Xiongguanlong: not a tyrannosauroid

I hate to keep doing this…
I know it pisses off theropod-o-philes.

A few years ago
Li, et al. 2010 described a new theropod dinosaur, Xiongguanlong, as “a longirostrine tyrannosauroid from the Early Cretaceous of China” which they nested between Eotyrannus + Dilong and Tyrannosaurus + other Late Cretaceous tyrannosaurs.

Figure 1. Xiongguanlong does not nest with tyrannosaurs, but with other long rostrum theropods, including Denocheirus and Sinocalliopteryx.

Figure 1. Xiongguanlong does not nest with tyrannosaurs, but with other long rostrum theropods, including Denocheirus and Sinocalliopteryx.

Unfortunately,
the large reptile tree nests Xiongguanlong along with other longistrine theropods, like Deinocheirus (Fig. 2), Sinocalliopteryx and the spinosaurs. I have not yet encountered any valid longirostrine tyrannosauroids. Dilong and Guanlong also nest close to these long-rostrum theropods. They were removed from the tyrannosauroids earlier here and here. Eotyrannus was likewise removed from the tyranosauroids here, and nested with Tanycologreus close to the base of the dromaeosaur/troodontid + bird split.

Figure 2. Deinocheirus skull. This long rostrum theropod nests close to Xiangguanlong and shares many traits with it.

Figure 2. Deinocheirus skull. This long rostrum theropod nests close to Xiongguanlong and shares many traits with it.

I keep hoping one of these taxa
are going to shift the tree topology back toward the traditional thinking, but each new taxon just drops into place, adding their leaf to the tree.

Figure 3. Theropod cladogram with the addition of Xiongguanlong nesting with Deinocheirus and Sinocalliopteryx.

Figure 3. Theropod cladogram with the addition of Xiongguanlong nesting with Deinocheirus and Sinocalliopteryx, not tyrannosaurs.

Li et al. report
“Xiongguanlong marks the earliest phylogenetic and temporal appearance of several tyrannosaurid hallmarks such as a sharp parietal sagittal crest, a quadratojugal with a dramatically flaring dorsal process and a flexed caudal edge, premaxillary teeth bearing a median lingual ridge, and a flaring axial neural spine surmounted by distinct processes at its corners.”

“Remarkably, Xiongguanlong has dorsally smooth nasals. Unlike the conical tooth crowns of taxa such as Tyrannosaurus, Xiongguanlong has mediolaterally compressed tooth crowns. The cervical vertebrae display only a single pair of pneumatic foramina, and the dorsal centra are not pneumatic in contrast to Albertosaurus and more derived tyrannosaurids. Xiongguanlong is remarkable in having a shallow and narrow snout forming more than two thirds of skull length…most tyrannosaur ids have short deep snouts mechanically optimized for powerful biting.”

No blame here. 
Li et al could have extended their comparative search to Sinocalliopteryx, which was published in 2007, but the skull of Deinocheirus was not published until 2014, so they are not to blame for missing such possibilities. These things happen.

References
Li D, Norell MA, Gao K-Q, Smith ND and Makovicky PJ 2010. A longirostrine tyrannosauroid from the Early Cretaceous of China. Proceedings of the Royal Society B 277:183-190.

Reconstructing the partial manus of Ceratosaurus and its bearing on Limusaurus

A recent paper
by Carrano and Choiniere 2016 excavated and described the metacarpus and forearm plus a few partial phalanges of the Ceratosaurus holotype  (USNM 4735).

FIguire 1. the partial manus of Ceratosaurus compared to that of Coelophysis, Dilophosaurus and Allosaurus.

FIguire 1. the partial manus of Ceratosaurus compared to that of Coelophysis, Dilophosaurus and Allosaurus. Restored areas are in gray.

Carrano and Choiniere reported,
“it is more parsimonious to identify the manus of Limusaurus as an autapomorphic condition instead of as primitive for Ceratosauria (Xu et al., 2009). This is particularly evidenced by the primitive metacarpal I in Ceratosaurus, nearly identical in morphology to that seen in other basal neotheropods and quite unlike that in Limusaurus.”

