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 last common ancestor of all dinosaurs in the LRT: ?Buriolestes

Müller et al. 2018
describe a new dinosaur skeleton they attribute to Buriolestes shultzi (Cabreria et al. 2016, ULBRA-PVT280, Figs. 2, 3). In the large reptile tree (LRT, 2015 taxa; subset Fig. 1) the holotype now nests at the base of the Phytodinosauria. The referred specimen is different enough to nest between the herrerasaurs and all other dinosaurs. This, of course, removes herrerasaurs from the definition of the Dinosauria (Passer + Triceratops, their last common ancestor (= CAPPA/UFSM 0035) and all descendants).

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

Figure 1. Subset of the LRT including the new specimen of Buriolestes (CAPPA/UFSM 0035) nesting at the base of all dinosaurs.

 

Buriolestes schultzi (Cabreria et al. 2016; Late Triassic, Carnian; 230mya) was originally and later (Müller et al. 2018) considered a carnivorous sauropodomorph, but here two specimens nest as the basalmost dinosaur (CAPPA/UFSM 0035) and the basalmost phytodinosaur (ULBRA-PVT280).

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs.

Figure 2. The two skulls attributed to Buriolestes (holotype on the right). The one on the left nests as the basalmost dinosaur, basal to theropods and phytodinosaurs. It should have a distinct name.

All cladograms agree that Buriolestes
is a very basal dinosaur. Taxon exclusion changes the tree topology of competing cladograms. The broad autapomorphic ‘eyebrow’ of the CAPPA specimen indicates it is a derived trait in this Late Triassic representative of an earlier genesis.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

Figure 3. Herrerasaurus, Buriolestes and Tawa to scale.

The Müller et al. cladogram
combined both specimens attributed to Buriolestes (never a good idea, but it happens all the time). The Müller et al. cladogram excluded a long list of basal bipedal crocodylomorpha, but did include Lewisuchus. It excluded the archosaur outgroups PVL 4597Turfanosuchus and Decuriasuchus. The Müller et al. cladogram nested Ornithischia basal to Saurischia (= Herrerasauridae + Agnophitys, Eodromaeus, Daemonosaurus + Theropoda + Sauropodomorpha) with Buriolestes nesting between Eoraptor and Panphagia. The CAPPA specimen of Buriolestes is also a sister to the basalmost theropod, Tawa (Fig. 3)… and not far from the other basal archosaur, Junggarsuchus (Fig. 4).

Figure 8. The CAPPA specimen of Buriolestes compared to the more primitive Junggarsuchus, basal to the other branch of archosaurs, the crocs.

Figure 4. The CAPPA specimen of Buriolestes compared to Junggarsuchus, basal to the other branch of archosaurs, the crocs.

References
Cabreira SF et al. (13 co-authors) 2016. A unique Late Triassic dinosauromorph assemblage reveals dinosaur ancestral anatomy and diet. Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040
Müller RT et al. (5 co-authors 2018. Early evolution of sauropodomorphs: anatomy and phylogenetic relationships of a remarkably well-preserved dinosaur from the Upper Triassic of southern Brazil. Zoological Journal of the Linnean Society, zly009 (advance online publication) doi: https://doi.org/10.1093/zoolinnean/zly009

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.

 

Massospondylus embryo joins the LRT

…and guess where it nests?

Figure 1. Massospondylus embryo from Reisz et al. 2010.

Figure 1. Massospondylus embryo from Reisz et al. 2010.

This should be easy:
The embryo nests with the adult Massospondylus in the large reptile tree (LRT, 1212 taxa), despite the many proportional and a few osteological changes that attend ontogeny in this basal sauropodomorpth from the Early Jurassic.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale. Note the bipedal pose based on hind and fore limb disparity… distinct from the quadrupedal embryo.

These embryos are the oldest known
dinosaur embryos and apparently they were just days from hatching.

Massospondylus kaalae was a short-snouted basal sauropodomorph from the Early Jurassic closely related to Efraasia and SaturnaliaMassospondylus had a short round snout and long blunt fangs. Another species, Massospondylus carinatus, had a relatively longer skull as an adult.

The embryo Massospondylus
includes a taller antorbital fenestra, a premaxilla lacking a posterior narial process, a naris closer to the jaw line, a straight (not descending) jaw joint, a smaller coronoid process, a lack of teeth, relatively shorter neck, larger fore limbs, a shorter ventral pelvis, distally broader chevrons and smaller feet.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx. The predator babies were larger than the bite-sized and more numerous prey babies. 

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. “Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.

wiki/Massospondylus

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