Chometokadmon is a basal gekko

A few years ago,
Evans et al. 2006 re-introduced us to the Lower Cretaceous lizard, Chometokadmon fitzingeri (MPN 539) from Italy. That genus was originally described by Costa 1864. The Evans team nested Chometokadmon between Dorsetisaurus and Xenousauridae at the base of the Anguimorpha (varanids + helodermatids). Note that Xenosaurus and Heloderma have laterally facing nares, not dorsal nares.

Figure 1. Chometokadmon in situ. Known for over 100 years, this flat skulled gekko had longer toes than typical.

Figure 1. Chometokadmon in situ. Known for over 100 years, this flat skulled gekko had longer toes than typical.

The large reptile tree (LRT) nests Chometokadmon at the base of the geckos, between Tchingisaurus and Gekko smithii. Like geckos, Chometokadmon lacks a postorbital and thus has a confluent orbit + both temporal fenestra. Helodermatids have a similar temporal architecture lacking temporal bars, but do not have a triangular rostrum in dorsal view.

Perhaps
the Evans team made a mistake in identifying a quadrate alone as a quadrate + squamosal (Fig. 2). In most geckos, the quadrate is a tall slender bone, but in the basalmost gecko in the LRT, Tchingisaurus (Fig. 2), the lateral quadrate has an anterior rim that dorsally bends posteriorly, like the purported squamosal in Chometokadmon. No close relatives have a squamosal with the shape proposed by Evans et al. The triangular outline of the skull in dorsal view along with the short teeth are also gekko traits not found in candidates proposed by the Evans team.

FIgue 2. Skull and reconstruction of Chometokdamon by Evans et al. 2006.

FIgue 2. Skull and reconstruction of Chometokdamon by Evans et al. 2006. Note the loss of the postorbital and jugal bars.

A comparison to other geckos
(Fig. 3) makes the case rather clear to Chometokdamon may be one of them. A skull twice as wide as tall plus the confluence of the orbit with the both the upper and lower temporal fenestrae are gecko traits.

Figure 1. Click to enlarge. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Figure 3. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Figure 3. Gekko smithii is an extant member of a genus that extends to the Early Cretaceous. Note the lack of temporal bars and the forward extension of the supratemporal along the lateral parietal.

Figure 4. Gekko smithii is an extant member of a genus that extends to the Early Cretaceous. Note the lack of temporal bars and the forward extension of the supratemporal along the lateral parietal, as in Chometokadmon.

As a basal gekko
Chometokadmon joins two rather closely related and coeval basal pro-snake genera Ardeosaurus and Eichstattisaurus that we discussed earlier here and were mistakenly  considered basal geckos by Simoes et al. 2016. Their mistake, once again, was taxon exclusion, a problem often solved by the large gamut of taxa in the LRT.

References
Costa OG 1864. Paleontologia del Regno di Napoli, III. Atti dell’Accademia Pontaniana 8, 1e198.
Evans SE, Raia P, Barbera C 2006. The Lower Cretaceous lizard genus Chometokadmon from Italy. Cretaceous Research 27:675-683.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

wiki/Chometokadmon

Stem geckos? Or stem snakes? – SVP abstract 2016

Earlier Simoes et al. 2016 published their paper and today their SVP abstract of Eichstaettisaurus and Ardeosaurus, two Jurassic squamates. Here’s how the LRT (subset Fig. 1, complete tree here) recovered geckos, snakes and stem snakes like Eichstaettisaurus and Ardeosaurus, the dual subjects of Simoes et al. 2016 paper and abstract.

Figure 1. Subset of the LRT focusing on geckos snakes and stem snakes that nest close to geckos.

Figure 1. Subset of the LRT focusing on geckos snakes and stem snakes that nest close to geckos.

