The juvenile enantiornithine STM-34-1 nests with Chiappeavis in the LRT

In a paper on Early Cretaceous fossilized feather molting,
O’Connor et al. 2020 presented several specimens, among them an unnamed juvenile STM-34-1 (Figs. 1–3). The specimen originally appeared in part in Zheng et al. 2012 in their study on sternum ontogeny. O’Connor was a co-author then, too.

Figure 1. STM-34-1 in situ along with select elements.

Note the shorter forelimb
and longer hind limb in the juvenile, which has no tail feathers preserved as well as those elsewhere on the body and limbs. Birds, like other archosaurs, develop allometrically, changing in shape as they mature. By contrast, pterosaurs, like other lepidosaurs, develop isometrically, not changing in shape as they mature, contra traditional thinking.

Figure 2. STM-34-1 skull in situ and reconstructed.

STM 34-1 is from
Liutiaogou, Ningcheng, Chifeng, Inner Mongolia, Lower Cretaceous.

Chiappeavis is from 
Jianchang, Liaoning Province, northeastern China. Jiufotang Formation, Lower Cretaceous

Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.

Added to
the large reptile tree (LRT, 1785+ taxa, subset Fig. 4) STM-34-1 nested with Chiappeavis (Fig. 3).

Figure 4. Subset of the LRT focusing on the bird clade, Enantiornithes.

A phylogenetic analysis that tested STM 34-1
was not presented by O’Connor et al. 2020, nor by Zheng et al. 2012.

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References
O’Connor JK, Falk A, Wang M and Zheng X-T 2020. First report of immature feathers in juvenile enantiornithines from the Early Cretaceous Jehol avifauna. Vertebrata PalAsiatica 58(1):24–44. DOI: 10.19615/j.cnki.1000-3118.190823
Zheng XT, Wang XL, O’Connor JK et al., 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nat Commun, 3: 1–8.

wki/Chiappeavis

Tiny Janusiscus enters the LRT in the lungfish clade

Giles et al. 2015 looked at
the tiny (1cm wide) fossil skull roof of Janusiscus schultzei (Fig. 1) and nested it between placoderms and bony fish + spiny sharks + sharks. This represents yet another example of taxon exclusion in a traditional family tree of fossil fish.

From the abstract:
“The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan-or osteichthyan-like model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans.”

Five years ago, when Giles et al. 2015 was published,the LRT included few to no fish. Today that problem has been rectified (subset Fig. x).

Figure 1. Tiny Janusiscus compared to the much larger lungfish relative, Uranolophus.

The large reptile tree (LRT, 1733+ taxa; subset Fig. x) employs a much wider gamut of taxa than traditional fish cladograms, like those used by Giles et al. 2015. Here tiny Janusiscus nests with the much larger and coeval Uranolophus, known since 1968.

Figure x. Subset of the LRT focusing on fish. Here Janussicus (not listed) nests with Uranolophus and other lungfish.

Given the tiny size of Janusiscus, 
one wonders if it is a hatchling or juvenile of a larger genus, like Uranolophus?

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References
Giles S, Friedman M and Brazeau MD 2015. Osteichthyan-like conditions in an Early Devonian stem gnathostome. Nature 520(7545):82–85.

A juvenile Eusthenopteron enters the LRT

Fish expert, John Long 1995 (p. 209) wrote:
“The juvenile skull of a crossopterygian fish, Eusthenopteron (Figs. 1,3) has more features in common with that of an early amphibian Crassigyrinus (Fig. 4), that it’s adult skull would have had.”

Long goes on to explain about paedomorphosis and heterochrony during the transition from fish to tetrapod.

Euthenopteron was a good transitional taxon several years ago. Recently it was replaced in the LRT by a flatter taxon, Cabonnichthys.

Figure 1. Eusthenopteron juvenile in situ from Schultze 1984. Large plate ventral to the mandible overlaps a convex ventral margin. The quadratojugal is not labeled here. Several bones are re-labeled here.

