Summary for those in a hurry:
Compared to traditional taxon lists (Figs. 3, 4), the LRT taxon list for the Troondontidae is greatly reduced (Fig. 2). That means many traditional troodontids nest elsewhere.
We start today with a new taxon.
Zanabazar junior (Norell et al. 2009, originally Sauronithoides junior Barsbold 1975; IGM 100/1; est. 2.3m long, 27cm skull length; Fig. 1), is a late-surviving (Late Cretaceous) basal troodontid in the large reptile tree (LRT, 1274+ taxa; subset Fig. 2). The specimen includes a nearly complete skull and braincase, part of the pelvis, some tail vertebrae, and parts of the right hindlimb. The teeth are relatively small.
Prior to the LRT
authors nested Zanabazar as a highly derived troodontid (Figs. 3, 4).
Those other authors
also nested LRT pre-bird anchiornithids (Sinovenator, Almas, Daliansaurus, Sinusonasus, Jinfengopteryx) and one scansoriopterygid bird (Mei) in the Troodontidae (Fig. 4). Prior authors include several taxa known from scrappy data that will not be tested in the LRT. These include Talos, Byronosaurus, Troodon, IGM 100/44, Linhevenator, and Philovenator.
On the other hand,
the LRT (Fig. 2) includes troodontid taxa not included or nested elsewhere (e.g. Rhamphocephalus, Haplocheirus, Shuvuuia, Halszkaraptor). Readers will note that several of these taxa are alvarezsaurids that now nest within the Troodontidae in the LRT. This is a novel hypothesis of interrelationships. If there is another prior citation, please let me know so that can be promoted.
According to Wikipedia
“During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages.” By contrast, most taxa included in the LRT are largely complete.
“More recent fossil discoveries of complete and articulated specimens (including specimens which preserve feathers, eggs, embryos, and complete juveniles), have helped to increase understanding about this group.” None of these sorts of taxa currently in the Troodontidae in the LRT (Fig. 2).
The first question is:
What is the definition of Troodontidae?
Looking for a definition online @ yourdictionary.com
“Any member of a family (Troodontidae) of small, bird-like theropod dinosaurs with large brains, large eyes, and a retractable claw on the second toe of each hind foot, similar to a farmer’s sickle, used for slashing at prey.”
This is a trait-based definition, subject to convergence. We call this “Pulling a Larry Martin.” Only a phylogenetic nesting in a wide gamut cladogram can determine what is and what is not a troodontid and that starts with a definition of the clade.
According to Wikipedia (Troodon)
“the entire genus is based only on a single tooth.” and this tooth has been considered to belong to a wide variety of Reptilia. “Phil Currie, reviewing the pertinent specimens in 1987, showed that supposed differences in tooth and jaw structure among troodontids and saurornithoidids were based on age and position of the tooth in the jaw, rather than a difference in species.”
So, there’s a definite problem
in defining both Troodon and the Troodontidae. Even so, the theropoddatabase.com has compiled a few that may prove useful.
- Troodontidae = Troodon formosus (Gilmore 1924)
- Troodontidae = Troodon formosus, Saurornithoides mongoliensis, Borogovia gracilicrus, Sinornithoides youngi but not Ornithomimus velox, Oviraptor philoceratops) (Varricchio 1997)
- Troodontoidea = Troodon + Saurornithoides (Livezey and Zusi 2007)
What these definitions have in common
are the more completely known taxa, Sinornithoides, Sauronithoides and Zanabazar. Let’s make these, plus their last common ancestor. our working definition. Let’s assume, until proven wrong, that Troodon is similar in most respects. Given these parameters many taxa leave the clade Troodontidae and nest within the bird-line of anchiornithids or within birds (Fig. 2).
Gobivenator, the most completely known troodontid,
(Fig. 5, 6) was added to the LRT just an hour ago, nesting alongside Zanabazar with very few scoring differences. So, Gobivenator was not forgotten.
(Fig. 7) nests not with troodontids in the LRT, but with the bird clade scansoriopterygids, between the private #12 Archaeopteryx specimen and Yi qi. Yes, it has small hands and could not fly (like Struthio the ostrich). Moving Mei to the troodontids adds 23 steps. Reversals do happen. A few traits compete against a larger suite. Let your software determine where a taxon nests and make sure you include enough taxa to let convergence happen.
