corresponding authors, and were corrected previous to the publication of this catalogue. In spite of this effort, unfortunately nine homonyms still remain. Two invalid nominal genera and two nomina nuda are also reported. The systematic revisions have validated 341 genera for the Jurassic-Cretaceous interval. At the end of this catalogue 24 additional photographs are presented as support for those genera having a poor original illustration of the type species.

Catalogue of Mesozoic radiolarian genera. Part 1: Triassic

ABSTRACT The Catalogue of Mesozoic radiolarian genera is a revision of all described genera with re-illustration of their type species. This project was organized under the auspices of the International Association of Radiolarian Paleontologists (Inter-Rad), and was carried out by the Mesozoic Working Group. This contribution (Part 1), deals with the Triassic period only. There are 381 known Triassic radiolarian genera. Most have been published since the 1970s following the introduction of scanning electron microscopy (SEM), which enabled good pictures for most type species. For this reason the Triassic period is characterized by a very low number of nomina dubia (only 14), contrary to the higher number in the Jurassic-Cretaceous interval. The Mesozoic Working Group has carefully reviewed and reexamined the taxonomy of all available genera, their family assignment and stratigraphic ranges. Following careful comparisons, 73 genera were declared synonyms. The review has also detected 11 cases of homonymy that were duly notified to their authors, and were corrected previous to the publication of this catalogue; unfortunately one homonym still remains. Two invalid nominal genera are also reported herein. The systematic revisions have validated 282 genera for the Triassic, and of these only 30 genera cross the Triassic-Jurassic boundary. At the end of the catalogue 15 additional photos are presented as support for those genera having a poor original illustration of the type species.

Triassic radiolarian biostratigraphy

Abstract This paper summarizes 30 years of research on the biostratigraphy of Triassic radiolarians and presents a correlation of currently-used radiolarian zonations established in North America, Europe, Japan and Far East Russia. An up-to-date stratigraphic distribution of all hitherto described and still valid Triassic genera is provided. This new range chart consists of 282 genera and allows an accurate dating to substage level. It also clearly manifests general trends in radiolarian evolution through the Triassic. The end-Permian extinction, the most severe extinction in the history of radiolarians, was followed by a long recovery until the early Anisian. The middle and late Anisian were then characterized by a rapid explosion of new morphologies. Maximum generic diversity was attained during the early Carnian, but the first severe extinctions also occurred in the Carnian. A progressive decline of diversity took place through the Norian and Rhaetian, and ended in a mass extinction around the Triassic–Jurassic boundary.

The Triassic-Jurassic (T-J) boundary in Queen Charlotte Islands, British Columbia defined by ammonites, conodonts and radiolarians

Abstract In the Queen Charlotte Islands, on the Pacific shore of Birtish Columbia, Canada, Triassic-Jurassic boundary beds are present in several well-exposed sections of the Sandilands Formation. Triassic and Jurassic ammonoids, Triassic conodonts and Triassic and Jurassic radiolarians indicate the position of the boundary to within a few metres. The section may be essentially continuous across the boundary. The evidence suggests more or less simultaneous extinction of ammonoid, conodont and radiolarian faunas at the T-J boundary.

Family Kungalariidae, n. fam., new Mesozoic entactinarian Radiolaria with a nassellarian-type initial spicule

Based on internal structure, a new family of entactinarian radiolarians, the Kungalariidae, is described with three new genera and four species: Kungalaria newcombi, Cachecreekaria californiensis, Transylvanaria devaensis, and T. hattorii. Members of this family have an eccentric internal, nassellarian-type initial spicule with bar MB, rays A, V, L, I, and spine Ax; a medullary shell built above the plane of lateral rays as in the cephalis of many nassellarians; and a spherical to subspherical cortical shell around the medullary shell. This new family is part of a group of Triassic entactinarians structurally intermediate between Entactinaria, or spicule-bearing Spumellaria, and Nassellaria. The new genera and species described occur in the Rhaetian of Queen Charlotte Islands, British Columbia, Aalenian to early-mid Bajocian of central Japan, Cenomanian of California, and Coniacian of Romania.

Evolutionary trends in Latest Norian through Hettangian radiolarians from the Queen Charlotte Islands, British Columbia

Abstract Uppermost Triassic and lowermost Jurassic (Hettangian) radiolarians from continuous sequences of the Sandilands Formation (Kunga Group), Queen Charlotte Islands, British Columbia, Canada, provide a rare glimpse into faunal patterns of evolution, radiation, extinction, and regeneration near a major stratigraphic boundary. The radiolarians are dated by Triassic ammonoids and conodonts, and Jurassic ammonites. Uppermost Triassic radiolarians are from strata equivalent to the Amoenum and Crickmayi ammonoid zones. Lowest Jurassic faunas are Planorbis Zone equivalent. The direction and pace of evolution in the highly diverse uppermost Triassic fauna is variable. Conservative taxonomic groups such as the pantanelliids and canoptids evolve gradually with only minor morphological change. Species extinctions occur regularly throughout the interval and across the boundary, with most genera ranging into the Jurassic. Current data confirm that Betraccium persists to the topmost Triassic but not into the Jurassic. Architecturally complex forms such as Squinabollela and Praecitriduma apparently have short ranges; they are common in uppermost Triassic beds but not found in the Lower Jurassic. Other radiolarian groups experience periodic bursts of radiation evidenced by multiple new species, and even new genera, most of which survive to the topmost Triassic but not beyond e.g. Ferresium and Laxtorum.. Finally, ancestral forms of some typical Lower Jurassic taxa are first recognized in uppermost Triassic beds e.g. Bipedis, Canutus, Crucella,, and Droltus.. Lowermost Jurassic radiolarians are easily distinguished from uppermost Triassic ones by their primitive appearance and low diversity, and by the absence of all distinctive uppermost Triassic taxa. Lower Hettangian faunas are characterized by latticed, spherical, irregularly spinose forms with poorly organized meshwork; non-distinctive spongy forms with spines; very simple nassellarians; and Archaeocenosphaera laseekensis. Pantanellium tanuense is the only pantanelliid species in Lower Hettangian collections.