John Ostrom’s Deinonychus enters the LRT

This is the dinosaur that started the dinosaur renaissance.
Deinonychus antirrhopus (Ostrom 1969, Early Cretaceous, Figs 1–4) had the first ‘killer’ claw, a tendon stiffened tail and an Archaeopteryx-like manus (hand). These traits indicated a highly active, likely warm-blooded predator, more like an osprey (Pandion), than a Komodo dragon (Varanus).

Figure 1. The Harvard specimen of Deinonychus. This is not a complete specimen. Some preserved parts are detailed below.

Here
in the large reptile tree (LRT, 2297 taxa) Deinonychus nests at the base of the Velociraptor clade, about where everyone else nested it.

Figure 2. Deinonychus skull. Colors added here. Note the long jugal-squamosal (cyan-magenta) contact.

Figure 2b. Figure from Ostrom 1970. Color added here to show the extent of the squamosal. Any differences between the original drawings and the sculptured skull are in the purview of the museum sculptors, who appear to have had access to the original materials.

Figure 2c. A preparator’s dilemma. Did the jugal contact the squamosal or not? The preparator made a choice to show contact (Fig 2). Ostrom’s 1970 drawing of the individual bones (assembled here) indicates vanishing bone at the key area. Here two possibilities for contact are shown. Of course, bone could have been absent here – but the model maker chose contact from data known to them. As readers know, corrections are part of the scientific process. This is correction #212,444 or thereabouts.

Distinct from tested relatives
the orbit of Deinonychus (Fig 2) is deeper than wide and not wider than the post-orbital length of the skull. Note the long jugal-squamosal (cyan-magenta) contact is also distinct.

Figure 3. Deinonychus manus. Parallel Interphalangeal Lines (PILs) added here.

PILs
(parallel interphalangeal lines) can be drawn through most, but not all of the phalangeal joints of the hand (Fig 3) and foot (Fig 4).

Figure 4. Deinonychus pes, extended and flexed in ventral view. Parallel Interphalangeal Lines (PILs) added here.

In the LRT Deinonychus is derived from
Late Jurassic Ornitholestes and Late Jurassic Sciurumimus, neither of which had a ‘killer’ claw nor a chevron-tendon-stiffened tail.

References
Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana”. Bulletin of the Peabody Museum of Natural History. 35: 1–234.

wiki/Deinonychus