Nasal crests on theropods… insight from Sinosaurus

The latest addition 
to the large reptile tree is the crested theropod, Sinosaurus (Young 1948, Hu 1993; Figs. 1,2, Early Jurassic). So far (provisionally), It nests basal to the Allosaurus + Yutyrannus clade and is a sister to the Proceratosaurus+ Spinosaurus clade that also gave rise Deinocheirus (Fig. 1).

Figure 1. Here's where the crested theropod, Sinosaurusn nests in this subset of the large reptile tree.

Figure 1. Here’s where the crested theropod, Sinosaurusn nests in this subset of the large reptile tree. Note that other crested theropods, like Dilong and Gaunlong nest nearby. Proceratosaurus might have had a crest, larger than the tiny remnant that was preserved.

 

Figure 2. Sinosaurus cast with premaxilla in yellow.

Figure 2. Sinosaurus cast with premaxilla in yellow.

Two nasal crests
top the rostrum in Sinosaurus, but they are very close together. Because Sinosaurus does not nest with Dilophosaurus, and crestless taxa separate them, those two taxa developed similar crests by convergence.

Not so oddly
those two crests on Sinosaurus are barely a crest width apart from one another. Moreover, those those two crests include a healthy portion of premaxillae — and that’s unexpected because in most dinosaurs the ascending process of the premaxilla generally does not extend beyond the naris. But it does in this clade, as we saw earlier with Deinocheirus.

Figure 3. Sinosaurus skull model along with tracing and line art from Hu 1993 then stretched to fit the model.

Figure 3. Sinosaurus skull model along with tracing and line art from Hu 1993 then stretched to fit the model. Note the extent of the premaxilla. Hu considered this another Dilophosaurus, but other workers corrected that hypothesis.

 

That sent me back looking at other clade members. 
And I found premaxillae extending beyond the naris in basal clade members. The derived forms have their own story to tell with the fused nasal boss overlying whatever premaxillary ascending process might have remained below it.

Figure 3. Yutyrannus with revised premaxilla extending beyond the naris.

Figure 3. Yutyrannus with revised premaxilla extending beyond the naris. Sinovenator and Majungasaurus both overlap the ascending process of the premaxilla with the nasal boss, so it appears much shorter. 

Is the crest of Ceratosaurus 
an emerging ascending process of the premaxilla? We’d have to look at the fossil itself, but this colorized version of an old illustration is a tantalizing clue to that possibility. In Allosaurus (Fig. 4) and Acrocanthosaurus the ascending process of the premaxilla is reduced to a slender rod that looks like a medial ridge of the nasal. I think this has been overlooked by prior workers.

Figure 4. Ceratosaurus with extended premaxilla. It is the horn sticking up between the nasals.

Figure 4. Ceratosaurus with extended premaxilla. It is the horn sticking up between the nasals.

What we’re seeing here is 
the counterintutiive phenomenon that crests came first in this clade, with convergent reduction, or coverup. in derived larger taxa.

Figure 5. Allosaurus skull with bones colorized. Note the extent of the premaxillary ascending processes over the nasals.

Figure 5. Allosaurus skull with bones colorized. Note the extent of the premaxillary ascending processes over the nasals.

With present taxa as data
the twin, barely separated crests of Sinosaurus apparently evolved from the similar morphology in its sister, Proceratosaurus, (Figs. 6, 7).

Figure 6. Proceratorsaurus skull with premaxilla (yellow) and nasal (pink) demonstrating how twin nasal crests could have originated with the loss of the premaxillary ascending process.

Figure 6. Proceratorsaurus skull with premaxilla (yellow) and nasal (pink) demonstrating how twin nasal crests could have originated with the reduction of the premaxillary ascending process.

A closeup in anterior view
of Proceratosaurus (Fig. 7) shows the early stages of splitting of the premaxilla and nasals to form two crests.

FIgure 7. Proceratorsaurus premaxilla. Note the tentative split at the top.

FIgure 7. Proceratorsaurus premaxilla. Note the tentative split at the top of the premaxilla. 

