SVP abstracts 13: Tiny Tiktaalik-like tetrapod

Lembert et al. 2020 bring us
a much smaller Tiktaalik-like tetrapod.

From the Lembert et al. abstract:
“The elpistostegalian stem-tetrapod Tiktaalik roseae (Fig. 1) is known from a single locality (NV2K17) within the Fram Formation of Ellesmere Island, Nunavut Territory, Canada. Specimens from this locality represent subadult to adult specimens, including specimens up to 61% larger than the holotype specimen (NUFV 108) and reaching an estimated 3 meters in length.”

Figure 3. Tiktaalik specimens compared to Ossinodus.

Figure 1. Tiktaalik specimens compared to Ossinodus.

“Here we present fossil material of a much smaller elpistostegalian specimen (NUFV 137) from a second, slightly older locality within the Fram Formation on Ellesmere Island (NV0401), possibly representing a juvenile T. roseae specimen or a new taxon.”

Not mentioned in this abstract, tiny Koilops (Figs. 2, 3) nests basal to Tiktaalik in the large reptile tree (LRT, 1251 taxa).

Figure 2. Koilops is a flat-headed sister to Spathicephalus, but with teeth, larger orbits and a shorter snout

Figure 2. Koilops is a flat-headed sister to Spathicephalus, but with teeth, larger orbits and a shorter snout

Figure x. The fin to finger transition in the LRT with the addition of Elpistostege.

Figure 3. The fin to finger transition in the LRT with the addition of Elpistostege.

Continuing from the Lembert et al. abstract:
“Preserved remains of NUFV 137 include fragmentary lower and upper jaws, gular plates, fragments of the rostrum, articulated body scales, articulated pectoral fin elements, and several other currently unidentified endoskeletal pieces. Linear proportions between homologous landmarks of lower jaws of NUFV 137 and NUFV 108 suggest an animal approximately 61% smaller than the holotype of T. roseae, and, with a reconstructed total jaw length of approximately 12.4 cm, NUFV 137 is similar in size to one of the smallest known elpistostegalian taxa (Rubrognathus kuleshovi).”

Taxon exclusion has evidently excluded the even smaller Koilops (Fig. 2) from the Lembert et al. studies.

“If NUFV 137 represents a juvenile T. roseae individual, it would expand the known size range of T. roseae specimens, with implications for understanding allometric growth in a tetrapodomorph taxon.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Continuing from the Lembert et al. abstract:
“While lower jaw characters appear to be similar to those in T. roseae, it is uncertain if some features, such as a posteriorly displaced postsplenial pit line, reduced adsymphyseal dentition, and varying postcranial proportions, are the result of differences in ontogeny or warrant a separate taxonomic grouping. These differences, and the presence of a potential operculum, indicate NUFV 137 might represent a distinct but similar, Tiktaalik-like taxon.”


References
Lemberg JB, Stewart TA, Daeschler E and Shubin NH 2020. Tomography of a tantalizingly tiny Tiktaalik-like taxon. SVP abstracts 2020.

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