Putting together a juvenile Sapeornis with fantastic feathers!

Two specimens attributed to Sapeornis, that nest together in the LRT. IVPPP V13276 is larger and more robust. DNHM-F3078 has a juvenile bone texture. Gao et al 2012 considered these two conspecific.

Two specimens attributed to Sapeornis, that nest together in the LRT. IVPPP V13276 is larger and more robust. DNHM-F3078 has a juvenile bone texture. Gao et al 2012 considered these two conspecific.

Sapeornis chaoyangensis (Zhou and Zhang 2002. 2003; Early Cretaceous; IVPP V13276) is a basal ornithurine bird, the clade that gave rise to modern birds. The short tail was tiped with a pygostyle. The coracoids were wide and relatively short. Manual digit 3 is a vestige. The claws on the remaining digits are all raptorial.

Another specimen, 
DNHM-F3078
 (Gao et al. 2012 (Figs 1, 2)  was smaller, considered a juvenile based on bone texture. It lived 3-5 million years earlier and had a pubic boot. It nests with the IVPP specimen in the LRT.

Figure 2. The DNHM specimen is wonderfully preserved. Note the incredible feathers! Here a little Photoshop digitally segregates the bones from each other and the matrix, then reassembles then in a lifelike pose.

Figure 2. The DNHM specimen is wonderfully preserved. Note the incredible feathers! Here a little Photoshop digitally segregates the bones from each other and the matrix, then reassembles then in a lifelike pose.

As a reminder…
None of these sapeornithid birds had an ossified sternum.

References
Gao C, Chiappe LM, Zhang F, Pomeroy DL, Shen C, Chinsamy A and Walsh MO 2012. A subadult specimen of the Early Cretaceous bird Sapeornis chaoyangensis and a taxonomic reassessment of sapeornithids. Journal of Vertebrate Paleontology. 32(5): 1103–1112.
Zhou Z and Zhang F-C 2003. 
Anatomy of the primitive bird Sapeornis chaoyangensis from the Early Cretaceous of Liaoning, China. Canadian Journal of Earth Sciences 40(5): 731–747.

wiki/Sapeornis

 

 

Let’s talk about the pygostyle in birds

…because Wang and O’Connor 2017 just wrote a paper on pygostyle evolution.

From their abstract: “The transformation from a long reptilian tail to a shortened tail ending in a pygostyle and accompanied by aerodynamic fanning rectrices is one of the most remarkable adaptations of early avian evolution. All birds with a pygostyle form a monophyletic clade, the Pygostylia (Chiappe, 2002), which excludes only the long bony-tailed birds, Archaeopteryx and the Jeholornithiformes (Jeholornis and kin).”

Key thought from their abstract: “There further exist distinct differences in pygostyle morphology between Sapeornithiformes, Confuciusornithiformes, Enantiornithes, and Ornithuromorpha.”

Figure 1. Flawed theropod cladogram according to Wang and O'Connor 2017 based on Brusatte 2014.

Figure 1. Flawed theropod cladogram according to Wang and O’Connor 2017 based on Brusatte 2014. This cladogram suffers from taxon exclusion and so tells us little about pygostyle evolution.  Only one clade here has a pygostyle. See figure 2 for more data.

Wikipedia reports, “The pygosylians fall into two distinct groups with regard to the pygostyle. The Ornithothoraces have a ploughshare-shaped pygostyle, while the more primitive members had longer, rod-shaped pygostyles. The earliest known member of the group is the enantiornithine species Protopteryx fengningensis, from the Sichakou Member of the Huajiying Formationof China, which dates to around 131 Ma ago,”

Figure 2. Subset of the LRT focusing on derived theropods. Those with a pygostyle are colored.

Figure 2. Subset of the LRT focusing on derived theropods. Those with a pygostyle are colored. Among birds, gray taxa have a distal fusion, as do other very derived non-bird taxa, some of which are not included here. Wnag and O’Connor apparently did not test several Solnhofen birds and so did not understand the basal division of bird clades that occurred  among the ‘Solnhofen birds’  shown here.

 

Wang and O’Connor correctly note
that some derived therizinosaurs and ovitrapotorsaurs have distal caudal vertebrae that are fused after a long string of unfused verts. Not correctly they consider this the first of many evolutionary steps toward the completely fused pygostyle of extant birds. A subset of the large reptile tree (LRT, figure 2) documents three origins for the pygostyle in Avialan taxa and a few other aborted attempts in other clades.

If only Wang and O’Connor
had used a half-dozen Solnhofen birds (they can’t ALL be Archaeopteryx) in their study they would have found the multiple convergent evolution of the pygostyle in basal Aves. Once again, taxon exclusion is keeping the blinders on paleontologists.

Wang and O’Connor do not recover
Sapeornis as a basal Ornithourmorph. The write: “Despite published diversity, the Sapeornithiformes is considered a monospecific clade with all taxa referable to Sapeornis chaoyangensis.

Wang and O’Connor were very interested in
Caudipteryx, traditionally considered a basal member of the Oviraptorosauria. It now nests with Limusaurus, or closer yet, the ‘juvenile’ Limusaurus, a sister to the oviraptorid, Khaan. It lacks a pygostyle, but has a fan of tail feathers.

