Clavicles, the furcula, and what’s going on in basal archosaurs

Updated within 24 hours of this post with a look at Vickaryous and Hall 2006, which just came to my attention. They consider the possibility of homologizing the interclavicle and furcula. See below.

Today’s post
comes from a paper on clavicles and furculae by Bryant and Russell (1993). The question was: since most theropods, and most dinosaurs, do/did not have clavicles, is the furcula of birds a neomorph (new structure)? Or is this the reappearance, after a phylogenetic gap, of topologically identical clavicles? The question becomes more complex with the occasional appearance of clavicles in the Dinosauria.

Nesbitt et al. 2009
updated the furcula issue. They write, “Given this absence of clavicles and interclavicle in dinosaurian outgroups, the homology of the furcula to other components of the shoulder girdle has been contentious (Bryant and Russell, 1993). This debate is based largely on absence of evidence and will be explored more fully latter in this article.” They continued, Additionally, topographic connectivity of the furcula to the other pectoral girdle elements in avian and other theropod dinosaurs is entirely consistent with and supportive of homology of the avian clavicle with the ancestral reptilian and tetrapod clavicle.” 

Of course, the Nesbitt et al. outgroups
are not the same outgroups in the LRT.

Before we start
Bryant and Russell followed the invalidated tradition of including pterosaurs with dinosaurs in the outmoded clade, Ornithodira. Worse than that, they and a number of high-profile paleontologists before them believed that pterosaurs had neither clavicles nor an interclavicle. Wild 1993 demonstrated that the pterosaur sternal complex is comprised of fused clavicles, interclavicle and sternum. These are separate in the pterosaur ancestor, Cosesaurus. Nesbitt et al. 2009 acknowledged that observation by Wild 1993 and agreed on the fusion of the sternal and clavicle elements in pterosaurs, However they followed in the wake of the invalid Ornithodira hypothesis.

In the large reptile tree
(LRT, 1012) clavicles that are mediallly broad are present in fish and basal tetrapods. That’s where we start. The situation changes in:

  1. Frogs and kin – clavicles are medially narrow
  2. The Tuditanus clade – clavicles are medially narrow
  3. Pantylus – clavicles are medially narrow
  4. The Microbrachis clade – clavicles are medially narrow
  5. Within the Reptilia/Lepidosauromorpha: the Milleretta clade (remaining Lepidosauromorpha – clavicles are medially narrow,
  6. Except the Caseasauria and except Turtles, where clavicles become part of the plastron
  7. And except Mecistotrachelos clade where the clavicles are absent
  8. and except Longisquama + Pterosauria where the clavicles are fused to the sternal complex
  9. and except Tetrapodophis + snakes.
  10. Within the Reptilia/Archosauromorpha: the Diplovertebron/Romeriscus clade – clavicles are medially narrow
  11. The Anomodontia – clavicles are medially narrow
  12. Titanophoneus + Cynodontia (including mammals) – clavicles are medially narrow
  13. Except in higher Carnivora – clavicles are absent
  14. Except in Odontoceti – clavicles are absent
  15. Except in Phenacodontidae (includes all hoofed mammals)
  16. Prodiapsida – clavicles are medially narrow except Petrolacosaurus where clavicles are medially broad.
  17. Except Nothosaurus – clavicles are medially broad
  18. Except the Simosaurus clade (plesiosaurs) – clavicles are medially broad
  19. Within basal Younginiformes (including Archosauriformes) – clavicles are medially narrow
  20. Except in certain Rauisuchids, Decuriasuchus, where clavicles are provisionally absent.
  21. Clavicles are present in the poposaurs, Poposaurus and Lotosaurus – except TurfanosuchusSilesaurusShuvosaurus + Effigia (derived poposaurs) where clavicles are provisionally absent.
  22. Except Crocodylomorpha (crocs) – clavicles are absent
  23. In basal Dinosauria and Prodinosauria the pectoral region is not well preserved (see below)
  24. Except possibly in Junggarsuchus (Fig. 1) – tiny clavicles may be present
  25. Within Orinithischia: Psittacosaurus – clavicles are medially narrow (neomorph)
  26. Within Sauropodomorpha: Massospondylus – clavicles are medially narrow (neomorph?)
  27. Segisaurus, Coelophysis and higher theropods – furcula is present, as in birds, but lost in ornithomimosaurs and several other derived theropod clades 

The furcula and the absence of clavicles
Then furcula goes back to basal theropods, but is lost in certain theropod clades, like Ornithomimosauria. In basal theropods it appears to be  a neomorph without direct antecedent. At present, as Newbitt et al. noted, in basal Archosauria (all crocs and basal dinos) the clavicles have not been found. In general the clavicle appears to be lost in taxa that are preserved incomplete and scattered.

