What makes a bird a bird? Everyone knows, it’s not feathers any more…)

The line between birds and theropod dinosaurs
has become increasingly fuzzy now that so many non-birds have feathers and other former bird-only traits.

This is a good sign
that evolutionary theory embraces: small changes and a gradual accumulation of traits in derived taxa.

Ultimately
it may come down to a single defining trait (like mammary glands in mammals, or alternatively a squamosal/dentary jaw joint when soft tissue is missing) when you have lots of taxa near the base of a new major clade. So what is that trait? Or what are those traits as recovered by the large reptile tree?

The basal bird and its proximal outgroup
At present the last common ancestor of all extant birds, scansoriopterygids and enantiornithes in the large reptile tree. is the Thermopolis specimen of Archaeopteryx (Fig. 1). The original authors (Mayr et al. 2007; Rauhut 2013) did not employ a phylogenetic analysis, so perhaps did not realize what they had.

For now
the pre-bird theropod, Eosinopteryx (Fig.1) nests just basal to the basal bird theropod, Archaeopteryx. You might find it interesting to see which traits differentiate the latter from the former in the large reptile tree. This list, short as it is, is by no means complete. It simply reflects the general characters used for all reptiles in the large reptile tree.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Archaeopteryx (Thermopolis) novelties vs. Eosinopteryx

  1. Frontal/parietal suture straight and > than frontal/nasal suture
  2. Metacarpals 2-3 subequal
  3. Pubis and ischium oriented posteriorly (convergent with some deinonychosaurs)
  4. Pedal 4 subequal to metatarsal 4  (convergent with some deinonychosaurs)
  5. Pedal 2.1 not > p2.2
  6. Metatarsal 5 shorter than pedal digit 5 (all vestigial, of course)
Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Unfortunately
none of these traits are unique to the bird clade.

I thought, perhaps
that an elongate and locked down coracoid (the key to the origin of flapping) would prove to be present in all basal birds. Such a coracoid is indeed present in other specimens of Solnhofen birds, but not in the Thermopolis specimen (Fig. 2), the basalmost example. 

So what we are seeing
in these six Solnhofen birds are discrete steps in the evolution of the flapping behavior, necessary for creating thrust and ultimately flight, as in many living birds. Just as in Late Jurassic pterosaurs, the island/lagoon environment of Solnhofen was as powerful an agent as the Galapagos islands at splitting basal birds into various clades.

From the Mayr et al. abstract on the Thermopolis specimen:
“We describe the tenth skeletal specimen of the Upper Jurassic Archaeopterygidae. The almost complete and well-preserved skeleton is assigned to  Archaeopteryx siemensii
 Dames, 1897 and provides significant new information on the osteology of the Archaeopterygidae. As is evident from the new specimen, the palatine of Archaeopteryx
 was tetra-radiate as in non-avian theropods, and not triradiate as in other avians. Also with respect to the position of the ectopterygoid, the data obtained from the new specimen lead to a revision of a previous reconstruction of the palate of Archaeopteryx. The morphology of the coracoid and that of the proximal tarsals is, for the first time, clearly visible in the new specimen. The new specimen demonstrates the presence of a hyperextendible second toe in Archaeopteryx*.  This feature is otherwise known only from the basal avian Rahonavis and deinonychosaurs (Dromaeosauridae and Troodontidae), and its presence in Archaeopteryx provides additional evidence for a close relationship between deinonychosaurs and avians**. The new specimen also shows that the first toe of Archaeopteryx was not fully reversed but spread medially, supporting previous  assumptions that Archaeopteryx was only facultatively arboreal*. Finally,we comment on the taxonomic composition of the Archaeopterygidae and conclude that Archaeopteryx bavarica Wellnhofer, 1993 is likely to be a junior synonym of  A. siemensii****, and Wellnhoferia grandis Elzanowski, 2001 a junior synonym of  A. lithographica***** von Meyer, 1861.”

* Actually not as prominent as in deinonychosaurs. Such a toe works just as well at climbing tree trunks as climbing dinosaur flanks.

