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Open Access Publications from the University of California


Puercolestes and Betonnia (Cimolestidae, Mammalia) from the early Paleocene (Puercan 3 Interval Zone) of northeastern Montana, U.S.A.

In northeastern Montana, fossil localities in the Garbani Channel Complex and other early Paleocene (Puercan 3 Interval Zone) localities are preserved in the Tullock Member of the Fort Union Formation. They document an early phase in the recovery of the terrestrial fauna of the North American Western Interior after the mass extinction marking the Cretaceous-Paleogene (K-Pg) boundary. The cimolestids Puercolestes simpsoni and Betonnia tsosia were typified on fragmentary jaws and isolated teeth found in Puercan 2 and 3 Interval Zones (Pu2, Pu3) in the Nacimiento Formation, San Juan Basin, New Mexico. The available samples of these genera from both New Mexico and Montana are small and dominantly consist of isolated teeth. Characters of upper cheek teeth, P4 and M1–M3, justify provisional recognition of Puercolestes sp. cf. Pu. simpsoni and the somewhat smaller Betonnia sp. cf. Be. tsosia in Pu3 local faunas in the Tullock Member. In contrast, discovery of characters distinguishing the isolated lower cheek teeth, p4s and m1–m3s, of these species must await recovery of dentulous dentaries documenting the patterns of morphological variation of their lower dentitions. Fossils from the Tullock Member add support to the current interpretation that cimolestids were taxonomically diverse and geographically widespread but relatively rare members of the faunas of the North American Western Interior during approximately the first million years of the Paleocene.

Revision of Eocene warm-water cassid gastropods from coastal southwestern North America: implications for paleobiogeographic distribution and faunal-turnover

The warm-water (thermophilic) Eocene cassid gastropods reported previously from coastal southwestern North America (CSWNA), a region extending from the Olympic Peninsula, Washington to Baja California Sur, Mexico, are revised in terms of taxonomy, description, geographic distribution, and biostratigraphy. Five species of the cassine Galeodea and a single species of the phaliine Echinophoria are recognized. Galeodea meganosensis, G. sutterensis, G. louella, G. californica and G. tuberculiformis are predominantly found in California and, collectively, range in age from early to middle Eocene. Echinophoria trituberculata of middle Eocene age in southern California and of earliest late Eocene age in southwestern Washington, is the earliest known record of this genus. Several poorly known supposed cassids are discussed. The pre-Oligocene global record of Galeodea is compiled for the first time. The first arrival of Galeodea in the CSWNA region occurred in the early Eocene just after the warmest peak and highest sea level of the Cenozoic. Some of the CSWNA Galeodea species are very similar morphologically to some found in the Tethys Realm of Western Europe, especially in England and France, and to some found in the Gulf Coast and Mexico (Nuevo León and Chiapas). These similar species are indicative that the migratory route of Galeodea into the CSWNA region was via a current system that emanated from the Old World, passed near southern Western Europe, the Gulf Coast of the United States, northern and southern Mexico, and eventually influenced the CSWNA region. Thermophilic CSWNA cassids radiated during the early Eocene but declined by the end of the middle Eocene, and, because of global cooling, disappeared near the beginning of the Oligocene.

Late Eocene (Priabonian) elasmobranchs from the Dry Branch Formation (Barnwell Group) of Aiken County, South Carolina, USA

A survey of the Eocene (Priabonian) Dry Branch Formation exposed in Aiken County, South Carolina, resulted in the collection of thousands of fossil teeth and bone fragments. Two sites located near the city of Aiken proved to be particularly productive, and 24 species of elasmobranchs, 11 osteichthyans, and three reptiles (one crocodilian and two turtles) have been identified. Herein we focus on the elasmobranch species (17 sharks and seven rays) that are part of the assemblage, which includes a new species of daggernose shark, Isogomphodon aikenensis n. sp. Cicimurri and Knight. The fossils are derived from the upper part of the Dry Branch Formation, and the fossiliferous strata accumulated within a high energy nearshore marine depositional environment that was influenced by a river system. Based on the vertebrate and invertebrate fossils we identified, the water depth was less than 40 m, and surface water temperature was at least 22° C . Elasmobranch species composition is similar to other late Eocene elasmobranch assemblages reported from the Gulf and Atlantic Coastal plains, particularly Georgia, and several of the taxa indicate affinities to the Tethyan region.