But all is not lost…
If we could only find a clavicle in Lewisuchus,. Gracilisuchus, Junggarsuchus, Herrrerasaurus and Tawa we would have a more or less continuous clavicle presence from fish to birds in the LRT. These taxa need to either have a set of clavicles, or some excuse for not preserving them. The latter appears to be the case often enough, as demonstrated here:

  1. Lewisuchus – incomplete and jumbled specimen in which the clavicles could have been washed away.
  2. Gracilisuchus – pertinent area lost during excavation
  3. Junggarsuchus – appears to be minimally and tentatively present (Fig. 1), but really,  who knows what that little green bone is?
  4. Herrerasaurus and Sanjuansaurus – pertinent area lost during excavation
  5. Tawa – represented by “two nearly complete skeletons and several other partial specimens collected in a tightly associated small grouping at a single locality.” but no clavicle was reported and no in situ images were published suggesting that the skeletons were disassociated. Moreover, any out-of-place clavicles could be mistaken for ribs.
  6. Eodromaeus – forelimbs and pectoral girdle missing from holotype.
  7. Eoraptor – clavicles were not found and the pectoral girdle has taphonomically shifted.

In summary,
the data is largely missing from the transitional taxa at and near the base of the Archosauria. So there’s still hope that the clavicles were present in these taxa and will someday be discovered among more complete fossils.

Figure 2. Junggarsuchus and its overlooked clavicle. Let's consider this provisional until confirmed.

Figure 1. Junggarsuchus and its overlooked clavicle. Let’s consider this provisional until confirmed.

Finding overlooked traits
For decades it was thought that no dinosaurs had a furcula or even clavicles. As it turns out, at least in Theropoda, they were largely overlooked. Nesbitt et al. 2009 write: “Furculae occur in nearly all major clades of theropods, as shown by new theropod specimens from the Early Cretaceous of China and a close inspection of previously collected specimens.” Finding overlooked traits is something we should all be doing. Some of these turn out to be important.

On a similar note…
earlier we looked at the homology of the central bones of the wrist and their migration to the medial rim in pterosaurs and pandas, and the previously overlooked evidence for that.

Update
Vickaryous and Hall 2006 employed embryology to determine that the Alligator interclavicle is equally parsimonious as a homolog of the Gallus furcula. They note:

  1. “the lateral processes (of the interclavicle in Alligator) are lost yielding a flattened bar-like element.” Actually that I-shaped bar goes back to basal crocodylomorphs.
  2. “At no time during skeletogenesis (in Alligator) are there any signs of any developmental stages of clavicles or clavicular rudiments, nor are there any signs of cartilage (primary or secondary).” — this statement speaks for itself.
  3. “The furcula is present (in Gallus) by HH 33 as a bilateral pair of condensations that have not fused in the midline” — This sounds like clavicles to me.
  4. “The pectoral apparatus of basal ornithodirans (falsely including pterosaurs) is incompletely known, and it remains unclear which if any mid-ventral dermal element was present.” That list is shown above. 
  5. Although previously interpreted as clavicles (in Psittacosaurus and Massospondylus), the identity of these elements is herein considered equivocal.” — no reason given, no phylogenetic path proposed.
  6. Vickaryous and Hall suggest the incorporation of the clavicle and interclavicle into the sternal complex of pterosaurs is restricted to one juvenile, and “has yet to be demonstrated in other taxa.” – This is what scientists and PterosaurHeresies readers would immediately call ‘recognizing a presence in the literature, but minimizing its impact on the present study and avoiding any effort at finding out what the situation actually is in other pterosaurs.’ I have also looked at the sternal complex of many pterosaurs and have observed that the interclavicle and clavicles are incorporated into the sternal complex of ALL pterosaurs and a few outgroup taxa, in which you can see the process happening. At present, and after reading Vicaryous and Hall 2006, I see no reason to homologize the interclavicle and the furcula.

References
Bryant HN and Russell  AP 1993. The occurrence of of clavicles within Dinosauria: Implications for the homology of the avian furcula and the utility of negative evidence. Journal of Vertebrate Paleontology 13(2):171–184.
Nesbitt S, Turner AH, Spaulding M and Norell MA 2009. The Theropod Furcula. Journal of Morphology 270(7):856–879.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95–120.
Vicaryous MK and Hall BK 2006. Homology of the reptilian coracoid and a reappraisal of the evolution and development of the amniote pectoral apparatus Journal of Experimental Zoology (Molecular and Developenmtal Evolution) 314B 196-207.

Variation among indricotheres (giant horse-rhinos)

Earlier we looked at the now heretical nesting of giant indricothere perissodactyls closer to horses than to living rhinos, their traditional relatives. We also touched on that subject here and here.

Also
there has been a movement (Lucas and Sobus 1989) to make many of the largest indricotheres congeneric. A look at the skulls (Figs. 1) suggests otherwise.

Figure 1. Indricothere skulls to scale along with horse and rhino skulls.

Figure 1. Indricothere skulls to scale along with horse and rhino skulls. Clearly the giant skulls, all indricotheres, are not congeneric. Aceratherium is more closely related to the extant horned rhino Ceratotherium.