**This may be a convergence as the two clades are separated by taxa without a hyper extensible pedal 2.

*** Perhaps facultatively able to perch, but arboreality would have been a precursor behavior.

**** These two are sisters in the large reptile tree.

***** These two are not sisters.

Other traits in the Theromopolis specimen 
visible in Figure 1 not present in the large reptile tree include the following:

  1. Smaller antorbital fenestra
  2. Longer attenuate tail
  3. Slightly narrower coracoids
  4. Slightly larger forelimb
  5. Bowed gap between ulna and radius
  6. More gracile pubis, posteriorly oriented
Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Mayr et al. looked at pedal digit 2
and noticed it was capable of hyperextension (Fig. 3). They likened it to pedal digit 2 in deinonychosaurs (Fig. 4) which is famous for its ability to elevate the ‘killer claw’.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

The large reptile tree
does not nest birds with deinonychosaurs. Rather Xiaotingia and Eosinopteryx nest between these clades. And Xiaotingia also has a similar pedal 2.1 (Fig. 5).

Figure 5. Pedal digit 2 in Xiaotiniga shows the ability to hyperextend pedal 2.2.

Figure 5. Pedal digit 2 in Xiaotiniga also shows the ability to hyperextend pedal 2.2.

On a final note:
Mayr et al. (2007) report four premaxillary teeth in the Thermopolis specimen. I think they might have missed counting the anteriormost premaxillary tooth (Fig. 6) bringing the total to five.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

References
Rauhut OWM 2013. New observations on the skull of Archaeopteryx. Paläontologische Zeitschrift 88(2)211-221.
Mayr G, Pohl, B, Hartmann S and Peters DS 2007. The tenth skeletal specimen of Archaeopteryx. Zoological Journal of the Linnean Society 149:97-116.

Reconstructing Cathayornis using DGS methodology

Updated October 23, 2015 with modifications to the ectopterygoids from data beneath the mandibles.. 

Cathayornis yandica (Zhou et al. 1992, Figs. 1-3, IVPP V9769) was an Early Cretaceous enantiornithine bird known from a virtually complete skeleton on plate and counter plate. It is crushed flat.

The best published tracings
of this specimen are shown here (Fig. 1). I wonder if you’ll agree there is too much left to the imagination in both of these professional tracings. The easy parts are correctly labeled, but I sense confusion in the more difficult details. Some of these were labeled originally with a “?”.

Figure 1. Above, Tracing of Cathayornis from Zhou and Zhang 1992. Below tracing of Cathayornis skull by O'Connor and Dyke 2010 traced using camera lucida. Some element labels are guesses. A few are mistakes.

Figure 1. Previous best efforts at tracing Cathayornis. Above, Tracing of Cathayornis from Zhou et al.  1992. Below tracing of Cathayornis skull by O’Connor and Dyke 2010 traced using camera lucida. Some element labels are guesses (See “?”). A few are mistakes.

Try DGS just once to see if it works for you.
Applying color overlays to digital images of Cathayornis (Fig. 2, 3) recovers more bones more accurately than prior efforts (Fig. 1). And these can be used in reconstructions (Fig. 3). Note the postorbital and squamosal both drifted over the right frontal. That was a surprise. Yes, a tiny postfrontal is present, not fused to the frontal. Broken bones can be identified and repaired. Even the palatal bones can be identified.

Figure 2. Cathayornis skull animated GIF. Each frame lasts 5 seconds. Here virtually all skull elements are identified and applied to the reconstruction in three views (below). Compare the results of this technique to figure 1. Note how the upper and lower jaws match curves.

Figure 2. Cathayornis skull animated GIF. Each frame lasts 5 seconds. Here virtually all skull elements are identified and applied to the reconstruction in three views (below). Compare the results of this technique to figure 1. Note how the upper and lower jaws match curves.

There is no guarantee you’re going to get things right the first time.
I don’t get things right the first time. I make changes as the interpretation runs its course. All DGS does is to remove some of the confusion inherent in the roadkill by segregating one bone after another until most – or all – of the bones are accounted for and fit the reconstruction while matching the patterns of sister taxa.

The postcrania
of Cathaysaurus is traced here (Fig. 3) and used to create a reconstruction in several views. The furcula can be traced here. Originally it was overlooked and misidentified.

