Wednesday, April 27, 2016

Characteristics

Here is a set of important characteristics to analyze in the evolution of primitive birds. We can see that they appear at Oviraptors/Paraves and not in coelurosaur dinosaurs:

1. Semilunate carpal. 
http://pterosaurnet.blogspot.ca/2016/04/semilunate-carpal.html

2. Feathers
This suggests that large pennaceous feathers first evolved distally on the hindlimbs, as on the forelimbs and tail. This distal-first development led to a four-winged condition at the base of the Paraves. (Hu et al 2009)
3. Breathing sacs
4. Uni-directional lungs
5. Miniaturization

Puttick et al were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," (Puttick et al 2014).Before the origin of Aves, on the branch leading to Paraves, high rates of evolution led to a smaller body size and a relatively larger forelimb in Paraves. These changes are on a single branch leading to Paraves, representing a shift to a new smaller size and larger forelimb at this point.Paraves, rather than Aves alone, shifted to a different evolutionary model relative to other coelurosaurian theropods (Table 2). On all trees and for both femur and forelimb size, the model with a regime shift at Paraves, rather than Aves, is favored (Table S10). (Puttick et al 2014)

Michael J. Benton (2015)
These studies of bird origins [5659] used different datasets, different phylogenies, and different analytical techniques, and yet they converged on the same result. As an example, Puttick et al. [56] showed that miniaturization and wing expansion, critical anatomical requirements to be a bird, arose some 10 Myr before Archaeopteryx among the wider clade Paraves (figure 4), and that the rate of change was 160 times the normal evolutionary rate, suggesting a rapid, adaptive switch that enabled the diversification and success of this clade of tiny, possibly tree-climbing and gliding dinosaurs.

6. Sternum

7. Enlarged brain



8. Ankle
More remarkably, however, this finding reveals an unexpected evolutionary transformation in birds. In embryos of the land egg-laying animals, the amniotes (which include crocodilians, lizards, turtles, and mammals, who secondarily evolved live birth) the intermedium fuses to the anklebone shortly after it forms, disappearing as a separate element. This does not occur in the bird ankle, which develops more like their very distant relatives that still lay their eggs in water, the amphibians. Since birds clearly belong within land egg-laying animals, their ankles have somehow resurrected a long-lost developmental pathway, still retained in the amphibians of today -- a surprising case of evolutionary reversal .
9. Fingers (digits)
For example, the unusually crouched hindlimb for bipedal locomotion that characterizes modern birds was acquired in stepwise fashion through much of theropod evolution (67), and both the furcula (68) and the “semilunate” carpal (69) appeared early in theropod evolution. Notably, major bird characteristics often exhibit a complex, mosaic evolutionary distribution throughout the theropod tree, and several evolutionary stages are characterized by accelerated changes (70). For example, the early evolution of paravian theropods features cerebral expansion and elaboration of visually associated brain regions (71), forelimb enlargement (22, 67), acquisition of a crouched, knee-based hindlimb locomotor system (67), and complex pinnate feathers associated with increased melanosome diversity, which implies a key physiological shift (72). Together these features may suggest the appearance of flight capability at the base of the Paraves (22, 67). (Xu et al 2014a)
10. Lengthening and thickening of the forelimbs
An Archaeopteryx-like theropod from China and the origin of Avialae
Xing Xu1,2, Hailu You3 , Kai Du4 & Fenglu Han2 (2011)
The significant lengthening and thickening of the forelimbs indicates a dramatic shift in forelimb function at the base of the Paraves, which might be related to the appearance of a degree of aerodynamic capability (Xu et al 2011) 

Xing Xu1,2, Hailu You3 , Kai Du4 & Fenglu Han2 (2011)
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China. This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs). 

11. Glenoid fossa  
The glenoid fossa faces ventrolaterally only shifted to a more lateral configuration at Paraves (Makovicky, Zanno 2011; Turner et al. 2012)
Paraves, exclusive of Epidexipteryx hui, is marked by a suite of modifications to the shoulder girdle typically associated with the origin of the ‘‘avian’’ flight stroke (Ostrom, 1976b; Jenkins, 1993). The acromion margin of the scapula has a laterally everted anterior edge (char. 133.1) (fig. 55), the coracoid is inflected medially from the scapula forming an L-shaped scapulocoracoid in lateral view (char. 137.1) and the glenoid fossa faces laterally (char. 138.1) as opposed to the plesiomorphic posterior orientation (fig. 50). Additionally, the furcula is nearly symmetrical in shape as opposed to the asymmetry present in the furcula of more basal taxa (char. 474.1).(Turner et al. 2012)

