Academic Bun Fight: Is There a Gap in the Middle Permian Strata?

Apparently back in 2005, Spencer Lucas argued there was a 2 to 3 million year gap in the known strata producing a hiatus.

Fossils of tetrapods (amphibians and reptiles) have long been used to correlate regionally Permian nonmarine strata (Lucas, 1998).
However, the development of a global Permian tetrapod biostratigraphy and biochronology has been hampered by several problems. The most serious may be the presence of a global gap (hiatus) in part of the Middle Permian record of tetrapods.

Michael Benton wrote in 2012 there is no gap in the Middle Permian Strata based on global evidence:

During the Permian, tetrapods showed a major transition from basal synapsid-dominated faunas in the first half to therapsid-dominated faunas in the second. The transition was significant in marking the beginning of richer and more complex communities, a precursor to modern terrestrial ecosystems. This changeover may have been gradual or abrupt, but its study has been complicated by the postulated occurrence of a substantial hiatus in the fossil record, termed “Olson's Gap”, which obscured the nature of the turnover. New evidence from redating of key tetrapod-bearing units of the American southwest and European Russia confirms that there is no gap in the fossil record of Permian tetrapods. Indeed, evidence for substantial sampling bias in the Permian tetrapod fossil record as a whole is queried.

Spencer Lucas replied in 2013:

Benton (2012) claims that there is no gap in the Middle Permian tetrapod fossil record, in contrast to my (2004) conclusion that a gap exists between the youngest pelycosaur-dominated tetrapod assemblages and the oldest therapsid-bearing tetrapod assemblages. I referred to this as Olson’s Gap and concluded that it is equivalent to most of the Roadian Stage. Instead, Benton (2012, his figure 1) correlates the youngest pelycosaur assemblages from Texas-Oklahoma with the oldest therapsid assemblages of Russia. However, in advocating this correlation, Benton does not address an extensive marine biostratigraphic database detailed by me (2004).

To which Benton replied in 2013:

In his comment, Lucas (2013) reiterates his earlier view that there was a marked gap in the tetrapod fossil record spanning the Roadian and Wordian of the Middle Permian, which I, and others (Reisz and Laurin 2001, 2002), have opposed. His arguments are far from certain, however. He says that the uppermost tetrapod-bearing terrestrial Permian beds in Oklahoma and Texas (United States) are Early Permian in age, and that the oldest Russian tetrapod-bearing beds are post-Roadian, so leaving a temporal gap of 2–3 m.y. On the first point, his view is not accepted by the majority of researchers, although the biostratigraphic evidence is far from watertight, and on the second, he is opposed by the majority of experts.