Wednesday, September 3, 2014

Oviraptors as secondarily flightless

Here is an accumulation of material on the idea that Oviraptors were secondarily flightless primitive birds. Being "secondarily" flightless means they evolved from earlier flying primitive birds.

Also see:
Oviraptorosaurs Temporal range: Cretaceous, 130–66 Ma
Oviraptorosaurs, like deinonychosaurs, are so bird-like that several scientists consider them to be true birds, more advanced than Archaeopteryx. Gregory S. Paul has written extensively on this possibility, and Teresa Maryańska and colleagues published a technical paper detailing this idea in 2002.[5][15][16] Michael Benton, in his widely-respected text Vertebrate Paleontology, also included oviraptorosaurs as an order within the class Aves.[17] However, a number of researchers have disagreed with this classification, retaining oviraptorosaurs as non-avialan maniraptorans slightly more primitive than the deinonychosaurs.[18]
Analyses like those of Maryanska et al (2002) and Osmólska et al. (2004) suggest that they may represent primitive flightless birds.[5][6]
The consensus view, based on several cladistic analyses, is that Caudipteryx is a basal (primitive) member of the Oviraptoridae, and the oviraptorids are nonavian theropod dinosaurs.[9] Incisivosaurus is the only oviraptorid that is more primitive.[10]
Halszka Osmólska et al. (2004) ran a cladistic analysis that came to a different conclusion. They found that the most birdlike features of oviraptorids actually place the whole clade within Aves itself, meaning that Caudipteryx is both an oviraptorid and a bird. In their analysis, birds evolved from more primitive theropods, and one lineage of birds became flightless, re-evolved some primitive features, and gave rise to the oviraptorids. This analyis was persuasive enough to be included in paleontological textbooks like Benton's Vertebrate Paleontology (2005).[11] The view that Caudipteryx was secondarily flightless is also preferred by Gregory S. Paul,[12] Lü et al.,[13] and Maryańska et al.[14]
Others, such as Stephen Czerkas and Larry Martin have concluded that Caudipteryx is not a theropod dinosaur at all.[15] They believe that Caudipteryx, like all maniraptorans, is a flightless bird, and that birds evolved from non-dinosaurian archosaurs.[16]
Avialan status for Oviraptorosauria
Oviraptorosauria is a clade of Cretaceous theropod dinosaurs of uncertain affinities within Maniraptoriformes. All previous phylogenetic analyses placed oviraptorosaurs outside a close relationship to birds (Avialae), recognizing Dromaeosauridae or Troodontidae, or a clade containing these two taxa (Deinonychosauria), as sister taxon to birds. Here we present the results of a phylogenetic analysis using 195 characters scored for four outgroup and 13 maniraptoriform (ingroup) terminal taxa, including new data on oviraptorids. This analysis places Oviraptorosauria within Avialae, in a sister−group relationship with Confuciusornis. Archaeopteryx, Therizinosauria, Dromaeosauridae, and Ornithomimosauria are successively more distant outgroups to the Confuciusornis−oviraptorosaur clade. Avimimus and Caudipteryx are successively more closely related to Oviraptoroidea, which contains the sister taxa Caenagnathidae and Oviraptoridae. Within Oviraptoridae, “Oviraptor” mongoliensis and Oviraptor philoceratops are successively more closely related to the
Conchoraptor−Ingenia clade. Oviraptorosaurs are hypothesized to be secondarily flightless. Emended phylogenetic definitions are provided for Oviraptoridae, Caenagnathidae, Oviraptoroidea, Oviraptorosauria, Avialae, Eumaniraptora, Maniraptora, and Maniraptoriformes.
Recent studies by Varricchio et al. reveal that males cared for the eggs of troodontids and oviraptorids, so-called "non-avian theropods" of the Cretaceous, just as do those of most Paleognathic birds (ratites and tinamous) today. Further, the clutches of both groups have large relative volumes, and consist of many eggs of relatively large size. By comparison, clutch care by most extant birds is biparental and the clutches are of small relative volume, and consist of but few small eggs. Varricchio et al. propose that troodontids and oviraptorids were pre-avian and that paternal egg care preceded the origin of birds. On the contrary, unmentioned by them is that abundant paleontological evidence has led several workers to conclude that troodontids and oviraptorids were secondary flightless birds. This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits.
Paraves, all maniraptorans closer to Neornithes than Oviraptor. Note that Sereno's excluding oviraptorosaurs from the paravian lineage is of questionable validity, as some of the most avian of all theropods, are oviraptorosaurs. Indeed, the clade may represent neoflightless [secondarily flightless] post-urvogels.
the scansoriopterygids Epidendrosaurus [53] and Epidexipteryx[54] are more similar to basal birds, such as Jeholornis and Sapeornis [64,65], than to Archaeopteryx in many of their derived features, particularly in a number of derived cranial features. Surprisingly these cranial features are also seen in the oviraptorosaurs [54]. Together, the Jurassic maniraptorans suggest a monophyletic group composed of the scansoriopterygids,
all other birds except Archaeopteryx, and probably also the oviraptorosaurs. This would represent a sister taxon to a monophyletic group containing the troodontids, the dromaeosaurids, and Archaeopteryx (Figure 1). Such a phylogenetic hypothesis would have significant implications for the reconstruction of the theropod-bird transition but it has yet to be tested by quantitative phylogenetic analysis.
Morphological gaps in the known fossil record separate only seven groups from the rest of Dinosauria. Those groups are Therizinosauroidea + Oviraptorosauria + Paraves, Tazoudasaurus + Eusauropoda, Ankylosauridae, Stegosauria, Neoceratopsia, basal Hadrosauriformes and Hadrosauridae.
Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus4, 5, forming a new clade at the base of Avialae6.,d.aWw
Jones et al (2000)
Caudipteryx has been described as a feathered dinosaur14,15 and
therefore would be expected to have had a dinosaurian mechanism
of cursoriality. However, relative total hindlimb proportions in
Caudipteryx contrast sharply with those in all other bipedal dinosaurs
and are indistinguishable from those in cursorial birds
(Fig. 1b). Accordingly, based on the tight linkage of hindlimb
proportions to cursorial mechanisms in bipedal archosaurs, we
suggest that Caudipteryx ran using a mechanism more similar to
that of modern cursorial birds than to typical dinosaurs.
Significantly, lower leg (tibia + metatarsal) length in Caudipteryx is also the
same as the `effective hindlimb' length of cursorial birds, which is
equivalent to total hindlimb length in theropods (Fig. 1a).

