SVP 17 Asilisaurus notes

Nesbitt et al. 2015 (svp abstract)
describe the poposaur, Asilisaurus, as highly convergent with dinosaurs, yet distinct.

True.
But there are still problems here. See the (*) asterisks.

From the abstract:
“Asilisaurus kongwe, from the Middle Triassic Manda beds of southwestern Tanzania, is one of the oldest known ornithodirans* and provides new insights into early dinosauriform evolution**. Originally represented by disarticulated bones and one semi articulated partial skeleton from a single locality, recent fieldwork has yielded six sites at approximately the same stratigraphic level, with specimens representing nearly the entire skeleton. A new, exquisitely preserved skeleton of a single individual includes much of the skull, pectoral girdle, forelimbs, pelvis, hind limbs, and tail, and confirms that all of the original, largely disarticulated material belongs to Asilisaurus. The skeleton of Asilisaurus shares several plesiomorphic character states with other dinosauriforms, including a well-developed metatarsal I with a distinct articulation surface for a phalanx, a calcaneum with a clear tuber, a closed acetabulum, and a short deltopectoral crest. Additionally, Asilisaurus shares several features with Silesaurus and other putative silesaurids (e.g., Sacisaurus), such as teeth ankylosed with the jaw, a distinctive scar on the proximal surface of the femur, a bony pointed beak at the rostral tip of the lower jaw, and a notch at the base of the femoral head. Classic ‘dinosaurian’ character states, such as the upper temporal musculature extending onto the frontal and epipophyses on the cervical vertebrae, must be considered plesiomorphies given the phylogenetic position of Asilisaurus. The nearly complete osteology of Asilisaurus allows re-evaluation of other problematic taxa; Agnosphitys*** and Lewisuchus share apomorphies with Asilisaurus and thus represent silesaurids with a carnivorous dentition****. Our comprehensive phylogenetic analysis demonstrates that silesaurids***** are monophyletic and fall just outside Dinosauria (which is diagnosed by very few character states). The most derived silesaurids (e.g., Silesaurus, Sacisaurus) share features with both ornithischian and theropod dinosaurs, illustrating the high degree of convergence among dinosauriforms in the Triassic. In addition, the results of our cladistic analysis imply at least three independent transformations towards quadrupedality and herbivory. The frequency of dietary (carnivorous vs. herbivorous) and locomotor (quadrupedal vs. bipedal) shifts within Dinosauriformes appears unique within Amniota.”

*a diphyletic clade with pterosaurs in the lepidosauromorpha and dinos in the archosauromorpha.
**actually a poposaur, just outside of the Archosauria/Dinosauria in the large reptile tree.
***no mystery, Agnosphitys is a theropod sister to Marasuchus. Lewisuchus is a basal archosaur, a little closer to dinos than to crocs in the large reptile tree.
****Nesbitt et al are confused by convergence, which is resolved by phylogenetic analysis.
*****or do they mean poposaurs? Silesaurus and Sacisaurus are poposaurs. Actually Gracilisuchus and the Crocodylomorpha ‘fall’ (= nest) just outside the Dinosauria with poposaurs the outgroup according to the large reptile tree.

References
Nesbitt SJ et al. 2015. The anatomy of Asilisaurus kongwe (Dinosauriformes: silesauridae) and closely related taxa provides new insights into the anatomical and chronological evolution of dinosauriforms. Journal of Vertebrate Paleontology abstracts.

Adding Compsognathus longipes to the large reptile tree

Updated 1.17.2016 with a revised figures based on higher resolution data. On this date, Compsognathus was nested with Struthiomimus.

Figure 1. Reconstruction of Compsognathus with revised face, fingers and foot.

Figure 1. Compsognathus in lateral view. Small inset at reduced scale shows complete tail. Note the variety of neural spines along the spinal column

For many decades
Compsognathus longipes
(Wagner 1859, Ostrom 1978, Late Jurassic, quarry unknown, 150 mya, 3 ft (89 cm) long, BSP AS I 563 ) was considered the smallest known dinosaur and something close to its contemporary, the first bird, Archaeopteryx, also from the Solnhofen formation.

Here with very few other theropods to nest with, Compsognathus nests in the large reptile tree (604 taxa) with the very much larger Tyrannosaurus. (updated January 17, 2016) This clade includes the feathered theropod, Sinocallioptery, at its base. Many have wondered if Compsognathus had feathers or not. With modern birds lacking body scales one wonders if subsequent scales are all derived from primordial feathers as the scales on the feet of modern birds appear to be. That would be the opposite of traditional thinking, discussed earlier here.

The number of fingers
in Compsognathus has been an issue largely resolved by Gishlick and Gauthier 2007. Here (Fgi. 2) I found four fingers, all from the left hand, except m1.2 from the right.

Figure 3. New reconstruction of Compsognathus fingers from grayscale data in Gischlick and Gauthier 2007, which has two extra phalanges not found in the online color image.

