I rarely venture into the land of dinosaurs (except very basal forms). So many others are doing such great work. The field is saturated with information.
Here I take a single exception to look at a very well known reptile evolutionary lineage. Nothing new here. What I’m showing has been well documented by others and is quite obvious at first glance. All I can offer is to put several of the characters of this ‘play’ onto the same ‘stage’ for the first time.
Figure 1. The evolution of the oviraptorid, Citipati from Scipionyx and Incisivosaurus and a distinct separate lineage leading to Velociraptor determined by the phylogenies of others. When birds went right, these lines took a left turn and ended up with some Franken-birds, like Citipati and Gigantoraptor. Some of the above taxa are considered juveniles (with a short rostrum, large eyes, etc.). Even so, they point the way and provide the evolutionary method by which oviraptorids developed such strange skull proportions.
The present evolutionary sequence has not been tested in the large reptile tree. I’m going by the phylogenies of others (basically everybody in the biz) and the gradual morphological changes demonstrated by these five. Here, then, is a visual representation of the evolutionary sequence from Scipionyx (Dal Sasso and Signore 1998) to Velociraptor (Osborn 1924) through Bambiraptor (Burnham et al. 2000) and another branch to Citipati (Clark et al. 2001), an oviraptorid through Incisivosaurus (Xu et al. 2002).
From Scipionyx (considered a juvenile) up through Bambiraptor to Velociraptor, the rostrum elongates and the postorbital region shrinks. The orbit moves deeper into the second half of the skull. The teeth become recurved. The prefrontal become restricted to the the posterior of the lacrimal. The jugal becomes deeper. The mandible dorsal profile flattens. The premaxilla deepens. The quadratojugal develops a posterior process.
From Scipionyx down through Incisivosaurus to Citipati the premaxilla deepens and the naris rises. The jugal becomes more gracile. The maxilla shortens. The rise of the coronoid, the depth of the palate and the downturned posterior skull are all restricted to Citipati in this sequence.
This blog and illustration were modified from an earlier one demonstrating a morph from Velociraptor to Citipati, both from the Cretaceous. The obvious trick did not go over so well with one reader, so I’m making repairs here. Most DMListers love their velociraptors. Don’t want to piss anybody off.
Time is important and is always a consideration. Earlier forms, like Scipionyx, typically evolve into later forms, and that’s the case here. Exceptions include Huehuecuetzpalli, the Cretaceous sister to the ancestor of Triassic tritosaurs, for instance.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data. If I have made any mistakes, please provide data for the correction.
Burnham DA, Derstler KL, Currie PJ, Bakker RT, Zhou Z and Ostrom JH 2000. Remarkable new birdlike dinosaur (Theropoda: Maniraptora) from the Upper Cretaceous of Montana, University of Kansas Paleontological Contributions 13: 1-14.
Clark JM, Norell MA and Barsbold R 2001. Two new oviraptorids (Theropoda:Oviraptorosauria), upper Cretaceous Djadokhta Formation, Ukhaa Tolgod, Mongolia. Journal of Vertebrate Paleontology 21(2): 209-213., June 2001.
Dal Sasso C and Signore M 1998. Scipionyx samniticus (Saurischia, Theropoda): the first Italian dinosaur, Third European Workshop on Vertebrate Paleontology, Abstract: 2.
Osborn HF 1924a. Three new Theropoda, Protoceratops zone, central Mongolia. American Museum Novitates 144: 1–12. hdl:2246/3223
Xu X, Cheng YN, Wang X-L and Chang C-H 2002. An unusual oviraptorosaurian dinosaur from China. Nature, 419: 291-293.