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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.

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The early evolution of Crocodylomorpha

Crocodylians started out as generally small-bodied and land-living animals during the Late Triassic. These early crocodylomorphs had very slender bodies and elongate legs, resembling foxes rather than lizards in many respects. I recently studied the Triassic crocodylomorphs Saltoposuchus connectens (from Germany) and Terrestrisuchus connectens (from Britain) in detail.


These revisions have revealed additional information on their postcranial evolution, as well as the configuration of their skulls, in particular the development of a highly complex system of pneumatic sinuses in their braincase region. Furthermore, histological sections that I studied suggest that animals were fast-growing through most of their lives, suggesting that they likely lived active lives. Finally, I found that Saltoposuchus and Terrestrisuchus are part of a Family of particularly small-sized crocodylomorphs, the Saltoposuchidae.

(Image from: Spiekman et al. 2023, Papers in Palaeontology)

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Decapitation in long-necked marine reptiles

The extreme long neck present in many Mesozoic marine reptiles has been considered a potential weakspot for predation for as long as they have been known, as indicated by this famous painting by Henry de La Beche from 1830.

Together with my colleague Eudald Mujal, I described two cases of decapitation in Tanystropheus, in which the neck was completely severed by predators. This provides the first evidence that these extremely elongated necks were indeed vulnerable to predation in at least some cases, despite their evident evolutionary success.

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The Late Triassic archosaur fauna from Pant-y-ffynnon, Wales

Together with colleagues at the Natural History Museum London, University of Birmingham, and National Museums Scotland, I am studying the unique reptile fauna from the Late Triassic fissure fills of the Bristol Channel area. Due to its unique depositional environment many small-bodied vertebrates have been discovered in the fissures. From Pant-y-Ffynnon Quarry in southern Wales, we published on a new coelophysoid theropod, Pendraig milnerae. In addition, we also redescribed the small, slender-bodied crocodylomorph Terrestrisuchus gracilis from Pant-y-Ffynnon and are currently working on (re)descriptions of further archosaur taxa.

(Image credit: James Robbins; Spiekman et al. 2021, RSOS)

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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.)

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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 TanystropheusMacrocnemus, 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)

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