Archelon enters the LRT with snapping turtles

This post was set in motion by a recent PBS Eons YouTube video
all about the biggest fossil turtle ever described, Archelon (Figs. 1, 2). Click to play.

The narrator reported
that Archelon (Figs. 1, 2) was not related to living sea turtles, not even to Dermochelys, the living leatherback (Fig. 4). Well that mystery sounds like a job for the LRT. Maybe it can do some good. And it’s good to get back to reptiles for an evening. It’s been awhile…

Figure 1. Classic photos of Archelon in ventral and dorsal views.

Figure 1. Classic photos of Archelon in ventral and dorsal views.

After testing
in the large reptile tree (LRT, 1802+ taxa) Archelon (Figs. 1, 2) nests firmly with Macrochelys, the alligator snapping turtle (Fig. 3). That’s why Archelon is not related to living sea turtles and perhaps why it’s terrestrial origin has remained a mystery until now.

Once again, testing taxa together that have never been tested together before sometimes recovers such unexpected, but inevitable results.

When you see the skulls together
(Figs. 2, 3), the relationship seems obvious. Most turtles do not extend their premaxilla like a hawk beak, but Archelon and snapping turtles do. The skull suture patterns are also distinct from other turtles and shared between only these two of all other turtles tested in the LRT.

Figure 2. Skull of Archelon with colors identifying bones. Compare to Macrochelys in figure 3.

Figure 2. Skull of Archelon with colors identifying bones. Compare to Macrochelys in figure 3.

In the ancient and dangerous Niobrara Sea covering much of North America,
it took a giant, mean-old snapping turtle with flippers to survive in a seaway full of other giant monster reptiles.

Figure 3. Macrochelys skull in three views with colors added to bones. Compare to Archelon in figure 2.

Figure 3. Macrochelys skull in three views with colors added to bones. Compare to Archelon in figure 2. Image from Catalogue of shield reptiles in the collection of the British Museum.

Archelon ischyros
 (Wieland 1896; Late Cretaceous; 4.6m or 15 feet in length; Figs 1,2) is the largest turtle ever documented. Along with ProtostegusArchelon is traditionally considered a member of the Protostegidae. In the LRT Archelon nests with Macrochelys, the alligator snapping turtle (Fig. 3). Distinct from Macrochelys, the naris opens dorsally in Archelon.

Figure 4. Macrochelys skeleton documenting the origin of the open ribs with small fenestrations.

Figure 4. Macrochelys skeleton documenting the origin of the open ribs with small fenestrations.

Archelon is distinct from and parrallel to
other sea turtles, all of which have a shorter, transverse premaxilla and different skull bone patterns (e.g. Fig. 4). Previous workers had already removed protostegids from other sea turtles, but then stopped there. The Archelon relationship to snapping turtles was not tested or known until now. If proposed previously, please send a citation so I can promote it here.

A leathery carapace,
like that of Dermochelys, covered the similarly open ribs of Archelon (Fig. 1), but the two tax are not related. Dermochelys is closer to sea turtles with a traditional hard-shelled carapace.

Figure 4. Skulls of Dermochelys, the extant leatherback turtle. The skull pattern here is distinct from patterns in Archelon and other snapping turtles (above).

Figure 4. Skulls of Dermochelys, the extant leatherback turtle. The skull pattern here is distinct from patterns in Archelon and other snapping turtles (above).

Not sure why snapping turtles and Archelon 
were never shown to be related to one another before. It seems obvious in hindsight. This struck me as low-hanging fruit left by PhDs for armchair amateurs to deduce. It just took one evening to nest this enigma. Let me know if there are any more enigmas lurking out there that need a good nesting. This is the fun part.

Postscript Feb. 19, 2021
Readers have reported that I might have colorized osteoderms or scales instead of bone sutures. Jura sent the images on the left, which I desaturated and burned to bring out details. Those seem to show scalation. The colored images appear to show sutures. Right? Or wrong?

Jura replied: top = sutures, bottom = welded osteoderms. Compare the top image with figure 4 from Sheil 2005′

The Shiel 2005 image of Macrochelys (= Macroclemys) is a diagram drawing from Gaffney 1979. The Gaffney 1979 image is a diagram drawing from Gaffney 1975e.

Figure x. Osteoderms on the left don't always align with bones on the right in these images of Macrochelys.

Figure x. Osteoderms on the left don’t always align with bones on the right in these images of Macrochelys.

