Perpetuating the Drepanosaurus elbow myth: Pritchard et al. 2016

First of all
it’s always good to see fresh, exciting material coming out of the Triassic. In this case a 3D preservation of a new type of Drepanosaurus forelimb (Figs. 1-3). but this time retaining only two fingers and digit 2 is quite robust. This specimen GR 737 deserves a new genus, but it was recognized by Pritchard et al. as conspecific with the holotype MCSNB 5728.

Figure 1. Italian Drepanosaurus at left, compared to the New Mexico drepanosaur at right. Original and corrected identifications are shown at 2 second intervals.

Previously (Renesto 1994)
identified the large bone at the elbow of Drepanosaurus as a displaced and flattened ulna while the ulnare and intermedium evidently fused and took the place and shape of the cylindrical, but proximally concave ulna. That interpretation was dismissed with evidence five years ago here by showing that the purported elbow bone was in reality an olecranon sesamoid, similar to that found in sisters Megalancosaurus (Fig. 4 in yellow) and Vallesaurus (Fig. 5). The new specimen does nothing to change that and has a long list of reconstruction and identification problems here solved by DGS (digital graphic segregation) using a computer monitor as a microscope having not seen the actual specimen firsthand.

Figure 2. Hayden Quarry drepanosaur as originally presented by Pritchard et al. 2016. No other tetrapod ever had such an arrangement of bones. Compare to figure 3 where the ulna is in its usual position and shape. Also, note the lack of detail presented here despite firsthand access. Finally, note that most scale bars do not scale with one another, nor with the reconstruction. These problems are repaired in figure 3.

Unfortunately
Pritchard et al. 2016 followed the earlier Renesto mistake. Occam’s razor is once again ignored in favor of bizarre morphologies never before seen. The ulna always has been a cylindrical bone parallel to the radius. The elbow sesamoid is a flattened plate. Moreover, Pritchard et al. were unable to see the fused sutures between the metacarpals and phalanges (Fig. 3) in their specimen. They did not realize that when cylindrical bones, like the ulna, are crushed and scattered they need to be put back together before you add them to a reconstruction (Fig. 3). Massive bones, like digit 2, are never backed up by gracile and perforated never-before-seen structures as Pritchard et al. reconstructed. Finally, bones Pritchard et al. identified as the intermedium and ulnare in Megalancosaurus are actually the intermediaum and pisiform (Fig. 4) based on taxa close to megalancosaurs preserving a complete carpus.

Figure 3. The Hayden Quarry drepanosaur as interpreted here with scale bars all to the same scale and the ulna in its usual place with an olecranon sesamoid at the elbow. Note DGS was able to tease out the former metacarpals and carpals here.

From the Pritchard et al. abstract:
“Along with the crushed type specimen from Italy, these specimens have a flattened, crescent-shaped ulna with a long axis perpendicular to that of the radius and hyperelongate, shaft-like carpal bones contacting the ulna that are proximodistally longer than the radius.”

Figure 4. Carpus of Megalancosaurus in situ, in vivo and compared to a relatively close outgroup taxon that preserves carpal elements, Daedalosaurus, a kuehneosaur. Note that bones Pritchard et al. identified as intermedium and ulnare are actually the intermediaum and pisiform. Here the megalancosaur ulnare continue to be located proximal to distal carpals 4 and 5. The medial carpal enlarges to replace the dislocated and elongated intermedium, parallel to an equally elongated pisiform. Finally, note that the artist of Daedalosaurus misidentifies distal carpals 1 and 5. Carpal 1, proximal to the thumb, should always be on the radius side.

Unfortunately
the keywords ‘sesamoid‘ and ‘olecranon‘ do not appear in this paper. So the authors did not test alternate identities that were presented online 5 years ago. Drepanosaurus is a highly derived drepanosaur and the elbow bone in question is quite large. It is reasonable to look for smaller versions of this olecranon sesamoid in more primitive taxa. And when you look for them, you find them in Megalancosaurus (Fig. 5) and Vallesaurus (Fig. 6).

Figure 5. The elbow of Megalancosaurus. The perfect alignment of the olecranon sesamoid with the ulna masked the separation of these two bones, which are often fused in taxa with an olecranon process, like the kuehneosaur, Daedalosaurus. Note the ulna no longer articulates with the humerus as in Drepanosaurus.

Figure 6. Vallesaurus forelimb as drawn by Renesto and Binellit 2006.

Pritchard et al. 
rely on the interpretation of the apparent elongation of the intermedium and ulnare (a misidentified pisiform) in Megalancosaurus as their transitional stage enabling the three-part forelimb in the Hayden Quarry drepanosaur. The more primitive Hypuronector has an unossified carpus. The more derived Vallesaurus has a poorly ossified carpus and a small elbow sesamoid. The more derived Megalancosaurus has a larger olecranon sesamoid and a more completely ossified carpus (Fig. 4). Not mentioned by the authors, the pes (foot) of Megalancosaurus has an identical elongation of the calcaneum and astragalus (Fig. 7).

Figure 7. Megalancosaurus showing the elongation of the astragalus and calcaneum in the pes.

