Monday, July 21, 2014

I want to pause here and talk about this notion of consensus, and the rise of what has been called consensus science. I regard consensus science as an extremely pernicious development that ought to be stopped cold in its tracks. Historically, the claim of consensus has been the first refuge of scoundrels; it is a way to avoid debate by claiming that the matter is already settled. Whenever you hear the consensus of scientists agrees on something or other, reach for your wallet, because you're being had.
Let's be clear: the work of science has nothing whatever to do with consensus. Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science consensus is irrelevant. What is relevant is reproducible results. The greatest scientists in history are great precisely because they broke with the consensus.
There is no such thing as consensus science. If it's consensus, it isn't science. If it's science, it isn't consensus. Period.
In addition, let me remind you that the track record of the consensus is nothing to be proud of. 
A lecture by Michael Crichton Caltech Michelin Lecture January 17, 2003

Saturday, May 24, 2014


The dino to bird theory postulates that "non-paraves maniraptors" were transitional between basal coelurosaurs and basal Paraves. One problem with this idea (one of many), is the enlarged brains these "non-paraves maniraptors" had, that they did not use for flight.

According to the dino to bird theory this "brainpower needed for flight" existed "long before" it was needed for flight. Not only that, but it existed "multiple times".

The more credible explanation is that they were not transitionals, but rather secondarily flightless paravians. In other words they developed from (and came after) basal paraves.
Several ancient dinosaurs [maniraptors] evolved the brainpower needed for flight long before they could take to the skies, scientists say.
Bird brains tend to be more enlarged compared to their body size than reptiles, vital for providing the vision and coordination needed for flight.
Scientists using high-resolution CT scans have now found that these "hyper-inflated" brains were present in many ancient dinosaurs [maniraptors], and had the neurological hardwiring needed to take to the skies. This included several bird-like oviraptorosaurs and the troodontids Zanabazar junior, which had larger brains relative to body size than that of Archaeopteryx.
Our new data indicate that the relative size of the cranial cavity of Archaeopteryx is reflective of a more generalized maniraptoran volumetric signature and in several instances is actually smaller than that of other non-avian dinosaurs. Thus, bird-like indices evolved multiple times, supporting the conclusion that if Archaeopteryx had the neurological capabilities required of flight, so did at least some other non-avian maniraptorans. This is congruent with recent findings that avialans were not unique among maniraptorans in their ability to fly in some form.
Secondarily flightless birds or Cretaceous non-avian theropods?
Kavanau JL.

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. Because ratites also are secondarily flightless and tinamous are reluctant, clumsy fliers, the new evidence strengthens the view that troodontids and oviraptorids were secondarily flightless. Although secondary flightlessness apparently favors paternal care of clutches of large, abundant eggs, such care is not likely to have been primitive. There are a suite of previously unknown independent findings that point to the evolution of, first, maternal, followed by biparental egg care in earliest ancestors of birds. This follows from the discovery of remarkable relict avian reproductive behaviors preserved by virtue of the highly conservative nature of vertebrate brain evolution. These behaviors can be elicited readily by exposing breeding birds to appropriate conditions, both environmental and with respect to their eggs and chicks. They give significant new clues for a coherent theory of avian origin and early evolution.

Thursday, May 15, 2014


Here is an accumulation of information related to characters analyzed in Nesbitt (2011) and Nesbitt et al (2009).
These support the pterosaur to bird theory and contradict the dino to bird theory.

NESBITT (2011) 

Nesbitt characters 212, 213, 214, 223, 230, 231 and 370.

212. Forelimb–hind limb, length ratio: (0) more than 0.55; (1) less than 0.55 (Gauthier,
1984; Sereno, 1991a; Juul, 1994; Benton, 1999).
Humerus + radius [forelimb] : Femur + tibia [hindlimb]

Dromaeosaurid forelimbs are among the longest in theropods, the ratio of forelimb length to hindlimb length being about 65% in Velociraptor, 70% in Deinonychus and 80% in Sinornithosaurus.

