Sapeornis vs. Balaur

Sapeornis (Fig. 1) was a basal bird that retained teeth, but had a short tail with a pygostyle and had large wings. It was certainly flapping and flying. Earlier we nested Sapeornis between Archaeopteryx and all higher birds, including all extant birds.

Yesterday the reported link between Sapeornis and Omnivoropteryx was snipped. The latter is a scansoropterygid bird. Workers, it appears, occasionally like to compare Sapeornis to novel fossils, even when comparisons are not warranted.

When the ‘bizarre’ dromaeosaur with double killer claws
Balaur (Csiki et al. 2010), was reexamined by Cau, Brougham and Naish 2015, one of their results nested Balaur with Sapeornis (Figs. 1, 2).

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird, a sort of dodo of the Cretaceous.

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird. A casual glance finds many similarities, but analysis sets the record straight.

Thus, Cau, Brougham and Naish 2015,
and later Naish’s own blog post, wondered if Balaur was the first flightless bird. They nested it after Archaeopteryx (Fig. 2). By contrast, in the large reptile tree, Balaur nests where both Csiki et al. (2010) and Brusatte et al. (2013) nested it: with dromaeosaurs. On a reduced list of traits (Balaur lacks a skull) shifting Balaur over to Sapeornis adds 12 steps, which is not a large number considering the number of intervening taxa (12 nodes).

Figure 2 The Cau et al tree based on the Brusatte et al. tree. Note the nesting of Balaur among long-tailed post-Archaeopteryx birds, but a sister to Sapeornis, which has a pygostyle. Click to enlarge. 

Figure 2 The Cau et al tree based on the Brusatte et al. tree. Note the nesting of Balaur among long-tailed post-Archaeopteryx birds, but a sister to Sapeornis, which has a pygostyle. Click to enlarge.

Naish notes (pro-dromaeosaurid):

  1. This dromaeosaurid interpretation of Balaur looks reasonable on the basis of the animal’s size and foot anatomy, and Balaur is certainly dromaeosaurid-like in a general sense.

Naish notes (pro-avian):

  1. “Balaur is anatomically weird when interpreted as a dromaeosaurid,
  2. Balaur is likely not a dromaeosaurid, but a secondarily flightless bird.
  3. It has a reduced third finger (lacking a claw),
  4. extensive fusion between the hand and wrist bones,
  5. a strangely broad, extensively fused pelvis with pubic bones that bow outwards for most of their length and are strongly swept back,
  6. fusion between the tibia and fibula,
  7. fusion between the tibia and ankle bones,
  8. an especially stocky, heavily built, partially fused-up foot
  9. and a long hallux (first toe) with an especially big claw.
  10. “All of the features I just mentioned – yes, all of them – are present in Avialae,”
  11. In addition, the manual unguals of Balaur are not as strongly curved as those of most dromaeosaurids
  12. the flexor tubercles (the bony lumps on the undersides of the unguals that anchor ligaments used in ungual flexion) are comparatively weakly developed, thus Balaur was in possession of a non-raptorial hand
  13. Godefroit et al. (2013), in their description of the Jurassic avialan Aurornis, published a phylogeny where Balaur is an avialan, closer to Pygostylia (the short-tailed bird clade) than is Archaeopteryx.
  14. And Foth et al. (2014), in their study of a new Archaeopteryx specimen, also found Balaur to be a member of Avialae, again closer to crown-birds than Archaeopteryx.”

The large reptile tree notes

  1.  if Balaur is avian purported avian sister taxa are all a magnitude smaller
  2. and developing larger wings, not smaller ones.
  3. the pes of Balaur is robust, not bird-like in general proportions or morphology.
  4. the non-raptorial manus and larger gut of Balaur (based on the wider pubis) suggests herbivory or omnivory. That alone would make it bizarre among dromaeosaurs, but not so bizarre among theropods.
  5. Balaur fuses the scapulocoracoid. Sapeornis does not.
  6. Balaur has a four-part sternum, like other dromaeosaurids. Sapeornis lacks a sternum, but sister taxa have a single sternum.
  7. Balaur has a large olecranon process. Sapeornis does not.
  8. Balaur has a subequal manus and pes. Sapeornis has a larger manus.
  9. Balaur has a smaller humerus than tibia. Sapeornis has a larger humerus.
  10. Balaur aligns mc2-3 with m1.1. Sapeornis aligns mc2-3 beyond m1.1
  11. Balaur mc2 is the longest. Sapeornis mc2=mc3.
  12. Balaur metatarsus is shorter than half the tibia. Sapeornis, not shorter
  13. Balaur aligns mt2-3 with mt1. Sapeornis aligns p1.1 IF rotated anteriorly, but it is rotated posteriorly.
  14. Balaur has one phalanx on mt5. Sapeornis has three.
  15. Balaur is larger than 60 cm long. Sapeornis is not.


  1. Balaur fuses distal tarsals to metatarsals. So does Velociraptor. Not Sapeornis.
  2. Balaur retains standard anterior caudal vertebrae. Sapeornis compresses them as part of a pygostyle morphology.
  3. Balaur does not have a bird-like expanded deltopectoral crest. Sapeornis does.
  4. Balaur does not retain any traits which would indicate that its ancestors were small, perching, flapping birds like Archaeopteryx and Sapeornis.