Wikipedia reports
Indricotheriinae is a subfamily oHyracodontidae, a group of long-limbed, hornless rhinoceroses convergently similar to the sauropod dinosaurs that evolved in the Eocene epoch and continued through to the early Miocene.” By contrast, in the large reptile tree (LRT, 1012 taxa) Hyracodon nests at the base of extant rhinos, apart from the horse/indricothere branch.

Figure 2. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology.

Figure 2. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology. All reconstructions are chimaeras of known specimens. That doesn’t mean they are congeneric.

A new Pappaceras illustration
(Wood 1963; fig. 3) is more horse-like than others in having an orbit in the (probable) posterior half of the skull.

Figure 3. Pappaceras confluens A.M.N.H. No. 26660 and A.M.N.H. No. 26666 (mandible)

Figure 3. Pappaceras confluens A.M.N.H. No. 26660 and A.M.N.H. No. 26666 (mandible). With such posetriorly-placed eyes, this skull is more horse-like than other rhinos. 

The post-crania of Indricotherium
appears to include the only vertebral column known for this clade. IF so the vertebrae cannot be imagined as similar to that of a rhino (Fig. 2). And maybe, just maybe those indricothere limbs were covered with more gracile muscles and thinner skin, like those of a horse, not a rhino, tradition not withstanding. based on phylogenetic bracketing.

References
Chow M and Chiu C-S 1964. An Eocene giant rhinoceros. Vertebrata Palasiatica, 1964 (8): 264–268.
Forster-Cooper C 1911. LXXVIII.—Paraceratherium bugtiense, a new genus of Rhinocerotidae from the Bugti Hills of Baluchistan.—Preliminary notice. Annals and Magazine of Natural History Series 8. 8 (48): 711–716.
Forster-Cooper C 1924. On the skull and dentition of Paraceratherium bugtiense: A genus of aberrant rhinoceroses from the Lower Miocene Deposits of Dera Bugti. Philosophical Transactions of the Royal Society B: Biological Sciences. 212 (391–401): 369–394.
Granger W and Gregory WK 1935. A revised restoration of the skeleton of Baluchitherium, gigantic fossil rhinoceros of Central Asia. American Museum Novitates. 787: 1–3.
Lucas SG and Sobus JC 1989. The Systematics of Indricotheres”. In Prothero DR and Schoch RM eds. The Evolution of Perissodactyls. New York, New York & Oxford, England: Oxford University Press: 358–378. ISBN 978-0-19-506039-3.
Osborn HF 1923. Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia. American Museum Novitates. 78: 1–15. PDF
Pilgrim GE 1910. Notices of new mammalian genera and species from the Tertiaries of India. Records of the Geological Survey of India. 40 (1): 63–71.
Wood HE 1963. A primitive rhinoceros from the Late Eocene of Mongolia. American Museum Novitates 2146:1-11.

wiki/Juxia
wiki/Paraceratherium

Arcticodactylus a tiny Greenland Triassic pterosaur

Arcticodactylus cromptonellus (Kellner 2015, originally Eudimorphodon cromptonellus Jenkins et al. 1999, 1999; MGUH VP 3393) Late Triassic ~210mya ~8 cm snout to vent length was a tiny pterosaur derived from a sister to Eudimorphodon ranzii and phylogenetically preceded Campylognathoides and BSp 1994 specimen attributed to Eudimorphodon. Whether it was a juvenile or a tiny adult cannot be determined because juveniles and even embryos are identical to adults in pterosaurs. Note that that rostrum was not shorter and the orbit was not larger than in sister taxa. This specimen is one of the smallest known pterosaurs., but not THE smallest (Fig. 1) contra the Wikipedia article. That honor goes to B St 1967 I 276.

Figure 1. Articodactylus is evidently NOT the smallest pterosaur. That honor still goes to an unnamed specimen (not a Pterodactylus kochi juvenile) B St 1967 I 276.

Figure 1. Articodactylus is evidently NOT the smallest pterosaur. That honor still goes to an unnamed specimen (not a Pterodactylus kochi juvenile) B St 1967 I 276.

Distinct from E. ranzii,
the skull of Arctiodactylus had a rounder, less triangular orbit. The jugal was not as deep. The sternal complex did not have small lateral processes. The humerus was not as robust. The fingers were longer an more gracile. The prepubis was distinctly shaped.

Distinct from
Bergamodactylus the femur and tibia were smaller but the metatarsals were longer, compact and nearly subequal in length with IV smaller than III.

References
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A primitive pterosaur of Late Triassic age from Greenland. Journal of the Society of Vertebrate Paleontology 19(3): 56A.
Jenkins FA Jr, Shubin NH, Gatesy SM and Padian K 1999. A diminutive pterosaur (Pterosauria: Eudimorphodontidae) from the Greenlandic Triassic. Bulletin of the Museum of Comparative Zoology, Harvard University 155(9): 487-506.
Kellner AWA 2015. Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa. Anais da Academia Brasileira de Ciências 87(2): 669–689

wiki/Eudimorphodon
wiki/Arcticodactylus

Can Vaughnictis attract caseasaurs back to the synapsids again?

