Drawing fossils

Fossils record the evolution of life on Earth and are crucial in the dating of sedimentary rocks through biostratigraphy. This chapter examines the methods used to record the taxonomy and sedimentological context of fossils within field sketches. The taxonomy and geological range of important fossil groups are described as well as their occurrence within sediments. Blocking-in sketches accurately is particularly important when drawing fossils since their quasi-regular shapes can lead to drawings that are overly schematic. Small-scale morphological features are often important in the interpretation of fossils. Four worked examples of sketches of fossils are given together with descriptions of their interpretation to illustrate techniques to record palaeontological specimens.

Marine tethysuchian crocodyliform from the ?Aptian-Albian (Early Cretaceous) of the Isle of Wight, England

A marine tethysuchian crocodyliform from the Isle of Wight, most likely from the Upper Greensand Formation (late Albian, Early Cretaceous), is described. However, we cannot preclude it being from the Ferruginous Sands Formation (late Aptian), or more remotely, the Sandrock Formation (late Aptian-early Albian). The specimen consists of the anterior region of the right dentary, from the tip of the dentary to the incomplete fourth alveolus. This specimen increases the known geological range of marine tethysuchians back into the late Early Cretaceous. While we refer it to Tethysuchia incertae sedis, there are seven anterior dentary characteristics which suggest a possible relationship with the Maastrichtian-Eocene clade Dyrosauridae. We also review 'middle' Cretaceous marine tethysuchians, including putative Cenomanian dyrosaurids. We conclude that there is insufficient evidence to be certain that any known Cenomanian specimen can be safely referred to Dyrosauridae, as there are some cranial similarities between basal dyrosaurids and Cenomanian-Turonian marine 'pholidosaurids'. Future study of middle Cretaceous tethysuchians could help unlock the origins of Dyrosauridae and improve our understanding of tethysuchian macroevolutionary trends.

A new mysid (Crustacea, Mysida) from the Ladinian Stage (Middle Triassic) of Conca de Barberà (Catalonia, NE Iberian Peninsula)

The oldest known fossil mysid (order Mysida) Aviamysis pinetellensis n. gen. n. sp. is described here from two nearly complete specimens found in the Alcover unit from El Pinetell (Catalonia). It differs significantly from other Mysida and is placed in a new genus assigned to the family Mysidae and tentatively to the subfamily Boreomysinae. These specimens represent the first described mysid material from the Alcover outcrops (Middle Triassic, upper Ladinian, 235–242 Ma), extending the known geological range of the poorly understood fossil fauna of the order Mysida by at least 70 Myr.

New marsupial from the Fort Union Formation, Swain Quarry, Wyoming

Previously described upper and lower molars from the Fort Union Formation (Swain Quarry, Wyoming) are referred to Swaindelphys cifellii new genus and species. This taxon is assigned to the subfamily Herpetotheriinae, family Didelphidae. These molars were originally referred to a new, unnamed species of Peradectes (subfamily Peradectinae), with similarities to P. pusillus (now Thylacodon pusillus) and P. elegans. However, upper molars differ from these taxa in being dilambdodont, in possessing more strongly developed stylar cusps, especially on M2 and M3, and in having a protocone that is shifted anteriorly. These characters suggest similarity to taxa such as Peratherium (subfamily Herpetotheriinae, family Didelphidae), rather than Peradectes. The assignment of the lower molars from Swain Quarry is more problematic: these molars are similar to the holotype Thylacodon pusillus in that the entoconid and hypoconulid separated by a strong notch; however, the Swain Quarry lower molars differ in being smaller overall and possessing an anteroposteriorly shorter talonid. These lower molars are similar to didelphid lower molars in having a hypoconulid that is lower than the entoconid (these are subequal in height on lower molars of Peradectes), but differ from didelphid lower molars in that the hypoconulid does not form a low, posteriorly projecting shelf. Nevertheless, the upper and lower molars from Swain Quarry are considered to belong to a single taxon, and with the assignment of the Swain Quarry materials to the subfamily Herpetotheriinae, the geological range of this subfamily is extended from the early Eocene back into the middle Paleocene (Torrejonian, or To3).

A new and typically Jurassic ichthyosaur from the Upper Triassic of British Columbia

A new ichthyosaur species is described from the Upper Triassic (middle Norian) of Williston Lake, northeastern British Columbia. Aside from the foramen enclosed between the radius and ulna–a characteristic of Triassic ichthyosaurs–the new specimen is typical of Lower Jurassic forms. Indeed, if the specimen had been collected from the English lower Liassic, there would have been no hesitation in referring it to the common English genus Ichthyosaurus, a taxonomic course I follow here. Referring the new species to Ichthyosaurus extends the geological range of the genus by approximately 9 Ma, to the middle Norian. Ichthyosaurus janiceps sp. nov. has an abbreviated snout, like that of Ichthyosaurus breviceps, but it is a much larger species, and has a distinctly different forefin.

Foraminifera

Foraminifera are testate protozoans that exhibit a bewildering variety of test composition and morphology (Figure 1). They inhabit all marine environments from the intertidal zone to the deep ocean floor, they range from the poles to the tropics, and they can be planktonic or benthonic. Their abundance in sediment samples may reach tens of thousands per square meter and their diversity in tropical environments may exceed 60 or 70 species in a sample of 300 individuals. A geological range stretching from the very earliest Cambrian through to the present day is characterized by varying patterns of evolution and extinction that have proven to be of considerable biological and geological significance.

An isolated ichthyosaur coracoid from the Maastrichtian of New Jersey

An isolated ichthyosaur coracoid from the Hornerstown Formation of New Jersey extends the geological range of the Ichthyosauria at least to the late Maastrichtian. The specimen cannot be referred to any known taxon but is too incomplete to be described as the type of a new species.