213. Clavicles: (0) present and unfused; (1) fused into a furcula (modified from Gauthier, 1986; Sereno, 1991a; Benton, 1999; Benton and Walker, 2002). Clavicles are present in non-archosaurian archosauriforms and basal crocodylian-line archosaurs. Clavicles are not present in crocodylomorphs (e.g., Hesperosuchus ‘‘agilis,’’ CM 29894; Protosuchus richardsoni, AMNH FR 3024) and, therefore, they are scored as inapplicable. Like the interclavicle, the clavicles of the pterosaur Eudimorphodon are separate ossifications in a small specimen and incorporated into the sternum (Wild, 1993). All other pterosaurs seem to lack distinct ossifications of the clavicles. Within Dinosauria, clavicles are present, but do not contact in some ornithischians (e.g., Psittacosaurus) and are unossified in others (Butler et al., 2008a). The clavicles of some nonsauropod sauropodomorphs (e.g., Massospondylus) may contact each other at the midline, but do not fuse (Yates and Vasconcelos, 2005). A furcula (fused clavicles) is present in nearly all theropods known from complete skeletons including Coelophysis bauri (AMNH FR 30647; Rinehart et al., 2007; Nesbitt et al., 2009d) and Allosaurus fragilis (UUVP 6102; Chure and Madsen, 1996). This character has been employed by various datasets exploring theropod relationships (e.g., Norell et al., 2001; Clarke, 2004).

Pterosaurs have clavicles and an interclavicle that are fused into the sternum.

214. Interclavicle: (0) present; (1) absent
(fig. 30) (Gauthier, 1986; Sereno, 1991a; Juul,
1994; Benton, 1999).
The interclavicle is present in archosauriforms
plesiomorphically (Sereno, 1991a) and
persists through Pseudosuchia. In Pterosauria,
an interclavicle appears to be present
in young individuals of Eudimorphodon
(MCSNB 8950), but fuse to the pectoral
elements in larger individuals (Wild, 1993). A
distinct interclavicle is not present in all other
pterosaurs. Ornithischians and saurischians
lack an interclavicle. However, the pectoral
girdles in the successive sister taxa to
Dinosauria (Silesaurus, Marasuchus, Lagerpeton)
do not have the pectoral region
completely preserved. As a result, the optimization
of this character within Dinosauromorpha
is not clear.


The evolutionary transformation of the furcula
from separate clavicles is nicely illustrated in
archosaurs and their close relatives. Euparkeria
capensis and early pseudosuchians retain both the
interclavicle and clavicles. The interclavicle is lost
at the dinosaur node or at an unknown node
among early dinosauromorphs.
 From there, the origin
of the furcula is well understood with the
addition of the work on basal sauropodomorphs of
Yates and Vasconcelos (2005) and the discovery of
furculae in early coelophysoid theropods (Tykoski
et al., 2002; Rinehart et al., 2007). Some ornithischians
have two small clavicles that do not
contact each other (Osborn, 1924a; Brown and
Schlaikjer, 1940; Sternberg, 1951; Chinnery and
Weishampel, 1998). In contrast, saurischians
retain clavicles with the clavicles contacting at the

Birds and pterosaurs have an interclavicle. Dinosaurs do not.

223. Coracoid, postglenoid process: (0) short; (1) elongate and expanded posteriorly only 

The significance of this is that a longer coracoid allows the bird scapula (attached to the coracoid) to be positioned high enough on the body (horizontally), to allow flapping (by the wings being raised high enough up).

230. Humerus, apex of deltopectoral crest situated at a point corresponding to: (0) less than 30% down the length of the humerus; (1) more than 30% down the length of the humerus (fig. 31) (modified from Bakker and Galton, 1974; Benton, 1990a; Juul, 1994; Novas, 1996; Benton, 1999).
Langer and Benton (2006) thoroughly discussed the distribution of the character states of this character and find that state (1) is restricted to dinosaurs within Archosauria. Here, I follow the conclusions and scorings of Langer and Benton (2006). 

The pterosaur deltopectoral crest is like birds. The dinosaur deltopectoral crest is not like birds. (See details below).

231. Humerus, length: (0) longer than or
subequal to 0.6 of the length of the femur; (1)
shorter than 0.6 of the length of the femur
(modified from Novas, 1996; Langer and
Benton, 2006).
Langer and Benton (2006) thoroughly
discussed the distribution of the character
states and find that state (1) is restricted to
Herrerasaurus (PVSJ 373), Eoraptor (PVSJ
512), and neotheropods.

Humerus length compared to femur length is similar for pterosaurs to birds but different than dinosaurs.

