During the Late
Cretaceous high sea levels split Europe up into a series of islands,
each with its own distinctive fauna, with fossils from different
parts of Europe show affinities to those from other continents,
notably Asia, North America and Gondwana (Africa & South
America). In recent years larger fossil vertebrates, such as
Dinosaurs, Pterosaurs, Crocodiles and Turtles, have been extensively
studied in Iberia, but less attention has been paid to smaller
vertebrates, which are often important when trying to assess connections between faunas of different regions.
In a paper published in
the journal Cretaceous Research on 30 July 2015, Alejandro Blanco and
Arnau Bolet of the Institut Catalàde Paleontologia Miquel Crusafont at the Universitat Autònomade Barcelona, Hugues-Alexandre Blain of the Institut Catalàde Paleoecologia Humana i EvoluciòSocial and the Area de Prehistòria at the
Universitat Rovira i Virgili, and Víctor Fondevilla of the
Departament de Geologia (Estratigrafia) at the Universitat Autònoma
de Barcelona describe a series of fossils of smaller vertebrates from
four exposures of the Late Cretaceous Tremp Formation of northeastern
Spain. The Tremp Formation comprises a series of beds laid down on a
floodplain with a meandering or braded river, occasional isolated
lakes and marine influences in places.
The first fossils
examined dome from the Serrat del Rostiar-1 locality, where the
exposure composes grey mudstones with pedogenic nodules which
represent portions of fossilized soil, thought to have formed on the
floodplain close to a meandering river (represented by sandstone
deposits).
This site has produced a
partial frontal bone (part of the skull) and three humerus fragments
assigned to an unknown Albanerpetontid, an extinct group of
Salamander-like Lisamphibians with bony scales, known from the
Middle Jurassic to the End Pliocene of Europe, North America and (in
one case) Morocco, and which have previously been recorded from
several sites in Iberia.
Albanerpetontid
Lisamphibians from Serrat del Rostiar-1. (A) Frontal in dorsal view.
(B) Proximal and (C) distal epiphyses of humeri in ventral view.
Blanco et al. (2015).
This site also produced a
fragment of right and two left illia, a partial scapula, a fragment
of humerus and one whole and one partial vertebrae assigned to an
unknown Painted Frog, Discoglossinae, a group of Frogs found today in
southern Europe, North Africa and Israel. The earliest known fossil
assigned to this group comes from the Jurassic of Spain, and Cretaceous specimens have previously been described from Spain,
Romania and Wyoming. The site also produced one fragment of ilium
assigned to an unknown Alytine Frog (Midwife Toad).
Alytid Anurans from
Serrat del Rostiar-1. (A) Right ilium in lateral view. (B) Left ilium
in lateral view. (C) Left ilium in lateral view. (D) Left scapula in
lateral view. (E) Sacral and (F) trunk vertebrae in ventral view. (G)
Alytinae: right ilium in lateral view. Blanco et al.
(2015).
In addition a fragment of
ilium and a partial vertebrae assigned to an unknown Palaeobatrachid
Frog were found at this site. Palaeobatrachid Frogs are well
documented from the Eocene-Pliocene of Europe, with a few fragmentary
specimens from Spain and North America.
Palaeobatrachid Anurans
from Serrat del Rostiar-1. (A) Left ilium in lateral view. (B) Trunk
vertebra in ventral view. Blanco et al.
(2015).
Serrat del Rostiar-1 also
produced fragment of an urostyle, the epiphysis of a radioulna, two
partial vertebrae and some tibiofibular and radioulnar fragments
assigned to unknown Frogs.
Indeterminate Anurans
from Serrat del Rostiar-1. (A) Radioulna in lateral view. (B)
Urostyle in dorsal view. Blanco et al.
(2015).
Also from Serrat del
Rostiar-1 is a frontal bone tentatively assigned to a Gecko. Geckos
are well known in the Cretaceous in Asia, but otherwise more-or-less
unknown, However this Serrat del Rostiar-1 specimen closely
resembles another possible Gecko specimen from the Cretaceous of
Romania, suggesting a possible unknown lineage of European Cretaceous
Geckos.
Frontal of an
indeterminate ?Gekkota from Serrat del Rostiar-1 in ventral view.
Blanco et al. (2015).
The Serrat del Rostiar-1
site also produced three tooth-bearing jaw fragments tentatively
assigned to ab unknown Skink. Skinks first appeared in the Jurassic
and by the end of the Cretaceous appear to have been distributed
across Europe, Asia and North America. In Europe they have been
previously described from the Late Cretaceous of Spain, France and
Romania.
Tooth-bearing bones of
an indeterminate ‘Scincomorph’ Lizard from Serrat del Rostiar-1
in lingual view. Blanco et al.