Let’s put Long’s 1995 statement to the test
by adding Eusthenopteron ‘junior’ (Schultze 1984) to the large reptile tree (LRT, 1698+ taxa; subset Fig. 5).

Results: The juvenile nested with the adult Eusthenopteron in the LRT, falsifying Long’s statement.
Note: Several bones are relabeled here vs. Schultze’s original designations.

Worthy of note:
The juvenile Eusthenopteron shares several traits with another, often overlooked, small taxon with similar large eyes, Koilops, which nests at the base of a nearby derived node in the LRT (Fig. 5). Based on phylogenetic bracketing, Koilops is also a juvenile. All sister taxa are larger and without juvenile proportions.

Figure 2. Koilops is a flat-headed smaller sister to Elpistostege, but with larger teeth, larger orbits and a shorter snout. These traits indicate Koilops is a juvenile.

So Long’s point about paedomorphosis and heterochrony
was  not correct in this case. His ‘matching tetrapod’, Crassigyrinus (Fig. 4), nests several nodes apart from pre-tetrapods in the LRT (off the subset chart in Fig. 5).

Koilops post-crania remains unknown,
but it nests at the base of Elpistostege, Tiktaalik and Spathicepahlus on one branch, Panderichthys + Tetrapoda on the other. So Koilops likely had lobe fins and a straight tail. Perhaps Koilops was a juvenile elpistostegid ready to mature into something larger, with smaller eyes, more like Elpistostege.

Figure 3. Juvenile and adult Eusthenopteron compared from Schultze 1984. The cranium of the juvenile appears convex here, but was likely flatter based on figure 1.

From the Schultze 1984 abstract:
“A size series of thirty-five specimens of Eusthenopteron foordi Whiteaves, 1881 , shows isometric and allometric changes. As in Recent fishes, the main difference between small (juvenile) and large (adult) specimens is the relative size of the orbit and of the head. With the exception of the caudal prolongation, all fin positions remain isometric to standard length.”

Figure 4. Crassigyrinus has little to no neck.

Contra Long 1995 and all prior basal tetrapod workers, the LRT indicates the transition from fish to tetrapod occurred among flat-head taxa, like Trypanognathus.  Crassigyrinus Fig. 4) is a distinctly different stegocephalid with a taller skull, more like those of the more famous traditional transitional taxa, Ichthyostega and Acanthostega. The new fish-to-tetrapod transitional taxa were recovered by simply adding taxa overlooked by prior workers. Taxon exclusion continues to be the number one problem with vertebrate paleontology today, according to results recovered by the LRT. This free, online resource minimizes taxon exclusion.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Not sure if fish expert John Long
would make the same statement today. Let’s hope things have changed in the last 25 years of vertebrate paleontology.

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References
Long JA 1995. The Rise of Fishes. The Johns Hopkins University Press, Baltimore and London 223 pp.
Schultze H-P 1984. Juvenile specimens of Eusthenopteron foordi Whiteaves, 1881 (Osteolepiform Rhipidistian, Pisces) from the Late Devonian of Miguasha, Quebec, Canada. Journal of Vertebrate Paleontology 4(1):1–16.

wiki/Eusthenopteron

Revisiting the Dendromaia tiny den-mate

Earlier I attempted a tracing of the 2cm skull of the Dendromaia (Maddin et al. 2020; Figs. 1–3) small den-mate using a low resolution image. That didn’t work out well due to using only one plate and misinterpreting the subtle grays in the photo. Even so, oddly enough, the error-filled scoring nested the small skull close to the same taxa that Maddin et al. nested the specimen.

As you might remember,
the much larger den-mate nested in the large reptile tree (LRT, 1628+ taxa) with Acleistorhinus and other skull-only taxa between the more complete Casea, Eocasea and Eunotosaurus taxa. The large den-mate was probably an herbivore based on phylogenetic bracketing. The tiny den-mate was a likely insectivore.

Today
with higher resolution images of the part and counterpart mated together in Photoshop layers (Fig. 1), the skull of the small den-mate is re-traced and reconstructed in much greater detail. (Still far from perfect.) The resulting plate and counter plate preserve the palate and the mandibles respectively in ventral view. Dorsal sutures are unknown.