Wikipedia – Mei long reports:
“It is most closely related to the troodontid Sinovenator, which places it near the base of the troodontid family.” In the LRT, Sinovenator (Fig. 8) is not in the Troodontidae, but nests in proximal bird outgroup clades. Moving Mei long to Sinovenator adds 19 steps to the LRT. Taxon exclusion has so far kept Mei long apart from other scansoriopteryids everywhere but here.
Figure 8. Sinovenator nests with anchiornithid birds in the LRT.Likewise,
Sinovenator nests not with troodontids in the LRT, but with the pre-bird anchiornithids, between Almas (Fig. 9) and the BMNHC PH804 specimen of Anchiornis.
The LRT documents a fast track for the origin of birds
from the last common ancestor of Bambiraptor + Zanabazar that leads to the following series of taxa: Anchiornis, Daliansaurus (Fig. 9), Almas, the Daiting specimen of Archaeopteryx, Xiaotingia and the Thermopolis specimen of Archaeopteryx, the last known common ancestor of all birds in the LRT.
(Shen et al. 2017; Early Cretaceous, Barremian, 128 mya; 1 m long) nests in the LRT as a basal anchiornithid, not a troodontid.
(Pei et al. 2017; Campanian, Late Cretaceous, IGM 100/1323) nests in the LRT as a basal anchiornithid, not a troodontid.
Several lineages approached and experimented with the bird grade
(e.g. Rahonavis, Microraptor, the Daiting specimen of Archaeopteryx), but only one lineage starting with the Thermopolis specimen of Archaeopteryx created robustly volant and extant birds.
In the LRT,
the reduced clade memberships of Troodontids indicate they are a splinter group,
closer to Bambiraptor + Velociraptor. That combined clade (Fig. 2) is a splinter group to the smaller compsognathids and anchiornithids lineage that led more directly to birds (Fig. 9).
Barsbold R 1974. Saurornithoididae, a new family of small theropod dinosaurs from Central Asia and North America. Palaeontologica Polonica. 30: 5−22.
Norell MA et al. 2009. A review of the Mongolian Cretaceous dinosaur Saurornithoides (Troodontidae, Theropoda). American Museum Novitates (3654): 1−63.
Short one today,
both in text length and taxon height.
Bambiraptor feinbergi (Burnham et al. 2000; Late Cretaceous, AMNH FR 30556) was originally considered a juvenile Sauronitholestes. The brain size is the largest among Mesozoic dinosaurs. Here it nests basal to Velociraptor + Balaur in the large reptile tree (LRT, 1724+ taxa, subset Fig. x). Proportions are closer to Arachaeopteryx according to the authors.
at Zanazabar soon.
Burnham DA, Derstler KL, Currie PJ, Bakker RT, Zhou Z and Ostrom J H 2000. Remarkable new birdlike dinosaur (Theropoda: Maniraptora) from the Upper Cretaceous of Montana. University of Kansas Paleontological Contributions 13: 1-14.
the small, but extremely robust hand claws of Mononykus and Shuvuuia (Figs. 1, 2) were considered digging tools. If so, their forelimbs would have been distinctly different from the digging forelimbs of all other fossorial tetrapods based on size alone, not to mention the rest of the bird-like morphology that does nothing to support a digging hypothesis.
Maybe there’s another answer.
For a moment, let’s not focus on Mononykus and Shuvuuia. Let’s broaden our view to see what related taxa are doing with their forelimbs. Let’s see if phylogenetic bracketing and environment can provide clues to the Mononykus forelimb mystery.
include Haplocheirus (Fig. 3) and, more distantly, Velociraptor (Fig. 3). These two have forelimbs more typical of theropods with three digits and digit 2 longer than 1. Both come with a reputation and ability to jump on large dinosaurs (Fig. 4).
That’s similar to
what extant tickbirds (oxpeckers) do to large African mammals (Fig. 4), though not with the intention of ripping into their flesh with a wicked pedal digit 2.
In modern day Africa
tickbirds are often seen happily perching atop rhinos and other larger mammals (Fig. 5), cleaning them of parasites and riding them like passengers on a bus… yet always able to fly away or jump off and run away.
To scale with other dinosaurs of their time and place
(Fig. 3) it becomes clear that alvarezsaurids and Mononykus were relatively about the size of tickbirds and able to do the same job (plucking off parasitic insects) for their mutual benefit.