370. Astragalus-calcaneum, articulation:
(0) free; (1) coossified (fig. 46) (Sereno and
Arcucci, 1994a; Irmis et al., 2007a).
In most archosauriforms, save avians and
close relatives
, the astragalus and calcaneum
are separate elements. In pterosaurs (e.g.,
Dimorphodon, YPM 9182), Lagerpeton (PVL
4619), and Dromomeron romeri (GR 223), the
astragalus and calcaneum are coossified.
Among basal dinosaurs, the proximal tarsals
are coossified in Heterodontosaurus (SAMPK-
1332) and coelophysoids (Rowe and
Gauthier, 1990; Tykoski, 2005b).

More info on the deltopectoral crest.
"Both tiny birds and tiny pterosaurs dispensed with their long stiff tail. In birds it became a pygostyle. In pterosaurs the long stiff tail became a reduced, string-like tail with bead-like verts. Note the similarities in the pectoral girdles. Both could stand with their toes beneath their shoulder glenoids. Both had retroverted pedal digits but of two distinct designs. The anterior ilium of both taxa supported large thigh muscles. A large deltopectoral crest supported large flight adductors anchored to the sternum."
Deltopectoral crest: a longitudinal ridge or crest on the (proximal) humerus. Cursorial forms typically do not have a large crest. It is typically an important attachment point for adductors, rather than retractors.
Dinosaurs evolved within a single lineage of archosaurs 232-234 Ma (million years ago) in the Ladinian age, the latter part of the middle Triassic. Dinosauria is a well-supported clade, present in 98% of bootstraps. It is diagnosed by many features including loss of the postfrontal on the skull and an ELONGATE deltopectoral crest on the humerus.[1]

The Dinosauria: Second Edition:

The humerus is slender and twisted. It has a caudally deflected proximal end and a moderately developed deltopectoral crest that is restricted to the PROXIMAL third of the humerus in Deinonychus and to the PROXIMAL quarter in Velociraptor.

Pterosaur humerus:

Description: The specimen MB.R. 2828 (Fig. 2; Table I) has a slightly dorso-ventral compression, showing several fractures. It possesses the characteristic saddle-shaped proximal articular head, common to the pterosaur humeri. The deltopectoral crest is well developed and inclined proximoventrally. It is tongue-shaped with a rounded distal end. In lateral view the proximal margin of the deltopectoral crest is markedly concave, while the distal margin is straight. There is an elongated ridge on the medial side of the crest running from the distal to the proximal edge, and is likely an attachment of a flight muscle (m. pectoralis, see Bennett 2003). There is an elongated concavity on the medial side, close to the distal margin, whose function is unknown. The ulnar crest is blunt and slightly crushed laterally. The dorsal margin shows a well developed pneumatic foramen, located close to the lateral side.
Miscellaneous bird humeri (proximal heads to the left). The top 2 face anteriorly & the bottom 3 face posteriorly.

Notice the bird deltopectoral crest is basically confined to the proximal end as in pterosaurs.
apex of deltopectoral crest (a projection on which the deltopectoral muscles attach) located at or more than 30% down the length of the humerus (upper arm bone)
Notice the dinosaur deltopectoral crest is not confined to the proximal end as in birds and pterosaurs.

NESBITT (2009) 

11. Furcula shape in anterior view: asymmetrical
(0) or symmetrical/nearly symmetrical (1).
The furculae of most nonparavian theropods
are markedly asymmetrical (e.g., Allosaurus,
Citipati). The furculae of paravians, with the
exception of Buitreraptor, are nearly symmetrical.

It is unclear if the asymmetry of the furcula
of Buitreraptor was the result of taphonomy
or represents morphological asymmetry.
We see that the dinosaur furcula is not like the Paravian furcula.
That supports the conclusion that they are not related.

Also see (page 77)

Monday, April 28, 2014

Pneumatic (air-filled) postcranial bones

We see that the postcranial bones of pterosaurs, maniraptors and birds are pneumatic.
In addition large sauropodomorph dinosaurs that are not on the purported line leading to dinosaurs, also had pneumatic bones.
Coelurosaur dinosaurs did not have pneumatic postcranial bones.