Figure 1. The small den-mate assigned to the genus Dendromaia traced using DGS methods and reconstructed in figure 2. Details are difficult to interpret. As before, this is a best guess based on current data.

Details are still difficult to interpret.
As before, this is a best guess based on current data. Now the small Late Carboniferous den-mate nests between two other much larger skull taxa both assigned to the genus Varanosaurus, known from Early Permian skeletons. So the small den-mate must be congeneric with Varanosaurus. The small size of the small den-mate is probably due to its young ontogenetic age.

These taxa are basal synapsids (in the lineage of humans), not protodiapsids.

Figure 2. The small den-mate nests between these two specimens assigned to Varanosaurus.

Morphologically flat skulls,
like those in Varanosaurus (Fig. 2) and the small den-mate (Fig. 3), tend to fossilize in dorsal or palatal view (Fig. 1). The shape of the mandible informs the reconstructed width of the skull. The dorsal sutures are best guesses based on phylogenetic bracketing.

Figure 3. Reconstruction of the small den-mate based on DGS tracings in figure 1.

The number of mistakes I’ve made
and corrected over the last eight years is now deep into six figures. These corrections are just the latest set to get corrected. Few other workers are attempting to identify bones to this degree on such tiny specimens. There’s no blueprint for this. Everyone who attempts such tracings are on their own. You might try practicing on some roadkill for starters.

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References
Maddin HC, Mann A and Hebert B 2020. Varanopid from the Carboniferous of Nova Scotia reveals evidence of parental care in amniotes. Nature ecology & evolution 4:50–56.

wiki/Varanosaurus
wiki/Dendromaia (not yet posted)

Dendromaia: Not mother + juvenile… just roommates

Updated December 26
with new tracings of the small den-mate now nesting as a juvenile Varanosaurus in the LRT.

Figure 1. The large and small Dendromaia specimens in part and counterpart, traced using DGS methods.

Dendromaia unamakiensis made big news
this week by with headlines like:

1. 305-Million-Year-Old Fossil Shows Parent Caring for Its Offspring
2. 300m-year-old fossil is early sign of creatures caring for their young
3. New Fossil Shows Parental Care Is At Least 300 Million Years Old

That’s the paleo PR machine at work.

Figure 2. Partial reconstructions of the two specimens found together in figure 1. The LRT separates these taxa phylogenetically, so the large one is not the parent of the small one, contra Maddin et al. 2020.

Unfortunately,
when both the little one and the big one were added to the large reptile tree (LRT, 1625+ taxa), only the little one nested near where Maddin, Mann and Hebert 2020 recovered it. They were using a taxon list that excluded too many taxa in comparison to the LRT.

Figure 3. Skull of the small specimen. In the LRT it nests with Heleosaurus within the Protodiapsida, a clade not recognized by Maddin et al. due to taxon exclusion.

From the Maddin et al. abstract:
“Here we report on a fossil synapsid, Dendromaia unamakiensis gen. et sp. nov., from the Carboniferous period of Nova Scotia that displays evidence of parental care—approximately 40 million years earlier than the previous earliest record based on a varanopid from the Guadalupian (middle Permian) period of South Africa. The specimen, consisting of an adult and associated conspecific juvenile, is also identified as a varanopid suggesting parental care is more deeply rooted within this clade and evolved very close to the origin of Synapsida and Amniota in general. This specimen adds to growing evidence that parental care was more widespread among Palaeozoic synapsids than previously thought and further provides data permitting the identification of potential ontogeny-dependent traits within varanopids, the implications of which impact recent competing hypotheses of the phylogenetic affinities of the group.”

The Maddin et al. cladogram
did not test both specimens separately. The Maddin et al. results nested Dendromaia with the poorly preserved Pyozia near the base of their Varanopidae.