Clearly Mononykus and Shuvuuia are highly specialized
taxa leaving no descendants. In the large reptile tree (LRT, 1692+ taxa) these alvarezsaurids evolve from larger theropods like Hapolocheirus. As the ancestors of Mononoykus and Shuvuuia grew smaller, so did their forelimbs, pelvis, killer toe and teeth. These tiny theropods became more and more specialized for their insect-plucking, hitchhiking niche. As they became phylogenetically-miniaturized, smaller alvarezsaurids were able to hitch rides on smaller and smaller dinosaurs.
So the little adducting forelimbs of Mononykus and Shuvuuia
acted like little hair clips, keeping these little dinosaurs attached to the skin and feathers of their hosts. That’s really all they were good for. Not flying. Not flapping. Not digging. Not display. Just mighty adduction. Those tiny forelimbs with big thumbs were perfect for clipping to giant host dinosaurs. The long legs of Mononykus would have been just long enough to walk through high feathers, like a human walks through tall grass. Or to run and hop on one new dinosaur after another. Active and highly coordinated, alvarezsaurids would have had the same agility as modern birds when they cavort on tree branches, tree trunks and rhino backs, all without using their ‘hands.’
This may be a novel hypothesis.
If not, please provide a citation so I can promote it.
Added a day later in response to the above promise:
Thank you, Tyler. From the abstract: “I propose that bizarre structures may have served to defend against parasitic dorsal attacks from riding dromaeosaurs. Frequent dismounts from large living dinosaurs may explain the origin of feathers, gliding and avian flight.”
Fraser G 2014. “Bizarre Structures” Point to Dromaeosaurs as Parasites and a New Theory for the Origin of Avian Flight. The Journal of Paleontological Sciences: JPS.C.2014.01 PDF
In counterpoint, Fraser was postulating the origin of larger wings and feathers for dismounting dromaeosaurs. He also discussed the origin of frills, plates and spikes on large host herbivores to dissuade dromaesaurs from mounting in the first place. Unfortunately, nowhere does he discuss the alvarerzsaurids or Mononykus and the development of its bizarre tiny forelimbs. Evidently they were not on his ‘radar’. Even so, thank you for bringing this paper to my attention. A good read!
A few more data points and citations:
Velociraptor mongoliensis (Osborn 1924; Late Cretaceous, 75 mya; 6.8m long) The tail was long and stiffened with elongate chevrons and zygapophyses. The deep pubis was oriented posteriorly with a large pubic ‘boot’.
Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) The tail was not stiffened with elongate accessory processes.
Mononykus olecranus (Perle et al, 1993; Late Cretaceous ~70 mya, 1 m in length) Only digit I remained full size on the stunted hand. The proximal ulna (the elbow) was enlarged. The pubis was shorter and lacked a pubic boot.
Shuvuuia deserti (Chiappe, Norell and Clark 1998, Late Cretaceous) was smaller and retained digits 2 and 3 as vestiges.
Halszkaraptor escuilliei (Cau et al. 2017; Late Cretaceous) was originally considered an aquatic dromaeosaur related to Mahakala, but here nests with Shuvuuia. A distinctly different manual digit 3 was the longest, but the gracile thumb retained the largest claw. The hands did not act like hair clips.
Cau A, et al. 2017. Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs. Nature. doi:10.1038/nature24679
Chiappe LM, Norell MA and Clark JM 1998. The skull of a relative of the stem-group bird Mononykus. Nature, 392(6673): 275-278.
Choiniere JN, Xu X, Clark JM, Forster CA, Guo Y, Han F 2010. A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China. Science 327 (5965): 571–574. Perle A, Norell MA, Chiappe LM and Clark JM 1993. Flightless bird from the Cretaceous of Mongolia. Nature 362:623-626.
Perle A, Chiappe LM, Rinchen B, Clark JM and Norell 1994. Skeletal Morphology of Mononykus olecranus (Theropoda: Avialae) from the Late Cretaceous of Mongolia. American Museum Novitates 3105:1-29.
Here’s the blogpost that inspired this one.
A Smithsonianmag.com writer is trying to make the ordinary extraordinary by claiming, “The Rise of Meat-Eating Dinosaurs Is More Complicated Than We Thought. “
Writer Riley Black (formerly Brian Switek)
writing in smithsonianmag.com declares: “The earliest dinosaurs arose about 235 million years ago during the Middle Triassic. They didn’t look much like modern favorites Triceratops or Spinosaurus. Instead, these lanky creatures didn’t get much bigger than a German shepherd. The current spate of evidence suggests they were omnivorous.”