This following is a counter to Jones et al (2000) but the problem with the following passage is that it uses the ambiguous phrase "non−avialan theropod". They do not rule out that oviraptors could be secondarily flightless members of Paraves.
Caudipteryx zoui [an oviraptor] is a small enigmatic theropod known from the Early Cretaceous Yixian Formation of the People’s Republic of China. From the time of its initial description, this taxon has stimulated a great deal of ongoing debate regarding the phylogenetic relationship between non−avialan theropods and birds (Avialae) because it preserves structures that have been uncontroversially accepted as feathers (albeit aerodynamically unsuitable for flight). However, it has also been proposed that both the relative proportions of the hind limb bones (when compared with overall leg length), and the position of the center of mass in Caudipteryx are more similar to those seen in extant cusorial birds than they are to other non−avialan theropod dinosaurs. This conclusion has been used to imply that Caudipteryx may not have been correctly interpreted as a feathered non−avialan theropod, but instead that this taxon represents some kind of flightless bird. We review the evidence for this claim at the level of both the included fossil specimen data, and in terms of the validity of the results presented. There is no reason—phylogenetic, morphometric or otherwise—to conclude that Caudipteryx is anything other than a small non−avialan theropod dinosaur.
Oviraptors were either secondarily flightless avialae or secondarily flightless non-avialae paraves.
They descended from flying ancestors. They are not transitional between dinosaurs and paraves.