The small specimen
The LRT nested the small specimen (Fig. 1) with Heleosaurus, sharing some traits with sister Mesenosaurus. These nest with other protodiapsids apart from Varanops and the Varanopidae in the clade Synapsida. Protodiapsids and synapsids are both derived from a sister to Vaughnictis their last common ancestor in the LRT.

The large specimen
The LRT nested the large skull-less specimen with several skull+pecs and skull-only taxa (Delorhynchus, Microleter and Acleistorhinus) close to the turtle mimics Eunotosaurus and Eorhynchochelys, which preserve post-crania.

So…
these two roommates are not conspecific parent and young, but distinctly different genera sharing a space. The larger one likely dug the tunnel. The smaller one likely found safe harbor under the thigh of the large one, a robust herbivore based on phylogenetic bracketing.

Perhaps
Maddin et al. might have come to the same conclusion if they had tested the two taxa separately… just to be sure their assertion was confirmed phylogenetically… and added enough taxa to recover a correct tree topology. That’s what the LRT is here for.

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References
Maddin HC, Mann A and Hebert B 2020. Varanopid from the Carboniferous of Nova Scotia reveals evidence of parental care in amniotes. Nature ecology & evolution 4:50–56.

http://www.sci-news.com
https://www.theguardian.com
https://www.iflscience.com

Revisiting Anteosaurus ‘junior’

Earlier we looked at the Kruger et al. 2017 hypothesis
that specimen BP/1/7074 (Fig. 1) was a juvenile Anteosaurus (Fig. 1; Watson 1921). The Therapsid Skull Tree (TST, 67 taxa, Fig. 4). Here, with better skull data, BP/1/7074 still does not nest with Anteosaurus, but I completely understand the earlier hypothesis.

Figure 1. Anteosaurus magnifies compared to the smaller and coeval BP/1/7074 specimen others considered a juvenile. Other more closely related specimens in the TT are also shown alongside BP/1/7074 specimen.

There are a variety of Anteosaurus skulls known.
Here (Fig. 2) is a second one, A. abeli, for comparison (no scale bars). Perhaps another Anteosaurus skull will attract BP/1/7074, but presently tested skulls do not yet do so. Titanophoneus potens (Fig. 1) still nests closer to Anteosaurus while coeval Australosyodon (Fig. 1) nests with BP/1/7074.

Figure 2. Anteosaurus abeli skull with right side grayed out and colors added.

The whole concept of juveniles of larger genera
looking like neotonous adults of less related genera has a long history with basal therapsids. We looked at one example earlier here with tiny Abadalon.

Figure 3. Anteosaurus scale model.

The TST
(Fig. 4) has seen many score changes over the past weekend, yet remained the same… or almost the same. One taxon shown below will move over one node. I look forward to telling that story.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

For those who really want to know…
Hipposaurus will move to the base of the Anomodontia.

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References
Boonstra LD 1963. Diversity within the South African Dinocephalia. S. Afr. J. Sci. 59: 196-206.
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia).
–Journal of Systematic Paleontology: Vol. 9, #2, pp. 261-304.
Kruger A 2014. Ontogeny and cranial morphology of the basal carnivorous dinocephalian, Anteosaurus magnificus from the Tapinocephalus assemblage zone of the South African Karoo. Masters dissertation, University of Wiwatersand, Johannesburg.
Kruger A, Rubidge BS and Abdala F 2017. A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2016.1276106
Watson, DMS 1921. The Bases of Classification of the Theriodontia: Proceedings of the Zoological Society of London, 1921: 35-98.

wiki/Anteosaurus

Juvenile Rhamphorhynchus and flightless pterosaur abstracts

Part 4
The following manuscripts are independently published online without peer-review at the DavidPetersStudio.com website. http://www.davidpetersstudio.com/papers.htm

Better to put them out there this way
than to let these works remain suppressed. Hope this helps clarify issues.