You may recall
that the putative digit 1 of Limusaurus is actually the reappearance of digit 0, a basal tetrapod digit medial to digit 1. We also looked at a possible digit 0 on a specimen of Coelophysis.

Although Ceratosaurus currently nests as a sister to Allosaurus
in the large reptile tree, the manus is more primitive (more like that of Dilophosaurus) with a smaller digit 1 and the retention of a vestigial digit and mc4. Limusaurus nests with the oviraptorid, Khaan.

Carrano and Choiniere correctly conclude:
“Therefore, extreme manus reduction occurred twice in ceratosaurs—once in Limusaurus (and possibly in closely related taxa) and once in derived abelisaurids—and differently in each.”

References
Carrano MT and Choiniere J 2016. New information on the forearm and manus of Ceratosaurus nasicornis Marsh, 1884 (Dinosauria, Theropoda), with implications for theropod forelimb evolution, Journal of Vertebrate Paleontology, DOI:10.1080/02724634.2015.1054497

Ornitholestes nests with Microraptor now

Earlier we looked at a new nesting for four-winged Microraptor in the Tyrannosaurus clade. Here a close relative (Figs. 1-2) supports that nesting (Fig. 2) and calls into question the currently accepted shrinking bird ancestor hypothesis (Fig. 3).

Ornitholestes hermanni 
(Ostrom 1903, 1917, 2m, incomplete skeleton, Late Jurassic, 154 mya) According to Wikipedia, “All published cladistic analyses have shown Ornitholestes to be a coelurosaur as defined by Gauthier.” A coelurosaur? That’s pretty general. As the arbiter of all that is known and accepted, can Wiki be more specific? Is Ornitholestes such an enigma? In the large reptile tree (subset in Fig. 4)  Ornitholestes nests between Compsognathus and Microraptor, close to Tianyuraptor in the lineage of Tyrannosaurus. The skeleton shown here was restored based on the AMNH restoration (Fig. 1), which may not be accurate with regard to the number of cervicals and dorsals (see below).

Figure 1. Ornitholestes, as originally mounted by the American Museum and revised together with Microraptor to scale. Click to enlarge.

Figure 1. Ornitholestes, as originally mounted by the American Museum and revised together with Microraptor to scale. Click to enlarge.

Ornithologist
Percy Lowe hypothesized in 1944 that Ornitholestes might have borne feathers. Now, as a close relative of Microraptor and Tianyuraptor, Ornitholestes probably had long wing and leg feathers.

Note the resemblance
of the skull of Microraptor to that of Ornitholestes (Fig. 3) and the very similar body proportions, distinct chiefly in size (Fig.1).

Figure 5. The skull of another Microraptor, QM V1002. The two nest together in the large reptile tree.

Figure 2. The skull of Microraptor, QM V1002. Note the resemblance to Ornitholestes.

Earlier phylogenetic studies
Wikipedia reports, “All published cladistic analyses have shown Ornitholestes to be a coelurosaur as defined by Gauthier. Some analysis have shown support for the hypothesis that it is the most primitive member of the group Maniraptora, though more thorough analyses have suggested it is more primitive than the Maniraptoriformes, and possibly a close relative of the “compsognathid” Juravenator starki.” That is not a very precise nesting. Here Ornitholestes supports the earlier hypothesis that Microraptor was not in the main lineage of birds, nor of dromaeosaurs, but this clade represents a pseudo-bird lineage that did not produce extant relatives. The pectoral girdle is not known for Ornitholestes, so we don’t know if it had long coracoids and a furcula suitable for flapping.

Behavior
Osborn (1903) originally considered Ornitholestes a bird catcher and “doubtless related as a family to Struthiomimus.” That behavior is unlikely (see below,) but the relationship is true in the large reptile tree as Struthiomimus nests with Compsognathus both proximal basal sisters to Ornitholestes.