Figure 2. Revised 1.17.2016. Note the addition of m2.1 and m2.2 on the grayscale data. All phalanges except one of the unguals are from the left hand. Here not two, not three, but four fingers are recovered. 

The entire skeleton was traced
and these elements were used in a similar fashion to create the Compsognathus reconstruction (Fig. 1). Inside this specimen is the ingested lizard Bavarisaurus.

References
Gishlick AD and Gauthier JA 2007. On the manual morphology of Compsognathus longipes and its bearing on the diagnosis of the Compsognathidae. Zoological Journal of the Linnean Society 149: 569–581. 
Ostrom JH 1978.
 The osteology of Compsognathus longipes. Zitteliana 4: 73–118.
Wagner JA 1859. Über einige im lithographischen Schiefer neu aufgefundene Schildkröten und Saurier. Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften 49: 553.
wiki/Compsognathus

 

 

SVP 16 – Cimoliopterus [crested pterosaur], now from Texas!

Myers 2015,
famous for his basal Pteranodon/Germanodactylus, describes a new ornithocheirid with a premaxillary crest in an abstract (see below) and in a JVP paper that just came out.

From the abstract
“Cretaceous strata of Texas have yielded an unexpectedly rich collection of pterosaurs that differ substantially from the prolific, Pteranodon-dominated assemblages of the Western Interior. Two new pterosaur specimens from the Upper Cretaceous Eagle Ford Group in the Dallas/􀂱Fort Worth area enhance our understanding of the fragmentary record of Texas pterosaurs. One specimen (SMU 76892), discovered in the upper Cenomanian portion of the Britton Formation, consists of the rostral section of an upper jaw that bears a prominent, thin premaxillary crest beginning just above the fourth pair of alveoli. The preserved portion of the jaw contains alveoli for 26 teeth, and there is a subtle lateral expansion at the anterior end of the jaw. This partial rostrum is identified as a new species of Cimoliopterus, a monotypic genus previously known only from Cenomanian deposits in England, and represents a significant geographic range extension for this genus. The second new specimen from the Eagle Ford Group (SMU 76942) is a partial upper jaw of Aetodactylus halli, heretofore known only from mandibular material. The jaw fragment was collected at the type locality of A. halli in the middle Cenomanian Tarrant Formation. The dorsoventrally compressed specimen represents part of the anterior half of the jaw, although the exact position within the palate cannot be determined with certainty. The ventral surface bears a thin palatal ridge, and the dorsal surface preserves no evidence of a premaxillary crest. Patterns in tooth spacing along the upper jaw are similar to those observed in the holotype mandible of A. halli (SMU 76383). A phylogenetic analysis of Pterosauria that incorporates the new Cimoliopterus species and new codings for the upper jaw of Aetodactylus indicates that both taxa are basal pteranodontoids. Aetodactylus and Cimoliopterus appear closely related, but are clearly distinct from each other. Identification of Cimoliopterus in North Texas provides further evidence of paleobiogeographic links between the Cretaceous pterosaur faunas of North America and Europe. Discovery of the upper jaw of Aetodactylus confirms that this pterosaur lacked both premaxillary and mandibular crests.”

The Cimoliopterus rostrum
confirms earlier observations of anterior extensions of the nasal and jugal found in other ornithocheirds that extend to the secondary and tertiary nares, both vestigial pores (Fig. 1) recovered by tracing without access to the original specimen.

Destruction
of part of the right side of the rostrum reveals little strips of bone that evidently extended just below the former surface that extend from the nasal and jugal. The fused vomers are the long reported “palatal ridge” described in several ornithocheirids.

Figure 1. Click to enlarge. The rostrum of the North American Cimoliopterus. Every 2 seconds the scenes change. Pink = nasal. Lavender = jugal. Yellow = premaxilla. Green = maxilla. Violet = vomers. DGS enabled the identification of these bones overlooked by first hand observation.

Figure 1. Click to enlarge. The rostrum of the North American Cimoliopterus. Every 2 seconds the scenes change. Pink = nasal. Lavender = jugal. Yellow = premaxilla. Green = maxilla. Violet = vomers. DGS enabled the identification of these bones overlooked by first hand observation.

These extra nares originate also as pores with Scaphognathus (Fig. 2), an ancestral taxon.

Figure 1. Click to enlarge. The reduction of the naris (red arrow), the appearance of the secondary naris, and the appearance of the secondary ascending process of the maxilla in a line of scaphognathids, all to the same scale.

Figure 2. Click to enlarge. The reduction of the naris (red arrow), the appearance of the secondary naris, and the appearance of the secondary ascending process of the maxilla in a line of scaphognathids, all to the same scale. GMu 10157 is basal to the much larger ornithocheirids as recovered in the large pterosaur tree and ignored in the cladograms of other workers.

Note that Myers also traced the nasals and vomers
in Cimoliopterus (Fig. 1) without realizing what they were. That’s where DGS and a good pterosaur cladogram become valuable.