Welcome to another taxon challenge from Dr. David Marjanović
Yesterday we looked at Diplovertebron, a taxon Dr. Marjanović suggested (as others have) was just another Gephyrostegus.

Today we’ll reexamine the traditional nesting of caseasaurs with synapsids with a focus on Vaughnictis (Fig. 1), which looks kind of like a caseasaur. Earlier we made the case that the Caseasauria nested better with Millerettidae than with Synapsida when more taxa are included. Since then Vaughnictis was added to the large reptile tree (LRT, 1012 taxa) and it nested as the last known common ancestor to birds and bats (= archosauromorph diapsids and synapsids). 

Despite great resemblance,
the basal prosynapsid Vaughnictis (Fig. 1) does not attract the clade Caseasauria (Fig. 2; Casea, Cotylorynchus and kin including Datheosaurus and Eothyris,Fig. 1) back to the base of the Synapsida (Fig. 3; Varanosaurus, Dimetrodon and kin). Given their phylogenetic distance from one another, the resemblance is indeed extraordinary, especially in the temporal area. Perhaps even more so between Vaughnictis and Milleretta, than with a basal caseasaurid, like Eothyris.

Figure 1. The basal synapsid, Vaughnictis, and the basal caseasaur, Eothyris. For starters, synapsids have a taller than wide skull and caseasaurs have a wider skull. See text for other details.

Figure 1. The basal prosynapsid, Vaughnictis, and the basal caseasaur, Eothyris. For starters, synapsids have a taller than wide skull and caseasaurs have a wider skull. See text for other details.

At present
the LRT nests caseasaurs with Eothyris + Oedaleops + Colobomycter) and slightly further from Feeserpeton + Australothyris + Eocasea and kin. A shift of the Caseasauria (Fig. 2) to the base of the Synapsida (Fig. 3) adds at least 26 steps.  

Figure 2. Milleretta, caseasaurs and kin. The LRT nests these taxa together apart from the Synapsida, with which they share a lateral temporal fenestra.

Figure 2. Milleretta, caseasaurs and kin. The LRT nests these taxa together apart from the Synapsida, with which they share a lateral temporal fenestra. If any taxon resembles Milleretta, Vaughnictis is a better candidate than any caseasaur.

Despite sharing a lateral temporal fenestra
caseasaurs share more traits with millerettids than with synapsids, which retain their predatory teeth and a taller, narrower skull. Vaughnictis retains a short rostrum from ancestors like Protorothyris (Fig. 3). Synapsids never had the rostral overbite found in caesars, nor did they have that arrowhead-shaped set of nasals. Caseids and kin had three premaxillary teeth, not four or more as found in synapsids and Vaughnictis. The surangular in caseids does not extend anterior to the coronoid process. The dentary tip rises in synapsids, but not caseids, among several other distinct traits.

Figure 3. Vaughnictis is basal to the Synapsida and the Prodiapsida, here represented by Mycterosaurus.

Figure 3. Vaughnictis is basal to the Synapsida and the Prodiapsida, here represented by Mycterosaurus.

Can Vaughnictis make Caseasauria a synapsid clade again?
No. Not with the present taxon list. The reason why experts continue to promote caseasaurs as synapsids goes back to a long-standing tradition of taxon exclusion. They exclude members of the Millerettidae. Expand the gamut of your taxon list, and let the taxa nest wherever they want to.

The Diplovertebron issue resolved…almost

Mystery solved!

Figure 1. Diplovertebron from Watson 1926. He drew this freehand. In DGS the traits are different enough to nest this specimen elsewhere on the LRT. Beware freehand!

Figure 1. Diplovertebron from Watson 1926. He drew this freehand. In DGS the traits are different enough to nest this specimen elsewhere on the LRT. Beware freehand!

Earlier I provided images from Watson 1926 describing a specimen of Diplovertebron (Fig. 1). It took the prodding of a reader (Dr. David M) and a reexamination of several journals to realize that Watson had drawn in freehand the same specimen others (refs. below) had referred to as Gephyrostegus watsoni or as small specimen of G. bohemicus. Since this specimen is not congeneric with Gephyrostegus in the LRT, perhaps the name should revert back to Diplovertebron. Unless the holotype (another specimens comprised of fewer bones) is not congeneric. Then it needs a new name.

Figure 1. Gephyrostegus watsoni (Westphalian, 310 mya) in situ and reconstructed. The egg shapes are near the hips as if recently laid.

Figure 2. The same specimen of Diplovertebron traced and reconstructed using DGS.

