Related mammals that nest at the bases of several hoofed clades

The value
of the large reptile tree (LRT, 1013 taxa) and the reconstructions gathered together at ReptileEvolution.com lie in their ability to put faces on names (Figs, 1) sometimes to scale (Fig. 2) to help one recognize patterns that may have gone unrecognized while just looking at names and scores.

These are the mammals that nest with one another
as sisters after deletion of more derived taxa in each of their several clades (listed at right, Fig. 1). Thus they, more or less, represent the basal radiation of hoofed mammals prior to each clade radiation. And to no one’s surprise, they look like each other, despite wide variations in size.

Frankly,
I’m reexamining the traits of these taxa because the LRT had trouble resolving them. There were mistakes in there. Now, after some score corrections, the resolution is complete again, but some Bootstrap scores have risen to just above 50. Not great, but better than below 50. Remember, I don’t have access to these specimens and sometimes work from published drawings.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids. The differences are harder to see than in derived taxa in each clade (column at right). See figure 2 for skeletons to scale.

Some of these basal taxa
gave rise to baleen whales. Others were ancestral to giraffes, elephants, horses and everything in between. None of these taxa are nearly so famous or interesting to the general public, but it is from these generalized (plesiomorphic) taxa that the few and subtle evolutionary changes that are key to each clade first make an appearance.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale. Note the presence of phylogenetic miniaturization at the base of the Artiodactyla. Consider this scenario: mesonychids radiated widely, including to create larger and smaller taxa. The larger homalotheres did not radiate greatly, as far as we know. On the other hand, the smaller taxa radiated to become a long list of extinct and exact hoofed taxa. And, of course, the mesonychid clade radiated to include today’s hippos and baleen whales. 

Sometimes a ‘show and tell’ drives a point home
better than just a ‘tell’. Even so, these are not the precise individuals in the direct lineage of known derived taxa, but the close relatives of those perhaps eternally unknown and hypothetical individuals. The suite of traits that lump and separate these taxa can be gleaned from the present MacClade file, continually added to and updated, and available here., which is where you can also see the cladogram from which the above taxa were pulled.

 

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