cretaceous continental fossils and ichnofossils

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CRETACEOUS CONTINENTAL
FOSSILS AND ICHNOFOSSILS
Above, complete body of a female wasp preserved in
amber. Deposit of Peñacerrada I, Burgos.
Below, dinosaur fossil tracks (ichnites) at Peñaportillo
(Munilla, Cameros Range, La Rioja).
Photo: Fundación Patrimonio Paleontológico de La Rioja.
Pérez Lorente, F.
Peñalver, E.
Poyato, F.J.
Caro, S.
Romero-Molina, M.M.
Using fossil evidence, is it possible to know how
dinosaurs behaved, or to reconstruct the soft tissues
(impossible to fossilize) from delicate insects living
millions of years ago? The solution to this problem is
once again within the rocks and environments where
they formed, preserving the footsteps of those great
saurians, and protecting in a “capsule” of fossil resin
the most subtle tissues of those small insects.
Lower Cretaceous rocks in Spain are scattered along
the eastern border of the Iberian Massif. Their main
exposures are found in the eastern area of the BasqueCantabrian Basin, the Pyrenees, and the Iberian and
Betic Mountain Ranges. They correspond to sedimentary environments: shallow marine (platform),
transition (estuary, lagoon, marshes and beaches) and
continental (fluvial, lacustrine and palustrine).
The sedimentary cycle comprising Lower Cretaceous
continental formations began in the Late Jurassic as
a consequence of general sea regression 140 to 100
million years ago, causing the predominance of continental conditions throughout the Early Cretaceous.
Within this time interval, two sedimentary continental
units have been here selected for description, containing abundant fossil remains of diverse faunal groups
such as dinosaurs and insects.
There are many deposits with dinosaur footprints
(ichnites) spread throughout all Mesozoic basins.
Due to their extraordinary significance, we herein
propose as geosites those of the Cameros Basin
(La Rioja, Figure 1, number 1). They are included
within different lithostratigraphic units (Tera, Oncala,
Urbión, Enciso and Oliván Groups), corresponding
to the classical Wealdian or Weald, a term used in
Figure 1. Location of:
1) Igea, Enciso, Munilla, Hornillos de Cameros
2) El Caleyu
3) Peñacerrada
4) Sant Just
5) Rubielos de Mora and Las Hoyas
western Europe for carbonate and siliciclastic continental facies with an age spanning 140 to 110 million
years, and comprising from the uppermost Jurassic
(Kimmeridgian) up to the Aptian (Lower Cretaceous).
Dinosaur footprints, as well as some dinosaur, turtle
and crocodile fossil bones, are found in all the aforementioned lithostratigraphic groups, but the most
interesting from the paleoichnological point of view
are those in the Urbión Group, dominated by fluvial
deposits (channel and flood plain facies), and the
Enciso Group, dominated by lacustrine and palustrine
deposits. The selected areas include almost any known
type of biped dinosaur ichnites present in the rest of
the world.
An ichnofossil is what is left from the activity of an
organism, and ichnofossils are thus vitally important
in order to discover the behavior of extinct animals.
Ichnites show the imprint on the floor of some soft
parts which usually do not fossilize with the bones,
as well as the working, or possible movements, of the
joints which make walking possible.
Usually, the foot tracks are recorded on the upper
surface of a deposit which is being formed, or they
may go through it penetrating up to more than one
meter underneath. At the same time, some protruded
edges appear due to mud extrusion. The study of
dinosaur fossil foot tracks is extremely interesting as
it enables the determination of ichnotaxons, the indirect analysis of the dynamic functions of their limbs
anatomy, the determination of their behavior, the
proportions of the dinosaur types, as well as knowledge about the environment where they lived.
Amongst the several known dinosaur foot tracks
deposits, four of them, located in La Rioja (Igea, Enciso,
Munilla and Hornillo de Campos), have been selected
for description. They all correspond to the same time
interval, the Aptian (Early Cretaceous).
The set of deposits of Igea (Cameros Basin, Iberian
Mountain Range) is of Aptian age and contains
around four thousand studied footprints, which
makes it the biggest in Europe and the third of its
kind in the world. It is possible to recognize tracks
of Theropods, Ornithopods and Sauropods, in
herds and groups with gregarious behavior. In addition, new ichnotaxons have been found (Figure 2)
which show the mark of the interfinger membrane
(Hadrasaurichnoides igeensis).
The set of deposits of Enciso (Figure 3; Cameros
Basin, Iberian Mountain Range) is of Aptian age and
comprises more than a thousand footprints including
Theropod, Ornithopod and Sauropod tracks (sequence
of footprints left by a dinosaur while moving on the
ground).