Black also provides this image (Fig. 1) of middle Triassic Herrerasaurus, the basalmost dinosaur in the large reptile tree (LRT, 1688+ taxa) and this is no omnivore. This taxon is 3 meters or 16 feet long, not the size of a German shepherd.
“Up until now, paleontologists thought theropods remained generally small and on the ecological sidelines from about 235 through 201 million years ago. It was only after a mass extinction at the end of the Triassic, at the 201 million-year mark, that carnivorous dinosaurs started to get big. But that view is starting to change thanks to a new reading of the bone trail by scientists who think large meat-eaters may have appeared much earlier. Virginia Tech paleontologist Christopher Griffin says a key player in this story is Herrerasaurus.”
Confused? So am I. This brings us back to where the LRT starts, regarding dinosaurs. Everyone in paleo knows Herrerasaurus is a Middle Triassic carnivorous dinosaur. The little German shepherd-sized dinos are either made up or never existed. In either case, Black doesn’t list or illustrate them.
“The known carnivorous dinosaurs during the later part of the Triassic appeared to be smaller and less imposing than the crocodile relatives they lived alongside (such as Postosuchus from the southwestern United States). Thanks to a better understanding of dinosaur growth, however, paleontologists have found that some of those little theropods were hiding a secret.”
Postosuchus is not a crocodile relative in the LRT. Herrerasaurus is closer to crocodiles in the LRT because only crocodylomorphs and dinosaurs make up the clade Archosauria.
“The few remains we’ve found of larger Triassic theropods come exclusively from immature animals that are still growing rapidly,” Griffin says. These young carnivores would have grown to lengths exceeding 18 feet in adulthood. That’s a little less than half a full-grown T. rex, but enough to make you want to avoid meeting such a carnivore face-to-face.”
A few Late Triassic theropod lengths: Tawa is 2m long. Coelophysis is 3m long. Both are represented by adult skeletons. Again, where are these imaginary few remains?
Black finally raises the curtain on her main attraction:
“Late last year, Ludwig-Maximilian University of Munich paleontologist Oliver Rauhut and colleague Diego Pol named an exceptional skeleton of a Middle Jurassic carnivore they called Asfaltovenator. This was a large animal, more than 25 feet long, that approached the average size of the later Allosaurus and bears more a passing resemblance to the later dinosaur.”
This is no big deal. Between the Late Triassic and the Late Jurassic we expect to find theropod dinosaurs bigger than their ancestors and smaller than their descendants with transitional morphologies.
Black concludes with a quote:
“There is much more to be learned about theropod evolution during this time,” Rauhut says, with finds like Asfaltovenator hinting at what remains to be uncovered.”
Again, no big deal. There is always ‘much more to be learned’ about all taxa ‘during this time.’ Some people complain because I was a journalism major. Sometimes that degree comes in handy.
Black R 2020. The Rise of Meat-Eating Dinosaurs Is More Complicated Than We Thought. online here.
We looked at tiny,
feathered Sciurumimus albersdoerferi (Germany, Rauhut et al. 2012; BMMS BK 11) and larger bones-only Ornitholestes (North America) earlier as Late Jurassic sisters in the large reptile tree (LRT, 1659+ taxa). After a recent review, these two continue to nest as sisters at the base of the Microraptor (Fig. 3) + Sinornithosaurus clade. So no news here… except now let’s combine the extraordinary size difference between the two and the widely accepted observation that Sciurumimus is a juvenile.
That brings to mind: a juvenile of what?
The LRT indicates a juvenile ornitholestid (Fig. 1). The overall morphologies are strikingly similar and the size difference is appropriate. Other published studies recover other nestings.
Rauhut, et al. 2012
(Suppdata) nested Ornitholestes between ornithomimosaurs and deinonychosaurs, far from Sciurumimus, which Rauhut et al. nested Sciurumimus between an unresolved clade of giant spinosaurs + megalosaurs and giant Monolophosaurus. Like Rauhut et al., the LRT nests also nests Ornitholestes between ornithomimosaurs (+ tyrannosaurs + oviraptors + therizinosaurs) and deinonychosaurs.
Key differences in the LRT include
- the use of two Compsognathus specimens. The each nest at the base of their own clade, a hypothesis of interrelationships overlooked by Rauhut et al.