Distinct from all tested sister taxa,
Ornitholestes
had a tibia not longer than the femur, a trait that usually occurs in much larger theropods, like T-rex, but also occurs in the unrelated Sinosauropteryx.

Repairing errors
Osborn (1917) thought the referred manus specimen (AMNH 587) was not adapted to seizing or holding a struggling live prey, as he originally imagined. Pertinent to an earlier discussion, Osborn 1917 noted several inaccuracies in Osborn 1903. This was not considered just cause for other paleontologist of that – or any era – to question everything Osborn produced from then on. He corrected a mistake and everyone accepted that as what Science does.

Figure 1. The evolution of birds as a consequence of miniaturization. Artist: Davide-Bonnadonna

Figure3. The evolution of birds as a consequence of miniaturization. Artist: Davide-Bonnadonna

The Shrinking Bird Ancestor Hypothesis
Earlier we looked at a paper on bird origins (Lee et al. 2014) that found a gradual size reduction in the theropod lineage that produced birds. Unfortunately, with the new cladogram, it is no longer reasonable to accept a Large > Medium > Small sequence. Rather it is more reasonable to follow a Medium > Mediium > Small  hypothesis OR a Small > Small  > Small hypothesis  of bird origins (Fig. 4). In other words, the lineage that ultimately produced birds may have stayed small and occasionally branched off medium and large-sized clade members.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade. Depending on how you look at it, either medium-size dinosaurs produced large and small dinosaurs, or small dinosaurs produced medium and large dinosaurs. In pterosaurs small always produced medium and large.

Figure 4. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade. Every 5 seconds the graphic will change, 3 frames. Depending on how you look at it, either medium-size dinosaurs produced large and small dinosaurs, or small dinosaurs produced medium and large dinosaurs. In pterosaurs small always produced medium and large.

Of course, a more complete fossil record
could solve this problem. But at present we should not loose sight of the fact that basalmost dinosaurs, like Barberenasuchus and Eodromaeus, were small, not medium or large (depending on your definition and cut-off, of course). With Tyrannosaurus in the mix, Struthio the ostrich becomes a medium-sized theropod, even though it is a large bird. The presence of small dinosaurs, like Compsognathus, at several basal nodes in the large reptile tree allow the possibility that theropod evolution happened at a small scale that occasionally produced medium and large-sized clade members. These did not directly contribute to the lineage of stem birds. Earlier we looked at the several bird-mimic clades that sprang from the basic bird lineage.

References
Lee MSY, Cau A, Naish D and Dyke GJ 2014. Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds.
Osborn HF 1903. 
Ornitholestes hermanni, a New Compsognathoid
Dinosaur from the Upper Jurassic. Bulletin of the AMNH 19:(12):459-464.
Osborn HF 1917. Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus. Bulletin of the AMNH 35 (43) pdf
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/Microraptor
wiki/Ornitholestes

Deinocheirus: not an ornithomimosaur

Following a long list of blog posts
that reported an inability here (Fig. 3), in the large reptile tree, to nest various theropods in their traditional nodes, today Deinocheirus (Fig. 1) nests not with ornithomimosaurs, like Struthiomimus, but at the base of the spinosaur clade. Here Deinocheirus nests between Sinocalliopteryx and Dilong + Guanlong, none of which have elongate dorsal spines and all of which have long teeth.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Figure 1. The skull of Deinocheirus. Note the new interpretation of the anteriorly flaring nasals. Note how the mandible does not completely close cranially when the anterior tips touch. I wonder if this was a sieving organ lined with baleen-like structures. That hypothesis goes with the very deep mandible and the equal lengths of both upper and lower jaws.

Previous studies
assumed that Deinocheirus was an ornithomimosaur, because it had very similar manus and forelimb proportions. When the skull was discovered, it was likewise toothless. The large reptile tree finds that those traits were convergent with ornithomimosaurs.

Figure 2. Deinocheirus specimens and a composite illustration.

Figure 2. Deinocheirus specimens and a composite illustration.