Ediacaran-Cambrian transition of the Southwestern USA—Field Trip of the North American Paleontological Convention, June 19–22, 2019

Participants should plan to arrive in Riverside by June 18. We will depart from the University of California, Riverside campus the morning of June 19. We will drive 5 hours to the White-Inyo Mountains. We will spend the remainder of June 19 and most of June 20 visiting the upper Ediacaran through lower Cambrian succession of this area, including a rich assemblage of trace fossils and some of the earliest Laurentian biomineralized fossils. We will drive to Beatty, NV the evening of June 20. On the morning of June 21, we will visit upper Ediacaran strata and an Ediacaran-Cambrian boundary section of the Reed Dolomite and Deep Spring Formation at Mount Dunfee and see Ediacaran microbialites, tubular body fossils and some of the oldest complex trace fossils. We will spend midday at the nearby ghost town of Gold Point, NV, and have an opportunity to see the spectacular early Cambrian archaeocyathan reefs of the Poleta Formation at Stewart’s Mill in the afternoon. We will depart Beatty the morning of June 22 and return to Riverside by way of Death Valley, where we will make brief stops to discuss the stratigraphy of the Death Valley region, Neogene lake deposits near Shoshone and Cryogenian diamictites and the Marinoan cap carbonate exposed in the Saddle Peak Hills and at Sperry Wash. We will be staying in motels in Big Pine, CA (June 19) and Beatty, NV (June 20–21); participant lodging for these days will be covered by field trip fees. Lunches on all four days (June 19–22) and breakfast on the third day of the trip (June 21) will be provided; participants will be responsible for all other meals. We will return to Riverside in the late afternoon on June 22, in time for participants to check in to conference lodging. See Figure 1 for a map of field trip destinations.

The middle Miocene in southern California: Mammals, environments, and tectonics of the Barstow, Crowder, and Cajon Valley formations—Field Trip of the North American Paleontological Convention, June 22, 2019

The Mojave Region preserves a rich and continuous Miocene mammal-fossil record that formed during a time of significant tectonic activity and climate change. We will visit exposures of the Crowder, Cajon Valley, and Barstow formations to look at the evolution of three different sedimentary basins through the middle Miocene. Participants will learn how depositional environments and habitats changed through time in relation to tectonics and climate and how they influenced patterns of mammal diversity and biostratigraphy.

First record of a leatherback sea turtle (Dermochelyidae) from the Mio-Pliocene Purisima Formation of northern California, USA

The leatherback sea turtle family Dermochelyidae has an extensive evolutionary history, though it is represented by only one living species today, Dermochelys coriacea. Dermochelyid fossils occur worldwide from upper Cretaceous to Pliocene marine strata. Herein described is the first occurrence of a sea turtle from the lowermost Pliocene Purisima Formation of northern California, a single carapacial non-ridge ossicle. The ossicle exhibits external morphological and internal structural characteristics (ossicle thickness, internal layering, serrate margins) that are comparable to both the extinct genus Psephophorus and to the extant genus Dermochelys. Identification of the ossicle as cf. Psephophorus is based on examination of its thickness, internal structure, surface textures and geochronological age. This paper reports the third occurrence of leatherback sea turtle fossils from the western coast of the United States.