References
Hu S-J 1993. Short Report on the Occurrence of Dilophosaurus from Jinning County, Yunnan Province. Vertebrata PalAsiatica 31(1):65-79. Translated by Will Downs 1998.
Young CC 1948. On two new saurischians from Lufeng, Yunnan. Bulletin of the Geological Society of China (Acta Geologica Sinca) 28 (1–2): 75–90. doi:10.1111/j.1755-6724.1948.mp281-2007.x.

Those Dilophosaurus crests…

Revised February 15, 2016 with the deletion of the putative sister taxa, Megapnosaurus, which did not nest with Dilophosaurus when finally put to the test in the large reptile tree today. 

Sometimes it is easy to see the sutures on a skull. 
Sometimes, not so easy. That’s the case with Dilophosaurus (Welles 19454) an early theropod dinosaur with a partial skull that is cracked in so many places, the skull sutures that create the crest are camouflaged. So some alternates are proposed here (Fig. 1) without seeing the original paper, unfortunately.

Figure 1. Dilophosaurus skull with alternates for the maxilla (green), nasal (pink), premaxilla (gold) and lacrimal (tan) colorized. I have not yet seen the paper, so I don't know where Welles identified sutures.

Figure 1. Dilophosaurus skull with alternates for the maxilla (green), nasal (pink), premaxilla (gold) and lacrimal (tan) colorized. I have not yet seen the paper, so I don’t know where
Welles identified sutures.

 

If anyone has more valid details on this problem
please send them here.

References
Welles SP 1954. New Jurassic dinosaur from the Kayenta formation of Arizona”. Bulletin of the Geological Society of America 65 (6): 591–598. doi:10.1130/0016-7606(1954)65[591:NJDFTK]2.0.CO;2.

The Theropoda: just a few (albeit heretical) changes to traditional trees

Adding taxa
is a method I have supported in order to discover taxonomic relationships among reptiles. The large reptile tree (theropod subset in Fig. 1) has now passed 650 taxa. The theropod subset has been considered at odds with traditional trees. But when you really look at it, maybe, not so much.

Figure 1. Theropod subset of the large reptile tree. Unresolved clades are resolved in heuristic analyses. Here traditional clades are named. A few taxa nest somewhere other than their traditional nestings here. Click to slightly enlarge.

Figure 1. Theropod subset of the large reptile tree. Unresolved clades are resolved in heuristic analyses. Those are due to incomplete skeletons. Here traditional clades are named. A few taxa nest somewhere other than their traditional nestings here. Click to slightly enlarge.

I added four more theropods
to the large reptile tree and applied traditional names to various clades (Fig. 1). Those additions and all scoring corrections did not change the overall tree topology.

Tradition is upheld overall here
as the major clades: 1. Neotheropoda; 2. Avetheropoda/Averostra; 3; Tetanurae; 4. Maniraptora; 5. Paraves; 6. Deinonychosauria/Eumaniraptora; 7. Troodontidae; and 8. Birds/Aves appear in their traditional order and with most of their traditional taxa.

Heresy is introduced here

  1. A clade between Tawa and Coelophysis includes Marasuchus, Segisaurus and Procompsognathus, taxa too often omitted from traditional theropod trees.
  2. Several former compsognathids, including Juravenator, Sinosauropteryx, now nest as derived maniraptors close to Limusaurus + Khaan and another former compsognathid, Sinocalliopteryx, now nests with spinosaurs.
  3. Several former tyrannosauroids, including Proceratorsaurus, Dilong, Guanlong and Xiongguanlong now nest with spinosaurs.
  4. A former ornithomimid, Deinocheirus, now nests with spinosaurs.
  5. Several former dromaeosaurs, including Microraptor, Sinornithosaurus, Zhenyuanlong and Tianyuraptor now nest with tyrannosauroids.
  6. A former bird/dromaeosaur, Rahonavis now nests with basal therizinosaurs.
  7. A former ceratosaur, Limusaurus, now nests with oviraptors.
  8. Eotyrannus and Tanycolagreus nest together as basal Paraves.

The following taxa do not belong in theropod studies
because they are basal phytodinosaurs.

  1. Eodromaeus
  2. Eoraptor
  3. Daemonosaurus
  4. Chilesaurus

The problem for traditional theropod workers is
the above heretical sisters really do look like sisters, both overall and in detail. With 651 nesting opportunities, this is where they found maximum parsimony (the fewest changes to their morphology).

