Wednesday 13 July 2022

Geckos from the Early Eocene Dormaal Site in Belgium.

The Middle and Late Eocene Lizard faunas of Europe are relatively well known, thanks to a number of lagerstätten (deposits with exceptional preservation) such as the Messel Shale of Germany. However, the Lizards of the Early Eocene are much less well understood, due to a paucity of such sites. This is unfortunate, as this interval starts with the Palaeocene-Eocene Thermal Maximum at 56 million  years ago, the which saw the warmest temperatures of the past 66 million years, with Northern Europe developing a sub-tropical to tropical climate, and therefore presumably being a particularly good environment for Lizards.

One exception to this lack of Early Eocene is the Dormaal locality at  Zoutleeuw, eastern Belgium, where a fluvial deposit comprised of layers of clayey and lignitic (coal-rich) sands are interbedded with lenses of grey clays. These deposits are thought to have been laid down in a system of rivers and lagoons in the earliest Eocene, and have yielded a diverse fauna of Mammals, Lizards, Fish, Turtles, and Crocodiles.

In a paper published in the journal Royal Society Open Science on 29 June 2022, Andrej Čerňanský of the Department of Ecology at Comenius University in BratislavaJuan Daza of the Department of Biological Sciences at Sam Houston State University, Richard Smith of the Directorate Earth and History of Life at the Royal Belgian Institute of Natural SciencesAaron Bauer of the Department of Biology and Center for Biodiversity and Ecosystem Stewardship at Villanova University, Thierry Smith, also of the Directorate Earth and History of Life at the Royal Belgian Institute of Natural Sciences, and Annelise Folie of the Scientific Survey of Heritage at the Royal Belgian Institute of Natural Sciences, describe A new species of Gacko from the Dormaal Site.

Location of the earliest Eocene locality of Dormaal (MP7, Belgium) that has yielded Dollogekko dormaalensis and the early Eocene locality of Prémontré (MP10, France) that has yielded Laonogekko lefevreiČerňanský et al. (2022).

Geckos as a group have a poor fossil record, due to their lightly mineralised and easily disarticulated skeletons. The oldest known Geckos come from the Early Cretaceous amber deposits of Myanmar, with Geckos also known from Eocene Baltic Amber and Miocene Dominican Amber. Outside of these amber deposits, however, almost all fossil Geckos are known from isolated skeletal elements. Geckos have previously been recorded from the Dormaal locality, but never actually formally described.

The new species is named Dollogekko dormaalensis, where 'Dollogekko' honours the prominent Belgian palaeontologist Louis Dollo (1857-1931), combined with '-gekko' the Malay root word of the English 'gecko', often used as a suffix for generic names within the group, and 'dormaalensis' means 'from Dormaal'. The species is described from a single incomplete frontal bone (the bone that forms the forehead in Humans).

Dollogekko dormaalensis, the holotypic frontal IRSNB R 452 in (a) dorsal, (b) ventral, (c) right lateral,(d) left lateral and (e) anterior views. Čerňanský et al. (2022).

The frontal bones of Geckos tend to be highly distinctive at the species level, making it possible to reliably describe new taxa on these bones alone. The specimen from which Dollogekko dormaalensis is described comprises about the anterior half of the frontal bone, with the posterior half being lost. The preserved portion is 4.3 mm in length, is tubular-to-funnel-shaped (the whole bone would almost certainly have been hourglass shaped), and would have extended about ¾ of the way around the orbit. 

Dorsal view of the skull of some extant Geckos exhibiting diversity of frontal bone shape and sculpturing (yellow). (a) Carphodactylidae, Underwoodisaurus  milii (CAS  74744),  (b)  Diplodactylidae, Rhacodactylus  leachianus (MCZ–R15967), (c) Phyllodactylidae, Thecadactylus rapicauda (CAS 95146) and (d) Gekkonidae, Chondrodactylus angulifer (CAS 126466). Čerňanský et al. (2022).

In addition to the partial frontal from which Dollogekko dormaalensis is described, Čerňanský et al. also describe two fragments of dentary and a partial mandible from the same deposit. The dentary fragments appear to be from a Gecko about the same size as Dollogekko dormaalensis, while the partial mandible appears to come from an Animal about twice the size. Since the frontal bone from which Dollogekko dormaalensis is described is fully fused, and therefore presumed to come from an adult individual which has stopped growing, this appears likely to represent a separate species. The dentary fragments are of a size compatible with he frontal bone, but it is impossible to confirm that they belong to the same species, derive from a juvenile of the species which produced the mandible, or represent a third species. Due to this uncertainty, and the low value of mandible fragments for taxonomic purposes, none of these specimens are named, but instead referred to as Gekkota indet 1 (dentaries) and Gekkota indet 2 (mandible).

Gekkota indet. 1, the dentaries IRSNB R 454 and IRSNB R 453; Gekkota indet. 2, the mandible fragment IRSNB R 456 in(a), (e), (i) lateral, (b), (f), (j) medial, (c), (g), (k) dorsal, (d) ventral and (h) anterior views. Čerňanský et al. (2022).

See also...

Online courses in Palaeontology

Follow Sciency Thoughts on Facebook.

Follow Sciency Thoughts on Twitter.