Wang and O’Connor conclude “Fusion or partial fusion of the terminal caudal vertebrae in maniraptorans is observed in the Therizinosauroidea, Oviraptorosauria and potentially also the Scansoriopterygidae. However, morphological differences between these phylogenetically separated taxa indicate these co-ossified structures cannot be considered equivalent to the avian pygostyle. Outside the Ornithuromorpha, no group preserves evidence of a tail complex.”

Scatter diagrams of pygostyle traits provided by Wang and O’Connor
(their figure 7) also show four clades of rarely and then barely overlapping data. The vast majority is non-overlapping data as the pygostyle really did evolve several times within Aves.

Notably the bird mimics
Microraptor and Sinornithosaurus, both closer to T-rex and Orinitholestes than to birds, have no trace of a pygostyle.

References
Chiappe LM 2002. Basal bird phylogeny: problems and solutions. In: Chiappe L M, Witmer L eds. Mesozoic Birds: Above the Heads of Dinosaurs. Berkeley: University of California Press. 448–472.
Wang W and O’Connor JK 2017. Morphological coevolution of the pygostyle and tail feathers in Early Cretaceous birds. Vertebrata PalAsiatica 2017:10: 55:3: 1-26.

wiki/Pygostylia

Another look at Microraptor

As reported earlier
the theropod community is not happy with the large reptile tree nesting of Yutyrannus with Allosaurus (see discussion yesterday). Today we’ll look at the heretical (non-traditional) nesting of Microraptor with Compsognathus (Fig. 1).

The traditional nesting of Microraptor
is with other ‘raptors’, like Velociraptor (Fig. 1). By contrast, the large reptile tree nested Microraptor between Compsognathus and Sinornithosaurus, and not far from Tianyuraptor at the base of the Tyrannosaurus clade.

Figure 3. Provisional sisters to Microraptor (middle) now include Compsognathus (above) and Velociraptor (below). Which ones appears to share more traits with Microraptor?

Figure 3. Provisional sisters to Microraptor (middle) now include Compsognathus (above) and Velociraptor (below). Which ones appears to share more traits with Microraptor?

 

Figure 2. Skull of Microraptor (color, middle) compared to Compsognathus (above) and Velociraptor (below). The two skulls that resemble each other more are more closely related.

Figure 2. Skull of Microraptor (color, middle) compared to Compsognathus (above) and Velociraptor (below). The two skulls that resemble each other more are more closely related.

The following traits
are shared between Microraptor with Compsognathus to the exclusion of Velociraptor in the large reptile tree, a study that includes a wide gamut of reptiles, not just theropods.

  1. lacrimal not deeper than maxilla
  2. narial opening dorsolaterally
  3. naris at snout tip, not elevated
  4. frontal separated from upper temporal fenestra
  5. posterior parietal 20-40º
  6. jaw joint descends
  7. caudal transverse processes present beyond eighth caudal
  8. Mc2-3 align at or beyond m1.2
  9. Mt2-3 align with p1.1

Of course
there is also a list of traits shared between Compsognathus and Velociraptor to the exclusion of Microraptor. And indeed there is also a list of traits linking Microraptor to Velociraptor to the exclusion of Compsognathus. 

Look at that face!
If you had to lump and split Compsognathus, Microraptor and Velociraptor based just on the skull alone (Fig. 2), which two would you lump together?

Feathers
The presences of extensive feathers on all four limbs of Microraptor — not in the direct ancestry of extant birds — points to a possible convergent evolution in this clade… OR more extensive (bit not preserved) feathers in a last common ancestor, like Compsognathus.

The presence of only protofeathers
in the contemporaneous Sinosauropteryx indicates a likely reduction in plumage in that short-legged taxon, slightly off the main line of bird evolution represented by Archaeopteryx of the Late Jurassic. Previously (Ji and Ji 1996) Sinosauropteryx was considered the basalmost taxon with the basalmost protofeathers. Not so both chronologically and phylogenetically.

Figure 2. Sinosauropteryx fossil.

Figure 3. Sinosauropteryx fossil. Apparently the presence of simple feathers here is derived from or a reversal of more primitive taxa with more extensive, more derived feathers according to its place on the large reptile tree. This dinosaur appears to be the Early Cretaceous analog to our extant squirrels in its niche and appearance.

 

References
Ji Q and Ji S-A 1996. On the Discovery of the earliest fossil bird in China (Sinosauropteryxgen. nov.) and the origin of birds. Chinese Geology 233:30-33.
Ostrom JH 1978. The osteology of Compsognathus longipes. Zitteliana 4: 73–118.
Osborn HF 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs. Bulletin of the AMNH (New York City: American Museum of Natural History) 21 (14): 259–265.
Osborn HF 1924. Three new Theropoda, Protoceratops zone, central Mongolia”. American Museum Novitates 144: 1–12.
Ostrom JH 1970. Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana. Bulletin of the Peabody Museum of Natural History 35: 1–234.
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.
Xing L, Persons WS, Bell PR, Xu X, Zhang J-P, Miyashita T, Wang F-P and Currie P 2013. Piscivery iin the feathered dinosaur Microraptor. Evolution 67(8):2441-2445.
Xu X, Zhou Z, Wang X, Kuang X, Zhang F and Du X 2003. Four-winged dinosaurs from China. Nature, 421: 335–340.

wiki/Tyrannosaurus
wiki/Compsognathus
wiki/Microraptor
wiki/Velociraptor
wiki/Sinosauropteryx

The Compsognathus-Tyrannosaurus clade to scale

There has been a recent rise in interest
in the new nestings of the theropods recovered here, here, here and here. The present post provides a summary of images and traits from the large reptile tree (Fig. 1).