References
Myers TS 2015. New pterosaur material from the Late Cretaceous of North Texas.
Myers TS 2015. First North American occurrence of the toothed pteranodontoid pterosaur Cimoliopterus, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1014904

SVP 15 – Erpetonyx. Still a milleropsid, not a bolosaurid

Modesto et al. 2015a
discuss Erpetonyx, which is still a sister to Milleropsis in the large reptile tree (not a bolosaur parareptile as originally described, Modesto et al. 2015b). And Milleropsis is not a millerosaur.

Note that Millerosauria is included as an ingroup taxon
Unfortunately Millerosaurus ornatus (Broom 1948, Watson 1957) Late Permian (Changhsingian, 30 cm est length) is based on a chimaera of over a dozen skeletons with many common elements distinct from one another. Millerosaurus has been removed from the large reptile tree. Milleropsis is a protodiapsid not related to Milleretta. Milleretta is likely the genera used for the original suprageneric taxon in the cladogram shown in Figure 1,

If this is too confusing, let me know and I’ll walk you through it.

This abstract
has already been published as a paper (Modesto et al. 2015b).

Figure 1. Click to enlarge. When you put the hands and feet and skull back together, you find Erpetonyx nests close to Eudibamus, but closer to Milleropsis.

Figure 1. Click to enlarge. When you put the hands and feet and skull back together, you find Erpetonyx nests close to Eudibamus, but closer to Milleropsis.

From the abstract
Erpetonyx arsenaultorum was recently erected for a single, nearly complete, and mostly articulated skeleton of a bolosaurian* parareptile** collected from the Gzhelian-age Egmont Bay Formation of Prince Edward Island. Erpetonyx arsenaultorum is autapomorphic in possessing 29 presacral vertebrae and a relatively small radiale, fifth distal carpal, and pisiform. The skull is characterized by the presence of plicidentine and by the absence of caniniform maxillary teeth. The neural arches closely resemble those of the Early Permian lanthanosuchian Delorhynchus cifelli in their broadly tongue-shaped zygapophyses, in which the lateral edges of the anterior zygapophyses pass posteriorly onto the lateral surface of the arch and form a conspicuous shelves, emphasized by an anteroventral pocket. The right carpus is well ossified. The preserved unguals are also well ossified, with a prominent flexor tubercle, a suboval proximal portion, and a stout, slightly ventrally curved tip. Together with the observation that the unguals are longer than their respective proximal phalanges, ungual morphology suggests adaptation to a fossorial or semi-fossorial lifestyle. Erpetonyx arsenaultorum is the oldest known amniote with digging adaptations, appearing ca. 3􀂱4 million years after the demise of th coal-swamp forests.

*Not a bolosaurian, but a milleropsid.
**Parareptile is an outmoded name based on traditional cladograms that have been falsified by the large reptile tree.

We looked at Erpetonyx earlier here in this blog.

References
Gow CE. 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Modesto SP, Reisz RR, Macdougall MJ and Scott DM 2015a. Skeletal anatomy of the oldest known parareptile from the Upper Carboniferous of Priince Edward Island, Canada. Journal of Vertebrate Paleontology abstacts
Modesto SP, Scott DM, MacDougall MJ, Sues H-D, Evans DC, Reisz RR 2015b. The oldest parareptile and the early diversification of reptiles. Proceedings of the Royal Society B 282: 20141912. http://dx.doi.org/10.1098/rspb.2014.1912
Watson DMS 1957. On Millerosaurus and the Early History of the Sauropsida. Philosophical Transactions of the Royal Society of London Series B 240(673):325-400.

A Tanystropheus from China

Figure 1. Click to enlarge GIF animation. The Tanystropheus specimen from China, GMPUKU-P-1527: 1)  in situ; 2) as traced by Rieppel et al. 2010; and 3) with colorized DGS tracings. Note: Rieppel et al. overlooked the interclavicle, and mistook the interclavicle + scapula for an over sized coracoid. Rieppel's clavicle is a dorsal rib. The so-called heterotopic bones are merely larger, unfused chevrons.

Figure 1. Click to enlarge GIF animation. The Tanystropheus specimen from China, GMPKU-P-1527: 1)  in situ; 2) as traced by Rieppel et al. 2010; and 3) with colorized DGS tracings. Note: Rieppel et al. overlooked the interclavicle, and mistook the interclavicle + scapula for an over sized coracoid. Rieppel’s clavicle is a dorsal rib. Clavicles here are in red. The so-called heterotopic bones are merely larger, unfused chevrons. What are those blue triangles in the dorsal area? The distal opposite rib tips apparently. Let me know if there’s a better answer.

Rieppel et al. (2010)
described a new, large (trunk length 93.5 cm), Late Triassic Tanystropheus (GMPKU-P-1527, Fig. 1), the first from China. All priors had come from the Alps of Europe. This one lacks a skull plus three cervicals and the distal tail. Based on the short rib of what used to be considered dorsal 1, the authors report it is now cervical 13. That appears to be the case across all large and small specimens. The last cervical is the size and shape of a dorsal, but the associated rib is not a dorsal-type rib. Every prior worker missed that one. Rieppel et al bucked traditions and relabeled the old first dorsal. Good job guys!