Unfortunately, Pritchard et al. have no clue as to what drepanosaurs are.
They report, “Drepanosaurus is a member of Drepanosauromorpha, a group of Triassic reptiles with lizard-like body proportions and elongate, slender digits likely adapted for specialized grasping.” By contrast the large reptile tree nests them as basal Lepidosauriformes, sisters to Jesairosaurus and this clade is a sister to the gliding kuehneosaurs and their immediate arboreal ancestors.

And finally, the link to supplementary material in the paper: http://dx.doi.org/10.1016/j.cub.2016.07.084 is broken and does not connect with it. There are several high-impact, new generation PhDs authoring this paper. Let’s hope next time they test alternate identities, conduct a proper phylogenetic analysis and produce more precise reconstructions.

References
Colbert EH and Olsen PE 2001. A New and Unusual Aquatic Reptile from the Lockatong Formation of New Jersey (Late Triassic, Newark Supergroup) American Museum Novitates, 3334: 15pp.
Olsen PE 1979. A new aquatic eosuchian from the Newark Supergroup LateTriassic-Early Jurassic) of North Carolina and Virginia. Postilla 176: 1-14.
Pinna G 1980. Drepanosaurus unguicaudatus, nuovo genere e nuova specie di Lepidosauro del trias alpino. atti Soc. It. Sc.Nat. 121:181-192.
Pinna G 1986. On Drepanosaurus unguicaudatus, an upper Triassic lepidosaurian from the Italian Alps. Journal of Paleontology 50(5):1127-1132.
Pritchard AC, Turner AH, Irmis RB, Nesbitt SJ and Smith ND 2016. Extreme Modification of the Tetrapod Forelimb in a Triassic Diapsid Reptile. Current Biology, 2016 DOI: 10.1016/j.cub.2016.07.084 online here
Renesto S 1994. Megalancosaurus, a possibly arboreal archosauromorph (Reptilia) from the Upper Triassic of Northern Italy. J. Vertebr. Paleontol. 14, 38–52.
Renesto S 1994. The shoulder girdle and anterior limb of Drepanosaurus unguicaudatus (Reptilia, Neodiapsida) from the upper Triassic (Norian of Northern Italy. Zoological Journal of the Linnean Society 111(3):247-264 December
Renesto S and Binelli G 2006. ’Vallesaurus Cenensis“’ Wild, 1991, A Drepanosurid (Reptilia, Diapsida): From the Late Triassic of Northern Italy”, Rivista Italiana di Paleontologia e Stratigrafia 112: 77–94, Milano.
Renesto S, Spielmann JA, Lucas SG and Spagnoli GT 2010. The taxonomy and paleobiology of the Late Triassic (Carnian-Norian: Adamanian-Apachean) drepnosaurs (Diapsida: Archosauromorpha: Drepanosauromorpha): Bulletin 46. Bull. NM Museum of Natural History 46, 1–81.

Earlier rebuttals
December 2011 rebuttal
January 2016 rebuttal

Publicity
livescience.com
www.nhregister.com
www.bbc.com
www.sciencedaily.com

Newsflash: Shrews evolved from Apatemyidae! (or vice versa)

Wikipedia reports,
“A shrew (Figs. 2, 3) or shrew mouse (family Soricidae) is a small mole-like mammal classified in the order Eulipotyphla.”

“Apatemyidae is an extinct family of placental mammals that took part in the first placental evolutionary radiation together with other early mammals such as the leptictids.” 

Figure 1a. Apatemys skull in situ and reconstructed shares several similar traits with the extant striped opossum, Dactylopsila, including a squirrel-like size, elongate fingers and similar teeth. Note the stronger similarities recovered by the LRT with the shrew, Scutisorex (figure 2).

Figure 1b. Apatemys, only complete fossil skeleton of an apatemyid, turns out to be an Eocene sister to the shrew. So this clade is not completely extinct.

As it turns out
shrews are less like moles in the large reptile tree and more like members of the Apatemyidae, like Apatemys (Marsh 1872; Fig. 1),  thought to have originated in the Paleocene and disappeared in the Eocene. Both are derived. At present they nest as sisters. Neither can be shown, at present, to be more primitive than the other.

Apatemys chardini (Eocene, 50-33 mya; Fig. 2) was a squirrel-lke arboreal herbivore with a massive skull. It had long slender fingers, a long flexible lumbar region, and a long gracile tail. From head to tail, the matrix scores for apatemyids and shrews are quite similar. It’s not just the dentition, which remains amazingly conservative in living shrews.

By contrast
moles have a set of small procumbent anterior dentary teeth and the posterolateral premaxillary teeth are large and canine-like while the medial premaxillary teeth are small like typical incisors. Moles nest closer to Solenodon and rodents [and I need to update that webpage].

Figure 2. The shrew Scutisorex compared to the apatemyid, Labidolemur from the early Eocene. Despite the difference in time, the teeth are still quite comparable and unique to themselves. Note sure how this was overlooked. The resemblance is remarkable.

Wikipedia reports,
“Like most Paleocene mammals, the Apatemyids were small and presumably insectivorous. Size ranged from that of a dormouse to a large rat. The toes were slender and well clawed, and the family were probably mainly arboreal.The skull was fairly massive compared to the otherwise slender skeleton, and the front teeth were long and hooked, resembling those of the modern aye-aye and marsupial Dactylopsila, both whom make their living by gnawing off bark with their front teeth to get at grubs and maggots beneath.”

