Bird, pterosaur, dinosaur simplified chronology

Following the earlier post on non-arboreal post K-T boundary birds…

…this one pretty much speaks for itself.
Here (Fig. 1) is a chronology, very much simplified, of birds, pterosaurs and dinosaurs according to the LRT.

Figure 1. Mesozoic chronology of bird, dinosaur and pterosaur clades.

Figure 1. Mesozoic chronology of bird, dinosaur and pterosaur clades based on taxa in the LRT.

If you’re curious about any of the taxa,
in the chronology, simply use Keywords to locate them.

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The assembly of the avian body plan (Cau 2018) pt. 2 of 3

Yesterday we looked at part 1 of the Cau 2018 cladogram of theropods (including birds). Certain taxa within this study were new to me, so I added several to the the large reptile tree (LRT, 1213 taxa). Today we’ll continue with Node 9, still within the Huxley stage of theropod evolution.

Figure 2. Zuolong skull revised with a backward tilting lacrimal and other minor modifications.

Figure 1. Zuolong skull revised with a backward tilting lacrimal and other minor modifications.

Node 9. Tetanurae: (Zuolong + Chilesaurus + Neotetanurae). Adding Zuolong to the LRT nests it as a basal theropod, basal to the rarely tested taxa in the Segisaurus + Marasuchus + Procompsognathus clade (Fig. 2). Zuolong is the first of these with a relatively complete skull. Cau 2018 nest Zuolong and the phytodinosaur, Chilesaurus, with Neotetanurae apparently by excluding certain relevant taxa.

Figure 1. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria.

Figure 2. Chilesaurus and kin, including Damonosaurus and basal phytodinosauria. No close relatives of theropods here!

Node 10. Chilesaurus + Neotetanurae: (See node 9). Cau also reports, “The parsimony analysis confirms the basal tetanuran affinities of the enigmatic Chilesaurus and dismisses ornithischian relationships suggested by Baron & Barrett (2017).” This is only true base on taxon exclusion. Add back the missing taxa, like Daemonosaurus , Jeholosaurus and Haya and the tree topology will change.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

Node 11. Neotetanurae (Carnosauria + Coelurosauria): The Cau tree and LRT share many taxa here, including Allosaurus with Sinraptor and Acrocanthosaurus. The Cau tree has only one Compsognathus. The LRT has two, each at the base of its own clade. The Cau tree nests Megalosaurus between the phytodinosaur, Chilesaurus, and the small compsognathid, Aorun, which is odd on the face of it (= no gradual accumulation of traits).

Node 12. Coelurosauria: The LRT indicates that Sinocalliopteryx does not belong in this clade, as Cau recovers it, but Sinocalliopteryx nests much more primitively, basal to Coelophysis and kin.

Nodes 13. Compsognathid grade + Tyrannoraptora: The spinosaurs and kin are not present in the Cau taxon list. When present these long rostrum taxa attract Guanllong and Megaraptor to more primitive theropods, away from tyrannosaurs, despite convergent traits.

Node 14. Sinocalliopteryx + Tyrannoraptora: See Node 13.

Node 15. Tyrannoraptora: (Tyrannosauroids and maniraptoromorphs) See Node 13.

Node 16. Maniraptoromorpha: (includes Vultur, excludes Tyrannosaurus). This definition is a little vague. Wish it had at least one included basal taxon. In the Cau tree Coelurus is a basal taxon. Unfortunately, too little of it is known to add it to the LRT.

Node 17. Ornitholestes + Maniraptoriformes: Distinct from the Cau tree, Ornitholestes is basal to microraptorids and tyrannosaurs, as well as dromaeosaurs, troodontids and birds.

Node 18. Maniraptoriformes: (Ornithomimosauria + Maniraptora). Distinct from the Cau tree, ornithomimosaurs in the LRT are derived directly from the holotype of Compsognathus, separate from oviraptorids and dromaeosaurs, closer to tyrannosaurs and kin. The LRT nests Ornitholestes and kin on the bird side of therizinosaurus + oviraptorids. The Cau tree does the opposite.

Figure 1. Cladogram subset of the LRT focusing on Theropoda.

Figure 2. Cladogram subset of the LRT focusing on Theropoda.

Part 3 tomorrow.

References
Cau A 2018. The assembly of the avian body plan: a 160-million-year long process. Invited Paper, Bollettino della Societa Paleontologica Italiana 57(1):1–25.

