F Rosa Rubicondior: Creationism in Crisis - How An Early Jawless Fish Was Feeding - About 400 Million Years Before 'Creation Week'

Friday 12 April 2024

Creationism in Crisis - How An Early Jawless Fish Was Feeding - About 400 Million Years Before 'Creation Week'

Fossil of Rhinopteraspis dunensis

Museum für Naturkunde, Berlin, Germany
3D mouth of an ancient jawless fish suggests they were filter-feeders, not scavengers or hunters - University of Birmingham

Today's incidental refutation of creationism comes to us from an international team of palaeontologists led by scientists from the University of Birmingham. They have shown how an early jawless fish was feeding, almost 400 million years before creationism's little pet god decided to create a small flat planet with a dome over it in the Middle East, in what creationists refer to as 'Creation Week'.

The researchers have used CT scanning techniques to construct a 3D image of the mouth-parts of Rhinopteraspis dunensis, an early, heavily-armoured boney fish that lived some 380 million years ago.

What information do you have on the Devonian jawless fish, Rhinopteraspis dunensis? Rhinopteraspis dunensis is a species of extinct jawless fish that lived during the Devonian period, approximately 380 million years ago. It belongs to the class Anaspida, which are primitive jawless fish characterized by their small size and unique body armor made of bony plates. Rhinopteraspis dunensis is particularly notable for its distinctive head shield, which is ornamented with distinctive ridges and tubercles.

These ancient fish are important for understanding the early evolution of vertebrates and the development of various anatomical features seen in modern vertebrates. They provide insights into the origins of jawed vertebrates and the diversity of early aquatic ecosystems.

Research on Rhinopteraspis dunensis and other members of the Anaspida group continues to contribute to our understanding of vertebrate evolution and the history of life on Earth during the Devonian period.
This reconstruction suggests they used the boney plates surrounding their mouth to filter food from their environment. Lacking jaws, they were unable to bite, so the question the team set out to answer was, how did they feed? This paper sheds light on that question and helps close another gap in the record of the early evolution of vertebrates.

The research team have explained the significance of their findings in a Birmingham University news release and published them in the Royal Society journal Proceedings of the Royal Society B:
3D mouth of an ancient jawless fish suggests they were filter-feeders, not scavengers or hunters

Early jawless fish were likely to have used bony projections surrounding their mouths to modify the mouth’s shape while they collected food.

Experts led by the University of Birmingham have used CT scanning techniques to build up the first 3D pictures of these creatures, which are some of the earliest vertebrates (animals with backbones) in which the mouth is fossilised. Their aim was to answer questions about feeding in early vertebrates without jaws in the early Devonian epoch – sometimes called the Age of Fishes – around 400 million years ago.

Feeding behaviours are commonly used by scientists to help piece together early evolution of vertebrates, and different jaw shapes and constructions can suggest a broad range of feeding strategies. In the absence of jaws, many competing theories have been developed ranging from biting and slicing, to filtering food from sediment or water.

In a new study, published in Proceedings of the Royal Society B, an international team of palaeontologists have been able to visualise the mouth parts of one of these jawless fish, called Rhinopteraspis dunensis, in detail. The images revealed the structure and arrangement of finger-like bones that project from the lower ‘lip’ of the animal’s mouth, which the scientists believe acted to control the mouth’s size and shape as it captured food particles from surrounding water.

The application of CT scanning techniques to the study of fossil fish is revealing so much new information about these ancient vertebrates and giving us the opportunity to study precious and unique specimens without destructive investigation.

Dr Ivan Sansom, senior author.
School of Geography, Earth & Environmental Sciences
University of Birmingham, Edgbaston, Birmingham, UK.

In this case, these methods have allowed us to fit all of the small bones of this animal’s mouth together, and try and understand how it fed from this integrated system rather than by using isolated bones. Instead of a steady trend towards ‘active food acquisition’ - scavenging or hunting – we see a real diversity and range of feeding behaviours among our earliest vertebrate relatives.