APPENDIX

The iconic features of extant birds, for the most part, evolved in a gradual and stepwise fashion throughout theropod evolution. However, new data highlight occasional bursts of morphological novelty at certain stages close to the origin of birds and an unavoidable complex, mosaic evolutionary distribution of major bird characteristics on the theropod tree. ........ Newly discovered fossils and relevant analyses demonstrate that salient bird characteristics have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, undergoing modifications through theropods, and finally approaching the modern condition close to the origin of the crown group birds (Fig. 2). For example, the unusually crouched hindlimb for bipedal locomotion that characterizes modern birds was acquired in stepwise fashion through much of theropod evolution (67), and both the furcula (68) and the “semilunate” carpal (69) appeared early in theropod evolution. Notably, major bird characteristics often exhibit a complex, mosaic evolutionary distribution throughout the theropod tree, and several evolutionary stages are characterized by accelerated changes (70). For example, the early evolution of paravian theropods features cerebral expansion and elaboration of visually associated brain regions (71), forelimb enlargement (22, 67), acquisition of a crouched, knee-based hindlimb locomotor system (67), and complex pinnate feathers associated with increased melanosome diversity, which implies a key physiological shift (72). Together these features may suggest the appearance of flight capability at the base of the Paraves (22, 67). (Xu et al 2014a) 

Xing Xu et al (2014)
An integrative approach to understanding bird origins
Several flight-related anatomical features, such as hollow bones and the furcula, originated in early theropods; basal paravians had many hallmark features necessary for flight, including extremely small body size (50, 70); a laterally oriented, long, and robust forelimb (22, 67); an enlarged forebrain and other derived neurological adaptations (71); and large flight feathers (Figs. 1 and 2). Particularly surprising are the recent discoveries of large flight feathers forming a planar surface on the legs of some basal paravians—for example, those with asymmetrical vanes on both the tibia and metatarsus of some basal dromaeosaurs, such as Microraptor (59); large feathers with symmetrical vanes on both the tibia and metatarsus of the troodontid Anchiornis (45), the basal bird Sapeornis, and several other basal paravians (135); and large vaned feathers on tibiae of several basal birds including Archaeopteryx, confuciusornithids, and enantiornithines (135). These structures clearly would have been relevant to flight origins.
several evolutionary stages are characterized by accelerated changes (70).
new data highlight occasional bursts of morphological novelty at certain stages close to the origin of birds 
It is possible that the SLC is not homologous throughout Tetanurae, in that different distal carpal elements may contribute to forming the SLC in different taxa or at least contribute to varying degrees (Chure 2001). 

REVERSALS
More remarkably, however, this finding reveals an unexpected evolutionary transformation in birds. In embryos of the land egg-laying animals, the amniotes (which include crocodilians, lizards, turtles, and mammals, who secondarily evolved live birth) the intermedium fuses to the anklebone shortly after it forms, disappearing as a separate element. This does not occur in the bird ankle, which develops more like their very distant relatives that still lay their eggs in water, the amphibians. Since birds clearly belong within land egg-laying animals, their ankles have somehow resurrected a long-lost developmental pathway, still retained in the amphibians of today -- a surprising case of evolutionary reversal .


The anklebone (astragalus) of dinosaurs presents a characteristic upward projection, the ‘ascending process’ (ASC). The ASC is present in modern birds, but develops a separate ossification centre, and projects from the calcaneum in most species. These differences have been argued to make it non-comparable to dinosaurs. We studied ASC development in six different orders of birds using traditional techniques and spin–disc microscopy for whole-mount immunofluorescence. Unexpectedly, we found the ASC derives from the embryonic intermedium, an ancient element of the tetrapod ankle. In some birds it comes in contact with the astragalus, and, in others, with the calcaneum. The fact that the intermedium fails to fuse early with the tibiale and develops an ossification centre is unlike any other amniotes, yet resembles basal, amphibian-grade tetrapods. The ASC originated in early dinosaurs along changes to upright posture and locomotion, revealing an intriguing combination of functional innovation and reversion in its evolution.

Wrist SEMILUNATE CARPAL
Interestingly, a key event in the carpal lateral shift appears to have been the reappearance of distal carpal 4 to contribute to the ‘semilunate' articular surface in derived maniraptorans.

We confirm the proximal–posterior bone is a pisiform in terms of embryonic position and its development as a sesamoid associated to a tendon. However, the pisiform is absent in bird-like dinosaurs, which are known from several articulated specimens. The combined data provide compelling evidence of a remarkable evolutionary reversal: A large, ossified pisiform re-evolved in the lineage leading to birds, after a period in which it was either absent, nonossified, or very small, consistently escaping fossil preservation.