The set of deposits of Munilla (Figure 4; Cameros
Basin, Iberian Mountain Range) shows abundant tracks
similar to the previous ones, and displays signals of tail
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Pérez Lorente, F., Peñalver, E., Poyato, F.J., Caro, S. and Romero-Molina, M.M.
dragging by an Ornitopod dinosaur which has been
used to infer the sauriform walking of this animal.
Finally, the set of deposits of Hornillos de Cameros,
Cameros Basin (Iberian Mountain Range) is also of
Aptian age and presents the same ichnotaxons as in
Figure 2, above. Hadrasaurichnoides igeensis.
Dinosaur ichnites at El Peladillo (Igea, La Rioja).
Photo: Fundación Patrimonio Paleontológico
de La Rioja.
the previously described deposits. Mud extrusion structures at El Contadero (Figure 5) helped to investigate
foot movement during the successive stepping stages.
Furthermore, the exposure near Valdemayor, includes
the only track of a quadruped walking Ornitopod of
La Rioja.
Figure 5, above. Dinosaur ichnites at El Contadero
(Hornillo de Cameros, La Rioja).
Figure 6, below. Dinosaur ichnites at La Canal
(Munilla, La Rioja).
Figure 3, below. Dinosaur ichnites at La Virgen del
Campo (Enciso, La Rioja). Photo: Fundación Patrimonio
Paleontológico de La Rioja.
CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS
101
Amber deposits with fossil insects are mainly found
in the regions of Asturias, Basque Country, Castilla
and León, and Aragón. All of them are included within
Albian (Lower Cretaceous) siliciclastic sediments and
have been dated between 110 and 100 million years.
Sediments hosting the amber are related to different
transitional sedimentary environments (bays, marshes,
deltas). The resin with insects inside, coming from
inland forested mountain areas, would have reached
the coast dragged by river currents.
The resin, produced by several kinds of conifer and
legume plants, easily traps plant remains, insects and
other arthropods. This phenomenon occurred in the
past similarly to what happens today. The resin holding
insects was buried millions of years ago and, through
a process of maturing and polymerization, became a
gem-like material called amber. The resin isolated the
organisms trapped within, desiccated them and inhibited their oxidation. The final result is the preservation
of the remains in great detail, including the occasional
preservation of soft tissue such as muscles or wings,
a circumstance which enables very accurate cytology
and anatomy studies. Amber is very rare in nature,
and Cretaceous amber deposits with fossil insects are
extraordinarily scarce in the world.
The deposit of El Caleyu, near Oviedo (Asturias,
Figure 1, number 2), is located in the lower part of
the Ullaga Formation (Asturian Central Depression)
within silty lagoonal facies deposits influenced
by river contributions, and with a late Albian age
(Arbizu et al., 1999).
Amber masses recently collected in El Caleyu reach 20
cm length, and they include within them several specimens of hymenoptera of the family Scelionidae, several
specimens of dipters (Figure 6) of the Chironomidae
and Hybotidae families (including the genus Alavesia),
a larva to be classified (Figure 7), some unidentifiable
insects, and a spider specimen (Arbizu et al., 1999).
Near El Caleyu there are two more amber deposits
which so far have not provided any insects.
The amber deposits from Peñacerrada I (Moraza,
Condado de Treviño, Burgos; Figure 8) and
Peñacerrada II (Peñacerrada, Álava) are both included
in the Nograro Formation (Basque-Cantabrian Basin,
Figure 1, number 3). This unit is formed by organicand sulphur-rich sandstones and shales deposited on
a deltaic plain during the middle-upper Albian, and
where small paralic basins with coal levels developed.
It is possible that the amber-bearing deposits represent overflowing or channel avulsion events, with subsequent deposition of the resin masses within clastic
sediments, or they might also correspond to marginal
bay deposits.
As a whole, Peñacerrada I and II have provided a
high number of biological inclusions (around 2000)
in little time, mainly corresponding to arthropods,
where mainly Diptera and Himenoptera Hexapoda
stand out. Other arthropods present in these deposits are Crustacea and Chelicerata. Among the first
group, specimens have appeared attributable to the
Malacostraca, specifically individuals of Amphipoda
Figure 6. Insect-bearing amber deposit of El Caleyu (Asturias). Fly specimen of the fossil genus Alavesia (family
Hybotidae) dorsal view.
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Pérez Lorente, F., Peñalver, E., Poyato, F.J., Caro, S. and Romero-Molina, M.M.
and Isopoda (Oniscoidea). Among the Chelicerata, it
has been possible to recognize mites from the order
Actinotrichida, having found several Actinedida
and one Oribatida. There is also a small number of
Araneida, some of them representing new families. It
is not unusual to find organic matter accumulations
which may well correspond to arthropods faeces or
possible egg-lays.