These nestings look like heresies, but they follow prior work

  1. Ornithomimosaurs and maniraptors were both derived from Compsognathidae (Compsognathus) according to Lee et al. 2014.
  2. A series of small troodontids give rise to birds according to Godefroit et al. 2013.
  3. Dilophosaurus nests with Coelophysis according to Sues et al., 2011.
  4. Others I missed? It’s better for everyone when I’m not the first to notice taxonomic similarities.

Added taxa
have, so far, only supported earlier clades from earlier large reptile tree topologies. There have been score changes, but that’s standard operating procedure when adding taxa. It goes to show that a pretty good tree CAN have scoring mistakes. The best tree, of course, has no mistakes.

It is so good to have photo references
to look over when trying to decide what an unidentified or misidentified crumb of bone might represent. I can’t imagine having to buy a ticket to go revisit a fossil every time I needed to see it again. The logistics would prove nightmarish. (You have to realize that NO ONE does this). Remember, no one is an expert on a fossil the moment they first see it. Spending time with data makes you an expert on it. How much of an expert do you need your experts to be?

References
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.
Godefroit P, Cau A, Hu D-Y, Escuillié, Wu, W-H and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498 (7454): 359–362.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B 278 (1723): 3459–3464

Proceratosaurus: another theropod leaves the tyrannosauroids for the spinosauroids

This blogpost
continues a series of prior blogposts featuring the tested removal of taxa traditionally considered to be in the ancestry of Tyrannosaurus. Find those posts here, here, here and here. There were also a few blogposts that added non-traditional taxa to the lineage of tyrannosaurs. Find those here, here and here.

Figure 1. Only the lower 7/8 of the skull of Proceratosaurus is known. Here the skull in siitu, A tracing modified from Tracy Ford. And another tracing by Rauhut et al. 2010 with anterior and occipital views.

Figure 1. Only the lower 7/8 of the skull of Proceratosaurus is known. Here the skull in siitu, A tracing modified from Tracy Ford. And another tracing by Rauhut et al. 2010 with anterior and occipital views. Note the entire skull is concave ventrally, but the maxilla and jugal are both straight.

Proceratosaurus bradleyi
(Middle Jurassic, Bathonian, England, NHM R 4860, Fig. 1) was originally considered another Megalosaurus (Woodward 1910), then identified as a unique taxon, a likely ancestor of a another much larger and more robust horned theropod, Ceratosaurus (von Huene 1926). Those reports were made back in the day when there were very few theropods to compare with one another.

In more recent times,
Proceratosaurus was phylogenetically nested (according to Wikipedia, Angela Milner and the BBC, Rauhut et al. (2010), Loewen et al. (2013) and Brusatte et al. (2015)) as the earliest member of the tyrannosaur lineage (Figs. 2-4).

Figure 3. Theropods from Rauhut et al. 2010. Here Proceratosaurus, Dilong and Guanlong nest with tyrannosaurs.

Figure 2. Theropods from Rauhut et al. 2010. Here Proceratosaurus, Dilong and Guanlong nest with tyrannosaurs, but key taxa are missing.

The question is why do their trees and the large reptile tree differ?
The answer could be (once again) due to taxon exclusion and tradition. The shift in nestings could be due to the lack of more attractive sister taxa in traditional tyrannosaur studies. The large reptile tree includes those more attractive sister taxa. But that is not the complete answer in every case.

Figure 4. Tyrannosaurs from Brusatte et al. 2013. Some taxa nest elsewhere in the large reptile tree. Others are missing from this tree.

Figure 3. Tyrannosaurs from Brusatte et al. 2013. Some taxa nest elsewhere in the large reptile tree. Others are missing from this tree. Click to enlarge.

Could it be scoring?
I have not checked the scores and matrices in other studies. I do know that the sisters in the large reptile tree do share long lists of character traits, but D-shaped premaxillary teeth (often touted as a key trait restricted to tyrannosaurs) are not among the traits listed there. Did Spinosaurus and Suchomimus also have D-shaped premaxillary teeth? I don’t know. If not, could that trait be in their relatively short-snouted ancestors by convergence? At this point the answer is, apparently so.

Rauhut (2010 reported, “As close relationships of Proceratosaurus with several of the clades included in this analysis (coelophysoids, spinosauroids, and maniraptorans) have never been proposed previously, these clades were collapsed [individually] into [a] single operational taxonomic unit[s] (OTU[s]).” 