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Peters D 2018g. First flightless pterosaur
PDF of manuscript and figures

Pterosaur fossils have been discovered all over the world, but so far no flightless pterosaurs have been reported. Here an old and rarely studied pterosaur fossil (Sos 2428) in the collection of the Jura Museum in Eichstätt, Germany, was re-examined and found to have a reduced pectoral girdle, small proximal wing elements (humerus, radius and ulna), three vestigial distal wing elements, the relatively longest pelvis of any pterosaur and the widest gastralia, or belly ribs. This discovery represents a unique morphology for pterosaurs. The Jura specimen lacked the wing size, forelimb muscularity and aerodynamic balance necessary to sustain flapping flight. It was a likely herbivore.

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Peters D 2018h. First juvenile Rhamphorhynchus recovered by phylogenetic analysis
PDF of manuscript and figures

Standing seven to 44 centimeters in height, a growing list of 120+ specimens assigned to the pterosaur genus Rhamphorhynchus are known chiefly from the Solnhofen Limestone (Late Jurassic, southern Germany). An early study recognized five species and only one juvenile. A later study recognized only one species and more than 100 immature specimens. Phylogenetic analyses were not employed in either study. Workers have avoided adding small Solnhofen pterosaurs to phylogenetic analyses concerned that these morphologically distinct specimens were juveniles that would confound results. Here a large phylogenetic analysis that includes tiny Solnhofen pterosaurs tests that concern and seeks an understanding of relationships and ontogeny within the Pterosauria with a focus on Rhamphorhynchus. 195 pterosaurs were compiled with 185 traits in phylogenetic analysis. Campylognathoides + Nesodactylus were recovered as the proximal outgroups to the 25 Rhamphorhynchus specimens. The ten smallest of these nested at the clade base demonstrating phylogenetic miniaturization. Two Rhamphorhynchus had identical phylogenetic scores, the mid-sized NHMW 1998z0077/0001, and the much larger, BMNH 37002. These scores document a juvenile/adult relationship and demonstrate isometry during pterosaur ontogeny, as in the azhdarchid, Zhejiangopterus, and other pterosaurs. Rather than confounding results, tiny Solnhofen pterosaurs illuminate relationships. All descended from larger long-tailed forms and nested as transitional taxa at the bases of the four clades that produced all of the larger Late Jurassic and Cretaceous pterodactyloids. No long-tailed pterosaurs survived into the Cretaceous, so miniaturization was the key to pterosaur survival beyond the Jurassic.

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These manuscripts benefit from
ongoing studies at the large reptile tree (LRT, 1256 taxa) in which taxon exclusion possibilities are minimized and all included taxa can trace their ancestry back to Devonian tetrapods.

Smallest Pteranodon: Bennett 2017

A new small partial wing specimen of Pteranodon
discovered by Glen Rockers, was described by Bennett 2017 (Figs. 1-4).

Young (small) Pteranodon specimens
were essentially unknown prior to the Bennett paper. So this is important news.

Figure 3. Small Pteranodon, FHSM 17956, carpus insitu and reconstructed. Here several bones were reidentified. See reconstruction in figure 3. It demonstrates that all the newly identified parts fit together.

Unfortunately
a reconstruction based on Digital Graphic Segregation (DGS, Fig. 4) shows that Bennett, widely known as THE expert on Pteranodon going back to his PhD thesis, misidentified several carpal bones here. In his defense, that was easy to do. The distal carpal is beneath the other carpal bones and it has splinters that extend beyond it. Rather than using DGS, Bennett chose to outline bones the old fashioned way. This leads to problems that can be solved when you color each bone and bone splinter THEN test your colors with a reconstruction. Bennett provided no reconstruction that tested his outline tracings. Bennett also overlooked manual digit 5. The fragment (FR) probably comes from the crushed and splintered distal carpal. Bennett reported, “All carpal elements are severely deformed by compression such that they preserve little of their original morphology…” That’s because he misidentified elements that are otherwise identical to those of adult specimens.

Figure 4. Small Pteranodon (FHSM 17956) carpus reconstructed after several bones were reidentified.

