Ichthyoliths and other microvertebrate remains from the Morrison Formation (Upper Jurassic) of northeastern Wyoming: A screen-washed sample indicates a significant aquatic component to the fauna

Abstract

A screenwashed microvertebrate site, the Mile 175 locality, in the Morrison Formation of Wyoming has yielded more than 3000 elements of actinopterygian fish and indicates that fish were not as rare in some parts of the formation as previously supposed. Actinopterygians are represented by diverse teeth and tooth-bearing bone fragments, fin elements, and thousands of scales and scale fragments that can be divided into three distinct morphotypes. Lungfish are rare, represented by nine toothplates and toothplate fragments that are provisionally assigned to Potamoceratodus. Tetrapods recovered from the Mile 175 locality include indeterminate salamanders, turtles, choristoderes, a squamate, goniopholid crocodyliforms, theropod and ornithopod dinosaurs, and several mammals, including Docodon and indeterminate multituberculates. Salamanders are represented by just a few indeterminate vertebrae. The turtle fauna includes numerous small shell fragments and limb elements. The authors assign a tooth-bearing jaw fragment and several vertebrae to the choristodere Cteniogenys, whereas a sole vertebra is the only squamate fossil recovered. Theropod dinosaurs are well represented by several teeth, as is the ornithopod dinosaur Othnielosaurus. Similarly, several mammalian tooth and jaw fragments can be referred to either Docodon or Multituberculata indet. Dominance of the sample by aquatic and semi-aquatic taxa suggests the paleodepositional environment was a permanent water source. Many of the specimens appear to represent small and presumably ontogenetically young individuals of larger, known taxa in the Morrison Formation, and the site includes the northernmost occurrences of several taxa in the formation. Screenwashing efforts at several other previously quarried large-vertebrate sites in the Morrison Formation have shown promising results for recovering previously unidentified taxa.

Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

“…microvertebrate assemblages, vertebrate microfossil assemblages, microsites), which are concentrations of predominantly small, disarticulated, and often taxonomically diverse vertebrate hard parts (Wood et al 1988; Eberth et al 2007; Rogers and Kidwell 2007; Rogers et al 2007; Rogers and Brady 2010). VMBs are fairly common in Mesozoic and Cenozoic terrestrial records, where they have been exploited to recover otherwise rarely found small-bodied taxa (e.g., Simpson 1926; Sloan and Van Valen 1965; Estes 1969; Sloan 1969; Sahni 1972; Archibald 1982; Lillegraven and McKenna 1986; Lillegraven and Eberle 1999; Foster and Heckert 2011) and studied to estimate relative taxonomic abundance and species richness in ancient vertebrate communities (e.g., Estes 1964, 1976; Estes and Berberian 1970; Dodson 1987; Bryant 1989; Brinkman 1990; Peng et al 2001; Sankey 2001; Jamniczky et al 2003; Brinkman et al 2004, 2007; Heckert 2004; Carrano and Velez-Juarbe 2006; DeMar and Breithaupt 2006; Heckert et al 2012). Workers have applied a variety of statistical tests to VMB assemblages to accomplish the latter.…”

An unusually diverse northern biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming

“…Actinopterygian fish are represented by many elements from the Little Houston Quarry, including numerous upper and lower jaw fragments (figure 7), and three types of scales similar to those illustrated from other sites by Kirkland (1998) and Foster and Heckert (2011). The scales include abundant, tiny ganoid scales (figures 7A and 7B), whereas the jaw elements include a diverse sample of upper and lower elements, with almost no two the same (figures 7C to 7I).…”

“…Microvertebrate taxa were identified in the formation relatively early on (Marsh, 1879;Gilmore, 1910Gilmore, , 1928 but large samples of such taxa were restricted to only a handful of sites until relatively recently. Work from the past few years has suggested that microvertebrate taxa, and specifically aquatic and semi-aquatic taxa, may be more abundant in the formation than commonly appreciated (Foster and Trujillo, 2004;Foster and Heckert, 2011;Foster and McMullen, 2017) and that the Morrison may show some paleobiogeographic zonation based on these small taxa and their preferred environments for habitat and preservation (Chure and Evans, 1998;Foster and Trujillo, 2000;Foster and others, 2006;Foster and McMullen, 2017). Paleobiogeo-graphic zonation is also becoming apparent for some groups of dinosaurs within the Morrison.…”

Guelb el Ahmar (Bathonian, Anoual Syncline, eastern Morocco): First continental flora and fauna including mammals from the Middle Jurassic of Africa

“…However, it should be noted that their distribution is not restricted to Europe within Laurasia. The GEA assemblage also shows some taxonomic affinities with the Late Jurassic fauna from the Morrison Formation, USA (Chure et al, 2006;Foster and Heckert, 2011).…”