Evidently others have missed the shrew connection. Let me know of any literature that predates this blogpost. I’d like to promote it, if it’s out there.

Figure 3. Scutisorex (below) and Crocidura (above) are extant shrews.

The book ‘Evolution of Shrews’ reports,
“Shrews are among the most ancient of all living mammals. They are small and have rather unspecialized body plans, retained almost unchanged since they evolved about 45 million years ago. They appear to be extremely successful as a group in comparison to all other families of Insectivora: the living species of shrews represent approximately 80% of all insectivorans, which in turn make up some 10% of all mammmalian species extant today.”

The apatemyid connection described here
pushes the origin of shrews back another 5-10 million years. True shrews are not to be confused with elephant shrews. They are more closely related now, then what was recovered earlier, but more work needs to be done to figure this out precisely. Then I’ll update the cladogram.

Afterthought
Earlier I posted on Hyopsodus, the pre-dog, former condylarth. One the images appeared in editing, but did not appear in publication. I was not aware of this until today. The JPEG had a ‘bad marker’, whatever that is. Please let me know if you see a technical problem here. That Hyopsodus image has been repaired and is visible now.

References
Churchfield S 1990. The Natural History of Shrews online. Comstock Publishing; 1st edition (January 1990) Amazon link.
Multiple Authors 1998. Evolution of Shrews. Edited By: JM Wójcik and M Wolsan. Cornell Paperbacks. 458 pp.  online.
Gingerich PD and Rose KD 1982. 1. Dentition of Clarkforkian Labidolemur kayi. Gingerich PD 1982. 2. Labidolemur and Apatemys from the early Wasatchian of the Clark’s Fork Basin, Wyoming. Studies on Paleocene and Early Eocene Apatemyidae (Mammalia, Insectivora). Contributions from the Museum of Paleontology. The University of Michigan. 26(4):49-69.
v. Koenigswald W, Schierning H-P 1987. The ecological niche of an extinct group of mammals, the early Tertiary apatemyids. Nature. 326 (6113): 595–597. doi:10.1038/326595a0.
Marsh OC 1872. Preliminary description of new Tertiary mammals. Part II. American Journal of Science 4(21):202-224.

wiki/Apatemyidae

 

What a large gamut phylogenetic analysis provides

During casual reading, I ran across the following…
in Reisz et al. 2000, “Paleozoic varanopid synapsids and diapsids, rare members of the terrestrial fossil assemblages, are not closely related to each other but appear to have acquired a number of interesting similarities that have resulted in their frequent misidentification.”

That is the view in traditional paleontology.
By contrast, in the large reptile tree (LRT) basal diapsid archosauromorphs (remember, lepidosaurs are convergent with their own diapsid temples) are derived from a series of former varanopid synapsids. Yet other varanopid synapsids are indeed basal to traditional synapsids. This is recovered only by testing in a large gamut analysis. So this is the value the LRT brings to paleontology.

Similar problems and solutions
can be found throughout the reptile family tree, as has been demonstrated here time and again through testing.

Let us hope that someday
traditional biases and paradigms will be tested by professionals and not let another generation of paleontologists stumble through these readily solved problems.

References
Reisz RR, Laurin M and Marjanovic D 2010. Apsisaurus witteri from the Lower Permian of Texas: yet another small varanopid synapsid, not a diapsid. Journal of Vertebrate Paleontology. 30 (5): 1628–1631.

A new set of ancestors for hippos

Updated November 18, 2016 with new data (Fig. 3) on Ocepeia.

Figure 4. Hippopotamus. This stout, wide-faced, fanged mammal does not nest with deer.

The following clears up
another fine mess traditional paleontologists have provided based on taxon exclusion and professional bias. Today, let’s talk about the ancestry of hippos (Fig. 1).

Figure 1. Living hippopotamus. Now I ask you, does this look like a relative to deer and giraffes? Or to mesonychids?

Wikipedia, representing traditonal paleontology, reports
here, “The earliest known hippopotamus fossils, belonging to the genus Kenyapotamus in Africa, date to around 16 million years ago. Hippopotamidae are classified along with other even-toed ungulates in the order Artiodactyla. Other artiodactyls include camels, cattle, deer and pigs, although hippopotamuses are not closely related to these groups.” 

Do you sense the underlying problem here?
They say, hippos are in the Artiodactyla, but not close. This is what is known as a ‘red flag’.

But wait, there’s more! “The most recent theory of the origins of Hippopotamidae suggests that hippos and whales shared a common semiaquatic ancestor that branched off from other artiodactyls around 60 million years ago.” 

This is all getting to be completely bogus (based on LRT results)
And very disturbing. Tenrecs are the sisters to whales, as we learned earlier here. But wait, there’s more. “A rough evolutionary lineage can be traced from Eocene and Oligocene species: Anthracotherium and Elomeryx to the Miocene species Merycopotamus and Libycosaurus and the very latest anthracotheres in the Pliocene. Look those taxa up. They’re all skinny, long-legged terrestrial grazers. Not hippo-like at all ~

As an example, here’s Anthracotherium….
a big artiodactyl and an anthracothere (Fig. 2). Does it have huge fangs on a wide gape like a hippo? No. It’s just a big old prehistoric deer. Superficially, it does look like a giant tenrec with that long rostrum, but it does not nest with Andrewsarchus, a real giant tenrec.