Bennett also upholds several invalid paradigms

1. Other small, short crested Pteranodon specimens represent young ones. Actually they represent taxa closer to the outgroup, Germanodacytylus. 
2. Short-crested specimens are females. No male/female pairs have ever been documented. Rather short-crested taxa are closer to the crestless outgroup. 
3. Large pelvis specimens  are females. No, they are large nyctosaurs. 
4. Small size Rhamphorhynchus were juveniles of larger ones. No, phylogenetic analysis indicates a period of phylogenetic miniaturization followed the genesis of Rhamphorhynchus from larger Campylognathoides ancestors. Bone histology would include juvenile bone tissue in adults of these small, precocial and fast-breeding taxa. It is important that someday Bennett runs a phylogenetic analysis, something he told me decades ago was critical to understanding taxonomy. 
5. There is no such thing as manual digit 5 in pterosaurs. He overlooked it here. 

Bennett now realizes:
“A new juvenile specimen of Pteranodon collected from the Smoky Hill Chalk Member is so small that it challenges the interpretation of rapid growth to large size before flying and feeding (Bennett, 2014a).” As everyone knows now, hatchling pterosaurs were able to fly shortly after hatching. To his credit, Bennett continues, “The interpretation of rapid growth while under parental care is rejected.”

Bennett examined the specimen under stereo microscope
and made mistakes here re-identified on a computer monitor applying colors to each bone to visually segregate one from another and facilitate accurate reconstruction. This is something that cannot take place using old-fashioned stereo microscopes.

Bennett occasionally
misidentifies small pterosaur bones. This was documented here dealing with the flat-headed anurognathid SMNS 81928, in which he considered the mandible a giant sclerotic ring in the front half the skull, different from all other pterosaurs. Bennett 2008 promoted an invalid hypothesis on the origin of the pterosaur wing based on imagination rather than taxa, documented here. Bennett’s (2007) interpretation of pteroid articulation against the preaxial carpal. was invalidated by Peters 2009 who nested it on the anterior radiale (Fig. 4).

Note
The extensor tendon process is articulated with the rest of m4.1, as in all Pteranodon specimens. Bennett once considered unfused  extensor tendon processes a sign of immaturity. This is not correct. As reported earlier, since pterosaurs are lepidosaurs they display lepidosaur fusion traits, typically not ontogenetic, but phylogenetic. As an example, in Nyctosaurus the extensor tendon process remains unfused, distinct from Pteranodon. Bennett insists that the extensor tendon process in the juvenile specimen is unfused but notes that the fragile cortical bone was lost during preparation. And just think about it.. the carpals, typically wrapped tightly in ligaments were scattered while the extensor tendon process didn’t move during taphonomy. By contrast, in Nyctosaurus the extensor tendon process popped off before the toes disarticulate.

Bennett avoid mentioning or citing
work by Peters 2009, which disputed Bennett 2007, who articulated the pteroid with the preaxial carpal. In order to do so, Bennett 2017 did not cite Bennett 2007, but did manage to cite nearly every other one of his papers. Kids.. sometimes you have to look for what’s not mentioned.

Pteranodon variety
is best seen and appreciated by direct comparison of the skulls and the post-crania. FHSM 17956 is a juvenile of a gracile form, similar to the Triebold specimen NMC41-358 (Fig. 1), a short-crested gracile variety.

Bennett describes ontogenetic niches
for hatchling, juvenile and adult Pteranodon. This is necessary for 8x smaller hatchlings incapable of handling adult-sized prey.

In Bennett’s Acknowledgements he reports, 
“Constructive reviews from M. Witton and L. Codorniú led to improvements in the manuscript, and an anonymous reviewer disagreed with everything.” That anonymous reviewer was not me. That would be blackwashing. I always try to find something of value in any manuscript I review, even if I disagree with some of what is presented.

Bennett first described this taxon
in a 2014 SVP abstract. See how long traditional studies take to get published? I was just about to call Chris to see if he was okay. I’m glad to see he is still out there publishing important specimens.

References
Bennett SC 2007. Articulation and Function of the Pteroid Bone of Pterosaurs. Journal of Vertebrate Paleontology 27(4):881–891.
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Bennett SC 2017. New smallest specimen of the pterosaur Pteranodon and ontogenetic niches in pterosaurs. Journal of Paleontology. pp.1-18. 0022-3360/15/0088-0906
doi: 10.1017/jpa.2017.84
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29:1327-1330.

