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.
Figure 1. Skull of Zanabazar from Digimorph.org and used with permission. Bones are colored here.
Figure 2. Subset of the LRT focusing on theropods leading to birds, including the Troodontidae and the two newest additions, Bambiraptor and Zanabazar.
Prior to the LRT
authors nested Zanabazar as a highly derived troodontid (Figs. 3, 4).
Figure 3. Current cladograms of the Troodontidae currently found in Wikipedia pages.
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.
Figure 4. Wikipedia cladogram from Shen et al. 2017. Overlay limits LRT Troodontidae to the taxa in the white box. Others are in the bird lineage.
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.
Wikipedia continues:
“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).
FIgure 5. Gobivenator is the most completely known troodontid. It nests with Zanabazar in the LRT.
Figure 6. Gobivenator skull, colors added here.
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.
Figure 7. Mei long is a scansoriopterygid bird in the LRT. Yes it has small hands and could not fly, but the rest of its traits nest Mei within the bird clade.
Mei
(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.
Figure 9. Daliansaurus and the origin of birds through Almas and Xiaotingia.
Daliansaurus liaoningensis
(Shen et al. 2017; Early Cretaceous, Barremian, 128 mya; 1 m long) nests in the LRT as a basal anchiornithid, not a troodontid.
Almas ukhaa
(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).
References
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.
wiki/Zanabazar_junior
wiki/Gobivenator
wiki/Troodontidae
wiki/Alvarezsauridae
wiki/Daliansaurus
wiki/Almas_ukhaa
Wulong: a new troodontid, not a microraptor-dromaeosaur
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.
Figure 1. Wulong in situ, plus the original published diagram. The specimen is somewhat surrounded by a few coprolites = cop.
By contrast,
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’.
Figure 2. Wulong skull, original diagram, DGS colors applied to bones and reconstruction based on the DGS tracings.
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…
Figure 4. Wukong manus DGS tracing and reconstruction. Note the 180º rotation of the manus relative to the radius and ulna.
… 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.
Figure 3. Wulong pelvis.
Figure 4. Wulong pedes, original tracing and reconstruction based on DGS tracings.
Uniquely
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.”
By contrast,
in the LRT Tianyuraptor and Zhenyuanlong are not related to troodontids, microraptorids or dromaoeosaurids. Tianyuraptor and Zhenyuanlong are basal to tyrannosaurids.
References
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
Anchiornis or not? And what about Pedopenna?
Xu et al. 2009
described a new genus, Anchiornis huxleyi IVPP V14378 (the holotype), along with LPM-B00169A, BMNHC PH828 as referred specimens), from the Late Jurassic of China. Two of these (Fig. 1) were added to the large reptile tree (LRT, 1315 taxa, subset Fig. 2). They nest in the LRT in the clade traditionally considered Troodontidae, between Velociraptor and Archaeopteryx. (Note other traditional troodontids, like Sinornithoides and Sauronithoides, do not nest in this pre-bird clade, but within the Haplocheirus clade.
Last year
a paper by Pei et al. 2017 described “new specimens of Anchiornis huxleyi“. Two of these (Fig. 1) were also added to the LRT (subset in Fig. 2).
Figure 1. Four specimens attributed to Anchiornis along with two others related to Anchiornis, but given different names. Two of these Anchiornis specimen nest apart from two others (see figure 2).
In the LRT
only two of the four tested Anchiornis specimens nested together (one was the holotype). That means the two other specimens were originally mislabeled. Moreover, a specimen attributed to a separate genus, Jinfengopteryx, nests with the holotype of Anchiornis and a referred specimen.
So do a few of the referred specimens need to be renamed? Perhaps so. Beyond the distinctly different skulls (Fig. 1), various aspects of the post-crania are also divergent.
Figure 2. Cladogram of taxa surrounding four specimens attributed to Anchiornis, which do not nest together in the LRT. The holotype is the IVPP specimen in a darker tone and white arrowhead.
Pedopenna daohugouensis
(Xu and Zhang 2005; IVPP V 12721, Fig. 3) is a fossil theropod foot with long stiff feathers from the Middle or Late Jurassic, 164mya.