That’s a problem
as the large reptile tree found Proceratosaurus to nest closest to basalmost spinosauroids (former tyrannosauroids). Now do you see why it is SO important NOT to employ suprageneric taxa — ever! It is possible that Rauhut et al. (and those that followed) created their own problems by creating suprageneric taxa where they should not have done so. In Science you have to be open to any and all answers, without bias or a priori assumptions wherever practicable and possible. That’s why it is so convenient to start with the large gamut of possibilities provided by the large reptile tree (now 647 taxa and growing).

Figure 5. Theropods from Loewen et al. with pertinent taxa highlighted.

Figure 4. Theropods from Loewen et al. with pertinent taxa highlighted.

Proceratosaurus was added
to the large reptile tree (subset in Fig. 5) and it did not nest with tyrannosaurs, but with smaller Early Cretaceous taxa that traditionally nest with tyrannosaurs, but now nest with spinosaurs. Everyone agrees that Proceratosaurus nests with Guanlong and Dilong. Everyone else agrees that these three nested with tyrannosaurs (Figs. 2-4). So, I am the only unorthodox heretic at present.

Figure 2. The Dinosauria subset of the large reptile tree as of February 5, 2016. Here Proceratosaurus nests with several former long-snouted tyrannosaurs now closer to spinosaurs and allosaurs.

Figure 5. The Dinosauria subset of the large reptile tree as of February 5, 2016. Here Proceratosaurus nests with several former long-snouted tyrannosaurs now closer to spinosaurs and allosaurs.

The large reptile tree
provides ancestral taxa that share more traits (see below) with Late Cretaceous tyrannosaurs than the traditional putative Jurassic and Early Cretaceous candidates provided by the authors listed in the references. I promote these recovered candidates so they will be tested by others, as I have tested their candidate taxa.

Without a doubt,
the Late Cretaceous tyrannosaurs are all monophyletic. The question is, which taxa phylogenetically preceded them in the Early Cretaceous and Jurassic? Note that none of the taxon lists in any of the studies totally match one another. On the other hand, all of the studies are in general agreement. However, the recovered topologies don’t exactly match one another. And so the game is afoot.

Getting back to Proceratosaurus
Take a look at its sister on the allosaur branch in the large reptile tree: it’s Ceratosaurus. So maybe von Huene (1926) was on to something… or he was lucky.

Basic traits that Proceratosaurus, Guanlong and Dilong
share with Sinocalliopteryx, Deinocheirus and the spinosaurs.

  1. Long, low rostrum
  2. Sometimes smaller premaxillary teeth vs. maxillary teeth
  3. Tall orbit
  4. Premaxillary postero-lateral processes that may be present due only to the down tip of the naris.
  5. Ventral border of elongate naris formed by premaxilla + nasal
  6. Long, strongly recurved maxillary teeth
  7. Majority coverage of the quadrate by the squamosal and quadratojugal.
  8. Often, but not always, a nasal median crest.
  9. Often, but not always, a descending posterior skull relative to the maxilla

Given that
Sinocalliopteryx and Dilong had primitive feathers, all (except perhaps the giants) probably shared that rarely preserved trait. Given that the above nine traits are all skull traits, it is likely that this clade was trending toward a specific feeding niche, in this case, an aquatic one.

Someday this will all come together. 

References
Brusatte SL and Carr TD 2016. The phylogeny and evolutionary history of tyrannosauroid dinosaurs. Nature, Scientifice Reports 6 (8 pages), 20252; doi: 10.1038/srep20252.
Loewen MA, Irmis RB, Sertich JJW, Currie PJ, Sampson SD 2013. Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. PLoS ONE 8(11): e79420. doi:10.1371/journal.pone.0079420
Rauhut OWM, Milner AC and Moore-Fay S 2010. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi(Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, published online before print November 2009. doi:10.1111/j.1096-3642.2009.00591
von Huene F 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Geologie und Palaeontologie (Serie 1), 4: 1–361.
Woodward AS 1910. On a Skull of Megalosaurus from the Great Oolite of Minchinhampton (Gloucestershire). Quarterly Journal of the Geological Society 66: 111–115.

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.

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

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