Monthly Archives: March 2025

Introducing Duonychus tsogtbaatari

Posted on by under Earth Science

Duonychus tsogtbaatari gen. et sp. nov. From Kobayashi et al., 2025

Therizinosauria is a group of unusual theropod dinosaurs known from Cretaceous deposits in Asia and North America. The clade exhibits unique features, including lanceolate teeth, a rostral rhamphotheca, and a broad, opisthopubic pelvis. Some of those characteristics are associated with a shift in dietary preferences and an adaptation to herbivory. But the most striking feature, as exemplified by the large-bodied Therizinosaurus from the Late Cretaceous of Mongolia, is the presence of tridactyl (three-fingered) hands with three large claw-like unguals.

Duonychus tsogtbaatari,  a new specimen from the Upper Cretaceous Bayanshiree Formation (Cenomanian to Santonian) of southeastern Mongolia, sheds light on the evolution of digit reduction in avetheropods and the implications for feeding behavior associated with large claws in therizinosaurs.

Manual digit I with a keratinous sheath of Duonychus tsogtbaatari. From Kobayashi et al., 2025

The holotype (MPC-D 100/85) is a partial skeleton consisting of: six articulated dorsal vertebrae, six articulated sacral vertebrae with sacral ribs, the anterior-most caudal vertebra, some dorsal ribs, a partial left scapula and coracoid, humeri, ulnae, radii, carpals, metacarpals, left and right manus, right ilium, both pubes, and the proximal end of the left ischium.

The generic name combines the word duo (two in Greek) in reference to the presence of a didactyl hand which is unusual in therizinosaurs, and the word onyx (claw). The specific name pays tribute to Khishigjav Tsogtbaatar, a palaeontologist and former head of the Institute of Paleontology of the Mongolian Academy of Sciences in Ulaanbaatar, Mongolia.

Cladogram of Avetheropoda highlighting forelimb shortening and digit III loss. From Kobayashi et al., 2025

Body mass estimates suggest that Duonychus is a medium-sized therizinosaur of approximately 260 kilograms (570 lb) and approximately 3 metres (9.8 ft) long. The well-preserved manus and three-dimensional claw of the new specimen reveal functions ranging from scansorial (climbing), and tensorial (grappling) to amplectorial (grasping).

Although Duonychus had only two functional digits, it was probably an effective grasper, given the extreme flexion (close to 90°) at the ungual joint and the strong curvature of the keratinous claw, features unknown in other therizinosaurs.

The study also shows that the loss of a functional third digit has occurred at least five times in the subclade Avetheropoda. The study also shows that the loss of a functional third digit appears to have occurred convergently in five clades: Tyrannosauridae, Alvarezsauridae, Therizinosauridae, and Oviraptorosauria.

Refernces:

Kobayashi et al., (2025), Didactyl therizinosaur with a preserved keratinous claw from the Late Cretaceous of Mongolia, iScience  https://doi.org/10.1016/j.isci.2025.112141

Lautenschlager S, et al., (2012) The Endocranial Anatomy of Therizinosauria and Its Implications for Sensory and Cognitive Function. PLoS ONE 7(12): e52289. https://doi.org/10.1371/journal.pone.0052289

The evolution of avian cranial kinesis

Posted on by under Earth Science

Protractor muscle forces changed in orientation and relative loading during the theropod-bird transition. From Wilken et al., 2025.

The evolution of the avian skull is marked by radical transformations of the braincase, palate, and snout. Brain size correlated with major evolutionary innovations like cognition, flight, environmental adaptability, and enhanced sensory capabilities. Due to the volumetric expansion of key brain regions, particularly the telencephalon (cerebrum) and cerebellum, the brain of crown birds is larger and more globular than other reptiles. Another key innovation behind the dietary diversity and evolutionary success of birds is the presence of powered kinesis (the ability to move different parts of the skull independently). Until recently, however, the processes driving the emergence of avian kinesis remained unclear. Now, a new study from the University of Chicago and the University of Missouri has quantified the changes in muscle forces and their effects on palatal mechanics during the transition from theropods to birds.

The study found that as the neurocranium expanded in non-avian theropods, the temporal muscles shifted to more rostrocaudal positions in birds, aiding pterygoid segmentation. This change led to a powered cranial kinesis. Ichthyornis might be an early evolutionary experiment in cranial mobility.

3D reconstruction of the skull of I. dispar (From Field et al., 2018)

Discovered in 1870 by Benjamin Franklin Mudge, a professor from Kansas State Agricultural College and good friend of Othniel Charles Marsh, Ichthyornis, which means‭ ‘‬fish bird‭’‭, was a small early ornithuromorph from the Late Cretaceous of North America. The arrangement of the rostrum, jugal, quadratojugal, mobile suspensorium, and narrow, linear palatine indicate that Ichthyornis possessed a fully functional avian cranial kinetic system.

A critical change in the evolution of the avian skull was the separation of the epipterygoid ossification from the braincase. This led to the breakdown of primitive kinematic linkages and the development of a new basic cranial joint, allowing greater cranial flexibility. These findings shed light on the co-evolution of the neurosensory and feeding systems during the origin of birds and provide new methods for identifying cranial kinesis in extinct vertebrates.

 

Refernces:

Wilken, Alec T. et al, Avian cranial kinesis is the result of increased encephalization during the origin of birds, Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2411138122. doi.org/10.1073/pnas.2411138122

Ksepka et al., Tempo and Pattern of Avian Brain Size Evolution, Current Biology (2020), https://doi.org/10.1016/j.cub.2020.03.060

Field, D.J., Hanson, M., Burnham, D. et al. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature 557, 96–100 (2018). https://doi.org/10.1038/s41586-018-0053-y