(2015).
This site also produced a
single vertebrae of a possible Anguid
(Glass) Lizard. Anguids
appeared in the Late Cretaceous of North America, and while common in
parts of that continent by the end of the period, are not previously
known in Europe till the Cainozoic.
Vertebra of Anguidae
indet. from Serrat del Rostiar-1 in dorsal (E), ventral (F) and
lateral (G) view. Blanco et al.
(2015).
Finally the Serrat del
Rostiar-1 site produced a tooth set in a fragment of bone from an
unknown Iguanid, and another tooth set in bone plus an ishium of an
unknown Lizard. The oldest known Iguanid comes from the Early
Jurassic of India, and the group were widespread by the End
Cretaceous.
Iguanid tooth from
Serrat del Rostiar-1 in lingual view. Blanco et al.
(2015).
The L'Espinau site
produces grey marly mudstones with organic inclusions, mostly in the
form of coaly material. It has a distinctive bone-bed, which has
produced numerous scattered Hadrosaur bones. The site is not close
to any fluvial (river) sandstone deposits, though some lucastrine
(lake) limestones are found nearby, and the site probably represents a
floodplain.
L'Espinau has produced a
partial premaxilla, a fragment of maxilla, five fragments of
dentaries and a portion of a humerus assigned to Albanerpetontid
Lisamphibians. These appear simlar to (less fragmentary) material
previosuly described from the Blasi-2 locality which is nearby, and
which have been assigned to the genus Albanerpeton,
which is otherwise known from fluvial, lucastrine and floodplain
environments in the Cretaceous of North America and Cainozoic of
Europe, surviving as late as the Pliocene in Hungary and Italy.
Albanerpetontid
Lisamphibians from L'Espinau. (D) Left premaxilla in lingual view.
(E) ?Maxilla in lingual view. (F) Left dentary and (G) right dentary
in lingual view. (H) Proximal fragment of humerus in ventral view.
Blanco et al. (2015).
The
L'Espinau also produced two sacral vertebrae and two partial ilia
assigned to an unknown Alytine Anuran (Midwife Toad), a group closely
related to the Painted Frogs, Discoglossinae. This group is also
found in southern Europe and North Africa today, but which in the
Cretaceous has previously been described from Central Asia and
Romania.
Alytid
Anurans from L'Espinau. (H) Sacral vertebra. (I) Sacral vertebra. (J)
Left and (K) right ilium in lateral view. Blanco et al.
(2015).
This
site also yielded two partial humerii of an unknown Palaeobatrachid
Frog, a fragment of maxila from either a Pelobatid (Spadefoot Toads,
which are found today in North America, Europe, North Africa and
western Asia, and which are known as fossils from the Jurassic and
Cretaceous of Norh America and the Eocene onwards in Europe) or a
Gobiatid (an extict group of Anurans known from the Cretaceous of
Central Asia), and a fragmentary vertebra, a urostyle, a coracoid, a
partial radioulna, a humeral epiphysis and six fragments of
tibiobifulae from unknown Frogs.
Maxilla
of Pelobatidae or Gobiatidae indet. from L'Espinau in lingual (C) and
lateral (D) view. Blanco et al. (2015).
L'Espinau
also produced a tooth from an indeterminate Iguanid Lizard in a piece
of bone.
Iguanid
tooth from L'Espinau in lingual view. Blanco et al. (2015).
The
Serrat del Pelleu site comprises grey mudstones overlying fine ochre
sandstones, probaby laid down on a quite, non-erosive part of a
meandering river system. This site has previously produced numerous
Turtle, Crocodylomorph and Hadrosaur specimens.
Blanco
et al. describe a partial humerous of a Albanerpetontid
Lisamphibian from this site, as well as one prearticular, three
partial humeri and six fragments of tibiofibulae from an unknown
Painted Frog.
Distal
epiphysis of humerus of an unknown Painted Frog from L'Espinau in
ventral view. Blanco et al. (2015).
Finally
the Camí del Soldat location comprises thinly interbedded grey
mudstones and fine sandstones thought to have been laid down on a
quite meander-loop of a river. This location produced one urostyle
and two partial vertebrae of an unknown Frog.
The
Tremp paleoriver valley has yielded a diverse fauna of Lisamphibians
and Lizards, much of it similar to other localities from the Late
Cretaceous of Spain. However it also contains the oldest, and only
Mesozoic, Midwife Toad remains known Europe to date and possibly the
oldest, and only Mesozoic, Gecko from Iberia (and possibly Europe).
Curiously the sites produced no Snake remains, despite the fact that
Snakes are thought to have been well established globally by the Late
Cretaceous, though this may be a result of taphonomic or sampling
bias, given the low number of specimens in the study.
See also...
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