From the Simoes et al. 2016 abstract:
“Late Jurassic lizards from Solnhofen, Germany, are some of the oldest known articulated lizard specimens in the world (1), and are also the most complete Jurassic squamates. These specimens are thus very important to our understanding of early squamate evolution, with valuable information regarding morphology, taxonomy, and phylogeny. Eichstaettisaurus schroederi and Ardeosaurus digitatellus are two of the best  preserved species from that locality, the former being represented by the most complete Jurassic lizard specimen known anywhere in the world. Despite their relevance to broad questions in squamate evolution, their morphology has never been described in detail, and their systematic placement has been under debate for decades. Here, we provide the first detailed morphological description, species level phylogeny and functional morphological evaluation of E. schroederi and A. digitatellus. We identified previously undescribed features of E. schroederi linking this taxon to gekkotans, such as the Meckelian canal being closed and fused medially, ectopterygoid lying dorsal to transverse process of pterygoid, and autopodial digit symmetry. Using a revised and updated dataset containing 610 characters and 193 taxa (2), we corroborate their initial placement as geckoes—stem gekkotans, more specifically. This is of fundamental importance to the early evolution of squamates, as it demonstrates the existence of yet another major extant squamate clade (Gekkonomorpha) in the Jurassic (3). Additionally, both taxa illustrate a number of climbing adaptations (e.g. shape of unguals, penultimate phalanges, and body proportions), which indicates a scansorial lifestyle arose earlier in the evolution of geckos than previously known. Autopodial modifications associated with digital hyperextension and adhesive toepads (e.g. depressed and reduced intermediate phalanges, and arcuate penultimate phalanges), which provide geckoes with a highly sophisticated climbing apparatus, are not present. Therefore, our findings further suggest that morphological adaptations for scansoriality evolved in geckoes prior to the first known occurrence of adhesive toepads in the Cretaceous. Our results provide support from the fossil record to most molecular and combined evidence estimates of the origin of most major clades of squamates, including geckoes, which usually place divergence times for their stem back in the Jurassic or the Triassic.”

Figure 1. From Simoes et al 2016, their cladogram of the squamates separate varanids from mosasaurs, link snakes to skinks and shows how close pre-snakes are to basal geckos.

Figure 1. From Simoes et al 2016, their cladogram of the squamates separate varanids from mosasaurs, link snakes to skinks and shows how close pre-snakes are to basal geckos.

Notes

  1. In the LRT lepidosaurs extend back to the Early Permian (TA 1045 specimen, close to Saniwa) and Lacertulus (Late Permian).
  2. The Ardeosaurus/Echstaettisaurus clade lies outside the geckos, inside the Pro-serpentes in the LRT as a single clade, but 3 ways by Simoes et al.
  3. No wonder those two taxa form a separate clade outside the geckos in the Simoes et al. report. The do so as well in the LRT, at the base of all snake and pro snakes.
  4. The LRT is a single, fully resolved tree, not the consensus of 3174 MPTs.

References
Simoes TR, Caldwell MW, Nydam RL and Jimenez Huidobro P 2016. Osteology, phylogeny and functional morphology of two Jurassic lizard species indicate the early evolution of scansoriality in geckoes. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

New paper on Ardeosaurus and Eichstaettisaurus as geckos

Ardeosaurus and Eichstaettisaurus (Fig. 1) have been traditional enigmas in paleo studies. Here is some progress from Simões et al. 2016, who nest these two with geckos, as they were initially placed. The large reptile tree nests these two at the base of snakes, as sisters to the gecko clade. So very close!
Eichstattisaurus and Ardeosaurus.

Figure 1. Eichstattisaurus and Ardeosaurus. Two Jurassic lizards in the lineage of snakes – but very close to geckos.

From the Simões abstract:
“Late Jurassic lizards from Solnhofen, Germany, include some of the oldest known articulated lizard specimens, sometimes including soft tissue preservation. These specimens are thus very important to our understanding of early squamate morphology and taxonomy, and also provide valuable information on squamate phylogeny. Eichstaettisaurus schroederi and Ardeosaurus digitatellus are two of the best-preserved species from that locality, the former being represented by one of the most complete lizard specimen known anywhere in the world from the Jurassic. Despite their relevance to broad questions in squamate evolution, their morphology has never been described in detail, and their systematic placement has been under debate for decades. Here, we provide the first detailed morphological description, species-level phylogeny, and functional morphological evaluation of E. schroederi and A. digitatellus. We corroborate their initial placement as geckoes (stem gekkotans, more specifically), and illustrate a number of climbing adaptations that indicate the early evolution of scansoriality in gekkonomorph lizards.”

A PDF has been requested.
We’ll see if they included any basal snakes in their analysis.
This just in. The PDF arrived
The Simoes et al. cladogram nests snakes within skinks, derived from amphisbaenids. I don’t see Tetrapodophis or other pre-snakes in their cladogram.
References
Broili F 1938. Ein neuer fund von ?Ardeosaurus H. von Meyer. S.-B. bayer. Akad. Wiss. München, math.-naturw. Abt. 97-114.
Conrad JL and Daza JD 2015. Naming and rediagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology 35:5, e980891
Conrad JL and Norell MA 2006. High-resolution x-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öosh ( €Ov€orkhangai; Mongolia). Historical Biology 18:405–431.
Daza JD, Bauer AM and Snively E 2013. Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities. Zoological Journal of the Linnean Society 167:430–448.ischen Akademie der Wissenschaften, München 1938: 97–114.
Evans SE, Raia P and Barbera C 2004. New lizards and rhynchocephalians from the Lower Cretaceous of southern Italy. Acta Palaeontologica Polonica 49:393-408.
Hoffstetter R 1953. Les Sauriens anté−crétacés. Bulletin de la Museum Nationale d’Histoire Naturelle 25: 345–352.
Kuhn O 1958. Ein neuer lacertilier aus dem fränkischen Lithographie−schiefer. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 1958: 437–440.
Mateer NJ 1982. Osteology of the Jurassic Lizard Ardeosaurus brevipes (Meyer). Palaeontology 25(3):461-469. online pdf
Meyer H von 1860. Zur Fauna der Vorwelt. Reptilien aus dem lithographischen Schiefer des Jura in Deutschland mit Franchreich. Frankfurt-am-Main.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

