The biostratigraphical distribution of earliest tetrapods (Late Devonian): a revised version with comments on biodiversification - The Terrestrialization Process: Modelling Complex Interactions at the Biosphere-Geosphere Interface - page 126

The biostratigraphical distribution of earliest tetrapods (Late
Devonian): a revised version with comments on biodiversification

A. BLIECK 1 *, G. CL ´ MENT 2 & M. STREEL 3
1 Universit´ de Lille 1, Sciences de la Terre, FRE 3298 du CNRS, G´osyst`mes,
Equipe de Pal´ontologie et Pal´og´ographie du Pal´ozo¨que (LP3),
F-59655 Villeneuve d'Ascq cedex, France
2 Mus´um national d'Histoire naturelle (MNHN), D´partement Histoire de la Terre,
UMR 7207 du CNRS, Centre de Recherche sur la Pal´obiodiversit´ et les Pal´oenvironnements,
Case Postale 38, 57 rue Cuvier, F-75231 Paris cedex 05, France
3 Universit´ de Li`ge, D´partement de G´ologie, Unit´ de recherche Pal´obotanique-
Pal´opalynologie-Micropal´ontologie, Sart Tilman, B18, B-4000 Li`ge 1, Belgium
*Corresponding author (e-mail: [e-mail])

Abstract: The 13 presently known genera of Late Devonian tetrapods are situated in the recently
completed miospore zonation of Western Gondwana and Euramerica, in relation to the standard
conodont zonation. Some of them are still unprecisely dated. The stratigraphic sequences of
East Greenland, North China and East Australia are briefly reviewed to discuss the age of the tetra-
pods collected there and to analyse consequences in relation to the Frasnian - Famennian and
Devonian - Carboniferous boundaries. Two episodes of biodiversification seem to have occurred:
the first in the Frasnian and the second in the late and latest Famennian. Due to the currently known
fossil evidence, the consensus scenario advocates a late Middle Devonian to early Late Devonian
origin of tetrapods on the Old Red Sandstone Continent (Euramerica) at a time of warm climate and
recovering atmospheric oxygen level during the building of a pre-Pangaean configuration
of landmasses.

The transition of life from water (either marine or
fresh) to land, that is, terrestrialization, is certainly
one of the most debated topics in evolutionary
biology. Most recent results in palaeontology have
shown that this event happened at various periods
in Earth's history: Precambrian for bacteria, fungi
and algae involved in the first palaeosoils (e.g.
Altinok 2006), Ordovician for land plants (Early
Ordovician for cryptospores and Late Ordovician
for trilete spores; see Steemans et al. 1996; Strother
et al. 1996), Silurian (or earlier in the Cambrian -
Ordovician) for many invertebrates (annelids,
arthropods, etc.; see MacNaughton et al. 2002)
and Devonian - Carboniferous for vertebrates.
Here, we focus on the Late Devonian, the earliest
phase of vertebrate terrestrialization, when limbed
vertebrates with digits (i.e. tetrapods) first appeared
in the fossil record.
Several papers have recently reviewed various
aspects of this earliest diversification of tetrapods
either in terms of its palaeobiological context (e.g.
Clack 1997, 2002, 2006, 2007; Schultze 1997,
2004; Ruta & Coates 2003; Ruta et al. 2003;
Lebedev 2004; Long & Gordon 2004; Ahlberg
et al. 2008) or its geological context (Young 2006;

Blieck et al. 2007). A correct evaluation of the
first diversification and adaptive radiation of tetra-
pods is in need of a well-controlled biostratigraphi-
cal framework of its successive steps (accurate
dating of the fossiliferous localities) (Blieck et al.
2007). We return to this necessary precise biostrati-
graphy because new data have since been published.
We will also explore some of the consequences that
this biostratigraphical framework has upon the
interpretation of the biodiversity and radiation of
earliest tetrapods after the most recently published
phylogenetic analysis (Ahlberg et al. 2008).

Biostratigraphical distribution

Blieck et al. (2007) have reviewed the Late Devo-
nian tetrapod-bearing localities that have yielded
bone remains (not the traces and trackways that
are reviewed by Clack 1997, 2002). They commen-
ted upon the biostratigraphical dating of those
localities to give the most precise ages possible to
the various taxa of tetrapods. Among the oldest,
three still have rather unprecise ages, namely: Sinos-
tega (N. China) originally thought to be Famennian