Figure 3. Cathayornis tracing and reconstruction from tracing. Boxed area are ventral and rib elements originally segregated on a distinct layer and offset here for clarity. Note the green furcula, overlooked originally.

Figure 3. Cathayornis tracing and reconstruction from tracing. Boxed area are ventral and rib elements originally segregated on a distinct layer and offset here for clarity. Note the green furcula, overlooked originally. Those green bones on either side of the sternum are considered part of the sternum in traditional works. Perhaps they are, but the visible one appears to overlay the sternum, rather than be a part of it.

It may just be a matter of applied effort
When you discover something in paleontology, all you have to do is unveil it. The discovery is the big deal. Not much effort is required, but it is always appreciated. Later workers can add details with appropriate levels of support and criticism. If I had access to the specimen or a higher resolution image, perhaps the level of accuracy would increase further.

Now I’ll ask of the bird people 
what I ask of the pterosaur people. Try to build a reconstruction. It helps when you realize there are parts missing and then you can apply more effort to look for that part in the specimen itself.

If I have made any mistakes here, please bring them to my attention. I’m no bird expert, but I’m learning as I go. Here is a new image of enantiornithine birds to scale (Fig. 4) including Sulcavis, which we looked at recently.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

References
O’Connor J-K and Dyke G 2010. A Reassessment of Sinornis santensis and
Cathayornis yandica (Aves: Enantiornithes). Records of the Australian Museum 62: 7-20.
Zhou Z.-H, Fan F-J and Zhang J 1992.
Preliminary report on a Mesozoic bird from Liaoning, China. Chinese Science Bulletin 37: 1365-1368.

Sulcavis – an enantiornithes bird without a sternum

Figure 1. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Figure 1. Click to enlarge. Pre-bird and bird sternae. Note the replacement of the sternum with gastralia in Sulcavis.

Ever since the advent
of the dual sternae in Velociraptor and kin, and of the single sternum in Archaeopteryx (Fig. 1), most birds had/have an ossified sternum. One exception is the enantiornithine bird, Sulcavis (Fig. 1-4).

Sulcavis geeorum (O’Connor et al. 2013, Early CretaceousBMNH Ph-000805) is a robin-sized enantiornithes with a relatively small skull and, remarkably, no sternum. Teeth with grooved enamel radiating from the tips gave it its name (sulcus = groove). That was seen as the most distinctive feature. A sternum replaced by gastralia was not considered an issue (see below).

Soft tissue
Although the specimen includes some soft tissue, O’Connor et al. report one pubis missing and another present only proximally. The ischium was reported missing. My examination identifies areas were both pubes (green) and ischia (magenta) used to be (Fig. 2).

Figure 1. Sulcavis in situ with GIF animation original tracing from O'Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan).

Figure 2. Sulcavis in situ with GIF animation original tracing from O’Connor et al. in black and white. Colors identify elements originally reported as missing. Pubis (green), ischium (magenta), ilium (cyan). Reconstruction in figure 2. A proximal ischium was mislabeled a sacral rib.

Enantiornithes are like basal birds
except for the following traditional traits listed by O’Connor et al. 2013 :

  1. Pygostyle proximally forked and distally constructed with ventrolateral processes
  2. Furcula Y-shaped and dorsolaterally excavated
  3. Coracoid with convex lateral margin
  4. Proximal humerus rises dorsally and ventrally to centrally on the concave head
  5. Metacarpal 3 longer than mc2
  6. Distal tarsals fused to metatarsals, but metatarsals unfused distally
Figure 2. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum.

Figure 3. Sulcavis reconstruction. PILs on foot. Note the lack of a sternum. The pedal ungual length and curvature indicate an arboreal lifestyle.

Unfortunately, none of theses traits are listed as characters in the large reptile tree, yet Sulcavis nests with Cathayornis sharing the following traits distinct from other birds:

  1. Skull not shorter than cervicals
  2. Posterior quadrate straight
  3. More than 4 premaxillary teeth
  4. Posterior mandible deeper anteriorly
  5. Retroarticular descends
  6. Metatarsals 2-3 aligned with 1
  7. Pedal 2.2 > p2.1

More pertinent taxa would reduce this list.

Figure 3. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below).