New interpretations
of the clavicle, interclavicle, scapula and one coracoid are introduced above, a little different than the original interpretations.

How similar to the European specimens?
the authors report: “The new Peking University specimen (GMPKU-P-1527) is remarkably similar to the larger specimens of Tanystropheus longobardicus housed in the paleontological collections of Zurich University. If there is any difference, then it is in the extent of chevron bones in the tail and the lack of the slight swellings and associated flexure described here for the first time along the length of the longest cervical ribs in PIMUZ T 2189 (Exemplar Q, Fig. 3.

At first glance (in situ) the Chinese specimen is indeed similar to the European specimens.

Figure 2. The Tanystropheus from China partly reconstructed using DGS methods. No foreshortening of the gastralia and limbs are present here. The preserved ilium is not a broad plate here, as in European specimens. The terminal tail vertebrae is circular suggesting the rest of the tail was preserved in another layer.

Figure 2. The Tanystropheus from China partly reconstructed using DGS methods. No foreshortening of the gastralia and limbs are present here. The preserved ilium is not a broad plate here, as in European specimens. That could be a taphonomic artifact or reality. The terminal tail vertebrae is circular suggesting the rest of the tail was preserved in another layer.

But not the same species
The China specimen is apparently more distinct from the European specimens than Rieppel et al. indicate., but then… they did not create any reconstructions. Sometimes comparisons are best seen directly with accurate reconstructions (Fig. 3). We’ve already seen that two very distinct skulls appear on the European specimens and both were distinct from the original Wild 1973 model based on a chimaera of specimens.

The China specimen
has larger girdles, larger vertebrae, more robust ribs and shorter toes (Fig. 4), among the more readily visible distinctions. The dorsal ilium appears to be much narrower, but it is obscured by an overlying femur. The interclavicle has a large, broad anterior process, making it cruciform, not T-shaped.

Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacking an interclavicle and other minor issues. 

Figure 3. The large Tanystropheus specimens to scale. On the right the new China specimen has large girdles, larger vertebrae, more robust ribs and shorter toes, among the more visible distinctions. Click to enlarge. Above right is the new M. Witton reconstruction with erect limbs, an overly large scapula, an overly large ilium, lacks an interclavicle and other minor issues. Otherwise it is very good looking.

Check those hands and feet!
Earlier we were able to separate Rhamphorhynchus specimens into clades using pedal traits alone. Here we’ll compare a European Tanystropheus with the Chinese one (Fig. 4). If they don’t match, they are not conspecific.

Figure 4. Above the Chinese Tanystropheus. Below a large European Tanystropheus. They are not conspecific.

Figure 4. Above the Chinese Tanystropheus. Below a large European Tanystropheus. They are not conspecific.This was overlooked by Rieppel et al. 2010. Reconstructions have value.

Mark Witton started this 
A recent blog post by Mark Witton introduced a new reconstruction of Tanystropheus (Fig. 3 top right). He wondered if the neck was too heavy to use on land while reminding readers that my work was “produced with techniques of questionable reliability”. Keep that phrase in mind.