Figure 2. Anthracotherium and the anthracotheres nest with their long narrow tiny tooth snouts with Ancodus, deer and other gracile artiodactyls, not hippos. Whale ancestors do have a long rostrum, but they are hoof-less like tenrecs, not hoofed like ungulates.

Figure 3. Ocepeia: before and after. The original reconstruction is here compared to a tracing of CT scan, duplicated left to right. From the Paleocene, Ocepeia is the current sister to Hippopotamus and mesonychids in the LRT. Already the wide rostrum and high orbit are apparent.

Here’s how the LRT sees it
Apparently hippos have an ancestry that extends at least into the Paleocene.

Ocepeia daouiensis (Gheerbrant et al 2001, 2014; Paleocene, 60 mya; 9 cm skull length) was considered the oldest known of the ‘Afrotherians’ known from skulls, but the ‘Afrotheria’ is an invalid clade. Gheerbrant et al. 2016 nested Ocepeia with aardvarks and Potamogale, an extant aquatic tenrec. These were all derived from a sister to Arctocyon nesting within the Arctocyonidae. The LRT nested Arctocyon as an omnivorous marsupial.

Here (Fig. 3) Ocepeia is a Paleocene basal to mesonychids like  Mesonyx (Fig. 5; Cope 1872) and Harpagolestes (Fig. 4; Matthew 1909) and also hippos and thereafter anthracobunids, desmostylians and mysticetes (baleen whales). The jaw joint is aligned with the maxillary tooth row. The original reconstruction (Fig. 3, left) differs greatly from tracings made on CT scans (Fig. 3, right) becoming less hippo-like and more mesonychid-like.

The pneumatized skull of Ocepeia
contains many air spaces, even though it is relatively small. Slightly larger skulls have larger canines and so are considered male.

Wikipedia reports, “Mammals are extremely rare in the Ouled Abdoun in contrast to the associated marine vertebrate fauna which includes sea birds, sharks, bony fish, and marine reptiles (including crocodilians, sea turtles, and the sea snake Palaeophis). Terrestrial species were probably transported off shore into the Moroccan sea before fossilization.” Apparently ignored by traditional paleontologists as possible candidates in this formation, hippos and their ancestors, like Ocepeia, could have been aquatic even at that early stage.

Figure 4 Robust Harpagolestes nests between the hippos and Mesonyx. Now, doesn’t this look more like a hippo? The LRT agrees with you.

Long known as a robust mesonychid
Harpagolestes makes a good interim taxon between Mesonyx and hippos. Look at hose tusks! Yet it had not yet developed the low, wide skull and elevated orbits that characterize surface dwelling hippos, like Hippopotamus and Ocepeia.

Figure 5. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater. Now with the addition of Ocepeia and Harpagolestes, it moves a little further away.

We should someday find
mesonychids, like Mesonyx, in Cretaceous strata based on its phylogenetic nesting and the Paleocene placement of Ocepeia.

References
Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465.
Gheerbrant E, Sudre J,Iarochene M, Moumni A 2001. First ascertained African “Condylarth” mammals (primitive ungulates: cf. Bulbulodentata and cf. Phenacodonta) from the earliest Ypresian of the Ouled Abdoun Basin, Morocco. Journal of Vertebrate Paleontology. 21(1):107–118.
Gheerbrant E, Amaghzaz M, Bouya B, Goussard F and Letenneur C 2014. Ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal”. PLoS ONE. 9 (2): e89739.
Gheerbrant E, Filippo A and Schmitt A 2016. Convergence of Afrotherian and Laurasiatherian Ungulate-Like Mammals: First Morphological Evidence from the Paleocene of Morocco”. PLOS ONE. 11 (7): e0157556.
Matthew WD 1909. The Carnivora and Insectivora of the Bridger Basin, middle Eocene. Memoirs of the American Museum of Natural History 9:289-567.
wiki/Harpagolestes
wiki/Ocepeia
wiki/Hippopotamus
wiki/Anthracotherium

A better sister for Astrapotherium: Meniscotherium

Revised Dec 5, 2016 and Oct 31, 2021 with new text and images. 

These are difficult taxa to nest:
The tusks of Astrapotherium (Fig. 1; Burmeister 1879; Hatcher 1902) are canines. The premaxilla is missing. The mandible of Astrapotherium really does stick out quite a bit further than the rostrum.

FIgure 1. Astrapotherium to scale with related taxa.

Finally a sister!
I didn’t have one really good enough sister taxon for Astrapotherium. Now I do.

Meet Meniscotherium
(Figs. 2, 3; Cope 1874; Williamson and Lucas 1992; Middle Eocene 54-38 mya; 25-50 cm long), which Wikipedia describes as a dog-sized herbivore with hooves found as a pack of individuals.

