SEXUAL DIMORPHISM: PLIENSBACHIAN APODEROCERAS

Apodoceras / Stonebarrow Fossils

Apoderoceras is a wonderful example of sexual dimorphism within ammonites as the macroconch (female) shell grew to diameters in excess of 40 cm – many times larger than the diameters of the microconch (male) shell.

Apoderoceras has been found in the Lower Jurassic of Argentina, Hungary, Italy, Portugal, and most of North-West and central Europe, including as this one is, the United Kingdom. This specimen was found on the beaches of Charmouth in West Dorset.

Neither Apoderoceras nor Bifericeras donovani are strictly index fossils for the Taylori subzone, the index being Phricodoceras taylori. Note that Bifericeras is typical of the earlier Oxynotum Zone, and ‘Bifericeras’ donovani is doubtfully attributable to the genus. The International Commission on Stratigraphy (ICS) has assigned the First Appearance Datum of genus Apoderoceras and of Bifericeras donovani the defining biological marker for the start of the Pliensbachian Stage of the Jurassic, 190.8 ± 1.0 million years ago.

Apoderoceras, Family Coeloceratidae, appears out of nowhere in the basal Pliensbachian and dominates the ammonite faunas of NW Europe. It is superficially similar to the earlier Eteoderoceras, Family Eoderoceratidae, of the Raricostatum Zone, but on close inspection can be seen to be quite different. It is therefore an ‘invader’ and its ancestry is cryptic.

The Pacific ammonite Andicoeloceras, known from Chile, appears quite closely related and may be ancestral, but the time correlation of Pacific and NW European ammonite faunas is challenging. Even if Andicoeloceras is ancestral to Apoderoceras, no other preceding ammonites attributable to Coeloceratidae are known. We may yet find clues in the Lias of Canada. Apoderoceras remains present in NW Europe throughout the Taylori Subzone, showing endemic evolution. It becomes progressively more inflated during this interval of time, the adult ribs more distant, and there is evidence that the diameter of the macroconch evolved to become larger. At the end of the Taylori Subzone, Apoderoceras disappeared as suddenly as it appeared in the region, and ammonite faunas of the remaining Jamesoni Zone are dominated by the Platypleuroceras–Uptonia lineage, generally assigned (though erroneously) to the Family Polymorphitidae.

In the NW European Taylori Subzone, Apoderoceras is accompanied (as well as by the Eoderoceratid, B. donovani, which is only documented from the Yorkshire coast, although there are known examples from Northern Ireland) by the oxycones Radstockiceras (quite common) and Oxynoticeras (very rare), the late Schlotheimid, Phricoderoceras (uncommon) Note: P. taylori is a microconch, and P. lamellosum, the macroconch), and the Eoderoceratid, Tetraspidoceras (very rare). The lovely large specimen (macroconch) of Apoderoceras pictured here is likely a female. Her larger body perfected for egg production.

DEINOTHERIUM: PREHISTORIC ELEPHANTS

This partial specimen of Deinotherium giganteum hails from Cerecinos de Campos, Zamora from the Middle-Upper miocene, c. 15.97-5.33 Million Years.

The genus Deinotherium could reach a height of over 3.5 meters. Its structure and size are similar to those of the present-day elephant. Deinotherium first appeared approximately 17 million years ago and became extinct relatively recently, just 1.6 million years ago.

One of the distinguishing features of Deinotherium is their curved tusks inserted only in the jaw. One of the tusks from this fellow, on display at the Museo Nacional De Ciencias Naturales in Madrid, Spain, while incomplete, was preserved rather nicely and shows the detail of where the tusk meets the jaw.

GIANT GROUND SLOTH

In 1788, this magnificent specimen of a Megatherium sloth was sent to the Royal Cabinet of Natural History from the Viceroyalty of Rio de la Plata.

The megatheria were large terrestrial sloths belonging to the group, Xenarthra. These herbivores inhabited large areas of land on the American continent. Their powerful skeleton enabled them to stand on their hind legs to reach leaves high in the trees, a huge advantage given the calories needed to be consumed each day to maintain their large size.

Avocados were one of the food preferences of our dear Giant ground sloths. They ate then pooped them out, spreading the pits far and wide. The next time you enjoy avocado toast, thank this large beastie. One of his ancestors may have had a hand (or butt) in your meal.

In 1788, Bru assembled the skeleton as you see it here. It is exhibited at the Museo Nacional De Ciencias Naturales in Madrid, Spain, in its original configuration for historic value. If you look closely, you'll see it is not anatomically correct. But all good paleontology is teamwork. Based upon the drawings of Juan Bautista Bru, George Cuvier used this specimen to describe the species for the very first time.

WESTERN EUROPEAN HEDGEHOG

This little cutie is a Western European hedgehog, Erinaceus europaus, in the subfamily Erinaceinae (Fischer, 1814). They are native to western Europe, Asia, Africa and have been introduced (oops!) to New Zealand.

There are seventeen species of hedgehog in five genera. They share a distant ancestry with the family Soricidae (shrews) and the gymnures.

Hedgehogs are considered "Living Fossils" as they have changed very little over the past 15 million years. These small mammals are loners with their own kind, but live in close proximity to our human population. They dwell in inhabited areas, farmland, deciduous forests and desert. You'll know them by their distinctive spiny look (which may remind you of a very tasty chocolate from Purdy's in Canada) and their adorable piglike snorts and grunts as they make their way through the underbrush looking for tasty snacks.

Look for them in the evening in hedgerows and undergrowth as they hunt for frogs, toads, snails, bird eggs, grass roots, berries, insects, worms and snakes. They fatten themselves up in preparation for hibernation. They'll find a nice burrow or built a nest in leaves or compost heaps. In Europe, they generally hibernate by October or November and become active again in March to mid-April once temperatures reach over 15 degrees.