VERTEBRATES
According to the molecular clock, a specific method
for dating phylogenetic events, vertebrates (Vertebrata) separated from
arthropods (Arthropoda) 976±97 Ma (2004HedgesSB_ShoeJL). The
latter began to dominate in species diversity with the Cambrian burst of
radiation, which occurred 520 Ma (2010EdgecombeGD). This ratio
in the fauna of the Earth is still preserved.
Approximately 525 Ma, the phylum
Chordates separated from the group of bilaterally symmetrical animals
(1995ChenJY_ZhouGQ). In turn, the evolution of chordate organisms led to the
formation of the first vertebrates at least 500 Ma, from which
the jawed mouths 450-400 Ma descended, becoming the ancestors of
the placoderms or "armored" fish (Placodermi) (1979НаумовНП_КарташевНН).
 |
| Sculptural reconstruction of the placoderm Coccosteus from the order Arthrodires, Middle Devonian, 393.3-382.7 Ma; exposition of the Orlov Paleontological Museum (Moscow); photo by the author. |
The first cartilaginous fish (Chondrichthyes) appeared
430 Ma (2001MärssT_GagnierPY). Bony fish (Osteichthyes)
descended from cartilaginous fish about 423 Ma (2004ZhuM_AhlbergPE). The earliest fossil of a lobe-finned fish (Sarcopterygii)
– Osteichthyes is about 418 million years old (1998YuX).
 |
| Cast of the fossil Holoptychius jarviki (clade Sarcopterygii, order Proleptiformes), late Devonian, 382.7-358.9 Ma; Exposition of the Orlov Paleontological Museum (Moscow); photo by the author. |
 |
| Cast of the living species Latimeria chalumnae (clade Sarcopterygii, order Actinistia); exposition of the Orlov Paleontological Museum (Moscow), photo by the author. |
One of the "offshoots” of the lobe-finned fish
branch is the lungfish (Dipnoi), the fossil record of which falls on the early
(lower) Devonian period, that is, on the interval of 419.2-393.3 Ma (2017KempA_GuinotG; 2023CohenKM_CarN). Lungfish became the immediate
ancestors of land animal species (2001CampbellKSW_BarwickRE). According to
updated data, the separation of lungfish and tetrapods (Tetrapod) occurred
426.5-416.0 Ma (2021ZhaoW_ZhuM). The clade of tetrapods
(Tetrapodomorpha) began to form approximately 409 Ma. The oldest
representative of the stem tetrapods Tungsenia, dates back to the Prague stage
(410.8-407.6 Ma) of the Devonian period (2012LuJ_QiaoT;
2023CohenKM_CarN).
 |
| Model of the osteolepiform rhipidistia Osteolepis (clade Tetrapodomorpha) of the Devonian period; exposition of the Orlov Paleontological Museum (Moscow), photo by the author. |
Previously, the oldest tetrapodomorph was considered
to be the fish Kenichthys, which flourished 395 Ma (2004ZhuM_AhlbergP; 2005MüllerJ_ReiszRR). Perhaps the animal had paired
pectoral and pelvic fins - the precursors of legs. Unfortunately, this is not
known for sure.
The tetrapodomorph sarcopterygian Tinirau clackae was
found in a layer dating to the late Givetian stage, or 387.7-382.7 Ma (2023CohenKM_CarN). The pelvis of this species was articulated caudally
with the femur via the acetabulum. Its shape was elliptical, elongated, with a
height/length ratio of 0.42 (2012SwartzB).
 |
| Complete restoration of Tinirau clackae (from 2012SwartzB: Fig. 2B). |
 |
| Articular fossae and pelvic limbs of some stem tetrapods (from 2012SwartzB: Fig. 5). |
The Megalichthyids clade of sarcopterygian
tetrapodomorph fishes appeared in the middle or late Devonian, i.e. 393.3-358.9 Ma, and existed until the Lower Permian, or 298.9 Ma (2012WitzmannF_SchochRR; 2021ClementAM_LongJ; 2023CohenKM_CarN). In
Megalichthys, half of the pelvis was probably an elongated cartilaginous
element covered with a layer of dense bone with a concave-truncated distal end
(1900WellburnED). This concavity is the acetabulum, was connected with the
bones of the pelvic fin.
 |
| Reconstruction of the appearance of Megalichthyids (from 1900WellburnED:Pl.XIII). |
 |
| Pelvis and pelvic fin of Megalichthyids; Pel. - the pelvis of an animal (from 1900WellburnED:Pl.XVII.E). |
The next stage of the transition from fish to
tetrapods was the formation of the Elpistostegalia clade. The most ancient fish
of the order - Panderichthys is dated to 385.3 Ma (2010NiedźwiedzkiG_AhlbergPE). These animals had two pairs of limbs: front and
back, resembling fins. The skeleton of the back fins contained femur
articulated with the pelvis and not directly connected to the spine. This fish
moved using its front fins and body bends. The acetabulum of Panderichthys was
oriented backwards, which made it impossible to push off with the pelvic fins,
which had an insignificant supporting role (2005BoisvertCA). As is evident from
the reconstruction, the femur of the mentioned animal is flattened, which
predetermines the elliptical shape of the acetabulum. Z. Johanson, P.E. Ahlberg
(2001) analyzed the pelvic bones of an early representative of tetrapodomorph
fishes of the rhizodontid order Gooloogongia loomesi, which lived in the Late
Devonian (382.7-358.9 Ma) and found a well-defined acetabulum.
