For more than a century, paleontologists studying the Late Jurassic seas that once covered southern Germany believed only one species of ichthyosaur, Aegirosaurus leptospondylus, had left its remains in the region’s famous Plattenkalk limestone deposits, the same fine-grained rock that produced the iconic fossil bird Archaeopteryx. Now, Dr. Erin Maxwell from the Staatliches Museum für Naturkunde Stuttgart and colleagues have identified a second species from the deposits: Jabalisaurus tethyensis, an ophthalmosaurian ichthyosaur based on specimens that had sat in museum collections for decades, misidentified as belonging to Aegirosaurus.
An artistic reconstruction of Jabalisaurus tethyensis, depicted in the water column close to the surface while pursuing halecomorph fishes. Image credit: Giovanni Serafini.
Jabalisaurus tethyensis swam in the warm waters of the Tethys Ocean during the Late Jurassic epoch, some 150 million years ago.
The species was a mid-sized ophthalmosaurian ichthyosaur estimated at 2-2.9 m (6.6-9.5 feet) long.
It had a slender, high-crowned skull, finely ridged teeth, and likely fed on small, bony fish.
Its skin appears to have been smooth, consistent with what has been found in other ichthyosaurs of similar lineage.
“Ichthyosaurs are Mesozoic marine reptiles that first appeared in the fossil record in the Early Triassic and persisted until the early Late Cretaceous,” Dr. Maxwell and co-authors wrote in their paper.
“The high point of ichthyopterygian diversity and disparity is widely understood to have been attained during the first 8.7 million years of the group’s evolution, attributed to high rates of morphological evolution early in the history of the clade during their initial radiation into diverse marine habitats and dietary niches.”
“By the Jurassic, and especially by the end of the Aalenian (early Middle Jurassic), ichthyosaurs occupied a reduced range of ecomorphotypes, and historically were viewed as being correspondingly reduced in taxonomic diversity.”
The paleontologists described Jabalisaurus tethyensis primarily from a small, immature skeleton held at the Bavarian State Collection for Palaeontology and Geology in Munich, first collected from the Geisberg quarry near Apfelthal, Bavaria.
They also assigned to the species two additional specimens: one from the Staatliches Museum für Naturkunde Stuttgart and another, remarkably well-preserved individual from the Jura-Museum Eichstätt that still retains its full soft-tissue outline.
Jabalisaurus tethyensis, holotype specimen. Image credit: Maxwell et al., doi: 10.26879/1676.
The discovery of Jabalisaurus tethyensis is notable not just because it doubles the known ichthyosaur diversity from the German plattenkalk deposits, but because of where else this genus has turned up: Mexico.
Until now, Jabalisaurus was known only from the Gulf of Mexico area, roughly 9,000 km away.
Its unexpected presence in Bavaria suggests these marine reptiles roamed a broad swath of the ancient Tethys Ocean and the connected proto-Caribbean, rather than evolving in isolation on separate coastlines as some scientists had proposed.
“Despite the apparent high Late Jurassic marine habitat connectivity, the Late Jurassic ichthyosaurian fauna from the proto-Gulf of Mexico has been interpreted as being highly endemic,” the researchers wrote in the paper.
“With the description of Jabalisaurus tethyensis, two closely related species-pairs have now been recovered from the German Plattenkalk deposits and the Gulf of Mexico region, namely Jabalisaurus meztli and Jabalisaurus tethyensis, and Parrassaurus yacahuitztli and Aegirosaurus leptospondylus.”
“These findings challenge the hypothesis of strong endemicity in the proto-Caribbean, and suggest instead a similar warm-temperate to tropical ichthyosaurian fauna across the northwestern Tethys and proto-Caribbean, possibly showing regional species-level divergence.”
“The occurrence of the genus Jabalisaurus in the northwestern Tethys weakens the interpretation of the proto-Caribbean region as a hotspot of ichthyosaur endemism during the Late Jurassic, suggesting instead that a tropical Tethyan ichthyosaurian fauna was broadly distributed globally, distinct from the more temperate to polar faunas described from the UK, Svalbard, and Eastern Europe and Argentina.”
The team’s paper was published online in the journal Palaeontologia Electronica.
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Erin E. Maxwell et al. Late Jurassic ichthyosaurs from Germany. Palaeontologia Electronica 29 (2): a30; doi: 10.26879/1676