Figure 4. Sulcavis skull as originally interpreted (above) and traced using the DGS method (middle) to create a reconstruction (below). Note, several bones here were not originally identified. It looks possible that a substantial mandibular fenestra might have been present.

Due to the contrived problem
of digit identification in birds and bird-like theropods described and falsified here, O’Connor et al. describe the three manual digits as the

  1. alular digit
  2. major digit
  3. minor digit

Such renaming of digits 1-3 is totally unnecessary.

Re: The sternum
O’Connor et al. report, “No direct information regarding the morphology of the sternum is preserved.” That’s because there is no sternum in this taxon (Figs, 1, 2). The gastralia run right up to the coracoids. So, does this taxon appear to demonstrate how the sternum in enatiornithine birds is formed? Yes, by enlarging and fusing the gastralia, not as a new single, complete bone.

Sternae also appear in dromaeosaurs and oviraptors by convergence. Twin sternae in these taxa do not appear to be homologous with the single sternum of birds. A single sternum originates as a small bone, wider than long followed by a long set of gastralia extending to the pubis, distinct from large twin sternae.

References
O’Connor JK, Zhang Y, Chiappe LM, Meng Q, Quanguo L, Di L 2013. A new enantiornithine from the Yixian Formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology 33(1):1-12.

One key fact overturns a bizarre interpretation steadily gaining steam

Figure 1. Jim Clark putting his best interpretive spin on the weird vestigial hand of Limusaurus. Click to play.

Figure 1. Jim Clark putting his best interpretive spin on the weird vestigial hand of Limusaurus. Click to play.

I ran across this YouTube video featuring Dr. Jim Clark talking about his then new ceratosaur dinosaur, Limusaurus, which we looked at earlier here. Clark addresses the importance of the hand of Limusaurus, which he claims with admirable confidence that this was a ‘transitional’ theropod that demonstrates how digit 1 was lost, digit 2 took on the appearance of digit 1, digit 3 took on the appearance of digit 2 and so on. That’s called a ‘phase shift’ as one digit takes on the identify of the one next to it and it is gaining wide acceptance, despite its bizarre premise.

That same hypothesis
is echoed here online at the Varagas Lab and it is becoming the standard paradigm on theropod hands. As an example, the recent paper on Haplocheirus labeled the three manual digits 2, 3 and 4.

This all started
with a report on chicken embryo hands by Thulborn and Hamely (1984), Thulburn (1993) and Burke and Feduccia (1997). Before then everyone labeled the three digits of theropod hands, 1, 2 and 3, which was eminently  logical. Shortly after the Burke and Feduccia study workers struggled against the new hypothesis, but recently (following the publication of Limusaurus) have rallied to support this hypothesis in papers appearing online here and here and here.

Let’s remind ourselves
Alan Feduccia has a vested interest in separating birds from dinosaurs.

This isn’t the first time Occam’s razor was ignored.
We’ve already seen several very odd paradigms arise in paleontology. A forelimb launch for giant pterosaurs is one such boondoggle. The extra bone in the wing of Yi qi is another. The nesting of Vancleavea and pterosaurs with archosauriformes are yet other examples. There are dozens of others. The theropod finger ‘phase shift’ is one more false paradigm that keeps spreading and needs to be stopped.

As discussed earlier, chicken embryos develop an extra medial finger as embryos. This finger bud ultimately disappears by the time of hatching. It is a relic from our basal tetrapod ancestry, from a time when our ancestors had six or more fingers. This has nothing to do with the normal count of five fingers in all post-Devonian tetrapods. We all develop through an embryonic stage when our hands are webbed mittens. In only one adult animal that we know of, Limusaurus, did this extra medial finger appear in an adult — and only because the hand of Limusaurus is a tiny vestige that stopped developing normally. Essentially it’s an embryo hand that retained the medial bud.

This one key fact
has been overlooked by other workers who have flocked to the ‘phase shift’ hypothesis. Which is the simpler explanation: 1) all the fingers suddenly appear like their neighbor finger, changing phalanx counts, or 2) an embryonic bud appears then disappears before hatching.