Do ceratopsid juveniles (phylogenetically) nest together?

The discovery of a second juvenile ceratopsid
(Currie et al. 2016) raised an interesting point: “In phylogenetic analysis, if all characters are coded as seen, the two juvenile ceratopsids (a partial Triceratops skull and the UALVP 52613 juvenile, Fig. 1) nest together. However, when size or age dependent characters are [not scored], the new juvenile (Chasmosaurus) specimen groups with other adult Chasmosaurus specimens.”

Figure 1. Chasmosaurus juvenile UALVP 52613 specimen lacking forelimbs due to  taphoniomic loss down a nearby sinkhole.

So, does phylogenetic analysis fail us?
The new UALVP juvenile was recognized/identified as being closer to Chasmosaurus, just as the juvenile Triceratops was recognized as being closer to Triceratops, both on the basis of character traits and prior to analysis. But the Currie et al. unedited analysis takes us in another direction…

From the introduction
“The specimen comprises a nearly complete skeleton lying on its left side, lacking only the front limbs and girdle, which were lost many years ago into a large sinkhole….”

“The juvenile nature of this specimen is based on several lines of reasoning. At approximately 1.5 min total length, it is the smallest articulated ceratopsid skeleton that has ever been recovered. Immature bone textures on cranial bones (Brown et al., 2009), open neurocentral sutures throughout most of the vertebral column, incomplete fusion of sacral vertebrae, lack of fusion between caudal ribs and vertebrae, poorly formed articulations between limb bones, and many other characters confirm that this is an immature ceratopsid….”

“Of all the chasmosaurines from Dinosaur Park, it is most similar to Chasmosaurus belli and C. russelli.”

This interpretation
was made by expert and experienced assessment. The question is, why would the unedited Currie et al. analysis separate the juveniles from the adults and nest the juveniles together? They’re not exactly tadpoles or caterpillars, but they do change somewhat during maturation, following basic archosauromorph (including synapsid/mammal) growth strategies, that lepidosauromorphs (including pterosaurs) are less likely to follow.

When an adult Chasmosaurus
and the juvenile Chasmosaurus are added to the large reptile tree, using a character list NOT specific to ceratoposids, the juveniles nest with their respective adults, not with each other. And this happens despite the very few bones that represent the juvenile Triceratops (posterior face and shield only). Notably there are no other competing ceratopsid candidates in the present taxon list. All data was gleaned from online images. The adult data may be  represented by chimaera mounts and chimaera drawings. If the Currie et al analysis was restricted to just an adult and juvenile Triceratops and just an adult and juvenile Chasmosaurus, would adults nest with juveniles as they do in the large reptile tree? We don’t know because that test was not run.

Here’s how the large reptile tree divides
the Chasmosaurus adult and juvenile from the Triceratops adult and juvenile (posterior skull traits only). Please feel free to provide better data or more precise readings for any of these interpretations. Some were difficult to figure from available sources. At present I do not include traits for parietal fontanelles or horn lengths, which are the easiest two traits that most commonly separate Chasmosaurus from Triceratops and are reflected in their juveniles.