Figure 1. Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Figure 1a. A more recent (2018) clade of Theropoda updated with more taxa. 

Figure 1. Latest cladogram of the Theropoda, including the Compsognathus-Tyrannosaurus clade.

Figure 1b. 2015 cladogram of the Theropoda, including the Compsognathus-Tyrannosaurus clade.

The large reptile tree 
nests Compsognathus at the base of a clade that includes Microraptor, Sinornithosaurus, Tianyuraptor, Zhenyuanlong and Tyrannosaurus (Fig. 2). The middle taxa (above) are traditionally considered dromaeosaurs and indeed nest with dromaeosaurs in very large cladograms focused on theropods (Cau et al. 2015).

Figure 2. Taxa in the Compsognathus/Tyrannosaurus clade, a subset of the large reptile tree to scale. Also included are Microraptor, Sinornithosaurus, Dilong and Zhenyuanlong.

Figure 2. Taxa in the Compsognathus/Tyrannosaurus clade, a subset of the large reptile tree to scale. Also included are Microraptor, Sinornithosaurus, Tianyuraptor and Zhenyuanlong.

Unfortunately
the large reptile tree does not confirm many of the nestings recovered by the Cau et al. study, which employed many more taxa and characters specific to theropods (to their credit), not generalized to all reptiles. They also did not create reconstructions of included taxa, so the researcher has to look at their character scores to confirm validity. Sometimes a picture streamlines difficult tasks like this. Cau eta al updated the matrix of Lee et al. 2014 (which included two of the former authors). So they didn’t have to examine each taxon, nor photographs or drawings of each and every taxon. Likely they accepted most of the data as correct — which it indeed may be. But in Science, remember, EVERYTHING is provisional, even what you read and see here.

The Cau et al. study
nested Archaeopteryx (as only one taxon) basal to Xiaotingia, Rahonavis and Balaur. By contrast the large reptile tree nests these taxa basal to six specimens of Archaeopteryx, each basal to distinct derived avian clades

Distinct from other theropods
(in the large reptile tree), this clade (Fig. 2) shares the following traits:

  1. skull not shorter than cervicals
  2. lateral rostral shape convex, smooth curve (reversed in T)
  3. frontals separated from upper temporal fenestrae (reversed in Z and T)
  4. procumbent premaxillary teeth (reversed in S and T)
  5. ventral mandible convex anteriorly, concave posteriorly (reversed in T)

The Tianyuraptor/Zhenyuanlong/Tyrannosaurus clade
shares the following traits:

  1. snout occiput length not less than half the presacral length
  2. dorsal nasal shape triangular, wider anteriorly
  3. ventral premaxilla tilted up
  4. orbit not larger than antorbital fenestra
  5. parietal skull table strongly constricted
  6. quadratojugal hourglass shaped
  7. posterior mandible deeper anteriorly
  8. midcervical centrum taller than long
  9. cervical size decreases cranially
  10. cervicals parallelogram shaped in lateral view
  11. anterior chevrons parallel to centra (reversed in T)
  12. pedal 4 length sub equal to mt4

Of course
these and many other traits are shared with other taxa by convergence. As always, it is the suite of traits that nests taxa.

Figure 3. Bird origins. Apparently the four-winged micro raptors were no in the direct line of living birds.

Figure 3. Bird origins. Apparently the four-winged microraptors were no in the direct line of living birds.

 

Figure 4. Sinornithosaurus (holotype) pelvis. Note the pubis is oriented ventrally, then curves posteriorly.

Figure 4. Sinornithosaurus (holotype) pelvis. Note the pubis is oriented ventrally, then curves or angles posteriorly.

The Sinornithosaurus pelvis
is indeed similar to that of Velociraptor pelvis (Fig. 3). Similar, yes, but also distinct in morphology.

I’m just reporting results
and they appear (Fig. 2) that make a certain amount of sense. There’s no reason to criticize a worker for methodology. If specific mistakes are found, please alert the author.

Let’s find common ground and figure this out.

References
Cau et al. 2015. The phylogenetic affinities of the bizarre Late Cretaceous Romanian theropod Balaur bondoc (Dinosauria, Maniraptora): dromaeosaurid or flightless bird? PeerJ 3:e1032; DOI 10.7717/peerj.1032

Lee MSY, Cau A, Naish D, Dyke GJ. 2014. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds. Science 345(6196):562–566. DOI 10.1126/science.1252243.