Dr Richard Dearden, lead author.
School of Geography, Earth & Environmental Sciences
University of Birmingham, Edgbaston, Birmingham, UK.
The reconstruction produced by the team shows that the bony plates around the mouth would have had limited movement, making it unlikely that the animals were hunters capable of ‘biting’. In combination with an elongated snout, they would also have found it difficult to scoop and filter sediment directly from the bottom of the sea. However these plates would have allowed it to control opening of the mouth, and perhaps strain food from water in a way also used by animals such as flamingos or oysters.

The findings offer a new perspective on theories of vertebrate evolution, since current hypotheses argue that long term evolutionary trends move from passive food consumption to increasingly predatory behaviour. In contrast, the work outlined in this paper suggests that in fact, early vertebrates had a broad range of different feeding behaviours long before jawed animals started to appear.

Technical details and background are given in the team's open access paper in Proceedings of the Royal Society B:

Attempts to explain the origin and diversification of vertebrates have commonly invoked the evolution of feeding ecology, contrasting the passive suspension feeding of invertebrate chordates and larval lampreys with active predation in living jawed vertebrates. Of the extinct jawless vertebrates that phylogenetically intercalate these living groups, the feeding apparatus is well-preserved only in the early diverging stem-gnathostome heterostracans. However, its anatomy remains poorly understood. Here, we use X-ray microtomography to characterize the feeding apparatus of the pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855). The apparatus is composed of 13 plates arranged approximately bilaterally, most of which articulate from the postoral plate. Our reconstruction shows that the oral plates were capable of rotating around the transverse axis, but likely with limited movement. It also suggests the nasohypophyseal organs opened internally, into the pharynx. The functional morphology of the apparatus in Rhinopteraspis precludes all proposed interpretations of feeding except for suspension/deposit feeding and we interpret the apparatus as having served primarily to moderate the oral gape. This is consistent with evidence that at least some early jawless gnathostomes were suspension feeders and runs contrary to macroecological scenarios that envisage early vertebrate evolution as characterized by a directional trend towards increasingly active food acquisition.

1. Introduction

Feeding figures prominently in attempts to understand the evolutionary origins of vertebrates [1,2]. In contrast to invertebrate chordates, which exclusively suspension feed with either a ciliated pharynx or a mucus net [3], the dorso-ventrally closing jaws of living jawed vertebrates (crown-gnathostomes) and ‘placoderms’ [46] or anteroposteriorly moving system of cartilages in cyclostomes (hagfishes and lampreys) [710] allow for a far broader range of feeding strategies. The evolution of these unique vertebrate feeding modes plays a major role in attempts to explain the evolution of vertebrate anatomy and the origins of its modern diversity [11,12]. Prominently, the New Head Hypothesis [1317] argues that the shift from suspension feeding to predation accompanied the emergence of neural crest, neurogenic placodes and the accompanying evolution of a prechordal head. The fossil record of the earliest vertebrates with a prechordal head (i.e. parts formed from trabecular elements of the neurocranium anterior to the notochord [18]) provides a test of this scenario [19], but the required data are currently lacking.

In particular, heterostracans, an extinct group of jawless stem-gnathostomes, have been a focus of the debate over feeding in early vertebrates. This is because their oral region is more commonly and completely preserved than in any other such group, and they are often interpreted as one of the earliest diverging lineages of stem-gnathostomes [1,2023]. As such, heterostracans have the potential to inform on the feeding ecology of the earliest members of the gnathostome lineage [24]. The heterostracan feeding apparatus is best known in pteraspids, where the oral region is characterized by distinctive macromeric dermal plates [2529]. The function of these plates has been much debated, variously interpreted as biting [26] or slicing [30] ‘jaws’, a cyclostome-like feeding apparatus [3134], a sediment scoop [29] or a filtering structure [3539]. Equally varied are the inferred ecologies, with heterostracans interpreted as active predators [26], macrophagous selective predators [14,40], hagfish-like scavengers [3134], herbivores [30], detritivores [29,41] or suspension feeders (including filter feeding) [12,27,4245]. The most recent investigation suggests that heterostracans were suspension feeders because the analysed oral plates exhibited no evidence of the wear anticipated of a ‘tooth-like’ function [27].