 

The assembly of the avian body plan (Cau 2018) pt. 1 of 3

Dr. Andrea Cau 2018 summarizes traditional knowledge
on the origin of birds breaking the process into three stages:

  1. Huxleyian stage: Early Triassic to Middle Jurassic the earliest ancestors of birds acquired postcranial pneumatisation, an obligate bipedal and digitigrade posture, the tridactyl hand and feather-like integument
  2. Ostromian stage: Middle to Late Jurassic is characterised by a higher evolutionary rate, the loss of hypercarnivory, the enlargement of the braincase, the dramatic reduction of the caudofemoral module, and the development of true pennaceous feathers.
  3. Marshian stage: Cretaceous. The transition to powered fl ight with the re-organisation of both forelimb and tail as fl ight-adapted organs and the full
    acquisition of the modern bauplan

This is a pretty good plan overall.
Unfortunately Dr. Cau uses an antiquated cladogram (Fig. 1) riddled with taxon exclusion (especially among the outgroups), so the details tend to get a little messed up. Let’s review the pluses and minuses.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

Figure 1. The origin of birds cladogram according to Cau 2018. Taxon exclusion forces a mixup of basal taxa.

The Cau cladogram and LRT
both feature many of the same basal theropods at the beginning, birds at derived nodes and a variety of carnivores in between, with dromaeosaurs then troodontids leading to birds.

Dr. Cau opens his paper
with several paragraphs devoted to nomenclature. He finds the term ‘non-avian’ particularly irksome. Cau employed 132 taxa and 1781 (1431 informative) characters. He reports that he decided not to include pterosaurs as outgroup taxa. That shows wisdom.

Unfortunately
Cau was not wise to largely ignore basal bipedal crocodylomorphs, including such favorites as Scleromochlus and Gracilisuchus. Thankfully Lewisuchus made his list.

So Cau starts off with four very distant outgroup taxa (Euparkeria, Teleocrator, Dormomeron and Lagerpeton), and that is never good (relevant taxon exclusion, again). It also shows a lack of understanding that could have been had with a quick glance at the large reptile tree (LRT, 1213 taxa). That’s what it’s there for.

Cau 2018 Results
3072 shortest trees (vs. LRT has one, fully resolved tree, last time I tested the whole tree).

Here are Cau’s nodes:

  1. Teleocrater + Dinosauromorpha: Unfortunately this clade does not include the Crocodylomorpha, so it is invalid. ‘Dinosauromorpha’, at best, is a junior synonym of Archosauria in the LRT.
  2. Dinosaurormorpha: (Lagerpetids + Dinosauriformes). Unfortunately this clade does not include the Crocodylomorpha, so it is invalid. When more taxa are added, lagerpetids nest with Tropidosuchus among the chanaresuchidae. Thus,  ‘Dinosauriformes’, at best, is a junior synonym of Archosauria in the LRT.
  3. Dinosauriformes: (Marasuchus + Dracohors). More taxa move Lewisuchus into the Crocodylomorpha, Silesaurus into the Poposauria and Pisanosaurus deep into the Phytodinosauria.
  4. Dracohors: (includes Megalosaurus, but not Marasuchus). More taxa (e.g. Segisaurus, Procompsognathus) move Marasuchus into the Theropoda and other taxa as listed above in the LRT.
  5. Dinosauria: (Eodromaeus, Herrerasauridae, Sauropodomorpha and Ornithoscelida). This is too many taxa and shows a lack of understanding. No basal dichotomy can be made. The LRT defines Dinosauria as Theropoda + Phytodinosauria, their last common ancestor (Herrerasaurus) and all descendants.
  6. Ornithoscelida: (Ornithischia + Theropoda) Adding more taxa will split up and invalidate this clade, based on LRT results.
  7. Theropoda: (Coelophysoidea + Averostra) In the LRT several theropods are listed as outgroups in the Cau analysis and it includes the phytodinosaur, Chilesaurus. (Daemonosaurus is curiously absent from this paper). Almost toothless Limusaurus should nest with oviraptorids. Elaphrosaurus has not been tested in the LRT. The basalmost coelophysoid (with feathers!), Sinocalliopteryx, nests as a derived compsognathid in the Cau taxon list.
  8. Averostra: (Ceratosauria + Tetaneurae) The LRT recovers a clade of large carnivores between Sinocalliopteryx and Compsognathus. This clade includes ProceratosaurusDeinocheirus, Xiongguanlong, Suchomimus and Spinosaurus, taxa not employed by Cau. These taxa attract Guanlong and Dilong to this basal feathered clade, away from tyrannosaurs. Otherwise, the LRT and Cau both place the same long list of medium to large basal theropods in clades at the base of this clade/grade.
Figure 1. Cladogram subset of the LRT focusing on Theropoda.