FINGERS

Based on this study, the most parsimonious alignment is for the four digits of ceratosaurs to be I-II-III-IV and the three (and sometimes four) digits of all Tetanurae to be II-III-IV(V). Accepting such a topological shift at the base of Tetanura requires that the positional homology of the three digits of tetanurans is II-III-IV(-V), as suggested by Wagner and Gauthier34. Because the four digits of ceratosaurs are therefore most parsimoniously interpreted as I-II-III-IV, the small lateral metacarpal ossification of Guanlong35, Sinraptor36, and Coelurus represents the re-ossification of metacarpal V after it is lost at the base of Ceratosauria. The poor phylogenetic resolution for basal tetanurans in our study precludes us from hypothesizing whether this re-ossification event occurred once or more than once in the evolution of Theropoda. Likewise, the fourth metacarpal, which is reduced in primitive theropods and bears an unknown number of phalanges in Ceratosauria, re-acquires at least three phalanges in Tetanurans.

This implies the reduction of digit I before the divergence of the Ceratosauria and the
Tetanurae, the appearance of some polleciform features in digit II and the acquisition of a novel phalangeal formula (X-2-3-4-X) early in tetanuran evolution. Both modifications are partially indicated by the manual morphologies of ceratosaurs and more basal theropods. Also, they are indirectly supported by observations in living animals that a digit will display features normally associated with the neighbouring medial digit if the latter fails to chondrify in early development21, that phalangeal counts can vary even within species29, 42 and that secondarily cartilaginous elements can regain their ability to ossify43.

If BDR [Bilateral Digit Reduction] applies to the more inclusive Averostra, as the II-III-IV hypothesis suggests, early stages of tetanuran evolution must have involved loss of the already highly reduced metacarpal I, reduction in the length of metacarpal II, and the reappearance of additional phalanges on metacarpal IV. Both the I-II-III and II-III-IV hypotheses can claim a degree of support from morphological data, but the II-III-IV hypothesis is more parsimonious when developmental data from extant birds are considered.

Monday, April 25, 2016

Semilunate carpal


http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4131224/
Homologies and homeotic transformation of the theropod ‘semilunate' carpal
Xing XuFenglu Han, and Qi Zhao (2014)

The homology of the ‘semilunate' carpal, an important structure linking non-avian and avian dinosaurs, has been controversial. 
The distribution of the morphological features pertaining to the trochlear facet across theropod phylogeny is consistent with a partial and gradual homeotic transformation of the ‘semilunate' carpal. Although no direct developmental data are available to support the occurrence of a homeotic transformation, this interpretation is suggested by the positional shift of the topologically unique articular surface from the medial side of the wrist to the lateral side (i.e. the trochlear facet shifts from medial carpals to lateral carpals). 
Interestingly, a key event in the carpal lateral shift appears to have been the reappearance of distal carpal 4 to contribute to the ‘semilunate' articular surface in derived maniraptorans.
The theropod wrist evolution is featured by the sequential occurrences of the following major modifications: enlargement of distal carpal 2 together with reduction of distal carpal 3 and loss of distal carpal 4, development of a transverse groove on a composite distal carpal composed of large distal carpal 2 and small distal carpal 3, development of a transverse trochlea on a large distal carpal composed of distal carpal 2 and enlarged distal carpal 3, development of a prominent transverse trochlea on a large distal carpal composed of distal carpals 2, 3, and the reappeared distal carpal 4, and development of a prominent transverse trochlea on the proximolateral portion of the metacarpus composed of distal carpals 3 and 4 .

When you look at Table 1 (in Supplementary Information) you see that the distal carpal 4 (character 9) is present beginning at oviraptors and all the following taxa. But NOT present in the preceding coelurosur dinosaurs.

