First turtle from the Ipubi Formation (Early Cretaceous), Santana Group, Araripe Basin, Brazil

Abstract

The Araripe Basin is located in northeastern Brazil between the states of Ceara, Piaui and Pernambuco (Figure 1). The Crato and Romualdo formations (Santana Group, see details in Neumann & Cabrera, 1999; Valenca et al., 2003) that comprise the most fossiliferous strata of this basin, are famous worldwide for the diverse and exquisitely well preserved fossil assemblages (e.g. Maisey, 1991). These two different lagerstatten were formed during the Lower Cretaceous, Aptian/Albian (Pons et al., 1990; ABSTRACT – Up to date turtle remains from the Early Cretaceous Santana Group are known only to the Crato and Romualdo formations (Aptian-Albian) that have yielded five species: Araripemys barretoi Price, 1973; Santanachelys gaffneyi Hirayama, 1998; Brasilemys josai Lapparent de Broin, 2000; Cearachelys placidoi Gaffney, Campos & Hirayama, 2001 and Euraxemys essweini Gaffney, Tong & Meylan, 2006. Except for A. barretoi, known from both, the Romualdo and Crato formations, all other turtle taxa are restricted to the Romualdo Formation. Fragments of the skull, an incomplete lower jaw and carapace of the first turtle remains from the Ipubi Formation are reported here. This material was collected in the shales above the gypsum layer, close to the contact with the Romualdo Formation (Aptian-Albian). Compared to other turtles from the Santana Group, this specimen is referred to Pelomedusoides, excluding Araripemys and Brasilemys, based on the following characteristics: absence of a cavum pterygoidei, absence of cervical scute, absence of fontanels in the carapace, contact between nuchal and first peripheral, and absence of nuchal emargination.