Guanlong and Dilong: basal allosaurs, not basal tyrannosaurs

I thought more taxa
would help the present shifting of taxa from their original designations, seen here, here and here.

Figure 1. Guanlong reconstructed by moving elements tracing Xu et al. 2006.

Figure 1. Guanlong reconstructed by moving elements tracing Xu et al. 2006. The robust foot and small skull are notable.

Giuanlong wucaii (Xu et al. 2006, Late Jurassic, China, 3m long) was originally considered a basal tyrannosauroid. An adult (IVPP V14531) and a more complete juvenile (IVPP V14532) are known. The adult had an elaborate medial nasal head crest. The juvenile had  a smaller crest restricted to the anterior.

Figure 1. Theropod cladogram. With the addition of Guanlong and the identification of prior errors, the nesting of the microraptors separates from the tyrannosaurs, but Guanlong nests with Sinocalliopteryx, Allosaurus and Yutyrannus, not tyrannosaurs.

Figure 2. Theropod cladogram. Guanlong nests with two other putative tyrannosaurs, Dilong and Yutyrannus, along with feathered Sinocalliopteryx and Allosaurus.

Here Guanlong nests
in the large reptile tree (Fig. 1) at the base of the Allosaurus clade, not the T-rex clade. But note the Allosaurus clade nests at the base of the T-rex clade. Remember I’m using generalized traits to lump and separate my taxa, not traits specific to theropods.

According to Xu et al. 2006
traits Guanlong shares with tyrannosauroids largely exclusive of other theropods include:

  1. large foramina on the lateral surface of the premaxilla
  2. tall premaxillary body
  3. fused nasals
  4. a large frontal contribution to the supratemporal fossa
  5. a pneumatic jugal foramen in the posterior rim of the antorbital fossa
  6. a deep basisphenoidal sinus with large foramina
  7. a subcondylar recess on the basisphenoid
  8. the supraoccipital excluded from the foramen magnum
  9. the short retroarticular process
  10. the relatively small, U-shaped premaxillary teeth that are arranged in a row more transversely than anteroposteriorly oriented
  11. and labio-lingually thick maxillary and dentary teeth
  12. Striking tyrannosauroid pelvic features include an ilium subequal to femoral length, a distinctive dorsal concavity on the pre-acetabular process, a supracetabular crest that is straight in dorsal view, a prominent median vertical crest on the lateral surface of the ilium, a concave anterior margin of the pubic peduncle, a pubic tubercle close to the dorsal part of the pubic shaft, an extremely large pubic boot (55% of pubic length), and a thin sheet of bone extending from the obturator process down the ischial shaft

None of these are character traits listed in the large reptile tree. The authors note, “Guanlong represents a specialized lineage in the early evolution of tyrannosauroids.”

Figure 2. The CM 31374 specimen of Coelophysis.

Figure 3. The CM 31374 specimen of Coelophysis. The long snout becomes progressively shortened in the Guanlong/Dilong clade.

The unusually long snout of Guanlong
might appears to be elongated in order to support a larger crest. The authors note, “Cranial horns, bosses and crests are present in many non-avian theropods and are best exemplified by Dilophosaurus, Monolophosaurus and oviraptorids, among others.” However, Guanlong is also derived from a sister to Coelophysis, which also had a longer rostrum and similar proportions.

Figure 4. Dilong paradoxus. Images from Xu et al. 2004. Colors added.

Figure 4. Dilong paradoxus. Images from Xu et al. 2004. Colors added.

Dilong paradoxus (Xu et al., 2004 TNP01109) Early Cretaceous ~125 mya, 2.75 m in length, was also originally considered a basal tyrannosauroid. In the large reptile tree (Fig. 2) it is derived from a sister to Guanlong at the base of the Allosaurus/Sinocalliopteryx clade. Dilong was larger than Guanlong and covered with feathers or protofeathers. Here the snout is shorter still.

None of these taxa 
are known to have stiff wing feathers as seen in the tyrannosaurs, like Zhenyuanlong, and later clades leading to birds.

References
Xu X, Clark JM, Forster CA, Norell MA, Erickson GM, Eberth DA, Jia C and Zhao Q 2006. A basal tyrannosauroid dinosaur from the Late Jurassic of China” (PDF). Nature 439 (7077): 715–718.
Xu X, Norell MA, Kuang X, Wang X, Zhao Q, Jia C 2004. Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroid (PDF). Nature 431 7009: 680–684.

wiki/Dilong_paradoxus

Zhenyuanlong: Dromaeosaur? No. Tyrannosaur with wings? Yes.

Lü and Brusatte 2015
described a short-armed, winged Early Cretaceous Liaoning theropod, Zhenyuanlong suni (Fig. 1, JPM-0008 Jinzhou Paleontological Museum), as a dromaeosaur. Their published phylogenetic analysis included only dromaeosaurs but their text indicates a large inclusion set.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3.

Figure 1. Zhenyuanlong in situ with colors applied to bones and feathers. These colors are transferred to create the reconstruction in figure 3. The pelvic elements are reconstructed at right. The manus and pes are reconstructed at left.  Scale bars are 10cm.