Deinocheirus mirificus (Osmólska & Roniewicz, 1970, Latest Cretaceous, 70 mya 11m) was originally and later considered a giant and basal ornithomimosaur. The large reptile tree (see below) nests Deinocheirus between Guanlong and Sinocalliopteryx in the spinosaur clade.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Figure 4. Sinocalliopteryx currently nests as a provisional sister to Deinocheirus, awaiting the discovery of transitional sister taxa.

Like ornithomimosaurs, Deinocheirus was toothless and had long slender arms with a metacarpus of subequal metacarpals. Like spinosaurs, Deinocheirus had long dorsal neural spines. Like SinocalliopteryxDeinocheirus had an elongate rostrum, a tall orbit and nasals that flared laterally at the nares.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

Figure 2. Here, in this subset of the large reptile tree, Ornitholestes nests at the base of the Microraptor clade, close to the base of the Tyrannosaurus clade.

I’m sure theropod workers
can’t be happy that the detailed nestings of their cladograms are not verified here. Tradition may have misguided them, perhaps in this case. Using the matrices of prior workers without testing them for typos and scoring errors may be another problem.

Pure speculatiion
I wonder if the very elongate teeth of Sinocalliiopteryx somehow evolved into water straining structures in Deinocheirus. Only a transitional taxon with more, longer, thinner teeth or similar structures are ever found. It will also likely have a deeper mandible. Both taxa may have fed in water. A third taxon, Spinosaurus, is also considered a piscivore.

References
Ibrahim N et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613–6.
Ji S, Ji Q, Lu J and Yuan C 2007. A new giant compsognathid dinosaur with long filamentous integuments from Lower Cretaceous of Northeastern China. Acta Geologica Sinica, 81(1): 8-15.
Lee YN, Barsbold R, Currie PJ, Kobayashi Y, Lee HJ, Godefroit P, Escuillié F and Chinzorig T 2014. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature 515 (7526): 257–260.
Osmólska H and Roniewicz E 1970. Deinocheiridae, a new family of theropod dinosaurs. Palaeontologica Polonica. 21:5-19.
Sereno PC, et al. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282 (5392): 1298–1302.

wiki/Sinocalliopteryx
wiki/Suchomimus
wiki/Deinocheirus

 

 

Eotyrannus: what is it?

Eotyrannus lengi
(Hutt et al. 2001, Naish 2011, Fig. 1) is a mid-sized Early Cretaceous, Barremian, theropod originally and later allied with tyrannosauroids like Tyrannosaurus.

From the Hutt et al. 2001 abstract:
“The teeth in the premaxilla are D-shaped in cross-section and the nasals are fused.”
These are traits shared with Tyrannosaurus. “The hands are elongate and slender and the hindlimbs are gracile.” These are not traits shared with Tyrannosaurus. “…the new taxon appears to be excluded from the group that comprises aublysodontine and tyrannosaurine tyrannosaurids. We conclude that the taxon is a basal tyrannosauroid and as such it is one of the earliest and (with the exception of some teeth and an isolated ilium from Portugal) the first from Europe.”

Figure 1. Eotyrannus lengi from images in Hutt et al. 2001 and Naish 2011. The scale bars are all over the place. This taxon seems not to nest with Tyrannosaurus, but with Tanycolagreus.

Figure 1. Eotyrannus lengi from images in Hutt et al. 2001 and Naish 2011. The scale bars are all over the place. This taxon seems not to nest with Tyrannosaurus, but with Tanycolagreus. The high angle of the naris is unique going back to Herrerasaurus.

Unfortunately
the large reptile tree nests Eotyrannus with Tanycolagreus (Fig. 2) at the base of the clade that ultimately gave rise to birds. These two taxa may represent a clade of tyrannosauroid mimics at the base of the pre-bird clade. They may share a naris with a higher ascending angle other theropods.

Figure 2. Tanycolagreus nests as a sister to Eotyrannus in the large reptile tree. This appears to be a clade of tyrannosaur mimics at the base of the pre-bird clade.