Sure, Balaur is a bizarre dromaeosaur. 
It might even be an herbivore. But those traits listed by Naish must be considered convergent with one bird or another, because they are not all found in one tested bird (like Sapeornis). The large reptile tree does not nest Balaur outside of the dromaeosaurs with present data. Birds have bowed pubes because they have enlarged air sacs. Ultimately bird pubes separate distally to accommodate even larger air sacs. That’s not the case with bulky Balaur. As a scientist, Naish should have thought about that and the following dromaeosaur synapomorphies shared with Balaur before suggesting that Balaur was a sister to the bird Sapeornis.

Unlike birds, Balaur has

  1. a four-part sternum, like other dromaeosaurs.
  2. a killer claw,  like other dromaeosaurs.
  3. an anteriorly-directed pedal digit 1, like other dromaeosaurs.
  4. is goose sized, like other dromaeoaurs.
  5. robust pedal bones, like other dromaeosaurs.
  6. smaller fore limbs than hind limbs, like other dromaeosaurs.
  7. deep, robust dorsal vertebrae, like other dromaeosaurs.

Naish should have listened to himself 
when he wrote, Balaur is certainly dromaeosaurid-like in a general sense.” 

Naish saw the specimens first hand.
I did not. Naish did not create his phylogenetic matrix first hand. I did. Naish did not include various specimens of Archaeopteryx as ITU (individual taxonomic units). I did. Naish did not put reconstructions of the two taxa, Balaur and Sapeornis, next to one another and next to competing candidates for a final check. I did. It’s good practice.

When someone is trying to prove a point,
whether valid or not, they generally don’t weigh all aspects evenly. They try to prove their point. We’ve seen Naish do this before with tragic consequences to his own reputation. I don’t think Naish and his team weighed all aspects of Balaur evenly. If Balaur really did nest between Archaeopteryx (but which one?) and Sapeornis, then it really should have looked like one or the other or an amalgam of both. Instead, it’s just one more example of an ‘strange bedfellow’ that actually nests elsewhere when tested on the large reptile tree.

Comments made above
should have been made by the manuscript referees. Some are listed in the acknowledgements to the paper. Critical thinking seems to be fading in paleontology. That’s why this blog exists.

One should never trust anyone’s interpretations,
observations or cladistic analyses, especially if things don’t look right. Instead, one should repeat the observation, experiment or analysis for oneself. That’s what I do here. As you already know, if something doesn’t look right, it probably isn’t. We’ve seen paleo-oddities paraded before that are not so odd after all when properly nested.

Brusatte, et al. 2013. The osteology of Balaur bondoc, an island-dwelling dromaeosaurid (Dinosauria: Theropod) from the Late Cretaceous of Romania. Bulletin of the American Museum of Natural History, 374:1-100.
Cau​ A, Brougham​ T and Naish​ D. 2015. The Phylogenetic Affinities of the Bizarre Late Cretaceous Romanian Theropod Balaur bondoc (Dinosauria, Maniraptora): Dromaeosaurid or Flightless Bird? PeerJ3: E1032. DOI:
Csiki Z, Vremir M, Brusatte SL, Norell MA 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences of the United States of America 107 (35): 15357–15361.
Foth C, Tischlinger H and Rauhut, OWM 2014. New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature 511, 79-82.
Godefroit P, Cau A., Dong-Yu H., Escuillié F, Wenhao W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498, 359-362.
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.

YouTube video by Wiz Science.


6 thoughts on “Sapeornis vs. Balaur

  1. Why are you specifically addressing Darren’s blog and not the primary source of the observations and conclusions? I understand that Darren will write about matters (slightly) differently on his blog than in a research paper, but in order properly critique the study, do so on the published research itself.

  2. You should listen to YOURSELF. Unlike YOU, actual scientists complete the experiments BEFORE deciding what point they want to enhance. The entire point of their paper was to redescribed Balaur, not radically change science forever. And they didn’t even do the latter. Their phylogeny, which I myself have checked, if quite excellent, and has a huge magnitude more characters, which results in more possible trees, so the most likely one is just that much better.

  3. Why frame your objection with hyperbole? If their phylogeny is ‘quite excellent’ then why don’t sister taxa look more alike? There should be, as you know, a gradual accumulation of derived traits. That’s not the case here. An earlier post noted that I looked at the first 500 traits of Cau et al and found several problems indicating that they did not proofread their matrix. So I question your assessment of their phylogeny. Please reread my suggestion to incorporate more Archaeopteryx specimens into analysis. You’ll find the tree topology will change. And thank you for your comment.

  4. Actually, I have already done exactly that, and guess what happened? The entire tree stayed the same, and the specimens of Archaeopteryx all are in the same branch as the most basal birds. No single taxon should be able to completely revolutionize any phylogeny, which is why I strongly respect theirs.

    • Please send your .nex file to and we’ll find out where the differences are. If you have reconstructions of the taxa, please send those as well. Otherwise I’ll assume you’ve taken data from personal examination of the pertinent fossils. If not, let me know if your sources of data are online photos or high rez images from your private stock.

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