1. skull table: C: depressed terrace, medial and lateral crests; T: convex
2. snout in dorsal view: C: not constricted; T: constricted
3. orbit positon: C: postorbital > preorbital; T: subequal
4. lateral rostral shape: C: convex, smooth curve; T: double convex
5. nasals/frontals: C: nasals >; T: subequal
6. antorbital fenestra: C: absent; T: without mx fossa
7. orbit/upper temporal fenestra: C: orbit not > T: orbit >
8. orbit position/skull: C: anterior half of skull; T: not
9. orbit shape: C: round to square: T: taller than wide
10. upper temporal fenestrae: C: not closed or slit-like; T: closed or slit-like
11. frontal shape: C: not wider posteriorly; T: wider posteriorly
12. frontal shape 2: C: without posterior processes; T: with posterior processes
13. posterior rim of parietal: C: transverse; T: anteriorly oriented or curved.
14. parietal skull table: C: forms a sagittal crest: T: broad
15. squamosal descent: C: mid level; T: ventral skull (ventral maxilla)
16. skull roof fusion: C: parietal fusion only; T: frontal fusion and parietal fusion
17. jaw joint orientation: C: descends from ventral mx; T: in line with ventral mx, after jugal arch.
18. last maxillary tooth: C: posterior orbit; T: mid orbit
19. mandible ventrally: C: 2-tier convex; T: straight
20. 2nd sacral rib: C: not: T: double wide laterally
21. manus/pes: C: subequal: T: manus smaller
22. ilium: C: posterior process >; T: not
23. metatarsal 1:4 ratio: C: 1 not > than half: 4 T: 1> half of 4
24. metatarsals 2-4: C: < than half the tibia; T: not
25. pedal 3.1 vs p2.1: C: not > T: 3.1>
26. metatarsals 2 and 3: C: aligns with mt1; T: aligns with pedal 1.1
27. pedal 4 length: C: subequal to mt 4; T: > mt4
28. pedal digit 3 vs 4: C: 4 narrower than 3; T: 4 is not narrower

Shifting the juvenile Triceratops
to the juvenile Chasmosaurus adds 12 steps. Doing the opposite adds 21 steps. Bootstrap scores are over 99-100 for the three nodes represented by the four taxa. I have not reviewed the scores or data in the Currie et al study, which obviously adds more ceratopsid traits.

Added < 24 hours after original publication Below is a new reconstruction of the Triceratops juvenile based on text measurements and an adult skull compared to the original reconstruction that does not appear to have correctly scaled the mandible to the skull elements.

Figure 4. A new reconstruction of the Triceratops juvenile with the mandible and squamosal scaled to text measurements and shaped to adult elements compared to the original (Goodwin et al.) reconstruction which appears to have shortened the mandible.

A YouTube video, Dinosaurs Decoded, shows Mark Goodwin reassembling the juvenile Triceratops skull. Click here to watch.

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Short notes for readers and critics
“Criticism of a writer is absolutely inevitable.” — Malcolm Gladwell.
Gladwell is one of the most respected and best-selling authors in current decades. Nevertheless, this interview on YouTube quotes several critics, many with scathing barbs. So, this give and take between writers and their critics is universal and ‘inevitable.’

On the other hand,
in Science, one either can or cannot duplicate experiments and observations. It should be cut and dried, but with errors and egos on both sides, it rarely is. Even so, most people think it is better to try/experiment with/refute alternate hypotheses. Aaaaaat least that’s the editorial policy at ReptileEvolution.com where occasional lack of talent and insight is sometimes overcome by tenacity, huge blocks of data and the ability to update online blunders.

References
Currie PJ,  Holmes RB, Ryan MJ and Coy C. 2016. A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1048348.

 

 

Tapejara Juvenile??

The post cranial skeleton of Tapejara (famous for its head crests) was published last year (Eck, Elgin and Frey 2011). It was smaller than the known skulls (Fig. 1). I had seen the 3D skeleton in a museum drawer several years ago. The skull despite its size, is very close in morphology to the holotype. The smaller specimen may bea juvenile and if so it demonstrates, once again, the largely isometric, rather than allometric growth pattern of pterosaurs, although in this case the rostrum is shorter and the eyeball greater. These clues might indicate that the specimen could be a smaller species on that basis alone, given the examples of embryos and other juveniles that do not share “juvenile” traits with adults. Too bad the feet are unknown in both cases. They usually tell the tale. A Tapejara foot was looked at earlier, but it was from another specimen.

Figure 1. Various Tapejara specimens including the purported juvenile. Click to learn more. The postcrania of the large Tapejara was based on the smaller specimen and the toes were from a disarticulated specimen.

References
Eck K, Elgin RA, Frey E 2011. On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil. Swiss Journal of Palaeontology, doi:10.1007/s13358-011-0024-5.