Tijubina – A New Tritosaur Sister to Huehuecuetzpalli

Tijubina pontei (Bonfim and Marques 1997) was a tiny Early Cretaceous lizard from the Crato Formation (late Aptian) of northeast Brazil. In a recent redescription Simões (2012) reported Tijubina lacked the posteroventral and posterodorsal processes of the dentary and the tibial/fibular length equaled the femoral length. Its posterior dentary teeth were robust, cylindrically based, unsculptured and bore no cuspids. Simoes (2012) nested Tijubina in a basal position among the Squamata. Reynoso (1998) reported a similar nesting for Huehuecuetzpalli. Neither considered the possibility that both specimens nested in a third squamate clade, the Tritosauria, outside of the Iguania + Scleroglossa.

Figure 1. The skull of Tijubina reconstructed (left) and in situ dorsal view, skull roof missing (right). Click for more info. Some skull parts identified here are disputed by Simoes (pers comm).

Late Survivors
Both Huehuecuetzpalli and Tijubina were late survivors of a 130 million year earlier Late Permian radiation of lizards. Tijubina is distinguished by its teeth, which are larger posteriorly and shaped like cylinders instead of sharp points. Tijubina was about half the size of its Huehuecuetzpalli.

Tijubina in situ

Figure 2. Tijubina in situ, nearly full size on a 72dpi screen. Click to enlarge.

Not a Juvenile
Simoes (2012) described Tijubina as immature due to a imcompletely calcified joints, a wide open sternal fontanelle (hole), unfused pectoral and pelvic elements. Adult tritosaur lizard sisters are likewise incompletely calcified. Unlike Huehuecuetzpalli, and despite its smaller size, the carpal elements of Tijubina were well ossified. The lack of dorsal and ventral processes of the posterior dentary are traits shared with Huehuecuetzpalli.

Manus of Tijubina identifying carpal elements.

Figure 2. Manus of Tijubina identifying carpal elements. Metacarpal 4 is largely beneath mc5. Here the two centrale are ossified along with the other carpal elements and present. The carpus is unossified in adult Huehuecuetzpalli.

The carpus is not ossified in Huehuecuetzpalli, but it is well ossified in the much smaller Tijubina and both centrale are present. Earlier I wondered if the pteroid and preaxial carpal were migrating at the evolutionary stage represented by Huehuecuetzpalli because the carpus was poorly ossified. That would have been an ideal time to do it! Here Tijubina may have been a sister Huehuecuetzpalli, but the latter was closer to fenestrasaurs including pterosaurs.

 

Figure 3. The pelvis and possible prepubis and Tijubina. Is this the origin of the prepubis? Or just a splinter or two of bone in the position of the prepubis. I can't tell for sure. Phylogenetically Tijubina was scored without a prepubis and pteroid.

Figure 3. The pelvis and possible prepubis and Tijubina. Is this the origin of the prepubis? Or just a splinter or two of bone in the position of the prepubis. I can’t tell for sure. Phylogenetically Tijubina was scored without a prepubis and pteroid.

Cosesaurus through pterosaurs all have a prepubis, a new bone extending beyond the ventral margin of the pubis. So the prepubis appeared some time prior to Cosesaurus. It may or may not be present in Langobardisaurus. It is not present in Huehuecuetzpalli. A possible prepubis may be present in Tijubina (Fig. 3). On the other hand, that little fleck of bone(s) may just be a splinter from the damaged pubis. No problem either way.

A Long Tibia
Since the tibia was subequal to the femur, Tijubina was likely a sprinter and a possible occasional biped, like many living lizards with similar proportions. Such traits and behaviors likely led to the development of a prepubis in sister taxa.

Pes of Tijubina.

Figure 4. Pes of Tijubina. PILs added.

Pes
The pes of Tijubina had tendril-like toes, indicating an arboreal lifestyle. Like Huehuecuetzpalli and Cosesaurus the proximal phalanges of digit 5 were long. The tarsals were not coossified, a trait typical of many (but not all) tritosaurs. Fenestrasaurs (including pterosaurs) did not ossify two distal tarsals. Drepanosaurs and all living lizards co-ossified the proximal tarsals.

Summary
Tijubina was a late-surviving representative of the Tritosauria, a clade of lizards that ultimately gave rise to tanystropheids, drepanosaurs and pterosaurs. The cylindrical teeth were autapomorphies not found in other clade members. The tiny size and crushed nature of the specimen prevent confirmation of several possible fenestrasaur-like traits.

Huehuecuetzpalli, Tijubina, Cosesaurus and Macrocnemus are basal tritosaurs.

Huehuecuetzpalli, Tijubina, Cosesaurus and Macrocnemus are basal tritosaurs.

References
Bonfim Júnior DC and Marques RB 1997. Um novo lagarto do Cretáceo do Brazil (Lepidosauria, Squamata, Lacertilia – Formação Santana, Aptiano da Bacia do Araripe. Anuário do Instituto do Geociencias 20:233-240
Bonfim-Júnior F de C and Rocha-Barbosa O 2006. A Paleoautoecologia de Tijubina pontei Bonfim-Júnior & Marques, 1997 (Lepidosauria, Squamata Basal da Formação Santana, Aptiano da Bacia do Araripe, Cretáceo Inferior do Nordeste do Brasil). Anuário do Instituto de Geociências – UFRJ ISSN 0101-9759 Vol. 29 – 2 / 2006 p. 54-65.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Simões TR 2012. Redescription of Tijubina pontei, an early cretaceous lizard (Reptilia; Squamata) from the crato formation of Brazil. An Acad Bras Cienc. Feb 2, 2012. pii: S0001-37652012005000001. [Epub ahead of print].

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