Table 1. Scorings for 18 characters for 31 theropod taxa
           

Character/taxon
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Herrerasaurus
0
0
0
0
0
0
0
0
0
0
?
?
?
?
?
?
?
?
Coelophysis
0
1
?
0
0
0
0
0
0
0
?
?
?
?
?
?
?
?
Dilophosaurus
0
0
0
0
0
0
0
0
0
0
?
?
?
?
?
?
?
?
Xuanhanosaurus
1
?
1
1
0
1
0
0
1
?
0
0
0
0
0
0
0
0
Allosaurus
1
?
1
1
1
1
0
1
1
?
1
0
0
0
0
0
0
0
Guanlong
1
?
1
1
1
1
0
0
1
?
1
0
0
0
0
0
0
0
Tyrannosaurus
1
?
0
1
1
0
0
0
?
?
1
0
0
1
0
0
0
0
Coelurus
1
?
1
1
1
?
?
?
?
?
1
0
1
0
1
0
0
0
Harpymimus
1
?
1
0
0
1
0
0
?
?
?
?
?
?
?
?
?
?
Nqwebasaurus
1
?
0
0
0
0
0
0
?
?
?
?
?
?
?
?
?
?
Falcarius
1
?
0
1
1
0
1
1
1
?
1
0
1
0
1
0
0
0
Alxasaurus
1
?
0
1
1
0
1
0
1
?
1
0
1
0
1
0
0
0
Haplocheirus
1
?
1
1
1
1
0
0
1
?
1
0
1
0
1
0
0
0
Similicaudipteryx
1
?
0
1
1
0
1
2
0
0
2
1
1
1
1
1
0
0
Oviraptor
1
?
0
1
1
0
1
2
?
?
2
1
1
1
1
1
0
0
Microraptor
1
?
0
1
1
0
1
2
0
1
2
1
1
1
1
1
0
1
Linheraptor
1
?
0
1
1
0
1
2
?
?
2
1
1
1
1
1
0
0
Mei
1
?
0
1
1
0
1
2
0
1
2
1
1
1
1
1
?
?
Sinovenator
1
?
0
1
1
0
1
2
0
1
2
1
1
1
1
1
0
1
Archaeopteryx
1
?
0
1
1
0
1
2
0
1
2
1
1
1
1
1
?
1
Anchiornis
1
?
0
1
1
0
1
2
0
1
2
1
1
1
1
1
0
1
Jeholornis
1
?
0
1
1
0
1
2
0
2
2
2
1
2
1
1
0
2
Sapeornis
1
?
0
1
1
0
1
2
0
2
2
2
1
2
1
1
0
2
Confuciusornis
1
?
?
?
?
?
1
2
0
2
2
2
1
2
1
1
0
2
Protopteryx
1
?
?
?
?
?
1
2
0
2
2
2
1
2
0
2
0
2
Yanornis
1
?
?
?
?
?
1
?
?
2
2
2
1
3
0
2
1
2
Struthio
1
?
?
?
?
2
1
?
0
2
2
2
1
3
0
3
1
2
Gallicrex
1
?
?
?
?
2
1
1
0
2
2
2
?
3
0
3
1
2
Sinosauropteryx
1
?
0
0
1
?
?
?
?
?
0
0
0
0
0
0
0
0
Mononykus
1
?
1
1
1
?
?
?
?
?
2
1
1
1
1
1
1
1
Tanycolagreus
1
?
?
0
0
?
0
1
?
?
0
0
1
0
0
0
0
0

The same is true for characteristics 8, 11, 12 and 16. Things are different beginning at Oviraptors. They are different from the coelurosaur dinosaurs.


8.         Distal carpal 3, fusion to distal carpal 2: absent (0) or occurs late in ontogeny (1) or occurs early in ontogeny (2)
9.         Distal carpal 4: present (0) or absent (1)
11.       ‘Semilunate’ carpal (distal carpal element with a transversely trochlear proximal articular facet), proximal margin of ventral surfacestraight (0) or moderately convex (1) or strongly convex (2).

12.       ‘Semilunate’ carpal, proximal margin of dorsal surface: straight (0) or moderately convex (1) or strongly convex (2).
16.      Articular facet on proximal surface of metacarpus: medial, facet absent on lateral portion of proximal surface of metacarpus (0) or central, facet present across entire proximal surface of metacarpus (1) or lateral, facet absent on medial portion of proximal surface of metacarpus (2) or extremely lateral, facet absent on medial portion of proximal surface of metacarpus and extends onto poximolateral surface of metacarpus (3).  



http://rspb.royalsocietypublishing.org/content/early/2010/02/24/rspb.2009.2281.full

Radiale angles in various theropods. 

taxonanglespecimen/source
Allosaurus fragilisChure (2001, fig. 2c)
Huaxiagnathus orientalis18°Hwang et al. (2004, fig. 8a)
Sinosauropteryx primaCurrie & Chen (2001, fig. 8a)
Guanlong wucaiiIVPP V14531
Alxasaurus elesitaiensis39°IVPP RV93001
Falcarius utahensis26°Utah Museum of Natural History, Salt Lake City, USA (UMNH) VP 12294
Caudipteryx sp.76°IVPP V12430
Haplocheirus15°IVPP V15988
Sinovenator changii35°IVPP V14009
Deinonychus antirrhopus31°YPM 5208
Eoconfuciusornis zhengi55°IVPP V11977
Meleagris gallopavo59°IVPP 1222

It is possible that the SLC is not homologous throughout Tetanurae, in that different distal carpal elements may contribute to forming the SLC in different taxa or at least contribute to varying degrees (Chure 2001).
However, the measured value of 76° in Caudipteryx suggests that the oviraptorosaur wrist may have independently evolved an even greater abductor bias than that existing in avialans.