There is always a simple explanation
for every seemingly magical event or paleontological problem. The six-fingered ancestry of chickens is a key fact overlooked by modern theropod paleontologists who apparently are content to just count the fingers. Sometimes it’s not what you see that counts, but what experience you bring to what you see that trumps logic-busting arguments.

In theropods, what you see is what you get.
Fingers 1, 2 and 3 are indeed fingers 1, 2 and 3. In embryos you may see another medial digit, but it’s not homologous with the medial digit in any other tetrapod, except Limusaurus, as noted above. There is no phase shift of theropod fingers.

References
Burke AC and Feduccia A 1997. Developmental patterns and the identification of homologies in the avian hand. Science 278: 666–668.
Thulborn RA and Hamley TL 1984. ON the hand of Archaeopteryx. Nature 311:218.
Thulborn RA 1993. A tale of three fingers: Ichnological evidence revealing the homologies of manual digits in theropod dinosaurs. New Mexico Museum of of Natural History and Science Bulletion 3:461-463.

Triassic? No, Eocene Bird Tracks: How to Fix a Mistake in “Nature”

The whole point of this post is to show that sometimes scientists AND referees make mistakes. This one (see below) the authors corrected themselves, likely after catching hell from colleagues for the last 11 years. The referees are probably glad to retain their anonymity.

Figure 1. Bird tracks originally considered Latest Triassic, now considered Eocene, from Argentina.

Figure 1. Bird tracks originally considered Latest Triassic, now considered Eocene, from Argentina.

It all started a decade ago
when Melchor, De Valais and Genise (2002) reported very bird-like tracks in Latest Triassic sediments in Argentina. This was deemed worthy of the academic journal Nature because, if valid, this would have pushed the origin of birds, or bird-like dinosaurs, back from the Latest Jurassic to the Latest Triassic. A very hot topic! Respected paleontologist referees gave this the green light and it was published.

However, recently this paper was retracted.

Here’s the apologetic abstract
from Melchor, De Valais and Genise (2013) 

“Bird-like tracks from northwest Argentina have been reported as being of Late Triassic age. They were attributed to an unknown group of theropods showing some avian characters. However, we believe that these tracks are of Late Eocene age on the basis of a new weighted mean 206Pb/238U date (isotope dilution–thermal ionization mass spectrometry method) on zircons from a tuff bed in the sedimentary succession containing the fossil tracks. In consequence, the mentioned tracks are assigned to birds and its occurrence matches the known fossil record of Aves.”

Hopefully apologies have been accepted worldwide.
These three “came clean” and made their mistake known and I’m sure all three will continue to make important contributions to paleontology.

Unfortunately
Some scientists do not accept apologies or corrections. Some rifle through trash for rejected ideas so they can pillory others. Some scientist can not accept their own mistakes. Some scientists reject solutions to problems by labeling them, “highly idiosyncratic (= a mode of behavior or way of thought peculiar to an individual)” just because they have new ideas not preciously considered by others. These are the scientists who are gumming up the works.

There are several papers that have been rejected by referees clinging to the status quo that solve several enigmas and clear up several mysteries using established scientific methods. Several of those rejections from referees who are “gumming up the works” provided the reason for this blog and reptileevolution.com.

References
Melchor RN, De Valais S and Genise JF 2002. Bird-like fossil footprints from the Late Triassic. Nature 417, 936–938 (2002)
Melchor RN, De Valais S and Genise JF 2013. A late Eocene date for Late Triassic bird tracks. Nature 495, E1–E2 (21 March 2013) doi:10.1038/nature11931

Eosinopteryx – part 1 – Feathers, but no flapping

Updated October 23, 2015 with a new skull.

Eosinopteryx brevipenna (Godefroit et al. 2013, Middle-Late Jurassic, Tiaojishan Formation) is represented by a new complete skeleton. It was a feathered theropod dinosaur about 30 cm long. The forelimb feathers were quite long (Fig. 1), but the tail feathers were not.

Paravian? or Preavian?
We’ve been looking for a feathered theropod without elongated coracoids to precede Archaeopteryx. We also need this taxon to be not pre-oviraptorid or pre-alvarezsaurid. The authors argue, with a very extensive phylogenetic analysis, that this is a troodontid resembling Anchiornis, with less extensive feathers on the hind limbs and tail. Anchiornis greatly resembled Archaeopteryx and is, therefore, closely related. Of that, there is no doubt.