Cooper et al. 2014 nested Meniscotherium with Phenacodus as a condylarth, a possible member of Afrotheria, perissodactyl. They did not test Astrapotherium.

Wible et al. 2007 nested Meniscotherium close to early cetioartiodactyls (an invalid clade) and close to early Carnivora. They, likewise, did not test Astrapotherium.

The LRT nests the clade of Astrapotherium + Meniscotherium between the clade of Edentates and the clade of Phenacodus.

Figure 2. Meniscotherium skull. In this is a smaller predecessor to Astrapotherium note the genesis of maxillary tusks here and then longer dentary when the teeth are matched to occlude correctly. Note the overlapping lacrimal.

The retention of five fingers and five toes
is key to the phylogenetic nesting of these taxa. More derived taxa start losing digit 1. We can see the genesis of canine tusks in Meniscotherium.

Figure 3. Meniscortherium skeleton. The fingers and toes are not known. This reconstruction differs from the original in that the pelvis is rotated more vertically. Some specimens were 25 cm long. Others were 50 cm long estimated.

Meniscotherium is the smaller and more plesiomorphic
of the two and is found in earlier strata (Eocene, 50-38 mya) than Astrapotherium (late Oligocene, Middle Miocene, 28-15 mya).

Figure 4. Astrapotherium to scale with two specimens of Meniscotherium.

References
Burmeister 1879. Description physique de al République Agentine, T. III 1879:517.
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014-10-08. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.
Hatcher JB 1901. Report of the Princeton University Expeditions to Patagonia 1869-1899. Mammalia of the Santa Cruz Beds. IV. Astrapotheria. Scott WB ed. Vol. 6, Paleontology 3. Princeton, NJ Stuttgart 1909-1928.
Wible JR, Rougier GW, Novacek MJ, Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary. Nature 447: 1003–1006. doi: 10.1038/nature05854
Williamson TE, Lucas SG 1992. Meniscotherium (Mammalia, “Condylarthra”) from the Paleocene-Eocene of western North America. Bulletin of the New Mexico Museum of Natural History and Science 1: 1–54.

Former ‘notoungulate’ Periphrangis is really a wombat

Periphrangis harmeri (Roth 1899; Fig. 1; Oligocene, 48-28 mya) has long been considered a notoungulate. Earlier the LRT nested two former notoungulates as wombats. Periphranigis also shares several wombat traits, including a jugal that contacts the jaw glenoid, procumbent incisors and a septomaxilla.

Figure 1. Periphrangis was considered a notoungulate, but it is clearly a wombat with four molars and a jugal that contacts the jaw glenoid, among several other identifying traits.

When we first looked at Haramiyavia
(Jenkins et al. 1997, Luo et al. 2005) here, this small Late Triassic mammal was considered a basal multituberculate. Now that several wombats have been added to the LRT Haramiyava could be another wombat. Wombats share procumbent incisors and a convex ventral mandible. Hard to tell with present data. In either case, both wombats and multituberculates are rather derived taxa for the Late Triassic.

Figure 2. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here.

Arctocyon
(Fig. 3; Blainville 1841, Gould and Rose 2014; YPM VP 021233; 60 mya) was long and widely considered (see Wikipedia page) a primitive plantigrade ungulate condylarth procreodi placental.  In the LRT Arctocyon nests with basal carnivorous/omnivorous marsupials. Essentially it is a giant opossum, like Didelphis, but with a few derived traits, more like Thylacinus, a taxon that reduces the epipubes and molar count, hence the earlier traditional confusion. Just look at these taxa side-by-side. It’s obvious, but it’s also in the matrix scores.

Figure 3. Arctocyon mumak is no longer an ungulate placental, but a carnivorous marsupial, close to Thylacinus.

Small brains and long jugals extending to the jaw glenoid
also give them away as metatherians. Not sure why even recent authors (Gould and Rose 2014) are not seeing this. They must be counting molars.

References
Blainville HM 1841. Osteographie et description iconographique des Mammiferes récentes et fossiles (Carnivores) 1, 2 Paris.
Gould FDH and Rose KD 2014. Gnathic and postcranial skeleton of the largest known arctocyonid ‘condylarth’ Arctocyon mumak (Mammalia, Procreodi) and ecomorphological diversity in Procreodi. Journal of Vertebrate Paleontology 34(5):1180-1202.
Jenkins FA, Jr, Gatesy SM, Shubin NH and Amaral WW 1997. Haramiyids and Triassic mammalian evolution. Nature 385(6618):715–718.
Luo Z-X, Gatesy SM, Jenkins FA, Jr, Amaralc WW and Shubin NH 2015. Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution. PNAS 112 (51) E7101–E7109.
Roth S 1899. Aviso preliminar sobre mamíferos mesozóicos encontrados en Patagonia [Preliminary notice on Mesozoic mammals found in Patagonia]. Revista del Museo de La Plata 9:381-388

 

What is Triopticus? (It’s not what they think it is…)

Updated July 13, 2017 with new bone identifications for Triopticus. These further cement the sisterhood to Tanytrachelos. 

It’s been a long time
since an interesting ‘reptile’ showed up in the literature. Especially an ‘enigma’ like this one.