From the Lü and Brusatte text
“We included Zhenyuanlong in the phylogenetic dataset of Han et al., based on the earlier analysis of Turner et al, which is one of the latest versions of the Theropod Working Group dataset. This analysis includes 116 taxa (two outgroups, 114 ingroup coelurosaurs) scored for 474 active phenotypic characters. Following Han et al., characters 6, 50, and 52 in the full dataset were excluded, 50 multistates were treated as ordered, and Unenlagia was included as a single genus-level OTU. The analysis was conducted in TNT v1.142 with Allosaurus as the outgroup.”

I reconstructed this theropod,
from published photographs (Figs. 1, 2) using (DGS digital graphic segregation), added it to the large reptile tree and found that it nested between tiny Compsognathus and gigantic Tyrannosaurus rex. Of course, Zhenyuanlong had the opportunity to nest with several dromaeosaurs, but it did not do so.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated.

Figure 2. Skull of Zhenyuanlong in situ, as originally traced, colorized with skull, palate and mandible segregated. Original quadrate may be a quadratojugal.

When you look at the reconstruction,
(Fig. 3) the similarity to T. rex becomes immediately apparent… except for those long feathered wings, of course.

I’ll run through several of the traits that link
Zhenyuanlong to Tyrannosaurus to the exclusion of dromaeosaurs here. It’s a pretty long list. Even so, if you see any traits that should not be listed, let me know and why.

  1. skull not < cervical series length
  2. skull not < half the presacral length
  3. premaxilla oriented up
  4. lacrimal not deeper than maxilla
  5. naris dorsolateral
  6. naris at snout tip, not displaced dorsally
  7. orbit length < postorbital skull
  8. orbit not > antorbital fenestra
  9. orbit no > lateral temporal fenestra
  10. orbit taller than wide
  11. frontal with posterior processes
  12. posterior parietal inverted ‘B’ shape
  13. jugal posterior process not < anterior
  14. parietal strongly constricted
  15. quadratojugal right angle
  16. majority of quadrate covered by qj and sq
  17. postorbital extends to minimum parietal rim
  18. maxillary teeth at least 2x longer than wide
  19. mandible tip rises
  20. angular not a third of mandible depth
  21. retroarticular process expands dorsally and ventrally
  22. cervicals taller than long
  23. cervicals decrease cranially
  24. mid cervical length < mid dorsal
  25. caudal transverse processes present beyond the 8th caudal
  26. humerus/femur ratio < 0.55
  27. metacarpals 2 & 3 do not align with manual one joints
  28. pubis angles ventrally – not posteriorly
  29. 4th trochanter of femur sharp
  30. metatarsals 2 & 3 align with p1.1

Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge.

Figure 3. Zhenyuanlong reconstructed in lateral view. Something behind the pelvis could be the remains of an egg, but needs further study. Both sets of wing feathers are superimposed here. Click to enlarge. Note the pubis is not oriented posteriorly. Note the longer legs of Zhenyuanlong compared to tested dromaeosaurs.

Shifting
Zhenyuanlong to the dromaeosaurs adds a minimum of 127 steps to the large reptile tree. There is one clade of theropods that nests between the current tyrannosaur and dromaeosaur clades.

Figure 3. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Figure 4. Cladogram subset of the large reptile tree showing the strong nesting of Zhenyuanlong as the current sister to Tyrannosaurus. Obviously many more theropod taxa are missing here. They have not been tested yet.

Note
I have not tested as many theropods as there are in several theropod cladograms.

The possible faults with the Lü and Brusatte study were

  1. a lack of reconstructions to work with, rather than just a score sheet that others had created and they trusted. Reconstructions test identifications by making sure the puzzle pieces actually fit, both morphologically and cladisitically.
  2. I think they were fooled by the apparent posterior orientation of the pubis in situ when in vivo it was not oriented posteriorly
  3. I’m guessing that the traits they used could be used on in situ fossils without making reconstructions. The traits I use require reconstructions.

Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

Figure 0. Taxa ancestral to tyrannosaurs beginning with the CNJ7 specimen of Compsognathus.

With this nesting
the origin of long pennaceous wing feathers is evidently more primitive than earlier considered, developed twice. And perhaps this is why T. rex had such tiny arms. They were former wings, not grasping appendages.

References
Lü J and Brusatte SL 2015. A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution. Scientific Reports 5, 11775; doi: 10.1038/srep11775.

The genesis of feathers tied to the genesis of bipedalism in dinosaurs

Earlier we looked at the origin of feathers and the evolution of epidermal structures in dinosaurs, noting that embryo birds first develop primal buds (primordia) in the middle of their otherwise naked back. As we learned earlier, feathers are not elaborate scales, but develop from naked skin. We see this every time we pluck a chicken. We also learned that leg scales on birds are derived from feathers. Remember those 4-winged Mesozoic birds?

Today some further thoughts on the genesis of feathers.

Figure 1. Sinosauropteryx in lateral view on a primitive conifer.

Figure 1. Sinosauropteryx in lateral view on a primitive conifer. Despite the complete preservation of several specimens attributed to Sinosauropteryx, very few reconstructions (Fig. 1) have been made of it. Clinging to trees ultimately led to clinging to dinosaurs in dromaeosaurids. Like Limusaurus, Sinsauropteryx is off the main line of bird evolution.