Figure 2. Cladogram subset of the LRT focusing on Theropoda.

More tomorrow.

References
Cau A 2018. The assembly of the avian body plan: a 160-million-year long process. Invited Paper, Bollettino della Societa Paleontologica Italiana 57(1):1–25.

 

Megaraptor: closer to spinosaurs than to tyrannosaurs

First of all,
what we know of Megaraptor is a chimaera. There is no complete skeleton. What we know comes from a little bit here (Fig. 1a) and a little bit there (Figs. 2, 3).

Wikipedia reports:
“Initially considered a giant dromaeosaur-like coelurosaur, then an eovenatorid allosauroid, then a basal tyrannosauroid coelurosaur…”

Here Megaraptor nests
with Xiongguanlong and other pre-spinosaurs, like Suchomimus (Fig. 7).

Porfiri et al. report,
“Megaraptorids are characterized by the formidable development of their manual claws on digits I and II and the transversely compressed and ventrally sharp ungual of the first manual digit. Phylogenetic relationships of megaraptorans have been the focus of recent debate. Megaraptorans have been alternatively interpreted as basal coelurosaurians (Novas,1998), basal tetanurans (Calvo et al., 2004; Smith et al., 2008), and allosauroids closely related with carcharodontosaurids (Smith et al., 2007; Benson et al., 2010; Carrano et al., 2012). However, recent evidence has been presented in favour of their inclusion within Coelurosauria, and possibly as basal members of Tyrannosauroidea (Novas et al., 2013). The [juvenile] skull material conforms a primary source of information for both coelurosaurian and tyrannosauroid features of Megaraptoridae, unavailable in previous studies.”

Figure 1. Megaraptor manus and ulna from xxx.

Figure 1a. Megaraptor manus and ulna from xxx.

Figure 1b. Suchomimus manus.

Figure 1b. Suchomimus manus.

Figure x. Suchomimus restoration.

Figure 1c. Suchomimus restoration. Note the large hands.

Novas et al. (2013) found Megaraptor and related taxa as deeply nested within Coelurosauria, notably as the sister group of Xiongguanlong + Tyrannosauridae. In the LRT Megaraptor also nests close to Xiongguanlong, but far from Tyrannosauridae.

Porifi et al. compared the juvenile skull
of Megaraptor to that of Dilong, which they nest (Fig. 4) as a basal tyranosauroid. In the LRT (Fig. 5) Dilong does indeed nest close to Megaraptor, but both nest far from Tyrannosaurus. Those long snouts are a spinosaur trait.

Figure 2. Scale bars seem to be amiss here, but these are the bones and scale bars from the MUCPv 595 specimen of the skull of Megaraptor.

Figure 2. Scale bars seem to be amiss here, but these are the bones and scale bars from the MUCPv 595 specimen of the skull of Megaraptor.

A new Megaraptor skull restoration
is presented below (Fig. 3), based on Xiongguanlong, a sister in the LRT.

Figure 1. Megaraptor skull restoration revised.

Figure 3. Megaraptor skull restoration revised (in blue). As in Xiongguanlong.

Several traditional long-snouted ‘tyrannosauroids’
nest with spinosauroids in the LRT. The two clades converge in many traits and paleontologists have, so far, been willing to accept that tyrannosaur ancestors had long snouts and elaborate rostral crests. Perhaps, someday, the consensus will swing the other way.

Figure x. The skull of Xiongguanlong is long and low, like that of spinosaurs and kin, not like that of tyrannosaurs and kin.

Figure 4. The skull of Xiongguanlong is long and low, like that of spinosaurs and kin, not like that of tyrannosaurs and kin.

Evidently
the Theropoda is a wicked clade to pylogenetically analyze. Workers have been shuffling the nodes trying to figure them out. Taxon exclusion may be the cause of this lack of consensus. The LRT lacks certain taxa. So do other studies.