According to Wikipedeia
“Pedopenna was originally classified as a paravian, the group of maniraptoran dinosaurs that includes both deinonychosaurs and avialans (the lineage including modern birds), but some scientists have classified it as a true avialan more closely related to modern birds than to deinonychosaurs.”
Figure 3. Pedopenna in situ. The large alphanumerics are original. The color is added here. Very little is known of this specimen, but clearly long feathers arise from the metatarsus.
The first step
in figuring out what Pedopenna is, is to create a clear reconstruction (Fig. 4). Only then will we be able to score the pedal elements in the LRT.
Figure 4. Pedopenna in situ and reconstructed using DGS techniques.
Surprisingly,
and despite the relatively few pedal traits, the LRT is able to nest Pedopenna between and among the several Anchiornis specimens (Fig. 5). Specifically it nests between the holotype IVPP specimen and the LPM specimen. So is Pedopenna really Anchiornis? Or do all these taxa, other than the holotype, need their own generic names?
Figure 5. Where feathers on the foot are preserved on the LRT.
Earlier we looked at the development of foot feathers to aid in stability in pre-birds and other bird-like taxa just learning to flap and fly, convergent with uropatagia in pre-volant pterosaur ancestors.
A note to Anchiornis workers:
Try to test all your specimens in a phylogenetic analysis for confirmation, refutation or modification of the above recovery. Pei et al. considered all the specimens conspecific. They are not conspecific, as one look at their skulls alone (Fig. 1) will tell the casual observer.
References
Pei R, Li Q-G, Meng Q-J, Norell MA and Gao K-Q 2017. New specimens of Anchiornis huxleyi (Theropoda: Paraves) from the Late Jurassic of Northeastern China. Bulletin of the American Museum of Natural History 411:66pp.
Xu X, Zhao Q, Norell M, Sullivan C, Hone D, Erickson G, Wang X, Han F and Guo Y 2009. A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin. Chinese Science Bulletin 54 (3): 430–435. doi:10.1007/s11434-009-0009-6
Xu X and Zhang F 2005. A new maniraptoran dinosaur from China with long feathers on the metatarsus. Naturwissenschaften. 92 (4): 173–177. doi:10.1007/s00114-004-0604-y.
SVP 2018: Stages in the origin of avian flight
Hartman, Mortimer and Lovelace 2018
reconstruct the origin of avian flight in a series of stages:
- Acquisition of theropod characters unrelated to avian flight, including bipedalism, three fingered hands, a furcula, and filamentous epidermal structures.
- Acquisition of characters directly exapted for flight such as enlarged forelimbs, pennaceous feathers on the forelimbs and tail, increased angle between scapula and distal coracoid, and laterally facing glenoid fossae.
- Characters acquired due to aerial locomotion, including tertial feathers, expansion of the flight stroke and associated muscles, and in more derived taxa an alula and reduction of the distal caudal series to a pygostyle.
- Characters associated with higher endurance crown avian-style flight including enlarged keeled sterna, hinged sternal ribs, loss of gastralia, and well-developed caudal air sacs.
Figure 1. Xiaotingia, the proximal outgroup to the Thermopolis specimen of Solnhofen birds, the basalmost bird.
Based on the outgroup taxon, Xiaotingia
(Fig. 1) and the basalmost Solnhofen bird, the Thermopolis specimen, missing from the above list of traits are:
- phylogenetic miniaturization
- more gracile bones overall
- a smaller skull
- a more gracile neck
- a longer tail
- an elongate coronoid, which signals the start of flapping
- a larger olecranon process
- avian-style wrist
- a more robust retro pedal digit 1 with a larger ungual
Hartman, Mortimer and Lovelace conclude:
“Stage 2 taxa with small body size and enlarged forelimbs may have utilized wing assisted incline running (WAIR) to access trees despite lacking unambiguously arboreal characters, breaking the ground-up/trees-down dichotomy.” Yes, but this seems like old news as Ken Dial published the same conclusion in 2003. Where in the author’s list is the elongate coracoid common to all flapping tetrapods? …and found in non-avian convergent micro raptors and sinornithosaurs?
…and the authors continue:
“Several Stage 2 taxa independently approached Stage 3 conditions, including some
microraptorians, Rahonavis, Archaeopteryx and scansoriopterygids; this suggests that
WAIR enabled several parallel experiments with aerial locomotion.” Good points first noted in the LRT, except that scansoriopterygids are birds when more Solnhofen birds are added to the taxon list. (Need to consider all Solnhofen birds as taxa, not just have one and label it Archaeopteryx). T-rex ancestor, Zhenyuanlong might also be added to this list, given its large wing feathers.