A recent paper by Stocker et al. 2016
reports on a domed and expanded Late Triassic cranium that they identify as an archosaur, but it’s unlike that of any other archosaur. Triopticus primus was named for its three eyes, with a big one on top (Fig. 1). The authors compared the domed appearance of the cranium in Triopticus with a Cretaceous dome-headed ornithischian dinosaur, Stegoceras.  They also discussed convergence in general and provided a CT scan brain endocast of Triopticus.

Unfortunately 
the authors employed a prior cladogram (Fig. 2) by Nesbit et al. 2015, expanded from Pritchard et al. 2015. that was shown to not recover sister taxa that looked alike and did not provide a gradual accumulation of derived traits at several nodes. In their cladogram Triopticus nested without resolution among basal archosauriforms like Proterosuchus, which looks nothing like it. By contrast, the LRT was able nest and fully resolve Triopticus elsewhere.

Figure 1. In round 1 I added characters shown here to the LRT in two passes. One recovered a sisterhood with mesosaurs. The other nested with Tanytrachelos, among the tanystropheid tritosaur lepidosaurs. Both shown here for comparison. Triopticus would be 2x the size of the giant Tanyrachelos from New Mexico.

From the Stocker et al. abstract:  “Exemplifying this extreme morphological convergence, we present here a new dome-headed taxon from the assemblage, which further illustrates the extraordinary range of morphological disparity present early in the Late Triassic.” That ‘extraordinary range’ should be — and will be — chopped down substantially with the right sister taxa.

A few problems with the archosauriform hypothesis include:

1. No other archosauriforms, until you get to pachycelphalosaurs in the Cretaceous, expand the cranium deleting the upper temporal fenestra.
2. The entire rostrum and mandible is absent, so no naris, antorbital fenestra or teeth are known, even in part.
3. They dubiously identified an antorbital fenestra and fossa at the edge of the fossil.
4. …and they were not aware that Tanytrachelos and kin, including pterosaurs within the – Lepidosauria -, also have an antorbital fenestra, but without a fossa.
5. A large pineal opening is present, but never present at such a size in archosauriforms.
6. The extreme angle of the rostrum coupled with the large orbit are traits not found in basal archosauriforms that typically have a long boxy rostrum.

Figure 2. Stocker et al. 2106 cladogram nesting Triopticus uncertainly within a set of unresolved basal archosauriforms and far from the Tanystropheidae. The LRT completely resolves all nodes. Note how this cladogram mixes Lepidosauromorpha with Archosauromorpha and separates the protorosaurus, Protorosaurus and Prolacerta.

This is a perfect problem
for the large reptile tree (LRT) which now provides then 820, now 1036 opportunities for Triopticus to nest in. With that large number of taxa, unfortunately I had to split the matrix in two, even for a simple Heuristic Search. By contrast, the Stocker et al. matrix included 30 taxa and 247 characters.

Stocker et al. report,
“We chose this dataset because the following combination of character states in Triopticus are also present in some archosauromorph taxa:

1. presence of a single occipital condyle;
2. ossified laterosphenoid;
3. presence of a metotic strut of the otoccipital;
4. presence of upper and lower temporal fenestrae;
5. presence of an antorbital fenestra and fossa formed by the lacrimal.”

They provided no reconstructions of included taxa.

First,
I tested Triopticus against basal tetrapods and the new Lepidosaurmorpha and found that Triopticus nested with the aquatic, long-necked tritosaur Tanytrachelos (Fig. 1), large specimens of which were recently found in New Mexico (Fig. 3). Like Triopticus the rostrum descends at a high angle from a tall cranium in Tanytrachelos, which also shares a large orbit and a large pineal foramen (at present known only from sister taxa). Like related fenestrasaurs and langobardisaurs, Tanytrachelos also had a small antorbital fenestra without a fossa, but that would have been beyond the rim of the broken skull in Triopticus (Fig. 5).

Figure 3. A large incomplete Tanytrachelos from New Mexico compared to the smaller more complete East Coast specimen. Triopticus would be twice as large as the New Mexico specimen.

Second,
I tested Triopticus with the rest of the matrix, the new Archosauromorpha, and found that Triopticus nested with the mesosaurs (Fig. 4), an aquatic enaliosaur clade close to thalattosaurs and ichthyosaurs, all derived from basal pachypleurosaurs. It did not nest with archosauriforms. While basal mesosaurs have typical diapsid temporal regions, Mesosaurus, like Triopticus, closes up the upper temporal fenestra, then the lateral temporal fenestra with bone expansion.  Mesosaurs also retain a relatively large pineal foramen and have large eyes, but they don’t have a sharply descending preorbital region.

Figure 4. Mesosaurus, like Triopticus, has a large pineal foramen and expands the skull bones to obliterate former temporal fenestrae.

Digital Graphic Segregation
was applied to the cranial lump that is Triopticus (Fig. 5) and the skull suture patterns, perhaps overlooked by those with firsthand access due to the expansion of the cranial bones, revealed a Tanytrachelos-like morphology (Fig. 2). I illustrate this interpretation here with the hope that this hypothesis can be either confirmed or falsified. This is a tough assignment.