Figure 2. Cladogram nesting Megaraptor from xxx.

Figure 6. Cladogram nesting Megaraptor from xxx.

Many branches are similar in many studies. Others are not.

Figure 5. Basal theropods with the addition of Zuolong and Megaraptor.

Figure 7. Basal theropods with the addition of Zuolong and Megaraptor. Scipionyx was added later (see figure 8).

Tyrannosauroids never had a long, low skull
in the LRT. They were derived from the the CNJ79 specimen of Compsognathus (yes, it needs a new generic name), which also includes ornithomimids, Fukuivenator, Tianyuraptor, Huaxiagnathus, Zhenyuanlong and traditional tyrannosaurids, like Alioramus.

Figure 3. The Scipionyx clade includes Allosaurus, Deinocheirus, Spinosaurus and other larger theropods.

Figure 8. The Scipionyx clade includes Allosaurus, Deinocheirus, Spinosaurus and other larger theropods.

References
Novas FE 1998. Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia. Journal of Vertebrate Paleontology. 18: 4–9.
Novas FE, Agnolin FL, Ezcurra MD.Porfiri J, Canale JI 2013.
Evolution of the carnivorous dinosaurs during the Cretaceous: the evidence from Patagonia. Cretaceous Research 45, 174e215.
Porfiri JD et al. (5 co-authors) 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51:35–55.

wiki/Megaraptor

Zuolong: a basal theropod

Wikipedia reports,
Zuolong sallleei (Choinere et al. 2010; IVPP V15912; Fig. 1; 3m in length) is a coelurosaur (related to Ornitholestes) dinosaur from the lower Oxfordian of the Late Jurassic.

Figure 1. Zuolong skull, very basic, very basal for Theropoda.

Figure 1. Zuolong skull, very basic, very basal for Theropoda. Using color can predict certain bones, like the nasals, dentary and jugal in this case.

Figure 2. Zuolong skull revised with a backward tilting lacrimal and other minor modifications.

Figure 1 revised. Zuolong skull revised with a backward tilting lacrimal and other minor modifications. No scores changed on the matrix.

By contrast
the large reptile tree (LRT, 1209 taxa) nests Zuolong at the base of the rarely included Segisaurus/Marasuchus clade, near the origin of the Theropoda between Tawa and Sinocalliopteryx. Apparently taxon exclusion was a problem with the original Zuolong results.

Figure 2. Zuolong skeleton from Choiniere et al.

Figure 2. Zuolong skeleton from Choiniere et al.

Choiniere et al. counted 5 sacrals (Fig. 3).
The LRT finds only 4 sacrals (Fig. 3) when compared to the ilium, which has a truncated anterior, like that of fellow clade members. Most traits in Zuolong are common and plesiomorphic, as one might expect of a basal theropod.

Figure 3. Zuolong pelvis and sacrum

Figure 3. Zuolong pelvis and sacrum. Originally the dorsal vertebra was considered sacral #1.

At last! Skull material!
Zuolong is the first member of this near basal theropod clade (Segisaurus, et al.) known from substantial skull material… and it’s suitably plesiomorphic. Also note the truncated anterior ilium, a trait of this clade. Four sacrals down to two in smaller taxa separate clade members from most 5-sacral theropods.

Figure 5. Basal theropods with the addition of Zuolong and Megaraptor.

Figure 5. Basal theropods with the addition of Zuolong and Megaraptor. We’ll look at Megaraptor tomorrow.

References
Choiniere JN, Clark JM, Forster CA and Xu X 2010. A basal coelurosaur (Dinosauria: Theropoda) from the Late Jurassic (Oxfordian) of the Shishugou Formation in Wucaiwan, People’s Republic of China. Journal of Vertebrate Paleontology. 30 (6): 1773–1796.

wiki/Zuolong

Halszkaraptor: what a story!

Published in Nature today
a Mongolian Late Cretaceous theropod that was rescued from the black market! It is supposed to be aquatic… but is it?

Figure 1. Halszkaraptor escuillei was originally considered an aquatic basal dromaosaur, but here nests with Shuvuuia, a sprinting biped.

Figure 1. Halszkaraptor escuillei was originally considered an aquatic basal dromaosaur, but here nests with Shuvuuia, a sprinting biped. It might not have been this chubby in the torso. All art is from Cau et al. 2017.