Figure y. Macrochelys skull with traditional labels (b&w) and LRT labels (color). The LRT prefrontal rims the orbit, as in all other tetrapods.

Figure y. Macrochelys skull with traditional labels (b&w) and LRT labels (color). The LRT prefrontal rims the orbit, as in all other tetrapods.

It seems to me,
and let me know if this is an error, that everybody recognizes the pair of bones over the naris. Traditionally these are labeled prefrontals (Fig. y), even though they don’t touch the orbit. Other bones have different traditional labels, too. My labels come from pareiasaur and Elginia homologs so those labels come from a valid phylogenetic context. Traditional labels are wrong because the pareiasaur ancestry is not yet widely, if at all, recognized. All other turtle ancestor candidates are tested in the LRT.


References
Gaffney ES 1975e. Phylogeny of the chelydrid turtles: a study of shared derived characters in the skull. Fieldiana:Geol., vol. 33, pp. 157-178.
Gaffney ES 1979. Comparative cranial morphology of recent and fossil turtles. Bulletin of the American Museum of Natural History 164(2):65–376.
Sheil CA 2005. Skeletal development of Macrochelys terrminckii (Reptilia: Testudines: Chelydridae) Journal of Morphology 263:71–106.
Wieland GR 1896. Archelon ischyros: a new gigantic cryptodire testudinate from the Fort Pierre Cretaceous of South Dakota. American Journal of Science. 4th series. 2 (12): 399–412.

wiki/Macrochelys
wiki/Archelon

 

AMNH 4908: at the genesis of Nyctosaurus and Pteranodon

Bennett 2017 described AMNH 4908:
“The smallest relatively complete previously known specimen of Pteranodon, AMNH 4908, consists of a partial trunk skeleton and tail, scapulocoracoid, humerus through WP2, both femora and tibiae, and a disarticulated foot (Bennett, 2001; Table 1), had an estimated wingspan in life of 3.33 m.”

AMNH 4908 is small because
it is primitive (Figs. 1–3), closer to its smaller germanodactylid ancestors (Fig. 4), not because it is ontogenetically young. That point was overlooked by Bennett 2017 who decided not to include a comprehensive phylogenetic analysis then or earlier (Bennett 1991, 1992). He thought smaller specimens, like AMNH 4908, were female.

Figure 1. The Niobrara specimen AMNH4908 in situ.

Figure 1. The Niobrara specimen AMNH4908 in situ. See figure 3 for reconstruction.

It is worth noting
AMNH 4908 has a type of pelvis with unfused ischia, a morphology common to Nyctosaurus. Earlier Bennett 1991, 1992 decided a large Nyctosaurus pelvis belonged to a female Pteranodon, which started that gender myth. Unfortunately, Bennett never used phylogenetic analysis to lump and split Pteranodon, the subject of his 1991 PhD thesis. Instead he relied on a statistical analysis, which led him astray. The large pterosaur tree (LPT, 246 taxa) is the only published pterosaur cladogram to include more than one or two Pteranodon and Nyctosaurus taxa. When you really want to know something in systermatics, use a comprehensive cladogram, not a graph.

Figure 2. Subset of the LPT focusing on pterandontids and their ancestors going back to Late Jurassic germanodactylids. AMNH 4908 nests between the Nyctosaurus clade and the Pteranodon clade.

Figure 2. Subset of the LPT focusing on pterandontids and their ancestors going back to Late Jurassic germanodactylids. AMNH 4908 nests between the Nyctosaurus clade and the Pteranodon clade.

Also worth noting
is the deltopectoral crest of the humerus in AMNH 4908, which has a round tongue shape like that of its predecessors among Eopteranodon and Germanodactylus (Fig. 4), rather than the hatchet shape found in Nyctosaurus or the warp found in Pteranodon.

Figure 3. AMNH 4908 pterosaur reconstructed. Transitional between Nyctosaurus and Pteranodon. Note the big feet, tiny sternal complex and round tip deltopectoral crest. Note the massive radius + ulna.

Figure 3. AMNH 4908 pterosaur reconstructed. Transitional between Nyctosaurus and Pteranodon. Note the big feet, tiny sternal complex and round tip deltopectoral crest. Note the massive radius + ulna.

Of course, any taxon basal to Nyctosaurus and Pteranodon
is also going to be close to the SMNK PAL 6592 specimen (Fig. 4) attributed to Germanodactylus.