  1. Witton labeled Tanystropheus as a protorosaur. Actually it’s a tritosaur lepidosaur as indicated by a four-year-old cladogram that now tests 602 taxa.
  2. On tradition alone, Witton includes drepanosaurs, Sharovipteryx, Tanytrachelos, Langobardisaurus and Dinocephalosaurus in the protorosaurs. All are indeed related to Tanystropheus, and are likewise tritosaur lepidosaurs.
  3. Witton reports, “I decided to try my hand at producing a new skeletal reconstruction based on the large, near complete Tanystropheus skeleton described in detail by Rieppel et al. (2010): PIMUZ T 2189.” Unfortunately the skeleton described by Rieppel et al. and traced by Witton is GMPKU-P-1527, the Chinese specimen (Figs. 1, 2). The 2189 specimen is European (Fig. 3), represented by a skull and neck only (Fig. 3). Witton’s technique was to trace a published photo. He makes no mention of visiting the specimen first hand. If you’ll remember, the technique of questionable reliability” mentioned above is my sin of tracing fossil from photographs. So Witton is doing exactly what I do. Is Witton aware of this possible hypocrisy?
  4. Witton reports, “I reconstructed missing parts using smaller Tanystropheus specimens (from Nosotti 2007) and Wild’s widely-used ‘adult’ skull reconstruction.” So he created a chimaera. That is almost never a good idea going as far back as to putting a Camarasaurus skull on a Brontosaurus body. It’s easy, but it’s wrong. “Widely used” doesn’t mean it is correct. As mentioned above, that skull is a chimaera, too.
  5. Witton’s reconstruction admits to cheating on the true sprawling pose for his geometrical analysis. That’s fine. I laid limb elements out straight,too, but not in a walking pose. That would be confusing to someone who didn’t know what the illustration was being used for.
  6. Adding to the confusion, Witton draws a medially directed femoral head which is not present in this lepidosaur.
  7. Witton’s Tanystropheus scapula is too large (see above). The pelvis is a chimaera and a shade too large. Otherwise it’s a beautiful reconstruction and part of that beauty comes from free handing certain elements. I won’t say Witton’s work as a whole is produced with techniques of questionable reliability.l like tracing, free handing and creating chimaeras… but I will say that free handing and creating chimaeras is not reliable. Tracing from photographs can be very reliable! Ad hominem blackwashing (see Witton’s comment) is never appropriate for colleagues. Everyone should realize that inappropriate habits, like creating chimaeras, never last forever. And everybody makes honest mistakes (like overlooking the interclavicle). Finally holding a grudge or never granting forgiveness for past errors is never good… Right guys? Okay. Let’s move on…
  8. Witton reports, “Our problem here is that finding a long-necked terrestrial carnivore to compare with Tanystropheus is challenging.” I realize that Witton is wondering if a large Tanystropheus could walk on land, but gut contents are marine organisms and fossils are found in marine sediments. So… what’s the point? And why were these factoids ignored? The big Tanystropheus doesn’t seem to be a terrestrial animal.
  9. Ironically, Witton compares the long neck of Tanystropheus to his favorite pterosaurs, the azhdarchids. And that’s a fair comparison. They are distantly related in the large reptile tree, but for Witton’s purposes shapes are more important.
  10. Witton’s technique for determining mass at every segment of a lateral view misses the greater mass in the wider dorsal and caudal areas visible only in dorsal view. There’s a fat rump there, but you can’t see it in lateral view.
  11. Little known pertinent fact: I once made a full scale model in wood of Tanystropheus and sold it to the AMNH. I had to add lead weights aft of the hind limbs to make it not tip over. All segments being equal, it was front heavy as a 3-D model, not just on paper.  In vivo the torso and tail would have been more dense, even with large lungs. And the air-filled cervical series and trachea would have been less dense.
  12. Check this out for a possible marine lifestyle that seems to fit the facts for Tanystropheus.

References
Rieppel O, Jiang D-Y,  Fraser NC, Hao W-C, Motani R, Sun Y-L & Sun ZY 2010. Tanystropheus cf. T. longobardicus from the early Late Triassic of Guizhou Province, southwestern China. Journal of Vertebrate Paleontology 30(4):1082-1089.
Wild R 1973. Die Triasfauna der Tessiner Kalkalpen XXIII. Tanystropheus longobardicus(Bassani) (Neue Ergebnisse). – Schweizerische Paläontologische Abhandlungen 95: 1-162 plus plates.
Witton blog post: here

SVP 14 – a new Diandongosaurus

Liu et al 2015
redescribe the basal sauropterygian/placodont Diandongosaurus with a new specimen.

Figure 2. Diandongosaurus exposed in ventral view, skull in dorsal view. Note the small size. At 72 dpi this image is 6/10 the original size.The last common ancestor of Diandongosaurus and Pachypleurosaurus was a sister to Anarosaurus at the base of the Sauropterygia.

Figure 1. Diandongosaurus exposed in ventral view, skull in dorsal view. Note the small size. At 72 dpi this image is 6/10 the original size.The last common ancestor of Diandongosaurus and Pachypleurosaurus was a sister to Anarosaurus at the base of the Sauropterygia.

From the abstract
“The eosauropterygian Diandongosaurus acutidentatus, first reported from the Upper Member of the Guanling Formation (Anisian, Middle Triassic) at Luoping, Yunnan Province, southwestern China, is a small pachypleurosaur-like form characterized by the following features: enlarged and procumbent teeth in the premaxilla and anterior portion of the dentary, fang-like maxillary teeth, clavicle with a distinct anterolateral process, 19 cervical and 19 dorsal vertebrae, and ungual phalanges of the pes extremely expanded. Except for the distinct anterolateral process of the clavicle, this taxon is very similar to Dinopachysaurus dingi, which is from the same locality and the same stratigraphic level, and of similar body size. Herein we describe a new, nearly complete skeleton of Diandongosaurus, which provides new information on the ventral side of the skull, the pectoral girdle and hind limbs. The posterior process of the interclavicle is absent, and the
coracoid foramen is present in the new specimen, features that cannot be seen in the holotype. The anterolateral process of the clavicle is more slender than that of the holotype. Furthermore, the phalangeal formula of the pes of the new specimen is 2-3-4-5-3, whereas the preserved phalangeal formula of the holotype is 2-3-4-6-4, and thus has a higher count for the fourth and fifth digits. The new specimen also shows that there are no vomerine teeth, the ‘anterior interpterygoid vacuity’ is absent, but a natural oval shaped ‘posterior interpterygoid vacuity’ is present, different from the referred specimen,
NMNS-000933-F03498. The results of our phylogenetic analysis also suggest Diandongosaurus is an eosauropterygian, closely related to the Eusauropterygia, and grouped together with Majiashanosaurus to form the sister-group of the Eusauropterygia.”