- the inclusion of three Microraptor specimens and two Sinornithosaurus specimens, adults of which are closer in size and morphology to Sciurumimus. This brings to mind the possibility that phylogenetic miniaturization and neotony played a part in the evolution of these bird-mimics. These closely related taxa were omitted by the Rauhut et al. selection process.
In their study of the wonderfully preserved
anchiornithid, Aurornis, Godefroit et al. nested Sciurumimus between Monolophosaurus + Sinraptor and Zuolong, all more primitive taxa in the LRT. In Godefroit et al. these taxa are far from Ornitholestes, which nested with another small compsognathid, Juravenator. Juravenator nests with equally small, but shorter limbed Sinosauropteryx in the LRT. Evidently few theropod studies agree with one another in the details.
Rauhut et al. 2012 reported,
“Our analysis confirms Sciurumimus as the basalmost known theropod with evidence of feather-like integument.” By contrast, in the LRT, Tawa-like, feathered Sincalliopteryx (Fig. 2) is more primitive, despite its late appearance (Early Cretaceous) in the fossil record.
currently nests basal to Late Triassic Coelophysis, and was derived from Late Triassic Tawa. In the LRT, Sinocalliopteryx has the most primitive presence of feathers among theropods despite its appearance tens of millions of years later than its phylogenetic genesis.
The Ornitholestes + Sciurumimus + Microraptor + Sinornithosaurus clade
were bird-mimics and bird-mimic ancestors not directly related to birds or bird ancestors in the LRT.
Godefroit P, Cau A, Hu D-Y, Escuillié F, Wu, W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature. 498 (7454): 359–362.
Rauhut OWM, Foth C, Tischlinger H and Norell MA 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences. 109 (29): 11746–11751.
Poust et al. 2020
bring us news of a small, subadult theropod with some interesting traits, Wulong bohaiensis (Early Cretaceous; D2933). They considered the specimen a microraptorine dromaeosaurid.
the large reptile tree (LRT, 1637+ taxa) nests Wulong among similar, small, long-legged troodontids, between Buitreraptor and Caihong. While this topology differs from that of other workers, the same can be said of nearly every clade in the LRT. That’s why this blog has been self-labeled ‘heretical’.
So, why the different views?
That appears to be due to taxon exclusion. There is no indication in the text that Buitreraptor and Caihong were included in analysis. There is no indication that the authors created a reconstruction, which helps identify bones, their ratios and proportion in crushed taxa like Wulong. More importantly…
… several taxa converge on birds
and small feathered theropods converge with each other in the LRT. The differences between the clades should not be determined by a few traits (= Pulling a Larry Martin), but here are gleaned after phylogenetic analysis of several hundred traits. As mentioned earlier, you can’t nest a specimen within a clade by a small number of cherry-picked traits because there is so much convergence within the Tetrapoda. Rather, run an analysis and find out which taxon is the last common ancestor of a derived clade. Those, then, are the validated clade members.
the coracoid is fenestrated in the middle. The ilium includes a prepubis process. Some feathers are preserved.
The authors report,
“Wulong is distinguished by several autapomorphic features and additionally, has many characteristics that distinguish it from its closest well-known relatives. Compared with Tianyuraptor and Zhenyuanlong, Wulong is small and its forelimbs are proportionally long.”
Poust AW, Gao C-L, Varricchio DJ, Wu J-L and Zhang F-J 2020. A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids. The Anatomical Record. American Association for Anatomy. DOI: 10.1002/ar.24343
O’Connor et al. 2019 report on
a small pre-squamate lizard, Indrasaurus wangi (Fig. 1; STM5-32), ingested just before the untimely death of its feathered predator, Microraptor (Fig. 3, STM5-32). Both were added to the large reptile tree (LRT, 1542 taxa). O’Connor et al. note, “This is the fourth specimen of Microraptor described with ingested remains preserved in the abdominal cavity, with enantiornithine birds, mammals, and fish previously documented.”
From their abstract:
“Phylogenetic analysis suggests Indrasaurus wangi gen. et sp. nov. is a basal scleroglossan closely related to the slightly older Liushusaurus. Comparison of ingested remains preserved across Paraves suggests that dromaeosaurids retained the plesiomorphic condition in which ingested prey were fully digested, rather than egested, as has been demonstrated was the case in the probable troodontid Anchiornis.”