Here is a suggestion about the change that would accommodate the idea that oviraptors are secondarily flightless members of Eumaniraptora:
Clade: Paraves
Sereno, 1997

And here is how the so-called "non-paraves maniraptors" could be more correctly categorized as secondarily flightless birds:

Clade: Paraves
†Troodontidae (including Jinfengopteryx)

The other even more likely possibility is that some of these taxa have both flying AND secondarily flightless members.
Feduccia and Czerkas
Considerable debate surrounds the numerous avian-like traits in core maniraptorans (oviraptorosaurs, troodontids, and dromaeosaurs), especially in the Chinese Early Cretaceous oviraptorosaur Caudipteryx, which preserves modern avian pennaceous primary remiges attached to the manus, as is the case in modern birds. Was Caudipteryx derived from earth-bound theropod dinosaurs, which is the predominant view among palaeontologists, or was it secondarily flightless, with volant avians or theropods as ancestors (the neoflightless hypothesis), which is another popular, but minority view. The discovery here of an aerodynamic propatagium in several specimens provides new evidence that Caudipteryx (and hence oviraptorosaurs) represent secondarily derived flightless ground dwellers, whether of theropod or avian affinity, and that their presence and radiation during the Cretaceous may have been a factor in the apparent scarcity of many other large flightless birds during that period.
A subsequent phylogenetic analysis conducted by Agnolín and Novas (2011) recovered scansoriopterygids not as avialans, but as basal members of the clade Paraves remaining in unresolved polytomy with alvarezsaurids and the clade Eumaniraptora (containing avialans and deinonychosaurs).[8]Turner, Makovicky and Norell (2012) included only Epidexipteryx hui in their primary phylogenetic analysis, as a full-grown specimen of this species is known; regarding Scansoriopteryx/Epidendrosaurus, the authors were worried that including it in the primary analysis would be problematic, because it is only known from juvenile specimens, which "do not necessarily preserve all the adult morphology needed to accurately place a taxon phylogenetically" (Turner, Makovicky and Norell 2012, p. 89). Epidexipteryx was recovered as basal paravian that didn't belong to Eumaniraptora. The authors did note that its phylogenetic position is unstable; constraining Epidexipteryx hui as a basal avialan required two additional steps compared to the most parsimonious solution, while constraining it as a basal member of Oviraptorosauria required only one additional step. A separate exploratory analysis included Scansoriopteryx/Epidendrosaurus, which was recovered as a basal member of Avialae; the authors noted that it did not clade with Epidexipteryx, which stayed outside Eumaniraptora. Constraining the monophyly of Scansoriopterygidae required four additional steps and moved Epidexipteryx into Avialae.[9]A monophyletic Scansoriopterygidae was recovered by Godefroit et al. (2013); the authors found scansoriopterygids to be basalmost members of Paraves and the sister group to the clade containing Avialae and Deinonychosauria.[10] Agnolín and Novas (2013) recovered scansoriopterygids as non-paravian maniraptorans and the sister group to Oviraptorosauria.[11]
Constraining Epidexipteryx as a basal oviraptorosaur requires only one additional step in our dataset (fig. 75). Three features support the inclusion of Epidexipteryx in Oviraptorosauria, which are caudal vertebrae without a transition point (char. 115.1), a dentary that has teeth only anteriorly (char. 220.1), and a first premaxillary tooth much larger than the succeeding teeth (char. 251.2). A tail without a transition point is unique to oviraptorosaurs and Epidexipteryx and premaxillary teeth greatly enlarged relative to other premaxillary teeth is unique to Incisivosaurus, Protarchaeopteryx, and Epidexipteryx.
Epidexipteryx resembles basal oviraptorosaurs
in several respects, particularly
in its cranial morphology. Zhang et al. (2008)
noted some of these, drawing attention to
the anteroposteriorly short but dorsoventrally
tall skull, the posterodorsally displaced
naris and anteroposteriorly long parietals.
Likewise, the highly procumbent anterior
dentition and the slightly downturned mandible
compares favorably to basal oviraptorosaurs
like Incisivosaurus, Caudipteryx, and
putatively Protarchaeopteryx.
Constraining Epidexipteryx as a basal oviraptorosaur
requires only one additional step in our dataset (fig. 75).”

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