Pneumatic (air-filled) postcranial bones are unique to birds among extant tetrapods. Unambiguous skeletal correlates of postcranial pneumaticity first appeared in the Late Triassic (approximately 210 million years ago), when they evolved independently in several groups of bird-line archosaurs (ornithodirans). These include the theropod dinosaurs [maniraptors] (of which birds are extant representatives), the pterosaurs, and sauropodomorph dinosaurs. [Note that sauropodomorph dinosaurs are not claimed to be on the purported line leading to birds].
Increases in skeletal pneumaticity occurred independently in as many as 12 lineages, highlighting a remarkably high number of parallel acquisitions of a bird-like feature among non-avian theropods. 
However, the body size threshold for extensive pneumatisation is lower in theropod lineages more closely related to birds (maniraptorans). Thus, relaxation of the relationship between body size and pneumatisation preceded the origin of birds and cannot be explained as an adaptation for flight. We hypothesise that skeletal density modulation in small, non-volant, maniraptorans resulted in energetic savings as part of a multi-system response to increased metabolic demands. Acquisition of extensive postcranial pneumaticity in small-bodied maniraptorans may indicate avian-like high-performance endothermy.
What about these small maniraptorans and their hypothesized "increased metabolic demands"?
The problem is that there is no evidence for "increased metabolic demands". So that does not stand up. "Increased metabolic demands" is just an unsupported ad-hoc hypothesis.

So what is actually the case with these small maniraptors? 

There are two possible explanations about how these maniraptors could be non-volant.
One is the way purported by the dino to bird theory (they are purported to be intermediate between dinosaur and Paraves). That fails because they came millions of years later.

The other is as secondarily flightless. And being secondarily flightless, they would have inherited their pneumaticity from their flying pterosaur ancestors. Their pneumaticity was to accommodate air sacs which is part of the unique breathing system that pterosaurs had and birds have.
So that explains the "postcranial pneumaticity in small-bodied maniraptorans". They were secondarily flightless.

Also see:

Tuesday, March 25, 2014

Body size and forelimb length

There are fossils of basal coelurosaur dinosaurs (eg. tyrannosaurs) and there are fossils of basal feathered flying Paraves (eg. dromaeosaurs).
The basal coelurosaurs show all the characteristics of basal coelurosaur dinosaurs.
The basal Paraves show all the characteristics of basal feathered flying Paraves.
But there is nothing in between the basal coelurosaurs and the basal Paraves. They are not related.

Let's look at body size and forelimb length.
Notice that the changes appear for the first time at the origin of Paraves (not earlier).
Mark Puttick and colleagues investigated the rates of evolution of the two key characteristics that preceded flight: body size and forelimb length.  In order to fly, hulking meat-eating dinosaurs had to shrink in size and grow much longer arms to support their feathered wings. 
"We were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," said Mr Puttick of Bristol's School of Earth Sciences.  "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps." 
Being small and light is important for a flyer, and it now seems a whole group of dozens of little dinosaurs were lightweight and had wings of one sort or another. Most were gliders or parachutists, spreading their feathered wings, but not flapping them.                                               
'High rates of evolution preceded the origin of birds' by Puttick, M.N., Thomas, G.H., and Benton, M.J. in Evolution: DOI: 10.1111/evo.12363 


Monday, March 17, 2014

Harry Govier Seeley - Pterosaurs to Birds

The idea that birds are descended from pterosaurs has an interesting history. The idea was proposed by Harry Govier Seeley. But note the negative reaction he received. Not much has changed in that respect.

Seeley was also an authority of pterosaurs, and in 1901 published a popular book on the subject, Dragons of the Air. In it, he gave an overview of animal flight, reptiles, the discovery of pterosaurs and pterosaur skeletal structure. He initially believed that birds descended from pterosaurs, but under intense criticism from his peers, backed off this assertion and argued that they shared common ancestry. "It would therefore appear from the vital community of structures with Birds, that Pterodactyles and Birds are two parallel groups, which may be regarded as ancient divergent forks of the same branch of animal life," he wrote. 

His popular book on Pterosaurs, Dragons of the Air (1901) found that birds and pterosaurs are closely parallel. His belief that they had a common origin has been proved, for both are archosaurs, just not as close as he thought.
I suggest that pterosaurs and birds are as close as Seeley thought. 

