Large palaeophiid and nigerophiid snakes from Paleogene Trans-Saharan Seaway deposits of Mali

Abstract

The Paleogene was a time of high diversity for snakes, and was characterized by some of the largest species known to have existed. Among these snakes were pan-Tethyan marine species of Nigerophiidae and Palaeophiidae. The latter family included the largest sea snake, Palaeophis colossaeus, known from the Trans-Saharan Seaway of Mali during the Eocene. This paper describes new material collected from Malian Trans-Saharan Seaway deposits, including additional material of Palaeophis colossaeus, a new, large species of nigerophiid, Amananulam sanogoi gen. et sp. nov., and a medium-sized snake of indeterminate affinities. The material provides new information on the intracolumnar variation of the vertebral column in Palaeophis colossaeus. We estimate the total length of each species by regression of vertebral measurements on body size. Both Palaeophis colossaeus and Amananulam sanogoi gen. et sp. nov. are the largest or among the largest members of their respective clades. The large size of Tethyan snakes may be indicative of higher temperatures in the tropics than are present today.

Frontispiece

“…Bioproxies for tempera¬ ture, such as body size in South American fossil snakes and the physiological limitations it imposes, have been used to suggest that the paleotropics may have been even hotter than the present-day tropics (Pearson et al, 2001;Head et al, 2009). Our discovery of relatively large extinct snakes in Mali is another body-size data point suggesting that the African paleo¬ tropics in and around the Trans-Saharan Sea¬ way may also have been relatively hot (McCartney et al, 2018).…”

“…The Teberemt Formation forms a series of recessive slopes made up of shales and distinctive benches, which are capped by lime¬ stones. An incredibly abundant fauna has been recovered from this formation, including numer¬ ous vertebrates, such as fish, crocodyliforms, and snakes from the phosphate conglomerates and an abundant invertebrate fauna from the shales and carbonates, dominated by echinoids, oysters, nautiloids, gastropods, and foraminiferans (Gaff¬ ney et al, 2007;Hill et al, 2008;McCartney et al, 2018). Interesting taphonomic situations are preserved, including turtle skeletons encrusted with ostreidan bivalves (fig.…”

“…The lowest phosphate conglomerate in the formation is the thickest and most richly fossiliferous unit in the study area, preserving a remarkable abundance of isolated vertebrate bones, including rare mammal fossils. This bed was described in detail in several papers by our team (Tapanila et al, 2004;O'Leary et al, 2006;Tapanila et al, 2008;McCartney et al, 2018).…”

“…Clasts are predominantly granule to cobble sized, but also include pieces of vertebrate bone as large as 25 cm. Bioclast shape and size analysis dem¬ onstrated a sorting in the thickest phosphatic deposit: Mali-20 unit 2 (also called "Mali-20a" [Tapanila et al, 2008;McCartney et al, 2018]).…”

“…The Republic of Mali has extensive sedimen¬ tary deposits left by an ancient epeiric sea known as the Trans-Saharan Seaway Based on geologi¬ cal and paleontological field data we collected on expeditions in northern Mali in 1999Mali in , 2003Mali in , and 2009 (the latter cut short for security reasons), we conducted two decades of analysis resulting in more than 10 publications that describe new discoveries and interpretations of the sedimentology, sequence stratigraphy, and paleobiology of this region of the Sahara (Bamford et al, 2002;Brochu et al, 2002;O'Leary et al, 2004a;Tapanila et al, 2004;O'Leary et al, 2006;Gaffney et al, 2007;Hill et al, 2008;Tapanila et al, 2008;Claeson et al, 2010;Hill et al, 2015;McCartney et al, 2018). We present here an integrated pic¬ ture of that work.…”