Different than the Liu et al. study,
the large reptile tree nests Diandongosaurus at the base of the Placodontia, derived from Anarosaurus, as described here. Shifting this specimen to the node suggested by Liu et al. adds 33 steps to the shortest tree.

Figure 2. Diandongosaurus family tree, nesting at the base of the Placodontia, yet still retaining its basal sauropterygian looks.

Figure 2. Diandongosaurus subset of the large reptile family tree, nesting at the base of the Placodontia, yet still retaining its basal sauropterygian looks.

References
Liu et al. 2015. A new specimen of Diandongosaurus acutidentatus (Sauropterygia) from the Middle Triassic of Yunnan, China. Journal of Vertebrate Paleontology abstracts.

 

SVP 13 new Brazilian pterosaur

Kellner et al. 2015
describe a new Early Creteacous pterosaur from Brazil in detail.

From the abstract
“A new fossil locality containing the first pterosaur bone bed from Brazil in the Bauru Basin, and preserved hundreds of isolated or partially articulated elements. Most belong to the tapejarine tapejarid Caiuajara but some larger elements recovered during the preparation revealed the presence of a second much larger azhdarchoid taxon in this region that is reported here. The skull is long, with the rostral part gently curving ventrally. The edentulous jaws have thickened lateral margins bordering a slightly concave palatal surface. The mandible shows a small dentary crest and a palatal ridge, the latter unique to this pterosaur. The cervical vertebrae are slightly elongated with the centrum pierced by a lateral pneumatic foramen which is absent in azhdarchids and chaoangopterids and is very reduced in tapejarids. The coracoid lacks a developed coracoidal flange but shows a developed tuberculum on the posteroventral margin. The articulation with the sternum is dorsoventrally flattened, fork-like and strongly asymmetrical, with the posterior half of the articulation more developed. The sternal plate is quadrangular, being slightly longer than wide. The cristospine is elongated and low and the coracoidal articulations are asymmetrical. The pubis is plate-like and has an obturator foramen that is open posteriorly. The ischium shows a small pneumatic foramen. The ilium had a strong developed postacetabular process with a constricted neck and a large iliac posterior process. The humerus (174 mm) has a long and proximally placed deltopectoral crest that curves ventrally. All recovered first phalanges of the wing finger (~370 mm) have the extension tendon process unfused and bear two pneumatic foramina on the ventral surface of the proximal articulation. Ulnae (170-225 mm) show unfused proximal epiphyses and all scapulae and coracoids are unfused, indicating that all recovered specimens so far represent young individuals*. The particular combination of characters observed suggests that this new species occupies a basal position within azhdarchoids and indicates that basal members of this clade had a more pneumatic skeleton than later forms.”

*Not so. Unfused bones are phylogenetic in character.

I have offered my services
to reconstruct this pterosaur. Sounds interesting. Haven’t heard back yet. Send me the paper when it comes out.

References
Kellner AW 2015.
A new basal azhdarchoid (Pterosauria, Pterodactyloidea) from the Cretaceous Bauru basin. Journal of Vertebrate Paleontology abstracts.

 

What makes a bird a bird? Everyone knows, it’s not feathers any more…)

The line between birds and theropod dinosaurs
has become increasingly fuzzy now that so many non-birds have feathers and other former bird-only traits.

This is a good sign
that evolutionary theory embraces: small changes and a gradual accumulation of traits in derived taxa.

Ultimately
it may come down to a single defining trait (like mammary glands in mammals, or alternatively a squamosal/dentary jaw joint when soft tissue is missing) when you have lots of taxa near the base of a new major clade. So what is that trait? Or what are those traits as recovered by the large reptile tree?

The basal bird and its proximal outgroup
At present the last common ancestor of all extant birds, scansoriopterygids and enantiornithes in the large reptile tree. is the Thermopolis specimen of Archaeopteryx (Fig. 1). The original authors (Mayr et al. 2007; Rauhut 2013) did not employ a phylogenetic analysis, so perhaps did not realize what they had.

For now
the pre-bird theropod, Eosinopteryx (Fig.1) nests just basal to the basal bird theropod, Archaeopteryx. You might find it interesting to see which traits differentiate the latter from the former in the large reptile tree. This list, short as it is, is by no means complete. It simply reflects the general characters used for all reptiles in the large reptile tree.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Figure 1. Eosinopteryx, a pre-bird, compared to Archaeopteryx, a basal bird to scale. Click to enlarge.

Archaeopteryx (Thermopolis) novelties vs. Eosinopteryx

  1. Frontal/parietal suture straight and > than frontal/nasal suture
  2. Metacarpals 2-3 subequal
  3. Pubis and ischium oriented posteriorly (convergent with some deinonychosaurs)
  4. Pedal 4 subequal to metatarsal 4  (convergent with some deinonychosaurs)
  5. Pedal 2.1 not > p2.2
  6. Metatarsal 5 shorter than pedal digit 5 (all vestigial, of course)
Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Figure 2. The coracoid of the Thermopolis specimen is not as elongate as in the more derived taxa. It is just barely not a disc. Thus, this basal taxon was not quite the flapper as the other Solnhofen birds.