Diplovertebron punctatum (Fritsch 1879, Waton 1926; DMSW B.65, UMZC T.1222a; Moscovian, Westphalian, Late Carboniferous, 300 mya) aka:  Gephyrostegus watsoni Brough and Brough 1967) and  Gephyrostegus bohemicus (Carroll 1970; Klembara et al. 2014) after several name changes perhaps this specimen should revert back to its original name as it nests a few nodes away from Gephyrostegus.

This amphiibian-like reptile was derived from a sister to Eldeceeon, close to the base of the Archosauromorpa and Amniota (= Reptiliai). Diplovertebron was basal to the larger Solenodonsaurus and the smaller BrouffiaCasineria and WestlothianaDiplovertebron was a contemporary of Gephyrostegus bohemicus, Upper Carboniferous (~310 mya), so it, too, was a late survivor.

Overall smaller and distinct from Eldeceeon, the skull of Diplovertebron had a shorter rostrum, larger orbit and greater quadrate lean. The dorsal vertebrae formed a hump and had elongate spines. The hind limbs were much longer than the forelimbs. The tail is incomplete, but appears to have been short and deep.

Seven sphere shapes were preserved alongside this specimen. They may be the most primitive amniote eggs known.

Watson 1926 attempted a freehand reconstruction (see below) that was so different from this specimen that for a time it nested as a separate taxon, now deleted.

Figure 1. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

Figure 3. Watson’s Diplovertebron, the present Diplovertebron (former ©. watsoni) and Gephyrostegus bohemicus. Not sure where Fr. Orig. 128 came from, but that specimen is the same as Watson’s DMSW B.65 specimen at upper right drawn using DGS methods.

The large reptile tree
along with several pages here (PterosaurHeresies) and at ReptileEvoluton.com have been updated.

References
Brough MC and Brough J 1967. The Genus Gephyrostegus. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 252 (776): 147–165.
Carroll RL 1970. The Ancestry of Reptiles. Philosophical Transactions of the Royal Society London B 257:267–308. online pdf
Fritsch A 1879. Fauna der Gaskohle und der Kalksteine der Permformation “B¨ ohmens. Band 1, Heft 1. Selbstverlag, Prague: 1–92.
Klembara J, Clack J, Milner AR and Ruta M 2014. Cranial anatomy, ontogeny, and relationships of the Late Carboniferous tetrapod Gephyrostegus bohemicus Jaekel, 1902. Journal of Vertebrate Paleontology 34:774–792.
Watson DMS 1926. VI. Croonian lecture. The evolution and origin of the Amphibia. Proceedings of the Zoological Society, London 214:189–257.

wiki/Gephyrostegus
wiki/Diplovertebron

Groeberia: no longer an enigma taxon and no longer an allothere

Wiikipedia reports,
Groeberiidae is a family of strange non-placental mammals from the Eocene and Oligocene epochs of South America. Chimento et al. 2013 determined that Groeberia was a member of the Allotheria, a mammal clade not recovered in the large reptile tree (LRT, 1013 taxa). Simpson & Wyss 1999, considered Groberia relatives to be diprotodontians (wombats), By contrast McKenna 1980 claiming that considering them metatherians was “an act of faith”. The LRT supports that nesting as Groeberia nests with Vintana, another former enigma, both within the Metatheria (marsupials).

Groeberia minoprioi (Patterson 1952,  MMP 738) and G. pattersoni (Simpson 1970) are best known from a tall and narrow anterior skull and mandibles (Fig. 1) with an unusual set of teeth.

Figure 1. Groeberia drawing, photo and color-coded bones and teeth. This taxon nests with Vintana in the LRT and that canine-ish tooth must be a premolar because canines are unknown in this clade going back several nodes.

Figure 1. Groeberia drawing, photo and color-coded bones and teeth. This taxon nests with Vintana in the LRT and that canine-ish tooth must be a premolar because canines are unknown in this clade going back several nodes. As in related taxa, the jugal contacts the premaxilla. The descending process on the jugal is just appearing here.

The large reptile tree (LRT, 1012 taxa) nests Groeberia with Vintana (Fig. 2) among the wombats.

Note the large gnawing incisors backed up by an long upper premolar in the place usually occuupied by a canine. The tooth is not a canine because no more primitive relatives have a canine. Not also the small bump below the jugal. This becomes much longer in relatives like Vintana.

Figure 1. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

Figure 2. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

References
Chimento NR, Agnolin  FL and Novas FE 2015. The bizarre ‘metatherians’ Groeberia and Patagonia, late surviving members of gondwanatherian mammals. Historical Biology: An International Journal of Paleobiology27 (5): 603–623. doi:10.1080/08912963.2014.903945]
McKenna MC 1980. Early history and biogeography of South America’s extinct land mammals.
Patterson B 1952. Un nuevo y extraordinario marsupial deseadiano. Rev Mus Mun Cienc Nat Mar del Plata. 1:39–44.

wiki/Groeberiidae

Oops! What’s wrong with this picture?

So far you’ve learned so much about the skeletons of vertebrates. Now, can you tell what is wrong with the published image below? It will be obvious once you know what to look for. Scroll down for the solution.

