SVP abstracts 17: Pederpes is a junior synonym for Whatcheeria

Otoo et al. 2020 bring us
a new reconstruction of Whatcheeria (Figs. 1, 2), evidently updated from a 2018 abstract by the same authors (less one).

Figure 1. Whatcheeria fossil.

Figure 1. Whatcheeria fossil.

From the Otoo et al. abstract:
“The early tetrapod Whatcheeria is represented by hundreds of specimens from the Mississippian Delta locality (Iowa, U.S.A.). Research on the postcranial anatomy allows a full-body reconstruction to be produced for the first time. The ribcage is strongly regionalized, with long anterior trunk ribs bearing large uncinate processes, and short posterior trunk ribs. The girdles and limbs are massive; in particular, the processes of the humerus are very large, and imply bulky forelimb and shoulder musculature, especially relating to the retraction of the forelimb. The cervical region is elongated and the tail is reduced in length relative to contemporary tetrapods such as embolomeres and colosteids.”

Whatcheeria nests in the large reptile tree (LRT, subset Fig. 3) alongside Pederpes (Fig. 4). The two share all traits scored in the LRT and are coeval in the Early Carboniferous.

Figure 2. Whatcheeria skull.

Figure 2. Early Carboniferous Whatcheeria skull.

More from the Otoo et al. abstract:
“The resulting proportions are more similar to terrestrial taxa such as Seymouria and Eryops. These taxa also share with Whatcheeria robust humeri with large processes, large olecranon processes, large scapular blades, and regionalized ribcages. Such similarities suggest convergent life habits, with an anteriorly stiffened trunk to increase the effectiveness of the powerful forelimbs and reduce lateral motion of the body.”

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

Figure 3. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

More from the Otoo et al. abstract:
“We hypothesize that Whatcheeria represents an independent experiment in appendicular-dominated locomotion, with improved ability to explore terrestrial environments The large (>2 m maximum) body size of Whatcheeria is larger than most Mississippian tetrapods, particularly those for which there is the most compelling evidence of terrestriality (e.g., Balanerpeton, Westlothiana). Aquatic locomotion may have been accomplished by bottom-walking, or rowing with the forelimbs.”

“Our new data include additional synapomorphies between Whatcheeria and Pederpes, and suggest that the latter is a juvenile.

Whatcheeria and Pederpes nest together in the LRT (Fig. 4). Of 235 traits, none differ between the two. Based on scale bars the two are identical in size, with 10cm measuring the snout to the posterior orbit on both. Pederpes (Clack 2002) is thus a junior synonym for Whatcheeria (Lombard and Bolt 1995). Hmmm. Wonder how this one got away from the experts over the last 18 years. Whatcheeria entered the LRT in 2017, so I had three years to see this, too.

Figure 3. Pederpes is a basal taxon in the Whatcheeria + Crassigyrinus clade.

Figure 4. Early Carboniferous Pederpes is a basal taxon in the Stegocephalia.

More from the Otoo et al. abstract:
These data contribute to a new diagnosis for the Whatcheeriidae and a reassessment of material and taxa referred or compared to the family; significantly, Ossinodus is not a whatcheeriid and represents a distinct morphotype.

The LRT (subset Fig. 3, Fig. 5) agrees with this.

Figure 2. Ossinodus, Pederpes were more primitive than the more aquatic Icthyostega.

Figure 5. Ossinodus,is more primitive than the more aquatic Icthyostega. Pederpes is more derived, but close. The black areas of Ossinodus are known. The rest is restoration.

More from the Otoo et al. abstract:
“However, these data do move Whatcheeria crownward in phylogenetic analyses. Rather, our findings highlight the disparity of stem tetrapods, and emphasizes Whatcheeria’s status as an early-diverging experiment in a morphology later revisited by crown tetrapods.”

The LRT (subset Fig. 3) does not agree with this conclusion. Ossinodus (Fig. 5) nests basal to both stegocephalians (including Whatcheeria) and crown tetrapods. It is the most basal tetrapod with substantially larger limbs than those of basalmost tetrapods like Trypanognathus. Ichthyostega and Pederpes are taxa leaving no Permian and Mesozoic descendants.

Ahlberg PE and Milner AR 1994. The origin and early diversification of tetrapods. Nature 368, 507-514.
Clack JA 2002. Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Clack JA 2002. An early tetrapod from ‘Romer’s Gap’. Nature. 418 (6893): 72–76. doi:10.1038/nature00824
Lydekker R 1890. On two new species of labyrinthodonts. Quarterly Journal of the Geological Society, London 46, 289-294.
Lombard RE and Bolt, J.R 1995. A new primitive tetrapod, Whatcheeria deltae, from the Lower Carboniferous of Iowa. Palaeontology 38(3):471–495.
Otoo B, Bolt J, Lombard E and Coates M 2020. A new reconstruction of Whatcheeria and the ecomorpholigcal disparity of early tetrapods. SVP abstracts 2020.
Otoo BK, Bolt JR, Lombard E 2018. A leg up: Whatcheeria and its new contributions to tetrapod anatomy. SVP abstracts.
Panchen AL 1991. The early tetrapods: classification and the shapes of cladograms in: Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Eds. Schultze HP and Trueb L. Comstock Publishing Associates, Cornell University Press, Ithaca and London.


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