Feathers are rarely preserved on dinosaur fossils.
One of the most primitive dinosaurs to preserve (admittedly very primitive) feathers is Sinosauropteryx (Figs. 1-3; Ji and Ji 1996) from the late Jurassic (with origins earlier in the Jurassic). It has short filamentous feathers running down its spine and around its throat and apparently nowhere else. This ‘mohawk haircut’- pattern could be due to the process of fossilization. Perhaps only those feathers on the parasagittal plane got preserved. However, from available evidence if the feathers were not restricted to the back, they did not stray very far from the spine at this stage. You don’t see feathers around the belly or legs in Sinosauropteryx (Fig. 2).

Figure 2. Sinosauropteryx fossil.

Figure 2. Sinosauropteryx fossil. As everyone knows, those are primitive feathers lining the spinal column and below the throat. Analysis indicates this is not the most primitive feathered theropod. Note the on/off appearance of the tail feathers indicating a decorative device: stripes!

 

Adding Sinosauropteryx to the large reptile tree
nests it with Limusaurus and both were basal to the much larger Sinocalliopteryx, which also had primitive feathers (Fig. 3). So Sinosauropteryx is not the most basal dinosaur with feathers or proto-feathers (contra Ji and Ji 1996). Unfortunately, more primitive theropods do not preserve feathers or scales. Scales do appear on later, larger dinosaurs of all sorts, not so much on the smaller, earlier dinos. Based on birds we can’t assume that small, early dinos had scales (contra Barrett et al. 2015). Rather, based on the appearance of primordia and feather-like structures on a wide variety of dinosaurs, feather primordia appears to precede scales, and perhaps many of these primordia ultimately became scales on larger dinos.

Figure 2. Sinocalliopteryx along with Limusaurus, Aurornis and Archaeopteryx to scale.

Figure 3. Sinocalliopteryx along with Limusaurus, Aurornis and Archaeopteryx to scale. Similar to Sinopteryx, but includes leg feathers here. Sinopteryx and Limusaurus are off the main line of bird evolution, which includes Haploceheirus and dromaeosaurs. Note the depth of the pelvis here compared to Scleromochlus (fig. 5).

 

Figure 1. Scales on the back of Scleromochlus, a basal bipedal croc and thus a distant sister to basal bipedal dinosaurs.

Figure 4. Scales on the back of Scleromochlus forming a lumbar girdle for support during bipedal excursions. This taxon nests as a basal bipedal croc and thus a distant sister to basal bipedal dinosaurs.

The genesis of feather primordia appears to be correlated to bipedal locomotion and a long torso. Before a feather was a feather, or even a quill, it was something else more primitive.

When one looks
at the pattern of dorsal scalation in Scleromochlus (Figs. 4, 5), a basal archosaur, one gets the impression that it was wearing a kind of lumbar girdle to support the long lower back. Indeed, as a newbie biped, Scleromochlus would have used such support near the fulcrum of the large leverage arm created by its stance, its long dorsal region and short ilium. Nothing appears to be sticking out above the dermal layer here. All of the scales (or whatever they were) appear to in lines, like a weave.

Unlike ancestral rauisuchians and the more closely related and larger Erpetosuchus and Gracilisuchus, there were no dorsal parasagittal scutes on Scleromochlus. It was a small animal that lost these structures as it evolved to depend on speed, not armor, to defend itself from predators.

 

Scleromochlus, a basal crocodylomorph

Figure 5. Scleromochlus, a basal crocodylomorph and an early biped in the archosaur line. Scleromochlus reinforced its long lower back with a dermal lumbar support or girdle. This is same area on a chicken embryo that first develops feathers. Compare torso length here to figure 3.

Primordia evolved into feathers only on the short torso basal dinos
Pre-dinosaurs are distinct from pre-crocs in many ways, but pre-dinos all have a shorter torso and a deeper pelvis (Fig. 3) reducing the leverage arm and the need for a reinforcing lumbar girdle. After the pelvis deepened and the torso shortened in early dinosaurs, the individual primordia of that old girdle were free to evolve into something else, in this case, something decorative.

Sinosauropteryx, with its dorsal line of feathery filaments extending from head to tail is one such example. When more feathers began to wrap around the body, that added insulation as a use. When wing feathers lengthened, the forelimbs began to flap to bring attention to those decorations. Later, wing feathers were co-opted for thrust and lift to enable flight.

But the genesis of feathers
still appears to be in the middle of the back, where primordia first appear on embryo chicks, replaying the old lumbar girdle innovation of Scleromochlus. The ornithischians, Tianyulong and Psittacosaurus had elongated primordia along their backs and tails indicating that this trait probably goes back to Herrerasaurus and Trialestes, no doubt in a smaller, more primitive state. With that small field of primordial  scales on the lower back of an otherwise naked Scleromochlus (Fig. 5), the genesis of extradermal structures appears to extend to basal archosaurs.

Figure 6. Feathers, scales and scutes in the Archosauria.