Figure 1. Can you tell what is wrong with this picture of a museum mount of Ernanodon published in Vickers-Rich and Rich 1993?

Figure 1. Can you tell what is wrong with this picture of a museum mount of Ernanodon published in Vickers-Rich and Rich 1993?

Earlier we looked at and nested the basal marsupial, Ernanodon (Figs. 1, 2). The museum mount published in Vickers-Rich and Rich 1993, has one glaring error. Can you spot it?

Ernanodon anteilos (Ting [Ding] 1979; Paleocene; 50 cm in length) was originally considered placental mammal, perhaps a primitive anteater, then regarded as a primitive pangolin, like Manis. Here Ernanodon nests with Hyaenodon and Deltatheridum as a creodont marsupial, sharing large canines with both.

The skull was robust with a jaw joint nearly as far back as the occiput. The claws were broad and long, ideal for digging. The tail was long, but very slender.

Figure 2. Here is the same museum mount repaired in Photoshop. The pelvis was originally installed backwards. Here the pelvis is correctly mounted.

Figure 2. Here is the same museum mount repaired in Photoshop. The pelvis was originally installed backwards. Here the pelvis is correctly mounted.

Answer
The pelvis of the museum mount was installed backwards. Here (Fig. 2) the pelvis has been flipped in Photoshop to its correct position.

References
Ding SY 1979. A new edentate from the Paleocene of Guangdong. Vertebrata PalAsiatica 17:57–64. [Chinese 57–61; English 62–64].
Vickers-Rich P and Rich TH 1993. Wildlife of Gondwana. REED, Chatswood, Australia. 276 pp.

wiki/Ernanodon

Reviewing the ‘Colosteidae’

Updated June 23, 2017 with the removal of Phlegethontia after taxon additions attracted that taxon to the Aïstopoda, where it traditionally nests. 

Updated March 26, 2019 with the addition of taxa and a revision of scores that moved Deltaherpeton to the base of the Collosteidae. 

I asked for the challenge.
Dr. David Marjanović (DM) responded. He thought the traditional collosteids should nest together, as they do in Marjanović and Laurin 2017. By contrast, in the large reptile tree (LRT, 1012 taxa) only two nest together. Dr. David Marjanović also did not like Colosteus and kin nesting between Osteolepis and Panderichthys. Rather, Marjanović and Laurin 2017 reported, “Colosteidae is consistently found in a position one node more rootward than Baphetoidea and one node more crownward than Crassigyrinus.” In the Marjanović and Laurin study, relatives of Baphetes include Spathicephalus, Eucritta and Megalocephalus and Crassigyrinus nests between the collosteids and Tulerpeton. The LRT does not support this topology.

The Colosteidae
is a clade of basal tetrapods that classically includes Pholidogaster, Colosteus, Greererpeton and the latest addition, Deltaherpeton (Fig. 1).

Figure 1. Classic Collosteidae include Collosteus, Pholidogaster, Greererpeton and Deltaherpeton all to scale.

Figure 1. Classic Collosteidae include Collosteus, Pholidogaster, Greererpeton and Deltaherpeton all to scale here. Classic synapomorphies are listed below. The LRT nests Colosteus and Pholidogaster together while the other two nest elsewhere.

Marjanović and Laurin report,
“Deltaherpeton is one of the oldest known colosteids.” Bolt and Lombard 2010 report, Deltaherpeton is unique among colosteids in having an internasal and single midline postparietal. An additional midline pair of cf. ‘interfrontonasals’ may be present. Synapomorphies which unite Deltaherpeton, Colosteus, Greererpeton, and Pholidogaster as Colosteidae are:

  1. premaxilla with fang pair;
  2. dentary with notch for receipt of premaxillary fang;
  3. mandible with single elongate exomeckelian fenestra;
  4. pre-narial infraorbital lateral line terminating at ventral margin of premaxilla just anterior to external naris; and
  5. post-narial infraorbital lateral line terminating at the ventral margin of the maxilla just posterior to the external naris.

Let’s test to see
if this list is just a Larry Martin list of a few traits that are overwhelmed by other synapomorphies in the LRT. And at the same time, let’s see if these few traits have a wider, but overlooked, distribution and to see if they are valid for every included taxon.

Premaxilla with (lateral) fang pair
is indeed present in the four named taxa, if only barely in Deltaherpeton. Overlooked, perhaps, the lateral premaxillary tooth is also the largest in Acanthostega, Ventastega, Pederpes, Sclerocephalus, Ichthyostega among taxa related to traditional colosteids. More on premaxillary fangs below.

The dentary notch
Unfortunaely I see this trait only on Greererpeton and Pholidogaster. In Colosteus (Figs. 1, 6) and Delatherpeton (Figs 3, 5) it is not apparent.

Figure 3. Drawing of Deltaherpeton sutures in Lombard and Bolt 2010 and colorized here. Note the lack of data around the naris (white glow).