References
Dial KP 2003. Wing-assisted incline running and the evolution of flight. Science 299:402-404.
Hartman S, Mortimer M and Lovelace DM 2018. A testable macroevolutionary framework for character acquisition in the origin of avian flight. SVP abstracts.
The Daiting specimen is not Archaeopteryx
Today
a break from a review of the SVP 2018 abstracts.
A new paper by Kundrát, et al. 2018
re-describes the Daiting specimen (Tischlinger 2009) attributed to Archaeopteryx and given a specific name A. albersdorfi (SNSB BSPG VN-2010/1; Kundrát et al. 2018, Late Jurassic, Lower Tithonian; Figs. 1, 2).
Figure 1. The Daiting specimen attributed to Archaeopteryx in white and UV light. Note the short coracoid. This is not a flapping tetrapod.
The skull of the Daiting specimen
is newly reconstructed here (Fig. 2). The former postorbital is now the squamosal. The former squamosal is here identified as three bones layers atop one another. The bones of the mandible are newly interpreted here.
Figure 2. The skull of the Daiting specimen wrongly attributed to Archaeopteryx reconstructed from µCT scans. Some bones are reidentified here.
Unfortunately,
the large reptile tree (LRT, 1313 taxa; subset Fig. 3) nests the Daiting specimen outside of the birds, between Sinovenator and Xiaotingia.
Figure 3. Subset of the LRT focusing on basal birds and pre-bird theropods. Note many of the various Solnhofen birds nest apart from one another and the Daiting specimen nests outside the birds (Aves). Preview: note the nesting of the four included Anchiornis specimens.
Kundrát et al. provided several cladograms
based on data sets provided by Xu et al. 2011; Turner et al. 2012 and Godefroit et al. 2013. They “unanimously resolved [the Daiting specimen] as both a basal avialan and an archaeopterygid, but does not unequivocally discriminate between a paraphyletic or monophyletic Archaeopteryx.”
- Xu et al. 2011 cladogram: nests the Daiting specimen between Anchiornis + Xiaotingia and Archaeopteryx + Wellnhoferia, all derived from a Sapeornis–Yanornis clade.
- Xu et al. 2011cladogram (Xiaotingia deleted): nests the Daiting specimen between a Sapeornis–Yanornis clade and Archaeopteryx + Wellnhoferia,
- Turner et al. 2012 cladogram: nests the Daiting specimen basal to a different Sapeornis clade, all derived from Archaeopteryx.
- Turner et al. 2012 cladogram (3 taxa deleted): nests the Daiting specimen basal to a different Sapeornis clade, all derived from Archaeopteryx.
- Godefroit et al. 2013 cladogram: nests the Daiting specimen with Archaeopteryx, basal to the Balaur–Rahonavis clade, all derived from Xiaotingia.
Not all of the nodes in the above cladograms
include a gradual accumulation of traits in all derived taxa.
Kundrát et al. report:
“Archaeopteryx albersdoerferi is the only Bavarian archaeopterygid that exhibits co-ossification of the carpals and metacarpals, differing from modern flying birds in that the distal postaxial carpal (usually missing – perhaps cartilaginous – in other archaeopterygid specimens; (Wellnhofer 2009)) co-ossified with the metacarpal of the major digit rather than with the semilunate and postaxialmetacarpal.”
“The most noteworthy feature of Archaeopteryx albersdoerferi is that it accummulated several characteristics of maturity (discussed above) during the juvenile period of ontogeny that were not seen either in smaller or in larger specimens of Archaeopteryx lithographica.”
The coracoids of the Daiting specimen
are still rather disc-like in appearance, not strap-like as in Xiaotingia and birds. The Daiting specimen was not a flapping taxon, or not a good flapping taxon. That comes at the next node.
Figure 4. Pectoral girdle of the Daiting specimen wrongly attributed to Archaeopteryx showing the clavicle (cv=furcula), scapula (sc), and the disc-like coracoids (co). Strap-like coracoids occur in more derived taxa and this shape marks the genesis of flapping.