Figure 6. Feathers, scales and scutes in the Archosauria.

If anyone can provide evidence for scales or any other dermal preservation in any Triassic or Early Jurassic dinosaur, please let us know of them.

If anyone has other thoughts on the origin of feathers, please share them. If the above scenario does not make sense, please tell us your thoughts.

References
Barrett PM, Evans DC, Campione NE 2015. Evolution of dinosaur epidermal structures. Biol. Lett. 11: 20150229. online
Ji Q and Ji S-A 1996. On the Discovery of the earliest fossil bird in China (Sinosauropteryx gen. nov.) and the origin of birds. Chinese Geology 233:30-33.

Evolution of dinosaur epidermal structures

Barrett, Evans and Campione (2015)
“find no compelling evidence for the appearance of protofeathers in the dinosaur common ancestor and scales are usually recovered as the plesiomorphic state, but results are sensitive to the outgroup condition in pterosaurs. Rare occurrences of ornithischian filamentous integument might represent independent acquisitions of novel epidermal structures that are not homologous with theropod feathers.”

Unfortunately
the Barrett team followed two false traditions with regard to pterosaurs, which gained their epidermal structures independent from dinos. The two clades are not related according to the large reptile tree which nests pterosaurs in a new clade of lepidosaurs.

Based on their false assumption of scaly pterosaurs
as an outgroup, their analysis recovered primitively scaled Dinosauria and Ornithischia. So we’re off to a bad start based on taxon exclusion and false inclusion. Scales have never been found on pterosaurs. Why didn’t they assume filamented pterosaurs? We have evidence for that. So there is a lack of logic here that would have changed their conclusion.

The actual outgroup
for dinosaurs is the Crocodylomorpha for which tiny back scales first appear on the lower back of tiny Scleromochlus and ultimately cover the entire dermal surface on large extinct and extant taxa. Tiny scales may have been present on basal dinos, but more likely they had naked skin, like birds without their feathers. Scales on bird feet are transformed feathers.

The Barrett team database
included 24 ornithischians, 6 sauropods and 40 theropods (including Mesozoic birds). All taxa were scored for the presence/absence of epidermal scales, unbranched filaments (protofeathers)/quills and more complex branched filaments (including feathers).

The Barrett team report,
“Additional examples of protofeathers would be required from early dinosaur lineages or non-dinosaurian dinosauromorphs to optimize this feature to the base of Dinosauria. In particular, the ancestral condition in pterosaurs is pivotal in this regard, but currently unknown.” Longtime readers know this is false based on a cladogram, the large reptile tree) that includes several hundred more taxa.

As noted above, scales are unknown in pterosaurs.
However, their known outgroup taxa, Longisquama, SharovipteryxCosesaurus and Macrocnemus all have scales. The former three also have ptero-hairs (pycnofibers) and are the only Triassic fenestrasaurs (including pterosaurs) known to have these epidermal structures.

Based on their appearance and location,
dinoaurian ‘quills’ appear to be hyper elongated primordia without branching.

The Barrett team concluded,
“It seems most likely that scaly skin, unadorned by feathers or their precursors, was primitive for Dinosauria and retained in the majority of ornithischians, all sauropodomorphs and some early-diverging theropods (filaments are thus far unknown in ceratosaurians, abelisaurids and allosauroids.” In Science “it seems most likely” is a very weak argument, further weakened by the fact that birds don’t have scales, except on their legs, and those are transformed feathers.

The Barrett team provided a cladogram
that depicted the extent to which scales, filaments and feathers were present. Notably they did not also include the extent of naked skin, which is a fourth possibility not covered by the text or graphic. The possibility exists that all dinosaur scales are transformed primordia (filaments) or transformed feathers. Dinosaur scales could also be novel epidermal structures that appear only on large dinosaurs just as croc scales are novel epidermal structures. Based on their appearance and location, dinoaurian ‘quills’ appear to be hyper elongated primordia.

Embryo birds
first develop primordial feathers in the middle of their backs, replaying phylogeny during ontogeny. With current data, that trait may go all the way back to basal archosaurs, like Scleromochlus.

Bottom line:
When you play with phylogenetic bracketing, you have to have a valid cladogram.

References
Barrett PM, Evans DC, Campione NE 2015. Evolution of dinosaur epidermal structures. Biol. Lett. 11: 20150229. online

 

 

 

 

 

 

 

Czerkas and Feduccia disconnect birds and dinos

Figure 1. Reconstruction of Scansoriopteryx with possible feather extent by Stephen Czerkas. Good thing that second branch or telephone wire is available for balance!

Figure 1. Reconstruction of Scansoriopteryx with possible feather extent by Stephen Czerkas. Good thing that second branch or telephone wire is available for balance!

A new paper by Czerkas and Feduccia
attempts to unlink birds with dinosaurs and to link birds with some unspecified archosaur by their reexamination of Scansoriopteryx, a tiny Chinese fossil of the Jurassic. Much has already been said about this paper — all negative.