Figure 3. Drawing of Deltaherpeton sutures in Bolt and Lombard 2010 and colorized here. Note the lack of data around the naris (white glow).

Collosteid traits 3-5 (above)
include the elongate exomeckelian fenestra and the two lateral lines (Fig. 3) are difficult to see or not see in some taxa. Note in the labeled image of Deltaherpeton by Bolt and Lombard 2010 (Fig. 3). Even they were unable to draw the naris and its surrounding lateral lines (white glow), but provided a diagram (Fig. 3) on another figure. 

Figure 4. Panderichthys palates. Note the lateral line below the naris is not continuous, contra Lombard and Bolt.

Figure 4. Panderichthys palates from Vorobyeva and Schultze 1991. Note the lateral line below the naris is not continuous, contra Bolt and Lombard.

I have not looked for lateral line/naris patterns
in other taxa, but Bolt and Lombard note the lateral line is continuous and straight below the naris along a lateral rostral plate in Eusthenopteron, Panderichthys (Fig. 4) and Ichthyostega. The lateral rostral plate is below the naris in Eusthenopteron. In Panderichthys the lateral line does not cross the lateral rostral plate, if that is what it is, because it is illustrated by Vorobyeva and Schultze (1991) with teeth, so it may just be a broken portion of the maxilla and the lateral rostral plate is no longer present. The naris of Ichthyostega is at the jawline leaving little room for a lateral rostral plate on the exterior surface. Would have been better for Bolt and Lombard to provide both the data, for verification, and the diagram, because now doubts arise.

Figure 4. Deltaherpeton in situ with inset showing location of naris and circumarial bones.

Figure 5. Deltaherpeton in situ with inset showing location of tiny inset naris and circumarial bones.

Two taxa separate Greererpeton and Pholidogaster in the LRT:
Panderichthys and Tiktaalik. Both lack the lateral premaxillary fang. Notably and despite their antiquity, both are derived and distinct from related taxa in having a very flat skull with orbits close to the midline. All marginal teeth are relatively tiny, which is also distinct from related taxa. Apparently when the skull flattened in these two the lateral premaxillary fangs shrank. Perhaps we should look for them in undiscovered basal taxa, probably originating n the early Late Devonian and lasting who knows how long.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

In the large reptile tree
(subset Fig. 3) flat Greererpeton nests with other flat taxa like Spathicephalus, Trimerorhachis and Gerrothorax and  Ossinodus. Deltaherpeton nests basal to the collosteids. Despite their readily apparent differences no other taxa in the LRT share as many traits with clade members. And these three are the few representatives of a radiation covering about 60 million years.

The taphonomic crushing of the Deltaherpeton skull suggests it was wider than it was. Finding the palate by excavating from the other side of the matrix would provide precise data.

Did temnospondyls return the water?
Or never leave it? Did tetrapods develop fingers and toes more than once? Did basal tetrapods develop the ability to raise their bellies off the substrate more than once? The LRT provides provisional answers to these questions (Fig. 7). Convergence is apparent here. The LRT collosteids are separated from start to finish by about 60 million years, so changes can be expected.

Synapomorphies
Rather than pulling a Larry Martin, I did not list the few or many traits shared by Collosteus relatives in the LRT. Those can be gleaned from the matrix and most certainly will find convergences elsewhere on the cladogram. Remember, its not just one or a dozen traits that nest taxa as a clade, but the suite of traits that can really only be recovered by software like PAUP.

As to Dr. Marjanović’s challenge:
The traditional list of collosteids certainly does fall into a much narrow spectrum of sizes (Fig. 1), as opposed to the LRT list of Collosteus relatives (Fig. 6). And I did reexamine several issues and red flags. Some scores were revised. Deltaherpeton shifted two nodes and I think I understand it much better now. The list of classic collosteid traits is not found in all members and some traits extend to other clades. Finally, the phylogenetic distance between classic collosteids is not far from each other in the LRT, and in both studies both collosteid clades nest toward the base of the Tetrapoda. The details will work themselves out with further study on both sides. All interpretations are provisional, especially in basal tetrapods given their lateral lines that sometimes look like sutures and both camouflaged by a maze of skull texture.

As a suggestion for the future:
if colleagues would colorize their skull photos, paying attention to broken pieces and parts that just barely peek out from overlying material, that would go a long way toward improving the present system of either just showing the specimen or creating a freehand outline of the specimen, or just labeling bones with abbreviations and arrows without noting sutures.

References
Marjanović D and Laurin M 2017. Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. PeerJPrePrints (not peer-reviewed).
Vorobyeva EI and Schultze H-P 1991. Description and systematics of panderichthyid fishes with comments on their relationship to tetrapods, in Schultze and Trueb (eds.), Origins of the Higher Groups of Tetrapods Comstock, pp 68-109.