Halszkaraptor escuilliei (Cau et al. 2017; Late Cretaceous, Fig. 1) was originally considered an aquatic basal dromaeosaur related to Mahakala, but here Halszkaraptor nests with ShuvuuiaHaplocheirus and other non-aquatic sprinting dromaeosaurids. Manual digit 3 was the longest, but the thumb had the largest claw. The naris was displaced posteriorly. The fossil is preserved in 3D, largely articulated.

Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.

Figure 2. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.

The Cau et al. cladogram
has many more bird-like theropods than the LRT. The taxa that nest together with Halszkaraptor in the LRT are sprinkled throughout the Cau et al. cladogram. In fact, all of the theropods that the two cladograms have in common nest in completely different nodes and leaves, except Haplocheirus nests in the same clade as Shuvuuia in both trees. Is this a case of taxon exclusion on the part of the LRT? Or just what happens when you score different traits? No reconstructions of sister taxa were provided.

FIgure 2. Subset of the LRT focusing on pre-bird theropods.

FIgure 2. Subset of the LRT focusing on pre-bird theropods. The taxa in the Velociraptor clade are sprinkled throughout the Cau et al. cladogram of theropods.

Let’s look at the pertinent parts of the Cau et al. abstract:
“Propagation X-ray phase-contrast synchrotron microtomography of a well-preserved maniraptoran from Mongolia, still partially embedded in the rock matrix, revealed a mosaic of features, most of them absent among non-avian maniraptorans but shared by reptilian and avian groups with aquatic or semiaquatic ecologies.

“This new theropod, Halszkaraptor escuillieigen. et sp. nov., is related to other enigmatic Late Cretaceous maniraptorans from Mongolia in a novel clade at the root of Dromaeosauridae. This lineage adds an amphibious ecomorphology to those evolved by maniraptorans: it acquired a predatory mode that relied mainly on neck hyperelongation for food procurement, it coupled the obligatory bipedalism of theropods with forelimb proportions that may support a swimming function, and it developed postural adaptations convergent with short-tailed birds.”
What about this theropod screams, “I’m aquatic!!” ?? This is one I just don’t see.
In the LRT
Halszkaraptor does not nest with other aquatic taxa. The neck is not particularly long compared to coeval Mononykus (Fig. 2), which has never been considered aquatic. The skull is very much like that of coeval Shuvuuia
Described in the press
as one of the oddest fossil yet found. This adjective usually gets attached to errors in identification. Halszkaraptor is not that odd. NatGeo reports, “Like modern aquatic predators, this dinosaur’s face seems to have had an exquisite sense of touch, useful for finding prey in murky waters. Its small teeth would have helped it nab tiny fish, and its limber backbone and flipper-like forelimbs suggest that it cut through the water with ease.”
This added later:
Apparently others have also seen the Shuvuuia connection. Author Andrea Cau listed 25 traits here that distinguish Halszkaraptor from Shuvuuia, but are found in dromaeosaurids. Perhaps this could all be cleared up easily, because in the LRT, Shuvuuia IS also a dromaeosaurid, not a distantly related theropod, as it nests in Cau et al. 2017.

References
Cau A, et al. 2017. Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs. Nature. doi:10.1038/nature24679

wiki/Halszkaraptor
wiki/Shuvuuia

Dinosaur outgroup taxon: Turfanosuchus

It was the Middle Triassic when
a sister to Turfanosuchus evolved into the basalmost dinosaur, Herrerasaurus (Figs. 1, 2)

Figure 1. Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Figure 1. Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur. Lower image to scale.

Figure 2. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Figure 2. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Quick one today.
I’ll let the pictures tell the story…

References
Novas FE 1994. New information on the systematics and postcranial skeleton of Herrerasaurus ischigualastensis (Theropoda: Herrerasauridae) from the Ischigualasto
Reig OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Sereno PC and Novas FE 1993. The skull and neck of the basal theropod Herrerasaurusischigualastensis. Journal of Vertebrate Paleontology 13: 451-476. doi:10.1080/02724634.1994.10011525.
Young CC 1973. [On a new pseudosuchian from Turfan, Sinking (Xinjiang).] Memoirs of the Institute of Vertebrate Paleontology and Paleoanthropology of the Academia Sinica, Series B 10:15-37.

wiki/Herrerasaurus
wiki/Turfanosuchus