Ornithodesmus (meaning "bird link") is a genus of small, deinonychosaurian dinosaur from the Isle of Wight in England, dating to about 125 million years ago. The name was originally assigned [by Harry Govier Seeley] to a bird-like sacrum (a series of vertebrae fused to the hip bones), initially believed to come from a pterosaur. More complete pterosaur remains were later assigned to Ornithodesmus, until recently a detailed analysis determined that the original specimen in fact came from a small theropod, specifically a dromaeosaur. All pterosaurian material previously assigned to this genus has been renamed Istiodactylus.

Saturday, March 15, 2014

Comparison of characters

(Click on the links for more detail).

Basal Pterosaur: Rhamphorhynchidae
Basal Paraves: Dromaeosauridae
Basal Coelurosaur: Proceratosauridae

Basal Basal Basal
Pterosaur  Paraves  Coelurosaur
Diff Diff
Back 1 Notarium: absent (0) present (1) 0 0 0
Breathing 2 Respiratory air sacs: absent (0) present (1) 1 1 x 0
3 Breathing pump: absent (0) present (1) 1 1 x 0
4 Rib lever processes: absent (0) present (1) 1 1 x 0
Chest 5 Keeled breastbone: absent (0) present (1)  1 1 x 0
6 Furcula (wishbone): absent (0) present (1) 1 ? ?
Feather 7 Stage 2 feathers: absent (0) present (1) 1 1 x 0
8 Pennaceous feather: absent (0) present (1) 0 x 1 x 0
Foot 9 Hyperextended second toe: absent (0) present (1) 0 x 1 x 0
10 Hinge-like ankle joint: absent (0) present (1) 1 1 1
Leg 11 Thigh bone: horizontal (0) not horizontal (1) ? ? 1
Pelvis 12 Pubic bone: pointing to back (0) to front (1) downward (2) ? ? ?
13 Pubic bones: not fused (0) fused (1) 0 0 x 1
14 Acetabulum: not perforated (0)  perforated (1) ? ? 1
15 Pelvic bones: not fused (0) fused (1) 1 1 x 0
Skull 16 Beak like jaw: absent (0) present (1) 1 ? 0
17 Teeth: absent (0) present (1) 1 1 1
18 Crest: absent (0) present (1)  1 1 1
19 Neck attaches to skull; from rear (0) from below (1) 0 0 0
20 Serrated teeth: absent (0) present (1) 1 1 1
21 Semicircular canals:  expanded (0) not expanded (1) ? ? ?
Tail 22 Caudal vertebrae: less than 15 (0) greater than 15 (1) 1 1 1
23 Caudal rods: absent (0) present (1) 1 1 x 0
24 Muscle mass of M. caudofemoralis longus: small (0) large (1) 0 0 x 1
Wing 25 Strap-like scapula: absent (0) present (1) 1 1 x 0
26 Scapula orientation to backbone: subparallel  (0) parallel (1) 1 1 x 0
27 Glenoid fossa: elevated (0) not elevated (1) 0 0 x 1
28 Propatagium: absent (0) present (1) 1 1 x 0
29 Patagium: absent (0) present (1)  1 1 x 0
30 Wing membrane: absent (0) present (1) 1 x 0 0
31 Elongated 4th finger: absent (0) present (1) 1 x 0 0
32 Number of fingers: 2 fingers (2) 3 fingers (3) 4  fingers (4) 4 x 3 2/3
33 Pteroid bone/thumb: absent (0) present (1) 1 x 0 0
34 Capable of flapping flight: absent (0) present (1) 1 1 x 0
Wrist 35 Semilunate carpal: absent (0) present (1) 0 x 1 x 0
36 Proximal carpals: not fused (0) fused (1) 1 ? ?
37 Distal carpals: not fused (0) fused (1) 1 ? ?
38 Carpometacarpus: absent (0) present(1) 0 x 1 x 0
39 Angle of abduction:  less than 25% (0) greater than 25% (1) ? ? 0
General 40 Warm blooded: absent (0) present (1) 1 1 ?
41 Neural flight control system: absent (0) present (1) 1 ? 0
42 Pneumatic bones: absent (0) present (1) 1 1 x 0

Sunday, March 9, 2014

Caudal Rods (2)
In the tails of dromaeosaurids dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally.
Remember the quickly reduced neural spines, caudal ribs, and chevrons? Those all indicate that the caudal muscles of both dromaeosaurids and pterosaurs were substantially reduced.

