Cephalopods and paleoenvironments of the Fort Cassin Formation (upper Lower Ordovician), eastern New York and adjacent Vermont

Abstract

The dramatic late Early Ordovician radiation of cephalopods on tropical paleocontinents is illustrated by the diverse fauna (21 genera, 30 species) of the Fort Cassin Formation (Floian and lower Blackhillsian Stage) in northeast Laurentia. Cephalopods occur through the thin (ca. 30–65 m) depositional sequence of the Fort Cassin but are most common and diverse in mollusk-rich, trilobite-poor parts of the formation that characterize the thrombolite-bearing intervals in the shoaling part of the highstand systems tract. This lithofacies-biofacies linkage persists from the Tribes Hill and Rochdale Formations (lower and lower upper Tremadocian, and upper Skullrockian and Stairsian Stages, respectively), and suggests that the Early Ordovician radiations of cephalopods took place in shallow-marine, thrombolite reef facies of tropical carbonate platforms. These habitats differed strongly from the near-shore, peritidal habitats of the older Cambrian evolutionary radiation. Genus-level diversity and absolute abundance changed little through the Skullrockian-Blackhillsian, but morphologic diversity and body size increased dramatically by the late Early Ordovician. The morphological diversification suggests cephalopods diversified into a wider variety of macropredators and more complex late Early Ordovician ecosystems. Anrangeroceras whitehallense n. gen. and n. sp. is proposed. The following are emended: the Protocycloceratidae, Centrotarphyceras and C. seelyi, Protocycloceras and P. lamarcki, and Rudolfoceras cornuoryx. The following are indeterminate and abandoned: Baltoceras? pusillum Ruedemann, 1906; Comeroceras annuliferum Flower, 1941; Cyptendoceras whitfieldi Ulrich et al., 1944; Endoceras? champlainense Ruedemann, 1906; Wolungoceras valcourense Flower, 1964. Beekmanoceras Ulrich and Foerste, 1936 is a gastropod.

Palaeoecology and palaeogeography of Late Ordovician (Katian–Hirnantian) cephalopods of the Boda Limestone, Siljan district, Sweden

“…These conditions lasted without significant interruptions over a comparatively long time interval of around 5 million years. Additionally, compared with a similar long time interval in Early Ordovician shallow water reefs (Kröger & Landing ), the evolutionary changes within the cephalopod fauna were minimal during the growth of the Boda mounds.…”

“…The taxonomic distinctness tripled throughout the entire Beekmantown Group and reached a maximum value in the Fort Cassin Formation of 3.67 (Kröger & Landing ). This value is nearly identical to that of the Boda Limestone cephalopods (Table ).…”

Review and palaeoecological analysis of the late Tremadocian - early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France

“…# without specimens from St. Chinian, * raw data are from Kraeger and Landing (2009 Table 2. Number of specimens collected from the St. Chinian, La Maurerie, and Foulon formations (Faunizones E/F, H, K respectively) from different localities of the Montagne Noire, France.…”

“…In emending the Baltoceratidae and restricting the family to Orthocerida taxa similar to Cochlioceras Eichwald, 1860, Kraeger et al (2007) excluded those genera possessing concave siphuncular segments with thickened connecting rings such as Rioceras Flower, 1964 originally included in the Baltoceratidae by Flower (1964). Similarly, revision of Protocycloceras lamarcki (Billings, 1859) by Kraeger & Landing (2009) has restricted the Protocycloceratidae to rod-bearing, annulate longicones of the Ellesmerocerida with concave siphuncular segments. As a consequence of these more restricted diagnoses Kraeger & Landing (2009) indicated that the remainder of the original Baltoceratidae were orphaned and the erection of a new higher taxon was required.…”

Review and palaeoecological analysis of the late Tremadocian – early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France

“…N ¼ number of specimens; S ¼ number of species; S rarified rarified S with census 55 specimens, lower and upper 95 % confidence interval in parentheses; J ¼ H 0 =log ðSÞ; where H 0 is the Shannon -Wiener index of the sample. # without specimens from St. Chinian, * raw data are from Kraeger and Landing (2009…”