Research interests
Most of my research focuses on different aspects of Triassic reptile evolution, including comparative anatomy, functional morphology, histology, phylogeny, and macroevolution. In addition, I am also interested in the influence of development on the evolution of vertebrate life. Below you can find a more detailed overview of my research.
The Late Triassic archosaur fauna from Pant-y-ffynnon, Wales
My current research focuses on the unique reptile fauna from the Late Triassic fissure fills of the Bristol Channel area, which likely formed an archipelago of small islands during this period. Due to its unique depositional environment many small-bodied vertebrates have been discovered in the fissures. Recently we published on a new coelophysoid theropod, Pendraig milnerae. In addition, I'm working on detailed revisions of the small, slender-bodied crocodylomorph Terrestrisuchus gracilis, and the enigmatic pseudosuchian Aenigmaspina pantyffynnonensis.
(Image credit: James Robbins; Spiekman et al. 2021, RSOS)
Tanystropheid phylogeny
I provided a revision of the phylogeny of the earliest stem-archosaurs (the lineage including birds, crocodylians and dinosaurs), focusing on the remarkably long-necked Tanystropheidae and closely related taxa. I studied the majority of the included species first-hand, visiting over 20 museum collections on four different continents, resulting in the most detailed cladistic analysis of this group to date.
This study incorporated morphological and taxonomic information from other research projects conducted during my PhD (see below), and among other things, let to the recognition of a new clade of (partially) marine archosauromorphs, the Dinocephalosauridae.
(Image from: Spiekman et al. 2021, PeerJ)
The anatomy and habits of the extremely long-necked Triassic reptile Tanystropheus
I have investigated the anatomy and functional morphology of the extremely long-necked Triassic reptile Tanystropheus. Using synchrotron radiation scanning, we were able to 3D-reconstruct the skull of large specimens of this genus in detail for the first time. This revealed several clear adaptations that this reptile was an aquatic ambush predator, a hypothesis that had previously been disputed.
In addition, the skull shows remarkable differences to the skull of smaller Tanystropheus specimens that were previously considered to represent juveniles of the same species. Histological sections of the limb bones of the small specimens showed that they were skeletally mature, thus corroborating our hypothesis that the two represent separate species. The co-occurrence of these two highly specialized reptiles in the same environment represents a remarkable case of niche partitioning within 10 million years of the largest mass extinction event of all time. The case of niche partitioning in Tanystropheus is particularly interesting, since it reveals that its remarkable and specialized neck was more adaptable than previously conceived. This shows that body plans that seem implausible or even comical today were in fact perfectly adapted to the world these animals lived in.
(Image from: Spiekman et al. 2020, Curr. Biol.)
Elucidating the cranial anatomy of enigmatic Triassic reptiles using synchrotron radiation and μCT-scanning
Using synchrotron radiation scanning at the ESRF in Grenoble (France) or more conventional μCT-scans, I use cutting edge high-resolution imaging technology to investigate the anatomy of often poorly preserved and rare Triassic reptiles. In addition, I use the open-source software Blender to digitally 're-assemble' skulls and skeletons of fossils that have been severely disarticulated during the fossilization process. Using this method, I have studied the tanystropheids Tanystropheus hydroides and Macrocnemus bassanii, as well as the small rhynchocephalian Colobops noviportensis.
(Image: personal image of Colobops digital model)
Taxonomy of Triassic reptiles
Taxonomy represents an often overlooked but fundamental aspect of (vertebrate) palaeontology. In my research, I have provided a taxonomic revision of the archosauromorph genera Tanystropheus, Macrocnemus, and Prolacerta, and named several new taxa (Sclerostropheus fossai n. gen., Tanystropheus hydroides n. sp., and Pendraig milnerae n. gen. et sp.).
(Image credit: Meredith Rivin and the Burke Museum, Seattle, USA)
Histology of tooth implantation and replacement in Triassic Sauropterygia
I have studied an enigmatic lower jaw from the Middle Triassic (Muschelkalk) locality of Winterswijk in the east of the Netherlands. In order to infer its evolutionary affinities, we applied both μCT-scanning and histological sectioning. The inner anatomy of the jaw revealed that it most likely belonged to an eosauropterygian marine reptile that is new to this locality. Our study also highlighted several aspects of tooth implantation (e.g. the presence of plicidentine) and tooth replacement, including some which were previously unknown for eosauropterygians, the clade that includes the famous Jurassic and Cretaceous plesiosaurs.
(Image from: Spiekman & Klein 2021, NJG)
Patterns of cranial ossification sequences in extant marsupials
During my MSc. research at the MfN in Berlin I studied mammalian development. In particular, I investigated cranial ossification in marsupials to infer adaptations to the unique life history of this mammalian clade (very early birth and subsequent development on the mother's teat, often in a pouch). We were able to sample a wide range of marsupial species by μCT-scanning specimens of the unique and historical James Peter Hill collection at the museum. Although my main research has since shifted to palaeontology, I still maintain a strong interest in evolutionary development.
(Image: personal image of koala neonate digital model)