At the same time, the authors noted the absence of sacral ribs and ischial
bones in this species. The acetabulum of Gooloogongia loomesi faces backwards,
is a large, strongly concave structure associated with the proximal parts of
the ilium and pubic processes. This depression on the pelvic surface lacks a
developed edge, and in the posterior section it smoothly merges with the
posteroventral surface of the ramus of the ilium (2001JohansonZ_AhlbergPE:Fig.
12).
A.H. Foord described in 1880 one of the early
tetrapodomorphs Eusthenopteron foordi (genus Eusthenopteron, family
Tristichopteridae) (1881WhiteavesJF). A review of the pelvis of a specimen of
Eusthenopteron foordi from the Faranian stage of the Upper Devonian
(382.7-372.2 Ma) is known, which had two halves connected into a
single structure, possibly by a cartilaginous element. Each half of the pelvis
is subdivided into the iliac and pubic parts, forming the acetabulum. It faces
caudally and downwards, is shallow, concave, oval-oblong, and must have been
covered with cartilage during life. At the edge of the acetabulum are two large
processes to which muscles were apparently attached (1970 AndrewsSM_WestollTS).
It is possible that the proximal parts of the pubofemoral and iliofemoral
ligaments were attached to them.
 |
| Reconstruction of the appearance of Eusthenodon tresnensis (exhibition of the Orlov Paleontological Museum, Moscow); clade Eotetrapodiformes, family Tristichopteridae, genus Eusthenodon flourished in the period 383-359 Ma (2002 Clément G; 2007 Blom H_Friedman M), photo by the author. |
 |
| Pelvis of the fish Eusthenopteron; ac. – acetabular (from 1970 Andrews SM_Westoll TS; Fig. 14). |
Recently, a new finned elpistostegalian Qikiqtania
wakei from the late Devonian period (382.7-358.9 Ma) was discovered,
which cannot yet be classified as a tetrapod (2022 Stewart TA_Shubin NH; 2023
Cohen KM_CarN). The pelvis and the hind fins of the specimen found were not
preserved, so it is not possible to clarify the shape of the acetabulum and the
stereotype of movement. At the same time, it is known that fish, even in the
absence of finger-like limbs, are able to move by walking movements using fins
and rotating the appendicular girdles relative to the long axis of the body
(2016FlammangBE_SoaresD). We believe that Qikiqtania wakei could move along the
bottom and shallow water in a similar manner.
It was previously believed that the diversification of
tetrapodomorphs occurred in the following order of taxa appearance:
Eusthenopteron, Panderichthys, Elpistostege, Tiktaalik, Elginerpeton,
Ventastega, Acanthostega and Ichthyostega (2007ClackJA). Currently, the
development of tetrapodomorphs looks like this: Tinirau, Eusthenopteron,
Megalichthys, Panderichthys, Qikiqtania, Tiktaalik, Elpistostege, Parmastega,
Ventastega, Acanthostega Elginerpeton, Ymeria, Ichthyostega (2022
StewartTA_ShubinNH).
We analyzed the shape of the femur and acetabulum in
ancient fish species before Tiktaalik. No signs of an acetabular fossa or a
fossa of the femoral head were noted in this group of the most ancient
vertebrates.
We have analyzed the shape of the femur and acetabulum
in ancient fish species before Tiktaalik. No signs of an acetabular fossa or a
femoral head fossa were noted in this group of the oldest vertebrates.
Therefore, the above-mentioned ancestors of tetrapods did not yet have a
ligamentum capitis femoris (LCF) attached directly to the bone.
