CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS

C H A P T E R 8

Pérez Lorente, F.

Peñalver, E.

Poyato, F.J.

Caro, S.

Romero-Molina, M.M.

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. and Romero-Molina, M.M.100

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 Basque-Cantabrian Basin, the Pyrenees, and the Iberian and Betic Mountain Ranges. They correspond to sedi-mentary 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 con-tinental conditions throughout the Early Cretaceous. Within this time interval, two sedimentary continental units have been here selected for description, contain-ing 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

western Europe for carbonate and siliciclastic conti-nental 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 afore-mentioned 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 indi-rect analysis of the dynamic functions of their limbs anatomy, the determination of their behavior, the proportions of the dinosaur types, as well as knowl-edge 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 addi-tion, 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

Figure 1. Location of:

1) Igea, Enciso, Munilla, Hornillos de Cameros2) El Caleyu3) Peñacerrada4) Sant Just5) Rubielos de Mora and Las Hoyas

101CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS

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

the previously described deposits. Mud extrusion struc-tures 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 2, above. Hadrasaurichnoides igeensis. Dinosaur ichnites at El Peladillo (Igea, La Rioja). Photo: Fundación Patrimonio Paleontológico de La Rioja.

Figure 3, below. Dinosaur ichnites at La Virgen del Campo (Enciso, La Rioja). Photo: Fundación Patrimonio Paleontológico de 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).

Pérez Lorente, F., Peñalver, E., Poyato, F.J., Caro, S. and Romero-Molina, M.M.

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 inhib-ited 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 speci-mens 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 organic- and 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 repre-sent overflowing or channel avulsion events, with sub-sequent 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 depos-its are Crustacea and Chelicerata. Among the first group, specimens have appeared attributable to the Malacostraca, specifically individuals of Amphipoda

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Figure 6. Insect-bearing amber deposit of El Caleyu (Asturias). Fly specimen of the fossil genus Alavesia (family Hybotidae) dorsal view.

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 preserva-tion state, the deposit of Peñacerrada II is a type local-ity 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).

CRETACEOUS CONTINENTAL FOSSILS AND ICHNOFOSSILS 103

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).

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 inter-bedded 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.

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 dur-ing 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 pres-ervation 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.104

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).

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 pre-served fossils), enabling the reconstruction of a unique paleosystem of this kind. The collected fos-sils 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 primi-tive 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

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).

Pérez Lorente, F., Peñalver, E., Poyato, F.J., Caro, S. and Romero-Molina, M.M.106

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