Czerkas and Feduccia report the “absence of fundamental dinosaurian characteristics,” but do not do so with phylogenetic analysis, which would have nested their study subject somewhere else that they could support, but can’t. They seem stuck in a trees-down vs. ground up battle when plenty of ground-dwelling dinosaurs seem fully capable of climbing a tree by grappling or simply by running up a vertical trunk bipedally, as some modern birds do (any Dial reference below). Their illustration (Fig. 1) seems to say that whether bird or dinosaur or non-dinosaur, Scansoriopteryx was not capable of standing balanced on its (apparently splayed?) hind limbs, despite the fact that it’s forelimbs appear poorly designed for walking. They’ve been accused of LarryMartinizing and it seems they have indeed been doing so. For those interested, Larry Martin preferred to discuss individual characters rather than suites of characters of a sort used in phylogenetic analysis.

I can’t buy into their particular heresy.
There’s no support for it. We need to see details and analyses. And they need to present their best alternative candidate among the non-dinosaurian archosaurs out there as a sister to Scansoriopteryx. 

The irony here
is that the same sort and style of argumentation is being used to support a pterosaur/archosaur connection by the same set of paleontologists who support the dino/bird connection. By that I mean, they present no archosaurian candidates that more closely match pterosaurs than our own favorites: the lepidosaur, tritosaur, fenestrasaurs.

So, if you’re a finger pointing paleontologist, be careful. Don’t fall into  that same trap.

References
Czerkas SA and Feduccia A 2014. Jurassic archosaur is a non-dinosaurian bird, Journal of OrnithologyDOI: 10.1007/s10336-014-1098-9
Dial KP, Jackson BE and Segre P 2008.  A fundamental avian wing-stroke provides a new perspective on the evolution of flight. Nature (online 23 Jan 08)
Padian K and Dial KP 2005. Could the “Four Winged” Dinosaurs Fly?  Nature: 438:E3-5.
Dial KP, Randall R and Dial TR 2006. What use is half a wing in the evolution of flapping flight? BioScience 56: 437-445.
Tobalske BW and Dial KP 2007. Aerodynamics of wing-assisted incline running. J. Exp. Biol. 210:1742-1751.
Bundle MW and Dial KP  2003. Mechanics of wing-assisted incline running.  J. Exp. Biol., 206:4553-4564.
Dial KP 2003.  Evolution of avian locomotion: Correlates of body size, reproductive biology, flight style, development and the origin of flapping flight. Auk 120:941-952.
Dial KP 2003. Wing-assisted incline running and the evolution of flight.  Science 299:402-404.
Read more at: http://phys.org/news/2014-07-declassify-dinosaurs-great-great-grandparents-birds.html#jCp

 

The origin and evolution of Longisquama “feather-like structures”

 

Figure 1. Click to enlarge. The origin and evolution of Longisquama's "feathers" - actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

Figure 1. Click to enlarge. The origin and evolution of Longisquama’s “feathers” – actually just an elaboration of the same dorsal frill found in Sphenodon, Iguana and Basiliscus. Here the origin can be found in the basal tritosaur squamate, Huehuecuetzpalli and becomes more elaborate in Cosesaurus and Longisquama.

A year ago
New Scientist covered a new paper on the dorsal appendages of Longisquama (Buchwitz and Voigt 2012) who wrote in his abstract, “We explain the existing feather similarity by their development from a filamentous primordium and a complex sequence of individual processes, some of which are reminiscent of processes observed in feather development. Such an interpretation is in agreement with a set of homologous mechanisms of appendage morphogenesis in an archosauromorph clade including Longisquama and feather-bearing archosaurs but does not necessarily require that the appendages of Longisquama themselves are feathers or high-level feather homologues.”

Here a larger and more parsimonious phylogenetic analysis
nests Longisquama with fenestrasaur, tritosaur squamates, derived from sisters to Huehuecuetzpalli and Cosesaurus (Fig. 1). With this lineage the origin and the development of the single line of dorsal plumes becomes easy to visualize. They were small originally and, through evolution, became enlarged. Among living reptiles, the tuatara (Sphenodon) and the iguana (Iguana) bear similar and homologous small structures.

Buchwitz reported in New Scientist, “The strange skin appendages of Longisquama are neither scales nor feathers,” says Michael Buchwitz of the Freiberg University of Mining and Technology, Germany. “They are perhaps linked to the early evolution of dino and pterosaur fuzz, though. Longisquama‘s skeleton is too incomplete to work out its exact evolutionary position, but Buchwitz says the little reptile was probably part of the lineage that gave rise to pterosaurs, crocodiles, dinosaurs and birds. Many of these groups later evolved their own skin appendages, including filaments on pterosaur wings, quills on the tails of some plant-eating ornithischian dinosaurs, and the proto-feathers of theropod dinosaurs. Longisquama shows that evolution was experimenting with the genes that gave rise to feathers long before any of these animals appeared on the scene.”

Tomorrow we’ll take a close look at the metatarsus of Longisquama courtesy of Buchwitz and Voigt (2012).

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
New Scientist article here
Buchwitz M and Voigt S 2012. The dorsal appendages of the Triassic reptile Longisquama insignis: reconsideration of a controversial integument type. Paläontologische Zeitschrift, Issue 3, pp 313-331