Ichthyosaurs are an extinct group of Mesozoic marine reptiles that have been known since the early 19th century. They are one of the group of marine reptiles that appeared abruptly in the Early Triassic period and thus contradict Darwinian expectations (Bechly 2022, 2023a, 2023b, Luskin 2023). This Fossil Friday features the remarkably well-preserved fossil of a “birthing“ ichthyosaur. The fossil belongs to the species Stenopterygius quadricissus from the Lower Jurassic (Liassic) Posidonia shale of Holzmaden in Germany, which is about 180 million years old. The photo shows a replica at the Natural History Museum in London, while the original fossil is deposited at the State Museum of Natural History in Stuttgart, where I worked for 16 years as a scientific curator in the Paleontology Department.
The first report of ichthyosaur embryos is often credited to Chaning Pearce (1846), but indeed was made long before by German paleontologist Georg Friedrich von Jäger. The latter described a specimen with a juvenile in its rib cage, which had already been discovered in 1749 (Jäger 1824), and later interpreted this small specimen as an embryo at a conference in 1842 (Jäger 1852, Böttcher 1990). Over 200 years of paleontological research, more than a hundred specimens with embryos or new born babies have been found (Woodward 1906, Fraas 1911, Swinton 1930, Böttcher 1990, Deeming et al. 1993, Maxwell & Caldwell 2003, Lomax & Massare 2012, Lomax & Sachs 2017, Boyd & Lomax 2018, Stöhr & Werneburg 2023; also see Wikipedia Timeline of ichthyosaur research), including Triassic ichthyosaurs (e.g., Brinkmann 1996, Dal Sasso & Pinna 1996, Motani et al. 2014, LePage & Hecht 2015, Miedema et al. 2023).
The Stuttgart museum holds more than 46 specimens of supposed ichthyosaur mothers with embryos, in different stages of the pregnancy and birthing process (Böttcher 1990). These include specimens with up to ten embryos in the belly, partial births, and specimens with newborn babies outside the body that were likely cases of postmortem fetal extrusion due to carcass implosion (Loon 2013). Most of these specimens suggest that the young were born tail-first, which was generally believed to be an adaptation to fully marine life, where live birth (vivipary) tail-first would have prevented drowning of the babies during the birth process, contrary to a usual head-first birth in terrestrial animals (Miedema et al. 2023). Newborn babies of the most abundant fossil Stenopterygius quadricissus had a length of about 50 cm (Fraas 1911).
Stomach Content or Babies?
An alternative interpretation of the specimens with embryos inside the belly as cannibalistic predation of ichthyosaurs on juvenile specimens was discussed for a long time (Branca 1908a, 1908b, Sehrwald 1913, Ottow 1950), but has been ultimately rejected based on the narrow esophagus and stomach, which were not suited for prey of this size (Böttcher 1990). Also the complete state of preservation of the young contradicts an interpretation as stomach content (Swinton 1930, Maxwell & Caldwell 2003). In 2018 a specimen of a mother ichthyosaur with remains of six to eight embryos was described from the Early Jurassic of Yorkshire (Boyd & Lomax 2018 and University of Manchester 2018), and interpreted as further evidence that the young are indeed embryos and not stomach content, since it seems “highly unlikely that an ichthyosaur would swallow six to eight aborted embryos or newborn ichthyosaurs at one time” (also see Trevino 2018 and BBC 2018).
In 2014 a specimen of the primitive ichthyosaur Chaohusaurus was described by Motani et al. (2014) from the Early Triassic of China (about 248 million years old). The specimen was preserved with three babies: one inside the body, one outside the body, and one in head-first partial birth. The authors suggested that this head-first birth represents a primitive state retained from already viviparous terrestrial ancestors of ichthyosaurs (also see Anonymous 2014 and LePage & Hecht 2015). Sounds reasonable, no?
New Study Challenges Old Ideas
According to a longstanding paradigm, aquatic amniotes, including the Mesozoic marine reptile group Ichthyopterygia, give birth tail-first because head-first birth leads to increased asphyxiation risk of the fetus in the aquatic environment. Here, we draw upon published and original evidence to test two hypotheses: (1) Ichthyosaurs inherited viviparity from a terrestrial ancestor. (2) Asphyxiation risk is the main reason aquatic amniotes give birth tail-first. From the fossil evidence, we conclude that head-first birth is more prevalent in Ichthyopterygia than previously recognized and that a preference for tail-first birth likely arose in derived forms. This weakens the support for the terrestrial ancestry of viviparity in Ichthyopterygia. Our survey of extant viviparous amniotes indicates that fetal orientation at birth reflects a broad diversity of factors unrelated to aquatic vs. terrestrial habitat, further undermining the asphyxiation hypothesis. We propose that birth preference is based on parturitional mechanics or carrying efficiency rather than habitat.
In other words, neither the longstanding paradigm of aquatic adaptation of viviparous tail-first birthing, nor the evolutionary speculations of Motani et al. (2014) about an alleged viviparous terrestrial ancestor of ichthyosaurs, stand up to scrutiny when challenged with actual empirical data.
Evolutionary biology again and again proves to be an enterprise in imaginative story-telling rather than hard science. But when intelligent design theorists question the Darwinist paradigm based on empirical data and a rational inference to the best explanation, they are accused of being science deniers. Which science? We ID theorists do not deny any science, but only challenge fancy stories that are driven more by a materialist worldview agenda and actually are contradicted by good science. And we will not let Darwinists get away with a dishonest appeal to the progress of science when they simply rewrite their stories every time conflicting evidence can no longer be denied. This is not how good science is supposed to work but is rather typical for pseudoscience that shields itself against empirical falsification.
- Anonymous 2014. Tod bei der Geburt – Meeressaurier-Weibchen starb mit einem Jungtier im Geburtskanal. Scinexx February 14, 2014. https://www.scinexx.de/news/biowissen/tod-bei-der-geburt/
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- Lomax DR & Sachs S 2017. On the largest Ichthyosaurus: A new specimen of Ichthyosaurus somersetensis containing an embryo. Acta Palaeontologica Polonica 62(3), 575–584. https://www.app.pan.pl/archive/published/app62/app003762017.html
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