Nestling-sized hadrosaurine cranial material from the Hell Creek Formation of northeastern Montana, USA, with an analysis of cranial ontogeny in Edmontosaurus annectens

Despite over a century of intense collecting, the Hell Creek Formation has produced exceedingly few specimens of small juveniles and nestling-sized dinosaurs. Here, we report on the first cranial material of nestling-sized hadrosaurid dinosaurs from the formation. The specimens were recovered from the Sandstone Basin locality in Garfield County, northeastern Montana. The material consists of two dentaries, a surangular, and a quadrate from disassociated individuals, which through ontogenetically independent characters allows assignment of the surangular (UCMP 235857) and quadrate (UCMP 235859) to Hadrosaurinae and the dentary (UCMP 235860) to Edmontosaurus. Since Edmontosaurus annectens is the only known hadrosaurid in the formation, we hypothesize that these specimens represent the earliest ontogenetic growth stage of E. annectens providing a significant ontogenetic extension when assessing aspects of cranial ontogeny in this taxon. Using the newly identified nestling cranial material as end members of ontogenetic series for each element in E. annectens, we evaluated ontogenetic variability in phylogenetic characters associated with these elements that are used in assessing phylogenetic relationships among hadrosaurids. Although the quadrate and surangular generally develop isometrically and show minimal ontogenetic variation in morphology, the dentary undergoes significant ontogenetic changes. In particular, the dental battery exhibits a high degree of intraspecific variability through ontogeny. Ontogenetic variability in the dentary should reflect a commensurate degree of variation in the jaws and facial skeleton, suggesting caution should be used when taxonomically identifying small edmontosaur material, such as that known from Alaska. Taxonomic identification of new taxa should be restricted to adult individuals until enough specimens are available to adequately assess taxonomic variation in ontogenetically equivalent semaphorants/ontogimorphs for a large range of complementing taxa.

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Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA

Excavation of the new fourth bore of the Caldecott Tunnel in the Berkeley Hills, Oakland, California reveals two faunas attributed to an unnamed glauconitic mudstone (=Sobrante Formation and mapped as Tsm) and the Claremont chert (both of Graymer 2000). The fossil assemblage from the unnamed glauconitic mudstone, referred to here as the Tsm Caldecott Tunnel fauna, consists of 32 taxa: one bryozoan, 22 Mollusca (16 Bivalvia, five Gastropoda and one Scaphopoda), two Arthropoda (one Decapoda and one Maxillopoda), two Echinodermata (one Crinoidae and one Echinoidea), and five Chordata. Mollusks indicate a middle Miocene age based on the co-occurrence of the provisionally identified bivalves Acila empirensis, Anadara osmonti, Yoldia submontereyensis, Y. supramontereyensis and the gastropod genera Bruclarkia and Trophoscyon. This fauna was likely deposited at water depths between 350 and 400 m. Although several taxa from shallower depths are present, these are assumed to have washed in from shallower depths. Only one taxon was found that typically occurs in deeper water. The fauna lived in a methane-rich environment based on the occurrence of vesicomyid bivalves and on a vesicomyid/lucinid bivalve association shown elsewhere to be associated with cold seep environments. Vertebrates include great numbers of small, pelagic fish and the piscivorous sharks and marine mammals which likely took advantage of them for food. The Tsm Caldecott Tunnel fauna represents the second fauna from a methane-rich environment from the greater San Francisco Bay area and the first attributed to a methane seep environment. In addition, this fauna contains the first reported Cenozoic crinoid from California and the new species Dentalium (Fissidentalium?) mcganna (Mollusca: Scaphopoda) is described. The fauna from the Claremont chert includes two bivalve mollusks, one scaphopod, one barnacle and three vertebrates. These taxa are all represented by single specimens. They represent a marine environment likely at continental shelf or slope water depths. The occurrence of the shark Carcharhinus obscurus may indicate water temperatures warmer than off the central California coast today.