Figure 2. Tanycolagreus nests as a sister to Eotyrannus in the large reptile tree. This appears to be a clade of tyrannosaur mimics at the base of the pre-bird clade.

Unfortunately
Eotyrannus is not known from more parts. What we do have, though, appears to be most similar to the contemporary Tanycolagreus among tested taxa. It’s a scrappy fossil. Not good for keeping up high resolution in the cladogram (Fig. 3).

Figure 3. Theropoda with the addition of Eotyrannus as a sister to Tanycolagreus.

Figure 3. Theropoda with the addition of Eotyrannus as a sister to Tanycolagreus.

References
Hutt S, Naish D, Martill DM, Barker MJ and Newbery P 2001. A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 22:227-242.
Naish D 2011. Theropod Dinosaurs, chapter 29 in Batten DJ (ed) English Wealden Fossils. The Palaeontological Association (London), pp. 526-559.
Senter, P 2007. A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)”, Journal of Systematic Palaeontology, 5(4): 429-463

Dracoraptor: a scrappy new earliest Jurassic theropod from Wales

Revised January 30, 2016. Additional taxa and revisions to Compsognathus now nest Dracoraptor with Coelophysis in the large reptile tree. 

A new paper
by Martill et al. 2016 describes a Late Triassic/Early Jurassic slender, mid-sized theropod, Dracoraptor hanigani, (NMW 2015.5G.1–2015.5G.11, Figs. 1-4).

Figure 1. Dracoraptor manus reinterpreted.

Figure 1. Dracoraptor manus reinterpreted. See figure figure 3 for original interpretation with long finger 3.

From the Martill et al. paper:
“Diagnosis. A basal neotheropod with the following autapomorphies and unique combination of plesiomorphies: Three teeth in the premaxilla, slender maxillary process of jugal, large narial opening with slender subnarial bar, anteriorly directed pubis considerably longer than ischium, and large dorsal process on distal tarsal IV.”

Figure 2. Dracoraptor premaxillae compared to one another. Almost hard to believe they came from the same plate/counterplate. Together they present a better basis for scoring.

Figure 2. Dracoraptor premaxillae compared to one another. Almost hard to believe they came from the same plate/counterplate. Together they present a better basis for scoring.

Martill et al nested
Dracroraptor (with long manual digit 3 interpretation, Fig. 3) between Tawa and Coelophysis. Tawas also has a longer manual digit 3. I could not confirm the longer manual digit 3.

Figure 3. Original interpretation of Dracoraptor with color codes for known bones. Above: putting the bones together.

Figure 3. Original interpretation of Dracoraptor with color codes for known bones. Above: putting the bones together. Ghosted image represents the jugal/lacrimal impression along with, perhaps two posterior teeth flipped. The reconstruction of the foot on the overall skeletal figure is at an odd tippy-toe angle. It should have more phalanges planted on the substrate and the metatarsus should be angled forward somewhat more.

In the large reptile tree (subset Fig. 4) Dracoraptor now nests with Coelophysis among tested taxa.

Figure 2. Here Dracoraptor nests with Coelophysis, another basal theropod.

Figure 2. Here Dracoraptor nests with Coelophysis, another basal theropod.

Scattered digits
One of the problems with scattered digits is producing scores in analysis. The best practice, IMHO, is to nest the taxon first without scoring the scattered digits, then use phylogenetic bracketing to reassemble the scattered phalanges based on sister taxa patterns.

Generally it is problematic
to score scrappy taxa like this. Basal taxa are always interesting. Happily, enough is known to nest Dracoraptor without losing resolution.

As you can see
(Fig. 3), the published drawing does not accurately reflect the shapes of the published skull bones. In addition, the published tracing of the phalanges had to be warped to fit the published photograph. I wish tracings were taken from published photos so there would be a one-to-one correspondence.

References
Martill DM, Vidovic SU, Howells C and Nudds JR 2016. The Oldest Jurassic Dinosaur: A Basal Neotheropod from the Hettangian of Great Britain. PLoS ONE 11(1): e0145713. doi:10.1371/journal.pone.0145713

Mei long: not bird-like, but a real basal flightless bird!