Figure 5. Triopticus reconstructed along the bauplan of Tanytrachelos. The upper temporal fenestra is the top half of a divided lateral temporal fenestra. At 72 dpi this is 90 percent of actual size.

Tanystropheids
have been reported from the Hayden Quarry of northern New Mexico (Chinle Formation) far from the west central Texas location of Otis Chalk. Stocker et al. included Tanytrachelos in their study, even though they have not provided a reconstruction of it, so it is difficult to imagine how they interpreted it. Tanystropheids, in general, have widely varying skull shapes. Triopticus appears to have expanded the morphospace just a little, not a lot.

The loss of ventral material in the Triopticus fossil
appears to have occurred at the roof the narial/oral opening.

So what other long-necked animal
expands the cranium like Triopticus? Giraffa, the giraffe. Maybe it will turn out to be a better analogy than short-necked Stegoceras?

References
Nesbitt SJ, Flynn JJ, Pritchard AC, Parrish JM, Ranivoharimanana L and Wyss AR 2015. Postcranial osteology of Azendohsaurus madagaskarensis (?Middle to Upper Triassic, Isalo Group, Madagascar) and its systematic position among stem archosaur reptiles. Bulletin of the American Museum of Natural History 899, 1-125.
Pritchard AC, Turner AH, Nesbitt SJ, Irmis RB and Smith ND 2015. Late Triassic tanystropheid (Reptilia, Archosauromorpha) remains from northern New Mexico (Petrified Forest Member, Chinle Formation): insights into distribution, morphology, and paleoecology of Tanystropheidae. Journal of Vertebrate Paleontology, 10.1080/02724634.02722014.02911186.
Stocker MR, NesbittSJ, Criswell KE, Parker WG, Witmer LM, Rowe TB, Ridgely R  Brown MA 2016. A Dome-Headed Stem Archosaur Exemplifies Convergence among Dinosaurs and Their Distant Relatives. Current Biology (advance online publication)DOI: http://dx.doi.org/10.1016/j.cub.2016.07.066   pdf

Hyopsodus: an Eocene pre-dog, not an archaic ungulate

Hyopsodus lepidus (H. paulus type specimen, Leady 1870; AMNH 143783; Eocene; Fig. 1) is traditionally considered an odd-toed ungulate, despite having a five-clawed manus and a four-clawed pes. Wikipedia also promotes this nesting, but unlike most ungulates, they report, “It is believed to have been swift and nimble, living in burrows, and perhaps able to use echolocation,” and it is shown climbing on a tree trunk. Another website lists Hyopsodus as a condyarth.

Here, in the LRT, 
Hyopsodus nests with Canis and more closely with Miacis (Fig. 2), two members of the Carnivora in the large reptile tree (LRT). Shifting Hyopsodus over to the Condylarthra adds nearly 30 steps. Those tiny feet beneath that long and wide body do not look to me like they could be used to excavate burrows or climb trees. Plus that short tail and long torso are not typical of climbing animals.

== Figure 1. Hyopsodus as originally reconstructed (below) and as reconstructed here above in two views. This former condylarth now nests with dogs.

From the Orliac et al. 2012 abstract:
“Hyopsodus presents one of the highest encephalization quotients of archaic ungulates and shows an “advanced version” of the basal ungulate brain pattern, with a mosaic of archaic characters such as large olfactory bulbs, weak ventral expansion of the neopallium, and absence of neopallium fissuration, as well as more specialized ones such as the relative reduction of the cerebellum compared to cerebrum or the enlargement of the inferior colliculus [hearing]. The detailed analysis of the overall morphology of the postcranial skeleton of Hyopsodus indicates a nimble, fast moving animal that likely lived in burrows.” Sounds like a member of the Carnivora…

Figure 2. Miacis, an Eocene ancestor to extant dogs, such as Canis. Note the transverse premaxilla and tiny premaxillary teeth as in Hyopsodus.

Miacis has long been known as a dog ancestor.
And here it also nests with Canis (Fig. 3). So, compare Miacis to Hyopsodus (Fig. 2) and you’ll find very few differences.

Figure 3. Canis lupus, the wolf that gave rise to extant dogs through selective breeding. Note the five phalanges on the manus and four on the pes.

Several specimens and species are known
of Hyopsodus, most from just teeth and jaws.

References
Orliac MJ, Argot C and Gilissen E 2012. Digital Cranial Endocast of Hyopsodus (Mammalia, “Condylarthra”): A Case of Paleogene Terrestrial Echolocation? PlosOne v.7(2); 2012PMC3277592

wiki/Hyopsodus

Thomashuxleya: another former notoungulate, joins the Interatheria

Updated September 1, 2022
with new tracings and new scored for Thomashuxleya (Figs 1,2), now nesting with similar interatheres, like Interatherium.

Yet another
former notoungulate, dog-bear-like Thomashuxleya rostrata (Ameghino 1901; Eocene, 48-40 mya; 0.33m skull length, 1.3 m overall length; Fig. 1). Named after Thomas Huxley, Darwin’s ‘bulldog’ (his strong supporter), this peccary-mimic had a generalized 11 teeth (per quadrant), four toes (per foot, but look at the odd distribution! and meanwhile several descendants retain five toes so this is a red flag on the data). Since all the data for this taxon currently comes from this drawing, based on several specimens and still incomplete, the manus data might be a little untrustworthy… to say the least. The pedal data is conjectural from the start.