Why There is Doubt
I have not created a competing analysis. Checking out Greg Paul’s figure of Anchiornis (Paul 2010), I note his Anchiornis has the short torso and elongated coracoid also seen in Archaeopteryx, troodontids and deinonychosaurs. On October 23, 2015 I added Eosinopteryx to the large reptile tree where it nests between Aurornis and Archaeopteryx as the last theropod that was not a bird. 

Figure 1. Eosinopteryx reconstructed in lateral view. Soft tissue impressions preserved on the fossil are represented here in gray. Note the small size of the coracoid (yellow) and its curved lower rim, which indicates this specimen was a pre-flapping dinosaur. Pedal digit 2 was not modified as a “killing” claw. Elements figured with DGS.

Figure 1. Eosinopteryx reconstructed in lateral view. Soft tissue impressions preserved on the fossil are represented here in gray. Note the small size of the coracoid (yellow) and its curved lower rim, which indicates this specimen was a pre-flapping dinosaur. Pedal digit 2 was not modified as a “killing” claw. Elements figured with DGS.

What sets Eosinopteryx apart from these?
A short coracoid with a broad curved ventral rim – Therefore Eosinopteryx did not flap and was not descended from flappers. We haven’t seen a terrestrial descendant of Archaeopteryx yet without elongated coracoids. For more on this, compare Huaxiagnathus (with its short coracoid) to Velociraptor, (with its long, tall coracoid). Otherwise these two greatly resemble one another, with the former lacking sternal plates, a retroverted pubis and caudal rods. These traits are also lacking in Eosinopteryx.

A relatively smaller skull – Much smaller than in Anchiornis.

A relatively longer torso – Much longer than in Anchiornis.

A relatively shorter pubis – Much shorter than in Anchiornis.

All these traits are primitive for theropods.

Unfortunately, 
Huaxiagnathus
 was not included in the analysis of Godefroit et al. (2013). Neither were oviraptorids or alvarezsaurids. Eosinopteryx
needs to be compared to these missing basal taxa along with the other taxa they previously tested. Once that’s done, let’s see if the topology of the tree doesn’t shift Eosinopteryx down below (more primitive than) Archaeopteryx. 

Addendum: The analysis of Godefroit et al. (2013) was based on and provided only a segment of an earlier analysis that DID include these more primitive taxa. Thus my doubt is reduced somewhat as all pertinent taxa were included.  Even so, I wonder why these two “sisters” don’t look more alike.

If anyone has details on why Godefroit et al. 2013 said the “bone structure would have limited its ability to flap its wings,” I’d like to see it.

Interesting that this birdy topic just came up a few days ago with Mahakala. Reminds me to be careful what I wish for.

References
Godefroit P, Demuynck H, Dyke G, Hu D, Escuillié FO and Claeys P. 2013. Reduced plumage and flight ability of a new Jurassic paravian theropod from China. Nature Communications 4: 1394. doi:10.1038/ncomms2389
Paul GS 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press 320 pp.

wiki/Eosinopteryx

Tiny Prehistoric Birds and Pterosaurs

Just a quick note. 
This blog is all about putting taxa together that don’t usually — or never — get together. Here I’ll just present a few birds and pterosaurs at the small end of the scale.

Small prehistoric birds and pterosaurs.

Figure 1. Small prehistoric birds and pterosaurs. From left to right, Sinornis, Cathayornis, No. 6 and No. 12 from the Wellnhofer (1970) catalog of “pterodactyloids.”

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.

Size-wise, the tiny birds were not considered juveniles, but the pterosaurs were. Phylogenetic analysis illustrates the uniqueness of the two small pterosaurs. They cannot be matched to any larger adults that are phylogenetically close. Rather they are parts of a phylogenetic sequence of other tiny pterosaurs descending from larger forms and leading toward larger forms.

With regard to the tiny pterosaurs, I sense prejudice here. Just like tiny birds, let’s give them full adult rights and add them to a few new analyses to test the large pterosaur tree topology.

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.

References
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.