Norellius nyctisaurops – a -very- basal pre-snake, -very- close to geckos

A new paper
by Conrad and Daza (2015) rediagnoses and names AMNH FR 21444 (Fig. 1, Early Cretaceous, ), “an important early and relatively basal lizard: (Conrad and Norell 2006).” Conrad and Daza describe the specimen as “a gecko-like basal squamate as identified by its braincase morphology.” it is tiny with a skull length of 1.5 cm. Postcrania is unknown.

Figure 1. Norellius from Conrad and Daza 2015. At upper right I highlight the 'missing' lacrimal and provide an alternate imagined rostrum based on that of sister taxa.

Figure 1. Norellius from Conrad and Daza 2015. At upper right I highlight the ‘missing’ lacrimal in red and provide an alternate imagined rostrum based on that of sister taxa. Look closely at the pterygoid. There are tiny teeth there, the origin of pterygoid teeth in snakes!

Added to 
the large reptile tree, Norelliius nests next to the Gekko clade that has Tchingisaurus at its base. Norelliius nests at the base of the clade that produced Eichstaettisaurus, Tetrapodophis and snakes, further cementing these two clades together. And it’s the fiirst good lock at the palate around this node.

Daza et al. 2013
was not able to resolve the position of AMNH FR 21444. According to Conrad and Daza, “It has large orbits, a complete postorbital bar and supratemporal arch, and a broad pyriform recess (Fig. 1). The skull is broadest at the level of the orbits and, apparently, tapered anteriorly. The lacrimal is absent; the maxilla and prefrontal form the margins of the lacrimal foramen.” 

Funny thing,
they say the lacrimal is absent, and it is absent on the left with a space left over to receive it, but it appears to be present on the right (Fig. 1). Sister taxa all have a lacrimal.

Norellius is difficult to nest
as it lacks important bones at the front and back of the skull. And it nests very close the the origin of several major scleroglossan clades. In other words, it is very plesiomorphic. Nevertheless a few traits do ally it with Ardeosaurus, Eichstaettisaurus and other pre-snakes to the exclusion of other clades.

Conrad and Daza
consider Gekkonomorpha as basal within Squamata. The large reptile tree does not support this, but recovers Iguania and several other taxa as more basal (splitting off earlier).  It should be noted that Conrad and Daza do not yet recognize the Protosquamata or the Tritosauria, two lepidosaur clades/grades basal to the Squamata. They haven’t added pertinent taxa to their studies, including the lepidosaur Macrocnemus and its kin.

Ironically
Conrad and Daza note: “Norellius nyctisaurops shows no gekkotan characteristics in its dermatocranium.” Only the braincase identifies it as a gekknomorph according to their study.

Conrad and Daza consider Norellius close to the base of Squamata (which it is not) and note, “Even so, the elongate postorbital skull, curved and elongate jugal, long postdentary part of the jaw, and very gecko-like braincase differ strikingly from the morphology seen in basal rhynchocephalians [Gephyrosaurus]. Clearly, more Jurassic and Triassic squamates are needed to help bridge the morphological gap between basal lepidosaurs and modern Squamata.” The large reptile tree provides several taxa to fill this purported gap. Again, the conclusions of Conrad and Daza appear to be based on taxon exclusion. The large number of pertinent taxa in the large reptile tree provide a gradual accumulation of derived characters.

Pterygoid teeth!
Look closely at the pterygoid of Norellius. There are tiny teeth there, the origin of large pterygoid teeth in snakes! Mosasaurs grew those pterygoid teeth convergently, hence the confusion with Pythonomorpha, another invalid clade (snakes + mosasaurs, Cope 1869).

References
Conrad JL and Daza JD 2015. Naming and rediagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology 35:5, e980891
Conrad JL and Norell MA 2006. High-resolution x-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öosh ( €Ov€orkhangai; Mongolia). Historical Biology 18:405–431.
Daza JD, Bauer AM and Snively E 2013. Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities. Zoological Journal of the Linnean Society 167:430–448.