Matching YPM 1179 to the post-crania of SMU 76476 (Myers 2010) and overprinted with SMNK PAL 6592. The resemblance is indeed remarkable.

Figure 4. Matching YPM 1179 to the post-crania of SMU 76476 (Myers 2010) and overprinted with SMNK PAL 6592. The resemblance is indeed remarkable.

Ever since 2003, traditional pterosaur workers (with PhDs)
have been linking toothless pteranodontids to toothy ornithocheirids. That they continue to do so, (due to taxon exclusion) is embarrassing to the profession.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen 'w' = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen 'z' = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Figure 5. Pteranodon and Nyctosaurus skulls. Click to enlarge.

Figure 6. AMNH 4908 specimen compared to a large Pteranodon specimen UNSM 50036.

Figure 6. AMNH 4908 specimen compared to a large Pteranodon specimen UNSM 50036.

In similar fashion and shame,
traditional paleontologists continue to insist that pterosaurs arose from Euparkeria, Scleromochlus or Erythrosuchus according to several authors, or from Macrocnemus bassaniiPostosuchus kirkpatricki and Herrerasaurus ischigualastensis according to Dalla Vecchia 2019. More closely related taxa (LangobardisaurusCosesaurus, Sharovipteryx and Longisquama) were validated as better pterosaur ancestors in four phylogenetic analyses 20 years ago.


References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
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
Dalla Vecchia FM 2019. Seazzadactylus venieri gen. et sp. nov., a new pterosaur (Diapsida: Pterosauria) from the Upper Triassic (Norian) of northeastern Italy. PeerJ 7:e7363 DOI 10.7717/peerj.7363

Thanks to Alex Schiller for posting this specimen on Facebook.

https://pterosaurheresies.wordpress.com/2012/04/09/female-pterosaurs/

http://www.reptileevolution.com/pteranodon-postcrania.htm

Pseudictops: what little we know is unique

There are not many mammals with crenulated/serrated teeth.
Pseudictops lophiodon (Matthews, Granger and Simpson 1929, Sulimski 1968, Late Paleocene, 57 mya; Fig. 1; AMNH 21727) is one such mammal. From the start Pseudictops was compared to anagalids like Leptictis (Fig. 2), a basal elephant shrew and ancestor to tenrecs, pakicetids and odontocete whales.

Figure 1. Pseudictops lophiodon compared to the slightly larger Siamotherium.

Figure 1. Pseudictops lophiodon compared to the slightly larger Siamotherium. The mandible is extremely robust and appears to nearly lack a coronoid process, distinct from most mammals.Note the crenulations and and/or robust serrations on the anterior teeth.

Figure 1a. Pseudictops anterior teeth.

Figure 1a. Pseudictops anterior teeth.

The dentary incisors
are deeply rooted in a deep dentary. Not sure why the two dentaries (Fig. 1) have distinct shapes. Perhaps they are not actually related to one another or perhaps some parts are missing from the smaller one and plasterered over.

Figure 2. Leptictis, an early Oligocene elephant shrew.

Figure 2. Leptictis, an early Oligocene elephant shrew.

Now that you’ve met Pseudictops, a quick look at Ictops
reveals a cranium with a double parasagittal crest, as in sister taxon, Leptictis

Figure 6. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Figure 3. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.


References
Matthew WD, Granger W and Simpson GG 1929. Additiions to the fauna of the Gashato Formatin of Mongolia. American Museum Novitates 376:1–12.
Sulimski A 1968. Paleocene genus Pseudictops Matthew, Granger and Simpson 1929 (Mammalia) and its revision. www.palaeontologia.pan.pl/Archive/1968-19–1011-129–10-14.pdf

 

The AMNH animated Jeholopterus

Updated March 3, 2015 with the addition of a dorsal view of Jeholopterus.

About a year ago
the American Museum of Natural History (AMNH) in New York City (NYC) put on a pterosaur display, both in their halls and online.

Their animated portrayal
of the Late Jurassic Chinese pterosaur, Jeholopterus, caught my eye (Fig. 1).

Figure 1. Animated GIF created by the AMNH for their web page on Jeholoopterus. Note the complete lack of an airfoil in the wing, the lack of muscles in the limbs, the presence of a uropatagium between the hind limbs, the lack of a tail, eyes set on the sides of a blockhead skull, and no care to reproduce the wide ribcage. In short, there is little that is accurate about this otherwise wonderfully animated pterosaur. And where is all the long hair that should be there?