Unfortunately
none of these traits are unique to the bird clade.

I thought, perhaps
that an elongate and locked down coracoid (the key to the origin of flapping) would prove to be present in all basal birds. Such a coracoid is indeed present in other specimens of Solnhofen birds, but not in the Thermopolis specimen (Fig. 2), the basalmost example. 

So what we are seeing
in these six Solnhofen birds are discrete steps in the evolution of the flapping behavior, necessary for creating thrust and ultimately flight, as in many living birds. Just as in Late Jurassic pterosaurs, the island/lagoon environment of Solnhofen was as powerful an agent as the Galapagos islands at splitting basal birds into various clades.

From the Mayr et al. abstract on the Thermopolis specimen:
“We describe the tenth skeletal specimen of the Upper Jurassic Archaeopterygidae. The almost complete and well-preserved skeleton is assigned to  Archaeopteryx siemensii
 Dames, 1897 and provides significant new information on the osteology of the Archaeopterygidae. As is evident from the new specimen, the palatine of Archaeopteryx
 was tetra-radiate as in non-avian theropods, and not triradiate as in other avians. Also with respect to the position of the ectopterygoid, the data obtained from the new specimen lead to a revision of a previous reconstruction of the palate of Archaeopteryx. The morphology of the coracoid and that of the proximal tarsals is, for the first time, clearly visible in the new specimen. The new specimen demonstrates the presence of a hyperextendible second toe in Archaeopteryx*.  This feature is otherwise known only from the basal avian Rahonavis and deinonychosaurs (Dromaeosauridae and Troodontidae), and its presence in Archaeopteryx provides additional evidence for a close relationship between deinonychosaurs and avians**. The new specimen also shows that the first toe of Archaeopteryx was not fully reversed but spread medially, supporting previous  assumptions that Archaeopteryx was only facultatively arboreal*. Finally,we comment on the taxonomic composition of the Archaeopterygidae and conclude that Archaeopteryx bavarica Wellnhofer, 1993 is likely to be a junior synonym of  A. siemensii****, and Wellnhoferia grandis Elzanowski, 2001 a junior synonym of  A. lithographica***** von Meyer, 1861.”

* Actually not as prominent as in deinonychosaurs. Such a toe works just as well at climbing tree trunks as climbing dinosaur flanks.

**This may be a convergence as the two clades are separated by taxa without a hyper extensible pedal 2.

*** Perhaps facultatively able to perch, but arboreality would have been a precursor behavior.

**** These two are sisters in the large reptile tree.

***** These two are not sisters.

Other traits in the Theromopolis specimen 
visible in Figure 1 not present in the large reptile tree include the following:

  1. Smaller antorbital fenestra
  2. Longer attenuate tail
  3. Slightly narrower coracoids
  4. Slightly larger forelimb
  5. Bowed gap between ulna and radius
  6. More gracile pubis, posteriorly oriented
Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Figure 3. Archaeopteryx Thermopolis pedal digit 2 (in pink). Pedal 2.2 was capable of hyperextension (see figure 4).

Mayr et al. looked at pedal digit 2
and noticed it was capable of hyperextension (Fig. 3). They likened it to pedal digit 2 in deinonychosaurs (Fig. 4) which is famous for its ability to elevate the ‘killer claw’.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

Figure 4. Deinonychus with elevated pedal digit 2 demonstrating hyperextension.

The large reptile tree
does not nest birds with deinonychosaurs. Rather Xiaotingia and Eosinopteryx nest between these clades. And Xiaotingia also has a similar pedal 2.1 (Fig. 5).

Figure 5. Pedal digit 2 in Xiaotiniga shows the ability to hyperextend pedal 2.2.

Figure 5. Pedal digit 2 in Xiaotiniga also shows the ability to hyperextend pedal 2.2.

On a final note:
Mayr et al. (2007) report four premaxillary teeth in the Thermopolis specimen. I think they might have missed counting the anteriormost premaxillary tooth (Fig. 6) bringing the total to five.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

Figure 6. Archaeopteryx, Thermopolis specimen, premaxilla with five teeth, not four, identified here.

References
Rauhut OWM 2013. New observations on the skull of Archaeopteryx. Paläontologische Zeitschrift 88(2)211-221.
Mayr G, Pohl, B, Hartmann S and Peters DS 2007. The tenth skeletal specimen of Archaeopteryx. Zoological Journal of the Linnean Society 149:97-116.

Archaeopteryx bavarica: the Munich specimen, is a basal scansoriopterygid

Earlier we looked at the nesting of other Archaeopteryx specimens. Here we’ll add a sixth, the Munich specimen, Archaeopteryx bavarica (Wellnhofer 1993, Figs. 1-4).

Figure 1. The Munich specimen of Archaeopteryx bavarica nests at the base of the scansoropterygids. It has a long third finger and other traits.