Due to the abundant fossil record of insects and other
arthropods held in amber, and their splendid preservation state, the deposit of Peñacerrada II is a type locality for several fossil insect species. As an example of its
rich record, it suffices to observe in detail the wings of
a specimen of parasite wasp of the family Scelionodae
(Figure 11).
Figure 7, above. Insect-bearing amber deposit of El
Caleyu (Asturias). Specimen of undetermined larva.
Figure 8, next below. Insect-bearing amber deposit
of Peñacerrada I, near Moraza (Condado de Treviño,
Burgos).
Figure 9, left. Hymenoptera specimen of the family
Scelionidae in the amber deposit of Peñacerrada I,
near Moraza (Condado de Treviño, Burgos).
Figure 10, below. Example of female hymenoptera
from the family Scelionidae in the deposit of
Peñacerrada II (Peñacerrada, Álava).
CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS
103
Figure 11. Detail of the exceptional preservation of
the wings of a parasite wasp.
Figure 12. Broken sample of amber with insects as
extracted from the deposit in Arroyo de la Pascueta
(Rubielos de Mora, Teruel).
The deposit of Arroyo de la Pascueta (Rubielos
de Mora, Teruel) is within the Escucha Formation,
of Lower and Middle Albian age, in the Maestrazgo
Basin (Figure 1, number 3). The amber (Figure 12) has
been found in grey shales (coaly and with abundant
plant remains) belonging to a sequence of sands interbedded within the grey clays of the lower third of the
Escucha Formation.
Specimens of the order Diptera, Homoptera and
Hymenoptera have been found in Arroyo de la
Pascueta. Among the magnificently preserved
specimens of Hymenoptera, a specimen of a strange
and extinct family, the Cretevaniidae, stands out.
Specifically, it is the only known genus of that family,
Cretevania, of which very few specimens are known
in the world. This specimen was recently found near
Escucha (Teruel, Figure 1, number 4) in the Escucha
Formation (Figure 13) and in the same facies as those
described for Arroyo de la Pascueta. Moreover, the
identical features of the amber (Figure 14) and the
same fossil insect contents (including the odd genus
Cretevania) allow to correlate both deposits.
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The Cretaceous is a key period in the evolution of
insects, and their study can shed some light on
the evolution of such an important animal group.
Furthermore, the Spanish deposits are assigned a
rather early age within the Cretaceous (Aptian-Albian;
Lower Cretaceous). On the other hand, it was during this period when important groups of insects
appeared. The ants, for example, whose origin is very
controversial and is one of the most interesting aspects
in paleoentomology. Most of the Spanish Cretaceous
amber originated in Araucariaceae forests developed
near the coast and which, during the Albian, would
have fringed the current Iberian Peninsula.
Finally, an extraordinary deposit has to be mentioned:
Las Hoyas (La Cierva, Cuenca, Figure 1, number 5),
in lacustrine carbonate sediments (Figures 15 and
16) of Upper Barremian age (middle part of the
Early Cretaceous). The exceptional character of this
deposit lies on the fact that it has provided more
than 14000 fossil specimens, in an excellent preservation state, belonging to very diverse species of
flora and fauna.
Pérez Lorente, F., Peñalver, E., Poyato, F.J., Caro, S. and Romero-Molina, M.M.
Figure 13, above left. Sant Just deposit (Teruel): levels of the Escucha Fm containing amber with insects.
Figure 14, below left. Examples of amber masses from San Just (Teruel), with insects and other arthropods.
Figure 15, above right. Iberonepa romerali Martínez-Delclós, Nel et Popov. Barremian of Las Hoyas (Cuenca).
Figure 16, below right. Austropotamobius Ilopisi (Vía). Barremian of Las Hoyas (Cuenca).
Due to the abundance, quality and interest of the
fossils from this deposit, it sets a unique example of
Lower Cretaceous lacustrine “Konservat-Lagerstätte”
(a deposit with a great variety of exceptionally preserved fossils), enabling the reconstruction of a
unique paleosystem of this kind. The collected fossils are providing very important information on the
paleoecology, time and space distribution, phylogeny
and taxonomy of plants, insects, crustaceans, fish,
amphibians, reptiles, crocodiles, dinosaurs and primitive birds. Furthermore, in the proximity of Las Hoyas,
it is possible to admire spectacular karstic formations
such as the sinkholes of Los Palancares, and the
Ciudad Encantada (Enchanted City).
CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS
105
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