That is very strong evidence for the pterosaur to bird theory.


The tails of pterosaurs and dromaeosaurids are so similar that, in the fossil-forging black-markets of China, the tail of one is often used to “complete” a partial skeleton of the other. Skeletal image of Rhamphorhynchus courtesy of Scott Hartman (

For comparison:


Friday, February 7, 2014

Caudal Rods (1)

Let's turn to the topic of "caudal rods" in the long-tailed pterosaurs and the dromaeosaurs:
In the tails of dromaeosaurid dinosaurs and rhamphorhynchid pterosaurs, elongate osteological rods extend anteriorly from the chevrons and the prezygapophyses. These caudal rods are positioned in parallel and are stacked dorsoventrally. The fully articulated and three-dimensionally preserved caudal series of some dromaeosaurid specimens show that individually these caudal rods were flexible, not rigid as previously thought. However, examination of the arrangement of the caudal rods in cross-section indicates that the combined effect of multiple caudal rods did provide substantial rigidity in the dorsoventral, but not in the lateral, plane. The results of digital muscle reconstructions confirm that dromaeosaurids and rhamphorhynchids also shared greatly reduced caudofemoral muscles in the anterior tail region. The striking similarities between the tails of dromaeosaurids and rhamphorhynchids suggest that both evolved under similar behavioral and biomechanical pressures. Combined with recent discoveries of primitive deinonychosaurs that phylogenetically bracket the evolution of dromaeosaurid caudal rods between two arboreal gliding/flying forms, these results are evidence that the unique caudal morphologies of dromaeosaurids and rhamphorhynchids were both adaptations for an aerial lifestyle.
Here is a link to the full pdf.

At the start, the tail skeleton of Deinonychus appears normal. Just past the hips, the neural spines, caudal ribs, and chevrons all have a typical shape and they all project to a respectable extent. But, as the tail progresses towards the tip (and it doesn’t take long) things start to get weird. The neural spines, caudal ribs, and chevrons all shrink in, with the former two disappearing entirely . . . and then come the caudal rods. Both the vertebrae and chevrons abruptly develop pairs of elongated rods of bone that project towards the hips. These rods are slender, but very long (the longest easily overlap seven other sequential vertebrae), and they split, each becoming two still thinner rods. Together, rods of the vertebrae form a quiver that virtually encapsulates the dorsal (upper) portion of the tail, and together the rods of the chevrons do the same to the ventral (lower) portion.
The tail of Deinonychus and its raptor relatives is bizarre, but it is not (as Professor Ostrom himself realized) unique. Among all known vertebrates, a similar tail anatomy has evolved in one other group. . . and now we come to why I have been allowed to spend so much time discussing dinosaurs on what is supposed to be a blog about pterosaurs.
While later and more advanced pterosaurs (like Pterodactylus) only had short, stubby tails, early pterosaurs had long ones. The caudal skeletons of these long-tailed pterosaurs (with the exceptions of the dimorphodontids and very primitive forms) are strikingly similar to that of Deinonychus. In the case of long-tailed pterosaurs, the function of the caudal rods has always seemed obvious. As flying animals, increased rigidity would have helped a tail to serve as a stabilizer or as a rudder.
It is now also possible to think a step further and consider the muscles of the tail. Let’s first try to do that in very general qualitative terms. Remember the quickly reduced neural spines, caudal ribs, and chevrons? Those all indicate that the caudal muscles of both dromaeosaurids and pterosaurs were substantially reduced.
To help consider the problem quantitatively, a technique I used was to create digital models of the tail skeleton of aVelociraptor and a Rhamphorhynchus (a pterosaur) and to sculpt the corresponding muscles over the skeletal models. The results of this modeling concur with the qualitative inference. In particular, raptors and pterosaurs were found to have very weak caudofemoral muscles (indeed, some pterosaurs may not have had caudofemoral muscles at all).
However in 2010, Scott Persons, a graduate student from the University of Alberta proposed that Tyrannosaurus's speed may have been enhanced by strong tail muscles.[108] He found that theropods such as T rex had certain muscle arrangements that are different from modern day birds and mammals but with some similarities to modern reptiles.[109]

I will post more material on this topic in the next post.