Figure 1. The Munich specimen of Archaeopteryx bavarica nests at the base of the scansoropterygids. It has a long third finger and other traits. Click to enlarge.

A. bavarica
is largely complete, lacking only a maxilla and a few rostral bones. What sets this specimen apart are several traits, among them a long finger three, longer than finger 2.

Figure 2. Archaeopteryx bavarica, the Munich specimen, is shown here with elements traced. The hands and feet are reconstructed and a possible clavicle is identified.

Figure 2. Archaeopteryx bavarica, the Munich specimen, is shown here with elements traced. The hands and feet are reconstructed and a possible clavicle is identified. Click to enlarge.

The skull has been disarticulated
but the parts can be put back together. (Fig. 3). If valid, the only large bones I can’t seem to identify are the maxillae. Perhaps they are buried are further scattered beyond the matrix. The premaxillae are broken into several pieces. The dentaries remain connected by anteriorly, taphonomically widened in situ.

Figure 3. The skull of Archaeopteryx bavarica traced and reconstructed.

Figure 3. The skull of Archaeopteryx bavarica traced and reconstructed. The maxilla is missing here.

Here I add
the Munich specimen of Archaeopteryx to the large reptile tree (Fig. 4) and recover it basal to the Scansoropterygidae, the clade of basal birds that shares a long finger 3. Here all of the employed Archaeoptetryx specimens are sisters, yet they nest at the bases of three clades of derived birds. This aspect of their interrelationships has not been explored previously (to my knowledge). Rather only one (or perhaps two when Wellnhoferia was employed) Solnhofen birds have been employed in prior studies.

Figure 4. Here I add the Munich specimen of Archaeopteryx to the large reptile tree and recover it basal to the Scansoropterygidae, the clade of basal birds that shares a long finger 3.

Figure 4. Here I add the Munich specimen of Archaeopteryx to the large reptile tree and recover it basal to the Scansoropterygidae, the clade of basal birds that shares a long finger 3. All of the employed Archaeoptetryx specimens are sisters, yet they nest at the bases of three clades of derived birds. This aspect of their phylogeny has not been explored previously. Rather only one Archaeopteryx has been employed in prior studies.

The nesting of A. bavarica 
at the base of the Scansoriopterygidae provides a fitting finish to this multi-post study, based on a hunch that there was more variety in Solnhofen basal birds than the generic name of Archaeopteryx might suggest. Others have also noticed differences (so no novel hypotheses here) and some have erected new species for referred specimens. Some have not. Others have created new genera. I don’t think anyone has yet employed these six, or any six specimens of Solnhofen birds in a large phylogenetic analysis. This post can be a starting point for for just such an experiment conducted by academics. I am not the person to do it, as so many referees on so many rejected papers have indicated previously. And… I have not seen any of these specimens firsthand. But I have included them in a large gamut phylogenetic analysis (Fig. 4).

Figure 1. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

Figure 5. The six tested Solnhofen birds currently named Archaeopteryx, Jurapteryx and Wellnhoferia.

References
Wellnhofer P 1993. Das siebte Exemplar von Archaeopteryx aus den Solnhofener Schichten. Archaeopteryx 11; pp. 1-48,

SVP 12 – Lotosaurus bonebed redated to Ladinian

Hagen et al. 2015 discuss the sedimentology of the Lotosaurus (now dated to Ladinian, Late Middle Triassic, Fig. 1) bone bed. This was suspected here three years ago and thankfully suspicions are now confirmed.

Figure 1. Lotosaurus, a finback poposaur.

Figure 1. Lotosaurus, a finback poposaur.

From the abstract
Lotosaurus adentus is a highly unusual, sail-backed, edentulous poposauroid pseudosuchian archosaur* known primarily from a single site in Sangzhi County, Hunan Province, south China. This locality, the Lotosaurus Quarry, is traditionally dated to the Anisian and is distinctive in being a dense bonebed from which dozens if not hundreds of individual bones and occasional partial skeletons of Lotosaurus have been collected since it was discovered in 1970. The site appears to have formed in a fluvial-floodplain depocenter with sediment derived from multiple sources, rather than in a tidal flat setting as previously suggested. The presence of a population of unexpectedly young detrital zircons from the bone bed unit indicates that Lotosaurus is likely to be Ladinian in age, rather than Anisian as previously reported. This result is more congruent with the phylogenetic position of Lotosaurus, which lies among or just outside a grouping of derived poposauroids known from the Upper Triassic of North and South America.”

*Poposaur, yes, but there is no such thing a pseudosuchian, which is not a monophyletic clade, and only crocs and dinos are archosaurs.

Previous to this reediting of the sediment, Lotosaurus was a chronological outlier and this date change comes as good news.

References
Hagen CJ et al.  2015. Taphonomy, age, and geological context of the original Lotosaurus adentus (Archosauria, Poposauroidea) bone bed in the Middle Triassic Badong Formation, Hunan China. Journal of Vertebrate Paleontology abstracts.