References
Hedges SB, Blair JE, Venturi ML, Shoe JL. A molecular timescale of eukaryote evolution and the rise of complex multicellular life. BMC evolutionary biology. 2004;4(1)1-9. [link.springer.com]
Edgecombe GD. Arthropod phylogeny: an overview from the perspectives of morphology, molecular data and the fossil record. Arthropod Structure & Development. 2010;39(2-3)74-87. [sciencedirect.com]
Chen JY, Dzik J, Edgecombe GD, Ramsköld L, Zhou GQ. A possible Early Cambrian chordate. Nature. 1995;377(6551)720-2. [nature.com]
Наумов НП, Карташев НН. Зоология позвоночных. Ч. 1. Низшие хордовые, бесчелюстные, рыбы, земноводные: Учебник для биолог. спец. ун-тов. Москва: Высшая школа, 1979. [batrachos.com]
Märss T, Gagnier PY. A new chondrichthyan from the Wenlock, lower Silurian, of Baillie-Hamilton Island, the Canadian Arctic. Journal of Vertebrate Paleontology. 2001;21(4):693-701. [tandfonline.com]
Zhu M, Ahlberg PE. The origin of the internal nostril of tetrapods. Nature. 2004;432(7013)94-7. [academia.edu]
Yu X. A new porolepiform-like fish, Psarolepis romeri, gen. et sp. nov. (Sarcopterygii, Osteichthyes) from the Lower Devonian of Yunnan, China. Journal of Vertebrate Paleontology. 1998;18(2)261-74. [tandfonline.com]
Kemp A, Cavin L, Guinot G. Evolutionary history of lungfishes with a new phylogeny of post-Devonian genera. Palaeogeography, Palaeoclimatology, Palaeoecology. 2017;471:209-19. [sciencedirect.com]
Cohen KM, Harper DAT, Gibbard PL, Car N. The International Commission on Stratigraphy (ICS) International Chronostratigraphic Chart. September 2023. [stratigraphy.org]
Campbell KSW, Barwick RE. Diabolepis and its relationship to the Dipnoi. Journal of Vertebrate Paleontology. 2001;21(2)227-41. [tandfonline.com]
Zhao W, Zhang X; Jia G, Shen Y, Zhu M. The Silurian-Devonian boundary in East Yunnan (South China) and the minimum constraint for the lungfish-tetrapod split. Science China Earth Sciences. 2021;64(10)1784-97. [link.springer.com]
Lu J, Zhu M, Long JA, Zhao W, Senden TJ, Jia L, Qiao T. The earliest known stem-tetrapod from the Lower Devonian of China. Nature communications. 2012;3(1)1-7. [nature.com]
Müller J, Reisz RR. Four well‐constrained calibration points from the vertebrate fossil record for molecular clock estimates. BioEssays. 2005;27(10)1069-75. [onlinelibrary.wiley.com]
Swartz B. A marine stem-tetrapod from the Devonian of Western North America. PLOS ONE. 2012;7(3)e33683. [ncbi.nlm.nih.gov]
Witzmann F, Schoch RR. A megalichthyid sarcopterygian fish from the Lower Permian (Autunian) of the Saar-Nahe Basin, Germany. Geobios. 2012;45(2)241-8. [academia.edu]
Clement AM, Cloutier R, Lu J, Perilli E, Maksimenko A, Long J. A fresh look at Cladarosymblema narrienense, a tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous of Australia, illuminated via X-ray tomography. PeerJ. 2021;9:e12597. [peerj.com]
Wellburn ED. On the Genus Megalichthys, Agassiz: Its History, Systematic Position, and Structure. In Proceedings of the Yorkshire Geological and Polytechnic Society. 1900;14(1)52-71. [scholar.archive.org]
Niedźwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M, Ahlberg PE. Tetrapod trackways from the early Middle Devonian period of Poland. Nature. 2010;463(7277)43-8. [academia.edu]
Boisvert CA. The pelvic fin and girdle of Panderichthys and the origin of tetrapod locomotion. Nature. 2005;438(7071)1145-7. [academia.edu]
Johanson Z, Ahlberg PE. Devonian rhizodontids and tristichopterids (Sarcopterygii; Tetrapodomorpha) from East Gondwana. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 2001;92(1):43-74. [academia.edu]
Whiteaves JF. On some remarkable fossil fishes from the Devonian rocks of Scaumenac Bay, in the Province of Quebec. Annals and Magazine of Natural History. 1881;8(44)159–62. [tandfonline.com]
Andrews SM, Westoll TS. IX - The postcranial skeleton of Eusthenopteron foordi Whiteaves. Transactions of the Royal Society of Edinburgh. 1970;68(9)207-329. [cambridge.org]
Clément G. Large Tristichopteridae (Sarcopterygii, Tetrapodomorpha) from the Late Famennian Evieux Formation of Belgium. Palaeontology. 2002;45(3)577-93. [onlinelibrary.wiley.com]
Blom H, Clack JA, Ahlberg PE, Friedman M. Devonian vertebrates from East Greenland: a review of faunal composition and distribution. Geodiversitas. 2007;29(1)119-41. [academia.edu]
Stewart TA, Lemberg JB, Daly A, Daeschler EB, Shubin NH. A new elpistostegalian from the Late Devonian of the Canadian Arctic. Nature. 2022;608(7923)563-8. [nature.com]
Flammang BE, Suvarnaraksha A, Markiewicz J, Soares D. Tetrapod-like pelvic girdle in a walking cavefish. Scientific reports. 2016;6(1)1-8. [nature.com]
Clack JA. Gaining Ground. Indiana: Indiana University Press, 2012. [books.google]
The original text in Russian is available at the link: Позвоночные животные
NB! Fair practice / use: copied for the purposes of criticism, review, comment, research and private study in accordance with Copyright Laws of the US: 17 U.S.C. §107; Copyright Law of the EU: Dir. 2001/29/EC, art.5/3a,d; Copyright Law of the RU: ГК РФ ст.1274/1.1-2,7
Comments
Post a Comment