The difficulty in studying the articulated heterostracan oral apparatus in situ contributes to this lack of consensus. In the rare cases where they are preserved, articulated heterostracan oral apparatuses consist of small plates suspended in encasing sediment. As a result, previous reconstructions of the oral apparatus have focused either on the gross arrangement of the apparatus, in which the morphology and detailed arrangement of the individual plates are not characterized [29,31,33,34], or describe isolated elements with little or no reference to articulated apparatuses [29,46,47]. Evidently, the feeding ecology of heterostracans remains in its infancy and so we sought to advance understanding through a detailed characterization and reconstruction of the heterostracan oral apparatus. We used X-ray microtomography to characterize the three-dimensionally articulated oral apparatus of an exceptionally well-preserved specimen of the pteraspid heterostracan Rhinopteraspis dunensis (Roemer, 1855). Using computed tomography, we generated volumetric models of the components of the oral apparatus and used these models to reconstruct their three-dimensional arrangement in vivo. We use this reconstruction to assess competing hypotheses of heterostracan feeding.
Figure 1. Rhinopteraspis dunensis NHMUK PV P 73217. (a–c) Rendering of head shield based on computed tomographic data in (a) sinistral, (b) dextral view and (c) transparent with scheme of anatomical axes. (d–h) Renders based on higher resolution data showing the oral apparatus in more detail in (d), ventral view, (e) sinistral view, (f) dextral view, (g) rostral view, (h) rostro-ventral view. Green and blue parts of three-dimensional renders represent oral region. Abbreviations: S, sinistral (left), D, dextral (right). Scale bars represent 5 cm in panels (a,b), 1 cm in (d–h).

Figure 2. Rhinopteraspis dunensis NHMUK PV P 73217 oral region. (a) Oral apparatus and surrounding plates as preserved, in ventral view, (b) ventral view of supraoral plate with three fragments rearticulated, (c) postoral plate in dorsal view, (d) oral apparatus as preserved with ventral plates removed, (e) dorsal view of oral plates as preserved, (f–i) oral plate R4 in aboral, (f) lateral, (g) adoral (h) and medial (i) views, alongside drawings depicting the inferred extent of dermal ornament in grey, based on comparison with isolated plates of Loricopteraspis dairydinglensis [25,45,59]. S, sinistral (left), D, dextral (right). Scale bars represent 1 cm in (a–e), 0.5 cm in (f–i).

Figure 3. Reconstruction of Rhinopteraspis dunensis based on NHMUK PV P 73217; anterior section of rostrum not shown. (a) Rostrolateral view, (b) ventral view, (c) rostral view, (d) caudal view of articulated oral plates, (e) sagittal cross-section through centre of the head, (f) close up cross-section lateral to (e) showing junction between base of oral plate and the postoral plate.

Figure 4. Reconstruction of Rhinopteraspis dunensis based on NHMUK PV P 73217 in lateral view with oral plates animated to open to 30°. (a,b) Lateral view at estimated resting position (a) and rotated aborally to 30° relative to resting (b). (c,d) Lateral view bisected, at estimated resting position (c) and rotated aborally to 30° relative to resting (d). Orange line is a hypothetical adductor muscle illustrating that the angle of this places a constraint on angle of rotation.
As well as closing another gap into which creationists try to shoe-horn their little god, this Devonian early fish from 380-400 million years ago utterly refutes the childish creationist superstition that the Universe consists of the small flat planet with a dome over it, created just 10,000 years ago.

Like almost all of the evolutionary history of life on Earth, this all took place in that vast pre-'Creation Week' history and involved a time scale and the early ancestors of modern organisms of which the Bible's authors had not the slightest inkling. Their world consisted of a small part of the Middle East and they knew nothing of anywhere else or of earlier times in the history of their planet, as can be seen from their ignorant and child-like description of reality and the tales they made up to satisfy their need for narrative to fill the gaps in their knowledge and understanding, just as children do nowadays.

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