Benjamin Sames

Earliest Cretaceous Mammals from the Western United States

Mammalian diversity in North America shifted significantly during the Early Cretaceous, from archaic groups dominant in the well-sampled faunas of the Late Jurassic to advanced forms (including early members of modern clades) by the Albian—Cenomanian. However, the dynamics of this transition are poorly understood, since faunas of earliest Cretaceous age are unknown. Here we describe the first fossil mammals from exposures of the Lakota Formation in the Black Hills of South Dakota, a unit correlated with the upper Berriasian—lower Barremian and positioned stratigraphically between the underlying Morrison Formation and Aptian—Albian units exposed elsewhere in North America. The mammalian fauna from the Lakota Formation is transitional with regard to the North American fossil record, representing a broad spectrum of both Jurassic and Cretaceous lineages: present are “plagiaulacidan” multituberculates allied with Late Jurassic Allodontoidea and Early Cretaceous Plagiaulacoidea; the geologically youngest dryolestoid(s) and “triconodontine” triconodontids (characteristic Late Jurassic taxa from the Morrison Formation); the oldest spalacotheriid “symmetro-dont”; the first record of an amphitheriid-like stem zatherian from North America (abundant in the Middle Jurassic-earliest Cretaceous of Europe); and the oldest North American tribosphenic mammal (abundant and diverse on the continent by the end of the Early Cretaceous). Taxa making their first North American appearance in the Lakota Formation (Plagiaulacoidea, including a genus also known from the Purbeck of Britain; Spalacotheriidae, stem Zatheria, Tribosphenida) are also known from the Early Cretaceous of Western Europe, suggesting the possibility that they represent immigrants.

Praecypridea: a new non-marine ostracod genus from the Jurassic and Early Cretaceous of Europe, North and South America, and Africa

The genus Praecypridea gen. nov. (Cypridoidea, Family Cyprideidae Martin, 1940) is described and thus far comprises four species: the type species Praecypridea acuticyatha (Schudack, 1998) comb. nov., Praecypridea postelongata (Oertli, 1957) comb. nov., Praecypridea suprajurassica (Mojon, Haddoumi & Charriére, 2009) comb. nov. and Praecypridea acuta (Moos, 1959 in Wicher, 1959) comb. nov. Representatives of the new genus have been described from the Middle to Late Jurassic of Europe, North America and Africa and the Early Cretaceous of South America, with other presumed representatives also occurring in the Early Cretaceous. Species of Praecypridea are considered to represent members of the ancestral lineage of the extinct genus Cypridea Bosquet, representatives of which flourished in non-marine habitats of latest Jurassic to Early Cretaceous age and account for the first period of abundance of the non-marine Cypridoidea.

To correlate or not to correlate--That is not the question anymore! Continental Late Jurassic to Early Cretaceous supraregional correlation based on freshwater to brackish-water ostracodes

On several occasions at paleontology-, geology-, and stratigraphy-related meetings during the past years, I noticed that many colleagues, even micropaleontologists, are not (anymore!) aware of the fundamental application potential of pre-Quaternary, fresh- and brackish-water ostracode fossils. Ostracodes, aquatic crawling or swimming microcrustaceans with a calcified bivalved shell and high fossilization potential, have rarely been considered as a major tool in biostratigraphy, fading mostly into the background compared to other fossil groups in the marine realm. In the continental realm, however, ostracodes are often the most common and abundant fossils, whether in freshwater or saline deposits. Yet, supraregional and intercontinental biostratigraphy based on aquatic organisms sounds absurd. It is not, however! Fresh- and brackish-water ostracodes have developed different strategies and mechanisms to facilitate their adaptation to temporary habitats and dispersal in such settings. Recent fresh- and brackish-water ostracodes, just as did their fossil counterparts, have a high potential to be passively distributed over long distances and across migration barriers by wind and larger animals, particularly owing to the desiccation- and freeze-resistant resting eggs of major groups (e.g., Horne and Martens, 1998) and, therefore, are a strong candidate for biostratigraphic application. Dealing with biostratigraphy of Lower Cretaceous continental deposits, it is important to understand that in most regions, except western Europe, we are not necessarily talking about high-resolution biostratigraphy. For example, many publications to-date on such deposits in Central Asia, South America, and Africa only provide an age of Early Cretaceous without further subdivision, and no attribution to stages. In the North American Western Interior foreland basin, Lower Cretaceous continental deposits are widely regarded to be of pre-middle Albian age, or to range from Aptian to Albian, sometimes Barremian–Albian in age (e.g., Cobban and Reeside, 1952; Peck, 1959; Mateer et al., 1992; Dyman et al. 1994; Way et …

A gigantic marine ostracod (Crustacea: Myodocopa) trapped in mid-Cretaceous Burmese amber

The mid-Cretaceous Burmese amber (~99 Ma, Myanmar), widely known for exquisite preservation of theropods, also yields microfossils, which can provide important contextual information on paleoenvironment and amber formation. We report the first Cretaceous ostracod in amber—the gigantic (12.9 mm) right valve of an exclusively marine group (Myodocopa: Myodocopida) preserved in Burmese amber. Ostracods are usually small (0.5–2 mm), with well-calcified carapaces that provide an excellent fossil record extending to at least the Ordovician (~485 million years ago), but they are rarely encountered in amber. The new specimen effectively doubles the age of the ostracod amber record, offering the first representative of the Myodocopa, a weakly calcified group with a poor fossil record. Its carapace morphology is atypical and likely plesiomorphic. The preserved valve appears to be either a moulted exuvium or a dead and disarticulated specimen, and subsequent resin flows contain forest floor inclusions with terrestrial arthropods, i.e., fragmentary remains of spiders, and insect frass. These features resolve an enigmatic taphonomic pathway, and support a marginal marine setting for resin production.