Earlier we looked at the variety of taxa present in Solnhofen birds,
(Fig. 3, 5) all of which have been called Archaeopteryx at their first publication. Later authors have renamed several of them. Remember, you can’t determine a genus or species without the context of a phylogenetic analysis.
Figure 5. Several Solnhofen birds, including Archaeopteryx, compared to Ostromia to scale.
References
Kundrát M, Nudds J, Kear BP, Lü J-C and Ahlberg P 2018. The first specimen of Archaeopteryx from the Upper Jurassic Mörnsheim Formation of Germany. Historical Biology 31(1):3-63.
Tischlinger H 2009. Der achte Archaeopteryx – das Daitinger Exemplar. Archaeopteryx. 27:1–20.
Wellnhofer P 2009. Archaeopteryx—the Icon of Evolution. München: Friedrich Pfeil.
Caihong: the iridescent Jurassic troodontid
The preservation in situ is spectacular,
(Figs. 1, 2), but probably pales in comparison to the in vivo appearance of early Late Jurassic Caihong juju (PMoL-B00175 (Paleontological Museum of Liaoning, 161 mya), a new troodontid theropod dinosaur, which includes iridescent feathers.
Figure 1. Skull of Caihong from Hu et al. 2018. Arrow points to bony lacrimal crest/protuberance. At a screen resolution of 72 dpi this image of a 6cm long skull is about twice life size.
Caihong differs from other theropods
- Accessory fenestra posteroventral to promaxillary fenestra
- Lacrimal with prominent dorsolaterally oriented crests
- Robust dentary with anterior tip dorsoventrally deeper than its midsection
- Short ilium (<50% of the femoral length, compared to considerably >50% in other theropods).
Furthermore,
Caihong shows the earliest asymmetrical feathers and proportionally long forearms in the theropod fossil record. But the coracoids remained short discs. So it was not flapping those long feathered arms. It had extensively feathered toes. (Remember, chicken leg scales are former feathers and otherwise birds are naked beneath their feathers.)
About that unique lacrimal crest…
Note that the parietal has taphonomically moved anterior to the frontal. That’s odd, but it sets up another possibility for that elliptical crest bone. Look how it would precisely fit into the space created by the posterior parietal in dorsal view (Fig. 1). More precise, higher resolution data might provide some insight into this possibility.
Figure 2. Caihong overall in situ. This taxon nests better with Buitraptor, not Xiaotingia.
Hu et al. nested Caihong
as a basal deinonyychosaur with the coeval Xiaotingia outside of the Troodontidae, but inside of the clade that includes two Solnhofen birds (only Archaeopteryx and Wellnhoferia). Microraptor, Dromaeosaurus and Rahonavis and others. The cladogram nests long-snouted Buitreraptor with Rahonavis and Unenlagia in an unresolved sister clade to the Xiaotingia/Caihong clade. Only a few nodes had Bootstrap scores higher than 50 and the nodes proximal to Caihong are not among them.
By contrast
the large reptile tree (LRT, 1153 taxa) nests long-snouted Caihong with even longer-snouted Buitreraptor in the troodontid clade that includes Anchiornis and Aurornis, basal to more derived troodontids and ‘Later’ Jurassic Solnhofen birds. Rahonavis and Microraptor nest with therizinosaurs and ornitholestids respectively.
Figure 3. Buitreraptor skull with bones and missing bones colorized. This skull is over 3x the size of Caihong.
Aurornis (Fig. 4) was basal, Caihong was transitional and Buitreraptor was derived in this clade of small troodontids with increasingly longer rostra.
Figure 4. Eosinopteryx and kin, including Xiaotingia, Aurornis and Archaeopteryx (Thermopolis).
Caihong may share these ‘unique’ traits
which are damaged in Buitreraptor.
- Accessory fenestra posteroventral to promaxillary fenestra
- Lacrimal with prominent dorsolaterally oriented crests
- Robust dentary with anterior tip dorsoventrally deeper than its midsection
- Short ilium (<50% of the femoral length, compared to considerably >50% in other theropods).
References
Hu et al. (9 co-authors) 2018. A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early par avian evolution. Nature.com/Nature Communications, 12 pp. DOI: 10.1038/s41467-017-02515-y
The Pterosaur Heresies 