Tred carefully here
|the reconstruction offered (Fig. 1) is based on an old line drawing and that is based on a chimaera of specimens. Back in the day, as we’ve seen with other museum mounts, that was common practice. Thomashuxleya has been referred to the Isotemnidae family of Notoungulata. Evidently other taxa in this family are known from isolated teeth or jaw fragments, but not enough to warrant their own Wikipedia page. Dr. Darin Croft includes Toxodon as a sister to this clade.

Figure 2. Thomashuxleya from Simpson 1936.

According to Croft 2016
Isotemnids have low-crowned teeth that gradually decrease in size from back to front without a diastema. That also sounds like Arsinoitherium, doesn’t it? So, it’s not a unique trait.

Several new basal condylarths
have been added to the LRT. We’ll look at them soon.

References
Ameghino F 1901. Notices préliminaires sur des ongulés nouveaux des terrains crétacés de Patagonie [Preliminary notes on new ungulates from the Cretaceous terrains of Patagonia]. Boletin de la Academia Nacional de Ciencias de Córdoba 16:349-429
Croft D 2016. Horned armadillos and rafting monkeys: the fascinating fossil mammals of South America. Indiana University Press 320 pp.
Simpson GG 1967. The beginning of the age of mammals in South America. Part II. Bulletin of the American Museum of Natural History 137, 1-260.
Simpson GG 1980. Splendid Isolation, the Curious History of South American Mammals. Yale University Press, New Haven, CT.

tetrapod-zoology/isotemnid-toxodonts-2012/
wiki/Thomashuxleya

Nesting twin-horned Arsinoitherium within the Condylarthra

FIgure 1. Subset of the large reptile tree, the Condylarthra, featuring Astrapotherium. Note the phylogenetic proximity of Astrapotherium and Tapirus.

Traditionally Arsinoitherium zitteli has been hard to classify.
Wikipedia reports, “Arsinoitherium (Beadnell 1902; Eocene-Oligocene, 36-30mya; 3 m in length; Fig. 1) is related to elephants, sirenians, hyraxes and the extinct desmostylians.” That’s a pretty broad gamut of taxa.

And they’re all wrong according to the large reptile tree (now 812 taxa, subset Fig. 2).

And this came as a surprise to me, too
among 811 other taxa, Arsinoitherium nests with Gobiatherium mirificum (Fig. 3; Osborn and Granger 1932; Middle Eocene), which Wikipedia considers, “one of the last uintatheres” of which Uintatherium is the titular and most famous member. Wikipedia goes on to report, “Gobiatherium lacked knob-like horns, or even fang-like tusks. Instead, it had enlarged cheekbones and an almost spherical snout. Because of the noticeable lack of many diagnostic uintathere features (the horns and tusks), the genus is placed within its own subfamily.” Here’s where tradition and the LRT agree… but let’s push this a little further to see where it takes us within the friendly confines of the current LRT taxon list.

Figure 3. Gobiatherium skull (A. M. 26624) in three views. Though not immediately apparent, Gobiatherium is closest to Arsinoitherium in the LRT. Image from Osborn and Granger 1932.

Among all tested placental taxa, and despite distinct overall appearances
only Arsinoitherium and Gobiatherium:

1. redevelop the ascending process of the premaxilla, completely enclosing the naris;
2. produce a wide, elevated set of nasals, further expanding into horns in Arsinoitherium;
3. only two molars, rare among placentals;
4. and no other condylarths have a wide flat cranium, usually a crest or a convex cranium is present.

That premaxillary ascending process
looks so normal. But among marsupial and placental mammals it is very rare indeed! Of course, the LRT does not depend on one or several traits, several dozen nest Arsinoitherium with Gobiatherium and their sisters.

Even without Gobiatherium
Arsinoitherium nests with Uintatherium. Coryphodon nests closer to Uintatherium. All descend from a sister to Thomashuxleya (Fig. 4), which we’ll look at soon in greater detail.

Figure 4. Thomashuxleya is basal to uintatheries and arsionoitheres. It is not a notoungulate, an invalid taxon.

We hold as an ideal
a gradual accumulation of derived traits in derived taxa, like Gobiatherium and Asinoitherium. In this clade, unfortunately we don’t have enough taxa to make that gradual accumulation of traits any more gradual than it currently is. This is the best we can do, at present, with available data and the present taxon list.

But it’s a good start!
And closer than anyone figured out before.

References
Beadnell HGC 1902. A preliminary note on Arsinoitherium zitteli, Beadnell, from the Upper Eocene strata of Egypt. Public Works Ministry, National Printing Department. Cairo: 1–4.
Lucas SG 2001. Gobiatherium (Mammalia: Dinocerata) from the Middle Eocene of Asia: Taxonomy and biochronological Significance. Paläontologische Zeitschrift 74 (4): 591–600.
Osborn HF and Granger W 1932. Coryphodonts and uintatheres from the Mongolian expedition of 1930. American Museum Novitates 552:1-16.

wiki/Arsinoitherium
wiki/Gobiatherium