In the LRT Liushusaurus is an outgroup taxon to the Squamata, a clade defined by extant taxa. Liushusaurus nests six nodes apart from Indrasaurus.
O’Connor et al. remarked,
“Phylogenetic relationships in fossil squamates are difficult to determine with currently available matrices. Given the uncertainty regarding squamate relationships at this time, we do not find it unusual that our results add to the current disparity.” O’Connor et al. did not realize the clade Protosquamata enclosed the clade Squamata. The LRT was the first to recover this clade and another previously overlooked lepidosaur clade, the Tritosauria, nesting between Sphenodontia and Squamata.
In the LRT,
Indrasaurus (STM5-32) nests close to the coeval Hoyalacerta (Fig. 2) in the Protosquamata, a more primitive clade than Squamata that includes Squamata and otherwise no extant taxa. O’Connor et al. are mistaken, according to the LRT, when they consider Indrasaurus a scleroglossan squamate.
Indrasaurus sister taxa do not have an antorbital fenestra, so the one that appears here (Fg. 1) is suspect, but possible.
The STM5-32 specimen of Microraptor (Fig. 3) nests as the basalmost tested Microraptor derived from a sister to Sciurumimus and Ornitholestes (Fig. 4), convergent with and distinct from pre-bird clades. Traditional cladograms, like the recently published Hartman et al. 2019, do not associate these three taxa apart from birds. O’Connor et al. consider Microraptor to be a dromaeosaurid. The LRT rejects that hypothesis of interrelationships.
Three Microraptor species
Since the three tested Microraptors nest apart from one another with high Bootstrap scores, two need to be given new specific names, not lumped under Microraptor zhaoianus, as O’Connor et al. do.
Was Microraptor volant?
O’Connor et al. consider all specimens of Microraptor to be volant (capable of flight). The short, nearly disc-like shape of the coracoid (Fig. 2) argues against this, despite the presence of large feathers in this genus. The key difference between Late Jurassic birds and pre-bird anchiornithids is the elongation of the locked-down coracoid, which marks the genesis of flapping in pterosaurs and birds. Like their ancestor, Ornitholestes, Microraptor had small, disc-like coracoids that slid like those of most tetrapods with coracoids. Based on the elongation and locking down of coracoids, evidently flapping occurred before forelimb elongation in pterosaurs, afterwards in basalmost birds, like the basal Archaeopteryx specimens. Microraptor was a glider at best, not a flapper, which requires locked-down elongate coracoids.
O’Connor et al. (six co-authors) 2019. Microraptor with ingested lizard suggests non-specialized digestive function. Current Biology 29, 1–7. https://doi.org/10.1016/j.cub.2019.06.020
Short note on a long rostrum today:
I just found this fascinating.
The naris of Spinosaurus (Stromer 1915; Cretaceous; MSNM V4047) was overlaid by the maxilla sealing off most of what had been the elongate opening (Fig. 1). I suppose that supports a semi-aquatic niche and reduced olfactory input. As others have noted, the rostrum has sensory pits, perhaps, as in crocodilians, for underwater vibration sensing.
Dal Sasso et al. 2005 wrote:
“The external naris is retracted farther caudally on the snout than in other spinosaurids and is bordered exclusively by the maxilla and nasal.” The authors identified the anterior naris as a ‘sub-narial foramen’. The naris continues to contact the premaxilla in all related taxa (Fig. 1). Here, just thinking about things differently, and more parsimoniously, the naris continues to contact the premaxilla.
According to Wikipedia
“MSNM V4047 (in the Museo di Storia Naturale di Milano), described by Dal Sasso and colleagues in 2005, consists of a snout (premaxillae, partial maxillae, and partial nasals) 98.8 centimetres (38.9 in) long from the Kem Kem Beds. Like UCPC-2, it is thought to have come from the early Cenomanian. Arden and colleagues in 2018 tentatively assinged this specimen to Sigilmassasaurus brevicollis given its size. In the absence of associated material, however, it is difficult to be certain which material belongs to which taxon.”
dal Sasso C, Maganuco S, Buffetaut E, Mendez MA 2005. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its sizes and affinities. Journal of Vertebrate Paleontology. 25 (4): 888–896.
Ibrahim N et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613–1616.
