Although knowledge of Mesozoic marine reptiles from Antarctica has improved considerably in recent years, associated and well-preserved skeletal material of these animals remains uncommon. Here we describe a largely complete, closely associated plesiosaur pelvic girdle recovered from the uppermost Cretaceous (Maastrichtian) Sandwich Bluff Member of the López de Bertodano Formation of Vega Island, in the James Ross Basin of the northernmost Antarctic Peninsula. The new specimen exhibits characters that allow its referral to Elasmosauridae, but its incompleteness precludes a more precise taxonomic determination. Ontogenetically variable and systematically useful features of the elasmosaurid pelvis are reviewed and discussed. The new specimen improves knowledge of Southern Hemisphere elasmosaurids just prior to the K/Pg extinction event.

Entoptychine gophers are a species-rich subfamily of the Geomyidae from the Oligo-Miocene known from countless teeth, numerous jaws, and rare skulls and skeletons. Because of this rich fossil record, entoptychine gophers have greatly contributed to our understanding of the biostratigraphy, biogeography, and paleoecology of fossil deposits of the western United States. Nonetheless, there is currently no phylogenetic framework for the subfamily. We describe four new species of entoptychines from the Arikareean-aged Cabbage Patch beds of Montana, including three species of the genus Pleurolicus (P. gwinni, P. nelsoni, and P. rensbergeri) and one species of Gregorymys (G. tavenneri) and include these taxa into the first phylogenetic analysis of Entoptychinae to include all species within PleurolicusCope, 1878, GregorymysWood, 1936, and ZiamysGawne, 1975, as well as a species of the genus EntoptychusCope, 1878. We recover a paraphyletic Pleurolicus at the base of the tree. Ziamys is a monophyletic genus, sister taxon to the clade formed by the genera Entoptychus and Gregorymys. Within Pleurolicus, the species strictly from the Great Plains form a clade. Gregorymys is divided into two major clades, one that includes the southern species G. riograndensisStevens, 1977, and G. veloxikua Jiménez-Hidalgo et al., 2018, as well as G. riggsiWood, 1936, and G. tavenneri and one including all other species from the northern Great Plains and Rocky Mountains. Gregorymys kayiWood, 1950, a poorly known outlier species of the genus is sister to the Entoptychus species included in our analysis. Our findings suggest a complicated evolutionary history for the Entoptychinae, but also offer the opportunity for fruitful future analyses of evolutionary ecology.

The genera AstivaliusSmit, 1953, and Obtusifrontia, Holland, 1969 endemic to Papua Province, Indonesia, and Astivalius, IdiochaetisJordan, 1937, MuesebeckellaTraub, 1969, and Obtusifrontia, endemic to Papua New Guinea, are reviewed as a continuation of the study of fleas in the Robert Traub flea collection deposited in the Carnegie Museum of Natural History, Pittsburgh, PA. This paper (Part V) is an extension of previous studies by Hastriter (2012), Hastriter and Easton (2013, Part I, Striopsylla), Hastriter (2014, Part II, Nestivalius, Orthopsylloides, and Parastivalius), Hastriter (2015, Part III, Traubia), and Hastriter (2016, Part IV, Rectidigitus). Prior to the current study, Astivalius and Idiochaetis were each comprised of one species (A. microphthalmusSmit, 1953, and I. illustrisJordan, 1937), Muesebeckella of two species (Mu. mannaeTraub, 1969, and Mu. nadiTraub, 1969), and Obtusifrontia of three species (O. falcataMardon, 1978b, O. simplexHolland, 1969, and O. simulaMardon, 1978b). The female of A. microphthalmusSmit, 1953, is described for the first time and the previously known distribution of this species is expanded from Papua Province, Indonesia to the western fringes of Papua New Guinea (Sandaun Province). The female of O. simplex is also described for the first time and its geographical distribution is expanded to two additional provinces (Southern Highlands and Western Highlands provinces, Papua New Guinea). An additional three new species of Astivalius, one new species each of Idiochaetis, Muesebeckella, and Obtusifrontia are described herein (A. archboldi, n. sp., A. mirzai, n. sp., A. toxopeusi, n. sp., I. rogersi, n. sp., Mu. niobiensis, n. sp., and O. comohamulus, n. sp.). With the description of six new species, the total number of species in the superfamily Pygiopsylloidea in Papua Province, Indonesia, Papua New Guinea (including Bismarck Archipelago) and the Solomon Islands is 111. An additional eight species belonging to three other flea families (Ischnopsyllidae (3), Pulicidae (3), and Leptopsyllidae (2) bring the total number of flea taxa to 119 species (including subspecies). Keys to the species of Astivalius, Idiochaetis, Muesebeckella, and Obtusifrontia are provided.

A new genus and species of sciuravid rodent, Perasciuravus mcintoshi, is named from the late Bridgerian (early Eocene) of the Washakie Formation, southcentral Wyoming. The most distinguishing characters of the species (and genus) are that it retains the primitive condition of the zygomasseteric structure for rodents, characteristic of sciuravids, but has a more specialized dental morphology of the cheek teeth (complete ectolophids and hypolophids on the lower molars; complete metalophs and protolophs on the upper molars) typical of the later-occurring family of geomyoid rodents, the Eomyidae. Perasciuravus is viewed as morphologically transitional between the Sciuravidae and the Eomyidae. Its occurrence also overlaps the temporal range of the Sciuravidae (Wasatchian [early Eocene] to Duchesnean [early-late Eocene]) and predates the first occurrence of the Eomyidae (Uintan [middle Eocene]).