Figure 1. Animated GIF created by the AMNH for their web page on Jeholoopterus. Note the complete disregard for its preserved anatomy, the  lack of an airfoil in the wing, the lack of muscles in the limbs, the presence of a uropatagium between the hind limbs, the lack of a tail, eyes set on the sides of a blockhead skull, and no care to reproduce the wide ribcage. In short, there is little that is accurate about this otherwise wonderfully animated pterosaur. And where is all the long hair that should be there? The animator was gifted, but the blueprint was largely imaginary.

One wonders what the animators used for reference… certainly not the fossil.
This animation lacks all the traits that make Jeholopterus unique: the up-curved jawline, the forward angled eyes, the very hairy body, the broad ribcage and belly, the deep chest, the low attachment of the wing, the large-boned limbs, the surgically curved claws, the huge feet with a very large digit 5, a longish tail and longer wings. Also lacking here is a wing with a decent airfoil section, a proper trailing edge stretched between the wing tip and elbow, large limb muscles and paired uropatagia behind each hind limb. And where does that box-like skull come from??

This is an old-school pterosaur cartoon,
lacking almost everything we know about this complete and articulated fossil. For comparison, a reconstruction is offered here (Fig. 2) based on precise tracings.

Figure 3. Click to enlarge. The Jeholopterus holotype (left) alongside the referred specimen (right). No doubt they were related, but were likely not conspecific. The one on the right was an insect eater. The one on the left was specialized for drinking dinosaur blood.

Figure 3. Click to enlarge. The Jeholopterus holotype (left) alongside the referred specimen (right). No doubt they were related, but were likely not conspecific. The one on the right was an insect eater. The one on the left was specialized for drinking dinosaur blood.

Jeholopterus had so many traits distinct from those of other anurognathid pterosaurs, that it deserves more respect than the AMNH gave it. Seems they purposely avoided describing it for what it is… a vampire pterosaur (details here). Would have been a bigger draw and a more accurate presentation had they just paid attention to the details.

The genesis of this post
came from an Ask.MetaFilter.com post on binocular vision in pterosaurs posted by Hactar, who wrote: “I am trying to find any information about binocular vision in pterosaurs. This past weekend, I went to the Museum of Natural History’s exhibition on pterosaurs. Their illustrations for Jeholopterus varied greatly in the placement of they eyes from on the sides of the head to facing forward (third picture on the page). (The second image caused me to dub it “freaky monkey pterosaur.”)  So how much binocular vision did pterosaurs have? I have found a couple of scattered references to family Anurognathus (of which Jeholopterus is a genus) having binocular vision, based on the structure of ear [sic] canals. Were these pterosaurs unique in having binocular vision, or did pteranodons and other pterosaurs have vision like a raptors instead of like a tern or pigeon? Links to academic articles are acceptable, I have confederates who can access articles for me. Please nothing by David Peters. From what I can read, his work on pterosaurs is at best somewhat wrong and generally completely inaccurate, which is a shame as he seems to be the only one who has posted anything online about this. (If the site mentions Jeholopterus as a vampire, skip it).”

Several things jump out here: 

  1. The AMNH did not edit their artwork. As noted above, one piece of artwork had lateral eyes. The other had anterior eyes.
  2. Science is a process that can be repeated by anyone. Therefore, Hactar could have taken a skull photo of Jeholopterus (or any other binocular pterosaur, like Batrachognathus), and traced the elements to arrive at his/her own skull reconstruction.
  3. If my work on pterosaurs varies from “somewhat wrong to completely inaccurate,” then I am at a loss as to how to explain the internal consistency of sister taxa that not only nest in complete resolution, but gradually evolve from one to another, apparently modeling the actual evolution of the group with stone cold logic. I also note that no one else is producing accurate tracings AND reconstructions based on those tracings. The alternative, of course, is to accept hopeful monsters, like Bennett’s anurognathid, or Andres’ hypothesis that anurognathids begat pterodactyloids, or Unwin’s uropatagium and other such fanciful hypotheses.

And like I said earlier,
this is Science, so you don’t have to accept anyone’s word for whatever you’re trying to figure out. You can find out for yourself by tracing the specimen and creating your own reconstruction. If my observations and hypotheses cannot be replicated, please send me your interpretations so they can be repaired here.

Figure 4. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

Figure 4. Jeholopterus in dorsal view. Here the robust hind limbs, broad belly and small skull stand out as distinct from other anurognathids. Click to enlarge.