Stromer E 1915. Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltier-Reste der Baharije-Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus aegyptiacus nov. gen., nov. spec. Abhandlungen der Königlich Bayerischen Akademie der Wissenschaften, Mathematisch-physikalische Klasse (in German). 28 (3): 1–32.
like Megaraptor namunhuaiquii (Novas 1998, Fig. 1) and Murusraptor barrosaensis (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; MCF-PVPH-411; Fig. 1), are currently only known from bits and pieces. Perhaps for these reasons Wikipedia reports, “the clade Megaraptora (Benson, Carrano and Brusatte 2010 ) has controversial relations to other theropods.”
According to Wikipedia
“Murusraptor is a megaraptoran, one of a group of large predatory dinosaurs whose exact classification remains disputed. Once believed to be dromaeosaurids, they have since been classified as either allosauroid carnosaurs or as tyrannosauroid coelurosaurs. While the discovery of Murusraptor does not clarify as of yet the placement of this group of theropods, the specimen does add further clarity to some aspects of megaraptoran anatomy and potentially, eventual classification of the Megaraptora within the theropod evolutionary tree.”
Megaraptora (Benson et al 2010) “The most inclusive clade comprising Megaraptor namunhuaiquii, but not Chilantaisaurus tashuikouensis.”
“Megaraptorans were most diverse in the early Late Cretaceous of South America, particularly Patagonia. However, they had a widespread distribution. Fukuiraptor, the most basal (“primitive”) known member of the group, lived in Japan. Megaraptoran material is also common in Australia, and the largest known predatory dinosaur from the continent, Australovenator, was a megaraptoran.”
Taxa traditionally included within Megaraptora:
- Megaraptor (known from a long maxilla and forelimb, Figs. 1, 2)
- Fukuiraptor (known from jaw fragments, coracoids, humeri, femur, acetabulum, two vertebrae
- Australovenator (known from a dentary, a few dorsal ribs, distal forelimbs and nearly complete hind limbs)
- Murusraptor (known from several skull elements and other bones Figs. 1, 2)
Of these, only two, Megaraptor and Murusraptor, are tested in the LRT.
Other megaraptoran traits according to Wikipedia
- “Their forelimbs were large and strongly built,
- The ulna bone had a unique shape (except Fukuiraptor).
- The first two fingers were elongated, with massive curved claws ,
- The third finger was small.
- Megaraptoran skull material is very incomplete, but a juvenile Megaraptor described in 2014 preserved a portion of the snout, which was long and slender.
- Leg bones referred to megaraptorans were also quite slender and similar to those of coelurosaurs adapted for running.
- Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The vertebrae, ribs, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in taxa such as Neovenator.
- Other characteristic features include opisthocoelous neck vertebrae
- and compsognathid-like teeth.”
Several of the above traits
are shared with other taxa. The LRT employes a suite of 231 shared, unique and often convergent traits to lump, split and ultimately nest all taxa. Surprisingly, even the poorly preserved, disarticulated and incomplete Megaraptor and Murusraptor found secure nodes.
Araciaga, Rolando, Novas and Agnolin 2019
bring us ‘new evidence about the phylogenetic relationships of Megaraptora.’ They report, “The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”
From their abstract:
“Murusraptor is particularly similar to juvenile specimens of tyrannosaurids; both share: 1) lacrimal with a long anterior prosess; 2) corneal process and; 3) lateral pneumatic fenestra; 4) square and dorsoventrally low frontals; 5) parietals with well-developed sagittal and nuchal crests, among other features. The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”
“Murusraptor is unique in having several diagnostic features that include anterodorsal process of lacrimal longer than height of preorbital process, and a thick, shelf-like thickening on the lateral surface of surangular ventral to the groove between the anterior surangular foramen and the insert for the uppermost intramandibular process of the dentary.
“Other characteristic features of Murusraptor barrosaensis n.gen. et n. sp. include a large mandibular fenestra, distal ends of caudal neural spines laterally thickened into lateral knob-like processes, short ischia distally flattened and slightly expanded dorsoventrally. Murusraptor belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor.”
A little backstory with links for more details:
Aerostean is a giant (9m) Late Cretaceous theropod with no skull material known. Orkorpator is a large (6m) Latest Cretaceous theropod includes only a post-orbital and quadratojugal for skull material and bits and pieces otherwise.
