Search bioRxiv⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2022.01.11.475364

40 new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds.

Benito, J.·Chen, A.·Wilson, L. E.·Bhullar, B.-A. S.·Burnham, D.·Field, D. J.
View original source ↗Export metadata ↓

Abstract

Ichthyornis has long been recognized as a pivotally important fossil taxon for understanding the latest stages of the dinosaur-bird transition, but little significant new postcranial material has been brought to light since initial descriptions of partial skeletons in the 19th Century. Here, we present new information on the postcranial morphology of Ichthyornis from 40 previously undescribed specimens, providing the most detailed morphological assessment of Ichthyornis to date. The new material includes four partially complete skeletons and numerous well-preserved isolated elements, enabling new anatomical observations such as muscle attachments previously undescribed for Mesozoic euornitheans. Among the elements that were previously unknown or poorly represented for Ichthyornis, the new specimens include an almost-complete axial series, a hypocleideum-bearing furcula, radial carpal bones, fibulae, a complete tarsometatarsus bearing a rudimentary hypotarsus, and one of the first-known nearly complete three-dimensional sterna from a Mesozoic avialan. Several pedal phalanges are preserved, revealing a remarkably enlarged pes presumably related to foot-propelled swimming. Although diagnosable as Ichthyornis, the new specimens exhibit a substantial degree of morphological variation, some of which may relate to ontogenetic changes. Phylogenetic analyses incorporating our new data and employing alternative morphological datasets recover Ichthyornis stemward of Hesperornithes and Iaceornis, in line with some recent hypotheses regarding the topology of the crownward-most portion of the avian stem group, and we establish phylogenetically-defined clade names for relevant avialan subclades to help facilitate consistent discourse in future work. The new information provided by these specimens improves our understanding of morphological evolution among the crownward-most non-neornithine avialans immediately preceding the origin of crown group birds.

Source connections

Explore related subjects

paleontologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Benito, J., Chen, A., Wilson, L. E., Bhullar, B.-A. S., Burnham, D., Field, D. J.. 2022-01-12. 40 new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds.. https://doi.org/10.1101/2022.01.11.475364

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Constraining Palaeogeography and Palaeotides for the Cambrian using cnidarian medusae

The ocean tides influence key Earth system processes at a range of spatial and temporal scales. It is known that the geometry of ocean basins is the leading controller of tidal energetics, so well-constrained palaeogeographic reconstructions and tidal properties for Earths past are imperative when investigating other Earth system processes. Here, we present a novel way to constrain both deep-time tidal model results and reconstructions, by combining palaeoecology with sedimentology. We compare new palaeo-tidal model simulations for the Cambrian period, significant for the early origin and radiation of major animal fauna, to tidal proxies. One of the most abundant soft-bodied organisms preserved during this time are cnidarian medusae (jellyfish). A total of 17 cnidarian medusae localities were obtained through the literature, which had an adequate global distribution and occurred at regular intervals throughout the period of study. In some locations there were also estimates of palaeo-tidal range. Our results show a good agreement between the simulations and proxy data. In the few locations where there is disagreement, it is proposed that the palaeogeographic reconstructions are missing details, e.g., island chains, and our results allow for the palaeogeographic reconstructions to be improved. The proxy method presented is promising and can be applied to other time-periods with different marine fossils, particularly at evolutionary and extinction periods where the marginal marine environment is of importance.

paleontology↗
bioRxiv2023

Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle

Measures of bone compactness in amniote tetrapods of varying lifestyle were used to infer that two spinosaurid dinosaurs (Spinosaurus aegyptiacus, Baryonyx walkeri) were diving "subaqueous foragers," whereas a third spinosaurid (Suchomimus tenerensis) and other sampled nonavian dinosaurs were non-diving terrestrial feeders entering water only as waders. We outline shortcomings in this analysis that involve bone compactness sampling and measurement, lifestyle categorization, the inclusion and exclusion of taxa in the dataset, and flawed statistical methods and inferences. These many shortcomings undermine the evidence used to conclude that two spinosaurid taxa were avid divers. Bone compactness indices remain a valuable tool for interpretation of lifestyle in extinct species when based on sound dataset composition, robust statistical analysis, and consilience with evidence from functional, biomechanical, or paleoenvironmental considerations.

paleontology↗
bioRxiv2023

Zooarchaeological investigation of the Hoabinhian exploitation of reptiles and amphibians in Thailand and Cambodia with a focus on the Yellow-Headed tortoise (Indotestudo elongata (Blyth, 1854))

While non-marine turtles are almost ubiquitous in the archaeological record of Southeast Asia, their zooarchaeological examination has been inadequately pursued within this tropical region. This gap in research hinders a complete comprehension of past human subsistence strategies and economies, as only a limited number of comprehensive studies encompassing all the taxa found in archaeological sites have been conducted thus far. This constraint becomes particularly significant in relation to prehistoric hunter-gatherer populations, who might have extensively utilized inland chelonian taxa. In order to initiate a new approach to the study of past human-turtle interactions in Southeast Asia, we propose an in-depth zooarchaeological analysis of turtle bone remains recovered from four Hoabinhian Hunter-gatherer archaeological assemblages located in Thailand and Cambodia, dating from the Late Pleistocene to the first half of the Holocene. Our study focuses on the bone remains attributed to the Yellow-headed Tortoise (Indotestudo elongata) as it is the most represented taxon in archaeological assemblages in the region of study. For this species, we developed osteometric equations enabling the estimation of the carapace size of the archaeological individuals. This allowed us to study the size structure of the archaeological populations at different sites and to reveal the human exploitation strategies of these animals. We observed a significant taphonomic homogeneity among the studied assemblages, along with similarities in the diversity of hunted reptile and amphibian taxa as well as the size of the exploited tortoises. These findings suggest consistent subsistence behaviors across distinct sites, despite their varying environmental conditions, and raise the possibility of cultural similarities across different periods and regions. Additionally, we provide a baseline for future zooarchaeological studies and a methodological framework for the detailed analysis of archaeological turtle bones in continental Southeast Asia.

paleontology↗