Linguliform brachiopods from the terminal Cambrian and lowest Ordovician of the Oaxaquia microcontinent (Southern Mexico)

Abstract

Eighteen taxa of linguliform brachiopods, mainly represented by acrotretoids, are reported from the Upper Cambrian (Furongian, Stage 10) and Lower Ordovician (Tremadocian) Tiñu Formation of Oaxaca State, Mexico. At the time of deposition, this area was part of Oaxaquia, which was either a microcontinent or an integral part of the Gondwanan margin. Whereas certain trilobites seem to indicate a Gondwanan affinity, the Tiñu brachiopod faunas show a less definite paleogeographic relationship. Some taxa have previously only been reported from Laurentia (Eurytreta cf. fillmorensis, Eurytreta cf. campaniformis), and one taxon is best known from the Avalon microcontinent (Eurytreta cf. sabrinae). However, the relatively high percentage of new and potentially endemic taxa (Oaxaquiatreta labrifera n. gen. n. sp., Tapuritreta reclinata n. sp., Oaxaquiatreta sp., Eurytreta? n. sp., Acrotretidae n. gen. n. sp., Obolinae gen. and sp. indet.) and the lack of other typical Laurentian, Gondwanan, or Avalonian taxa suggest either a certain degree of insularity of Oaxaquia or reflects a more temperate, unrestricted marine environment during the Early Paleozoic. Other taxa reported from the Tiñu Formation include Semitreta sp., Lingulella? spp., Obolinae gen. and sp. indet., Eoscaphelasma? sp., Ottenbyella? sp. A and sp. B, and Acrotretidae gen. and sp. indet. A, B, and C. Eurytreta and Semitreta are critically reviewed and several taxa previously assigned to them have been excluded. An emended diagnosis for the genus Eurytreta is presented. The presence of delthyrium and notothyrium-like structures in the siphonotretid Oaxaquiatreta n. gen. further strengthens the previously proposed relationship between the Siphonotretida and Paterinida.

Chapter 10 Biogeography of Ordovician linguliform and craniiform brachiopods

“…The Tremadocian micromorphic brachiopod associations mostly have a low diversity and they are dominated by Eurytreta and Ottenbyella, which have almost cosmopolitan distribution. Similar Tremadocian micromorphic brachiopod associations have been documented from Baltica , Laurentia Holmer et al 2005) and Kazakhstanian terranes Holmer et al 2001), and from various peri-Gondwanan regions Streng et al 2011).…”

Lingulate brachiopods and the Early Palaeozoic history of the Iapetus Ocean

“…A number of excluded faunas have also been described from other regions, most notably Gondwana (e.g. Percival & Engelbretsen 2007;Popov et al 2008;Ghobadi Pour et al 2011;Percival et al 2011;Streng et al 2011) which do not impact directly on the analysis of the Iapetus region.…”

Carboniferous brachiopods (Productida and Orthotetida) from Santiago Ixtaltepec, Oaxaca, Southern Mexico

“…The earliest sedimentary Paleozoic unit is the Tiñú Formation, composed of limestone and shale strata. This unit is divided in a Lower Member of limestone with abundant trilobites, linguliform brachiopods and other invertebrates from the Furongian (late Cambrian) (Robison & Pantoja-Alor, 1968;Landing et al, 2007;Streng et al, 2011), and an Upper Member of shale that records graptolites from the Lower Ordovician (Tremadocian) (Pantoja-Alor, 1970;Sour-Tovar & Buitrón-Sánchez, 1987;Sour-Tovar, 1990).…”