Don’t just repeat the propaganda ad nauseum.
The data is set in stone. Go get it and you’ll find the process rewarding.

References
Cheng X, Wang X, Jiang S and Kellner AWA 2014. Short note on a non-pterodactyloid pterosaur from Upper Jurassic deposits of Inner Mongolia, China. Historical Biology (advance online publication) DOI:10.1080/08912963.2014.974038
Kellner AWA, Wang X, Tischlinger H, Campos DA, Hone DWE and Meng X 2010. The soft tissue of Jeholopterus (Pterosauria, Anurognathidae, Batrachognathinae) and the structure of the pterosaur wing membrane. Proc Royal Soc B 277: 321–329.
Peters D 2003. The Chinese vampire and other overlooked pterosaur ptreasures. Journal of Vertebrate Paleontology 23(3): 87A.
Wang X, Zhou Z, Zhang F and Xu X 2002. A nearly completely articulated rhamphorhynchoid pterosaur with exceptionally well-preserved wing membranes and “hairs” from Inner Mongolia, northeast China. Chinese Science Bulletin 47(3): 226-230.

wiki/Jeholopterus

Behind the Scenes at the AMNH pterosaur exhibit

Here‘s a NY Times article about the new AMNH pterosaur exhibit. We looked at the AMNH pterosaur exhibit website earlier here. The online article url was sent to me by “I love pterosaurs” who wants me to “Please, learn how real scientist work.” [sic]

Okay, let’s see how real scientists work.
The following is from the online article (unfortunately, only a fraction focused on the pterosaurs and their artistic creation):

“Most of the questions that we actually get from artists, the answer is, ‘I don’t know,’” Dr. Kellner said. But the more research that’s done, the closer their guess can be on an animal that’s been extinct for 66 million years.

“In art you can do whatever you want,” Dr. Kellner said. “You have an expression of how you feel about a certain subject. But in paleo art, you don’t have that liberty. You must try to present the reconstruction of those animals the best way that you can based on true scientific evidence.”

“Sometimes, changes in science happen so quickly that an artist’s creation must be considerably altered. The feet of Quetzalcoatlus underwent major changes as well: Five toes per foot were edited down to four; they were shortened and the toenails removed.”

Sounds like the artists are getting good advice “based on scientific evidence” from the curators, but then…

Good gravy!
I haven’t seen any pterosaurs with four toes. There’s always a vestige to #5. And if these are the toes (they’re big ones, Fig. 1) the AMNH is advertising their inaccuracies early. Someone must have been influenced by theropods here (Fig. 1) because azhdarchid toes don’t go short on number 1.

Figure 1. Based on their size, these must be the Quetzalcoatlus feet and hands. I've added some real azhdarchid feet and ichnites here. Metatarsals should be appressed to match the fossils and tracks. All metatarsals should be subequal. Claws are not supported be really big. It's too bad no one looked at the data here.

Figure 1. Based on their size, these must be the Quetzalcoatlus feet and hands. I’ve added some real azhdarchid feet and ichnites here. Metatarsals should be appressed to match the fossils and tracks. All four medial metatarsals should be subequal. Claws should not be so thck. Remember the bones are more like soda straws than robust dino feet. It’s too bad no one looked at the data here.

Azhdarchid feet were narrow, with appressed metatarsals, as their fossils and ichnites show (Fig. 1). The evidence does not support these feet.

However
Not all giant pterosaurs were azhdarchids. Earlier we looked at some wider giant bipedal Korean pterosaur tracks here, likely made my tapejarids or shenzhoupterids with webbed feet, as shown in the AMNH feet (Fig. 1) . Even so four long metatarsals and toes is the rule. If the above pterosaur made tracks they would be mistaken for theropod tracks.

Figure 2. Basic errors in the big Quetzalcoatlus model.

Figure 2. Basic errors in the big Quetzalcoatlus model. The short wings and ultra size give away the genus.

Damn, I hate to see this.
I know those artists are working hard to get things as accurate as possible. So don’t blame them. They’re only taking orders.

On the good side:
The color, texture and size of the model pterosaurs is great. And so is their presentation. I just think they missed the excitement of pterosaurs the way the fossils reveal them to be.

And that’s the reason behind this blog. It’s a crusade for scientific accuracy supported by evidence.

Quetzalcoatlus in dorsal view, flight configuration.

Figure 3. Quetzalcoatlus in dorsal view, flight configuration based on bones from Q sp.  and wing membranes form other pteros.