A protocol for differentiating late Quaternary leporids in southern California with remarks on Project 23 lagomorphs at Rancho La Brea, Los Angeles, California, USA

Leporid remains are common in Quaternary fossil assemblages and are useful paleoenvironmental indicators. Identifying leporid fossils to species is challenging, though previous work has shown that identifications are more feasible if fossils can be narrowed down to a subset of potential species occurring across limited spatial scales. We sampled 120 adult and nine juvenile dentaries of six extant western North American species (Lepus americanus, L. californicus, L. townsendii, Sylvilagus audubonii, S. bachmani, and S. nuttallii) to establish useful characters for genus and species-level identification of late Quaternary leporid fossils in California. Most individuals can be differentiated from individuals of other species using a combination of lower third premolar enamel folding patterns and dental measurements. However, it is difficult to discriminate dental elements among L. californicus and L. townsendii and elements of S. nuttallii from S. audubonii, S. bachmani, and L. americanus. Here we present criteria for differentiating western leporid dental remains, apply the criteria to identify specimens recovered from several late Quaternary fossil deposits at Rancho La Brea (RLB), California, collectively known as Project 23, and reconstruct changes in relative fossil leporid abundances there. Using our criteria, we identified two extant species, S. audubonii and S. bachmani, among the Project 23 fossils. In addition to relative abundance changes across several RLB deposits, S. audubonii and S. bachmani generally become larger through time, possibly in response to local environmental changes. Establishing region-specific identification criteria as done here may prove useful for discerning morphologically similar species at prehistoric sites elsewhere.

A new drepanosauromorph, Ancistronychus paradoxus n. gen. et sp., from the Chinle Formation of Petrified Forest National Park, Arizona, USA

Drepanosauromorpha is an extinct group of reptiles known from the Middle Triassic to Late Triassic (237–212 Ma). The clade currently includes seven genera (Avicranium, Dolabrosaurus, Drepanosaurus, Hypuronector, Kyrgzsaurus, Megalancosaurus, and Vallesaurus) that are known from fossils collected in Europe, North America, and Asia. These discoveries have helped shape our understanding of the biology and diversity of drepanosauromorphs. Here we describe Ancistronychus paradoxus n. gen. et sp. from the Chinle Formation in Petrified Forest National Park, Arizona based on the ungual phalanx of the second digit of the manus. A characteristic that this taxon shares with Drepanosaurus unguicaudatus is the pronounced size of the ungual relative to the penultimate element. It differs significantly from D. unguicaudatus and the Hayden Quarry Drepanosaurus in the shortened proximal dorsoventral height of the claw, its great transverse breath, the presence of both a furrow on the midline of the extensor surface and a cleft on the apex, and a broad and flattened terminus. We suggest that A. paradoxus is likely closely related to D. unguicaudatus and the Hayden Quarry Drepanosaurus, but missing phylogenetic data precludes a more definitive assessment at this point. Ancistronychus paradoxus highlights unsuspected morphological variation within Drepanosauromorpha and suggests that different drepanosauromorphs used their enlarged second manual unguals for distinct functions enabling them to fill different ecological niches.

Two new Miocene limpets (Fissurellidae) from southern California, with notes on other fossil occurrences of the family in northwestern North America

Two new fissurellid limpets (Mollusca: Gastropoda: Fissurellidae), Fissurella? stantoni n. sp. and Scelidotoma aldersoni n. sp., are described from Miocene deposits in southern California. Fissurella? stantoni is described from a single specimen from the middle Miocene Topanga Canyon Formation in the Santa Monica Mountains, Los Angeles County, California. Scelidotoma aldersoni is described from two specimens, one from the middle Miocene Topanga Canyon Formation, and another provisionally (cf.) identified specimen of an internal mold from the middle Miocene “Vaqueros” Formation on Santa Cruz Island, Santa Barbara County, southern California. Other unreported fossil occurrences of Scelidotoma are a juvenile specimen attributed only to genus collected in the middle Eocene Crescent Formation in Washington state and S. bella from the Pliocene part of the San Diego Formation, San Diego County, California. The Scelidotoma occurrences extend the chronostratigraphic range of S. bella from the Holocene (living) to the middle Pliocene, and the range of the genus back to the middle Eocene.