In the large reptile tree (LRT, 1415 taxa; Fig. 4) Megaraptor (Fig. 1) nests with the basal theropod, Sinocalliopteryx. Murusraptor (Fig. 1) nests between long-snouted Dilong and the long-snouted Guanlong / Spinosaurus clade.
One problem comes from
the hypothesis of relationships published by Coria and Currie 2016 that nests long-snouted Xiongguanlong, Dilong, Proceratosaurus and Guanlong with robust-snouted Tyrannosaurus, rather than with long-snouted spinosaurs. Even so, Coria and Currie
nest Murusraptor with Megaraptor. The closest theropod also tested in the LRT is the finback allosaur, Acrocanthosaurus. So, the Coria and Currie cladogram is different in most respects from the LRT. Coria and Currie also nest the giant horned theropod, Ceratosaurus, as a basalmost/outgroup taxon. In the LRT (Fig. 4) Ceratosaurus has no descendants.
In counterpoint to Coria and Currie 2016,
Novas et al. 2016 reported, “megaraptorids retained several of the manual features present in basal tetanurans, such as Allosaurus. In this regard, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus).”
In the LRT,
(Fig. 4) Guanlong is closer to Allosaurus than to Tyrannosaurus.
According to the writers of Wikipedia,
the large compsognathid, Sinocallioteryx (Figs. 1-3) is not related to megaraptorids, despite the many similarities in the skull. Curiously, other long-snouted theropods with massive curved claws on their forelimbs, like Suchomimus (Fig. 3), are also not traditionally considered related to megaraptorids. I wish they were. Everyone wishes they were. However, I have to report results, no matter how controversial, as I have for the last eight years. That way, if I made mistakes, someone will tell me. If someone has forgotten certain taxa, perhaps next time they will add them.
Murusraptor barrosaensis (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; Late Cretaceous) was originally considered a sister to Megaraptor and close to tyrannosaurs. Here (Fig. 4) Murusraptor nests between Dilong and Guanlong closer to spinosaurs. Megaraptor nests with Sinocalliopteryx, a basal theropod, not close to Murusraptor. Wherever other traditional megaraptorans (see list above) nest has not yet been tested in the LRT. We looked at the relationship of long-snouted theropods with spinosaurs, rather than tyrannosaurs earlier here.
Rolando AMA, Novas FE and Agnolin FL 2019. A reanalysis of Murusraptor barrosaensis Coria & Currie (2016) affords new evidence about the phylogenetical relationships of Megaraptora. Cretaceous Research. https://doi.org/10.1016/j.cretres.2019.02.021
Benson RBJ, Carrano MT and Brusatte SL 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic.
Naturwissenschaften 97(1): 71–78.
Coria RA and Currie PJ 2016. A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLoS ONE 11(7): e0157973. doi:10.1371/journal.pone.0157973
Novas FE 1998. Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia. Journal of Vertebrate Paleontology. 18: 4–9. doi:10.1080/02724634.1998.10011030
Novas FE, Rolando AMA and Agnolín FL 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria. 74: 49–61.
Porfiri JD, Novas FE, Calvo JO.; Agnolín FL.; Ezcurra MD and Cerda IA. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research. 51: 35–55.
Everyone knows Carnotaurus
(Fig. 1; Bonaparte 1985, Bonaparte, Novas and Coria 1990), the slender theropod with skull horns. In the large reptile tree (LRT, 1391 taxa) Carnotaurus nests with Majungasaurus, members of the first clade of giant theropods, the one that includes Spinosaurus, Allosaurus, Ceratosaurus and many others.
That comes as no surprise.
The only contribution I can make to this popular dinosaur is to note the horns arise from laterally extended lacrimals and prefrontals, not laterally extended frontals, as originally proposed (Fig. 1). In stating this, I may be late to the party. If others have already published on this bit of trivia, I am not aware of it. If so, let me know.
Carnotaurus sastrei (Bonaparte 1985; Bonaparte, Novas and Coria 1990; Late Cretaceous, 70 mya; 7.5m in length) is an abelisaurid theropod dinosaur related to Majungasaurus. Carnotaurus had a shorter, upturned snout, a shorter mandible, frontal horns, a deeper jugal, a narrower skull (below the horns) and a down-turned naris.
Bonaparte JF 1985. A horned Cretaceous carnosaur from Patagonia. National Geographic Research. 1 (1): 149–151.
Bonaparte JF, Novas FE and Coria RA 1990. Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia. Contributions in Science. 416: 1–41. PDF