Cambaytherium: not a basal perissodactyl

Rose et al. 2014
considered pig-sized Cambaytherium thewissi (Eocene, 55 mya; 45-75 lbs; Fig. 1) to be a basal perissodactyl (odd-toed ungulates like Tapirus, Equus and Ceratotherium), but with four fingers. Rose et al. pieced together 200 bones from several individuals of which only some were published.

Figure 1. Cabaytherium does not nest as a basal perissodactyl, but between Hippopotamus and Anthracobune in the LRT. Note the long retroarticular process.

Figure 1. Cabaytherium does not nest as a basal perissodactyl, but between Hippopotamus and Anthracobune in the LRT. Note the long retroarticular process.

In their phylogenetic analysis,
Rose et al. report, “In these nine shortest trees, cambaytheres and anthracobunids were always united with perissodactyls to the exclusion of afrotheres, artiodactyls and phenacodontids, with cambaytheres always recovered at the base of the perissodactyl stem.”

Figure 3. Mesonychids including Cambaytherium nesting between Hippopotamus and Anthracobune. This is a subset of the LRT.

Figure 2. Mesonychids including Cambaytherium nesting between Hippopotamus and Anthracobune. This is a subset of the LRT.

Unfortunately
Rose et al. 2014 did not have access to Cooper  et al. 2014, which featured a more or less complete Anthracobune skull and mandible (Fig. 3). Among all mammals, no other taxa have such an elongate retroarticular process — except Cambaytherium. That and several other traits nested Cambaytherium in the large reptile tree (LRT, 1012 taxa) between Hippopotamus and Anthracobune, ultimately in the lineage of desmostylians and baleen whales.

The Rose et al. cladogram included both rhinos and horses, Unfortunately indricotheres were not included. Dang!

Figure 3. Anthracobune reconstructed with a larger skull to match the teeth on the mandible.

Figure 3. Anthracobune reconstructed with a larger skull (in color) to match the teeth on the mandible.

During this study 
I realized the skull I had used for Anthracobune did not match the teeth of the larger mandible. They were likely from different sized specimens. So I enlarged the skull and reidentified some teeth (Fig. 3). No change in tree topology took place following these changes.

Figure 3. An image falsely attributed to Cambaytherium.

Figure 4. An image falsely attributed to Cambaytherium that appears on the Internet.

Cambaytherium was found
on the marine coastline of island India, close to where odontocete whales were also evolving from terrestrial tenreci ancestors. like Pakicetus. Based on its relationships Cambaytherium was likely much more aquatic than is typical for perissodactyls, which makes it easer to reach the island continent. Ocepeia, another relative, was found in Morocco.

References
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014. 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.
Rose, KD et al. (8 other authors) 2014.
 Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications. 5 (5570). doi:10.1038/ncomms6570.

LA Times article online
wiki/Cambaytherium

New Pappaceras chewing data from Wang et al. 2017

At the base of the giant indricotheres
we find Pappaceras (Fig. 1). To that everyone agrees. Where the disagreements start is what came before Pappaceras? In the large reptile tree (LRT, 1012 taxa) it’s Miohippus (Fig.1 1) and Equus the extant horse.

Figure 1. Miohippus, Pappaceras and a freehand sketch of Pappaceraus, the latter two from Wang et al. 2017, but colorized here.

Figure 1. Miohippus, Pappaceras and a freehand sketch of Pappaceraus, the latter two from Wang et al. 2017, but colorized here. Note the freehand sketch differs from the CT scan in several subtle and not so subtle ways.

Wang et al. 2017
bring new insight into the chewing mechanism in Pappaceras. They write: “The paraceratheriid Pappaceras is the earliest unequivocal rhinocerotoid genus to date, for which the osteological morphology is relatively unique compared to other perissodactyls. The reconstruction of the masticatory muscles suggests that Pappaceras meiomenus is strictly herbivorous, probably folivorous, with a primary component of vertical biting.”

Distinct from the LRT
The Wang et al. cladogram nests horses at the base of the Perissodactyla. Chalicotheres and brontotheres nest together without resolution. Indricotheres nest with rhinos as sisters to tapirs. The LRT does not support that tree topology at all. The Wang et al. cladogram also nests a perissodactyl outgroup taxon I had never heard of before: Cambaytherium. which I just added to the LRT and we’ll talk about tomorrow. It is not related to perissodactyls in the LRT.

The freehand drawing of Pappaceras
by Wang et al. (Fig. 1`) is distinct in certain subtle aspects from their CT scan (Fig. 1). It’s better to trace directly from photos. Or just use the CT scans. Freehand drawing, by its nature, emphasizes things that catch the eye and deemphasizes things that don’t catch the eye, but perhaps should.

References
Wang H-B, Bai B, Gong Y-X, Meng J and Wang Y-Q 2017. Reconstruction of the cranial musculature of the paraceratheriid rhinocerotoid Pappaceras meiomenus and inferences of its feeding and chewing habits. Acta Palaeontologica Polonica 62 (2): 259–271.