Mei long (IVPP V12733, Xu and Norell 2004, Early Cretaceous, 130 mya, Figs. 1-3) is famous for its 3D preservation in a curled up sleeping posture. Originally considered a young juvenile, bird-like troodontid, Mei long instead nests in the large reptile tree between the Munich specimen of Archaeopteryx BSp 1999 I 50 and Scansoriopteryx along with other scansoriopterygid basal birds. A second specimen, DNHM D2154 (Gao et al. 2012), was also preserved in a sleeping posture.

Troodontidae
Wikipedia reports, “There are multiple possibilities of the genera included in Troodontidae as well as how they are related.” Adding to this problem, in the large reptile tree several taxa sometimes included in the Troodontidae instead nest sequentially basal to birds (Archaeopteryx), not in a single offshoot clade.

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.

From Xu and Norell (2004):
“Mei long is distinguishable from all other troodontids on the basis of extremely large nares extending posteriorly over one half of the maxillary tooth row*; closely packed middle maxillary teeth; maxillary tooth row extending posteriorly to the level of the preorbital bar”; a robust, sub-‘U’-shaped furcula*; presence of a lateral process on distal tarsal IV; and the most proximal end of the pubic shaft is significantly compressed anteroposteriorly* and extends laterally just ventral to the articulation with the ilium*.” 

*These happen to be traits found in sister taxa, the Munich Archaeopteryx and/or Scansoriopteryx.

Figure 2. Mei long compared to the BSP 1999 I 50, Munich specimen of Archaeopteryx and Scansoriopteryx to scale. Click to enlarge.

Figure 2. Mei long compared to the BSP 1999 I 50, Munich specimen of Archaeopteryx and Scansoriopteryx to scale. Click to enlarge.

Scansoriopterygids
One branch of basal birds, the scansoriopterygids (Fig. 3), famous for their long third finger, now includes a new sister, Mei long. 

Figure 3.  GIF animation - the skull of Mei long IVPP specimen in situ and reconstructed.

Figure 3.  GIF animation – the skull of Mei long IVPP specimen in situ and reconstructed.

Juvenile?
The orbit is comparatively large in Mei long and several cranial and vertebral features are unfused. Gao et al. 2012 report, “Although the skeleton exhibits several juvenile-like features including free cervical ribs, unfused frontals and nasals, and a short snouted skull, other attributes, full fusion of all neurocentral synostoses and the sacrum, and dense exteriors to cortical bone, suggest a small, mature individual. Microscopic examination of tibia and fibula histology confirms maturity and suggests an individual greater than two years old with slowed growth. Despite being one of the smallest dinosaurs, Mei long exhibits multi-year growth and cortical bone consisting largely of fibro-lamellar tissue marked by lines of arrested growth as in much larger and more basal theropods.”

Distinct from its new sister taxa
Mei has shorter forelimbs and longer hind limbs. It is also a little larger even if not fully grown. Pedal digit 3 is much longer. The sacrum is much wider. The facial bones are much more gracile. The jugal may not have had an ascending process. Some of these are indeed juvenile traits that may have been retained into adulthood. Such fragility may have contributed to its general lack of fusion (less bone, lighter weight, but not for flying despite being (no doubt, but not preserved) fully feathered. Metatarsal 3 appears to be pinched between 2 and 4. Pedal 2.1 is less than half the length of p2.2 and pedal ungual 2 is quite long, but not tightly curved.

Shifting
Mei to any node prior to Archaeopteryx currently and provisionally adds at least 12 steps.

References
Xu X and Norell MA 2004. A new troodontid dinosaur from China with avian-like sleeping posture. Nature 431:838-841.
Gao C, Morschhauser EM, Varricchio DJ, Liu J, Zhao B 2012. Farke AA ed. “A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy”. PLoS ONE 7 (9): e45203. doi:10.1371/journal.pone.0045203. PMC 3459897. PMID 23028847.

wiki/Mei_(dinosaur)